Save 75 Model Railway Projects:  .doc (7.2MB) or .pdf (5.1MB) 
                                                                                                                   4-7-2019                          4-7-2019

Our other free eBooks,
 50 - 555 Circuits
 1 - 100 Transistor Circuits  and:  101 - 200 Transistor Circuits
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Talking Electronics has produced two books on Model Railway Electronics.
They are
Electronics for Model Railways-1 (pdf) and Electronics for Model Railways-2 (pdf)
These books have completely sold out so we have provided them in .doc format (Word) and .pdf
All the kits from the two books are still available and we get lots of orders, but you must make sure
you are good at soldering and see what the module does, before ordering.
Some of the modules are available fully assembled and tested and some have been improved or simplified
and you need to contact us before ordering anything.

Electronics for Model Railways-1  .pdf (35MB)  free
Electronics for Model Railways-1  .doc (13MB)  free

Electronics for Model Railways-2 .pdf  (56MB) free
Electronics for Model Railways-2 .doc  (13MB) free


For a list of every electronic symbol, see: Circuit Symbols.

For more articles and projects for the hobbyist: see TALKING ELECTRONICS WEBSITE                                                          

                                           email Colin Mitchell: 

More than 24 CIRCUITS as of  12-8-2019  Talking Electronics website has the remaining 50 projects as kits
and the instructions are available in the two books shown above. As well as more projects on the website.


Arc Welder Simulator
Aircraft Navigation Beacon
Atlas #56 Switch
Automatic Point
Automatic Reverser - To-Fro
Capacitor Discharge Modules - 8 Types
Capacitor Discharge Unit MkII
Capacitor Discharge Unit MkII - modification
CDU - discussion
CDU MkII - Jim's
CDU 1,000u - slim
CDU 18,000u - flat version
CDU 18,000u - slimline version
CDU 18,000u - slimline - AC or DC in
CDU Jim's CDU - lots of features
CDU - for Kato Point Motor
Crossing Lights - Jim's
Current overload Detection
Flashing Railroad Lights - a simple project
Flashing Lights - a simple project
Hall Device (Hall Switch)
Jim's CDU MkII
Jim's Crossing Lights -
for type A & B
Jim's Slow Servo
JIM's LEDs  - distribution board
Kato Point Motor Controller
LED Tester
Linkage between servo and point
Make your own Point Motor using a servo
Model Railway Time
Overload Current Detection
Point Controller
      using 555 IC 70
movement for servo
Point Motor Driver

Power Supply MkII
Reed Switch    Reed Switch
Resistor colours
Reversing A Motor
Servo as Point Motor
Slow Servo - Jim's
Servo Speed - animate things
Servo's  - a description and problems
Signals - 6
Surface Mount Resistors
Terminal Block
To-Fro  Automatic reverser
Track Tester
Track Pick-off (voltage)
Traffic Lights - a very simple project
Train Throttle
Wiring a Point Motor
1,000u CDU - slim
18,000u CDU - flat version
18,000u CDU - slimline version
18,000u CDU - slimline - AC or DC in
4-Way Traffic Lights
6 Signals
27MHz Link
36v Plug Pack
                                         to Index
This e-book presents a lot of interesting projects for Model Railways.
Talking Electronics has produced two books for Model Railway enthusiasts (book-2 is now out of print).
The two books are:
Electronics for Model Railways-1
Electronics for Model Railways-2
Since releasing these two books, we have designed lots of extra projects and more are being released all the time.

There is a very large group of Model Railway enthusiasts in the world and nearly everyone's layout includes more and more electronic devices, modules and controllers.
But a lot of enthusiasts are not electronically attuned and have either not studied electronics or had the fortune to have built electronic projects.
That's why many of the projects we have designed recently are available as a kit or already built and tested.
Even to put a kit together you have to be able to identify each part and fit it correctly as well as owning a fine tipped soldering iron and knowing how to solder quickly and cleanly to prevent overheating the component.
Most Model Railway magazines don't have circuits and projects you can build, mainly because they don't have the back-up of component suppliers, reliable kit suppliers or the staff needed to answer questions on fixing kits that don't work.
We have all these features at TALKING ELECTRONICS and everything is backed by emails and service.
Most emails from us are very short as we have hundreds of emails to attend to each week but you must reply with one question at a time and eventually your problem will be solved.   

Colin Mitchell

If you have DCC Digital Command Control on your model railway, or are thinking about using it or starting a layout with this feature, here is a website dedicated to helping you:

Digital Command Control is a standard for a system to operate model railways so that two or more locomotives can be controlled independently on the same section of track.
Talking Electronics has a simple DCC controller for two trains on the same track and decoders that convert your DC locos to DCC.
But there are more than 3 different manufacturers and each has a different set of "code-signals" to perform a particular operation.
The system (coding) we use is the USA: NMRA National Model Railroad Association
And the hand-held COMMAND CONTROL, NCE Power CAB, has been used to design all our DCC projects.

Many of the projects and circuit and ideas in this eBook are available from Talking Electronics as complete kits, fully assembled, or as components at very low prices.
Talking Electronics has sold over 300,000 kits during the past 40 years and about 100,000 have been Model Railway kits. You can now get many of the kits fully assembled and tested for those who have a layout but not a soldiering iron.
Many of the projects are so new and different and complex that you will not understand them fully. Email: Colin Mitchell and ask for assistance before buying or doing anything.

Here are some wonderful layouts and videos taken from the front and back of the trains on the layouts  . . . .   from MODEL RAILWAY LAYOUTS"

You must join:   MODEL RAILWAY LAYOUTS because they send a new layout every day with videos.
This link show the enormous amount of wiring required for a layout with points and signals.

This is the latest:

Here are 2 of the latest images:

There are 200 more photos of layouts on the website:  
MODEL RAILWAY LAYOUTS and by joining them via email you will get an email each day with more wonderful layouts.
These layouts show the enthusiasm and skill and interest and dedication and endless amounts of money invested in this hobby.
Talking Electronics is only able to help with the electronics side-of-things and you will find most of the layouts in
MODEL RAILWAY LAYOUTS have very little in the way of street lighting, billboard signs, crossing lights, boom gates etc because few people know about our range of products.    Now you know, your layout can include lots more. So, don't think you have "gone too far" until you see all the layouts and spent all your spare money for the next 5 years. Your layout can always be "passed-on" or sold, so nothing is wasted. The biggest electronics hobby is model railways. And the greatest joy is squatting-down and watching a train come "head-on." The first time Edison presented a train like this on the "big screen," women fainted. You will just be over-joyed with the realism it produces. And we have a To-Fro project to do this for you automatically.




Every project needs POWER. Power is ENERGY (actually: Power over a period of TIME is energy) and it comes from a battery or a POWER SUPPLY.
We are going to describe a POWER SUPPLY that connects to the mains of your house.
A Power Supply provides TWO THINGS. It provide a VOLTAGE and a CURRENT.
The voltage can be oscillating "up-and-down" and we call this ALTERNATING VOLTAGE and it is given the letters AC. The letters AC actually mean ALTERNATING CURRENT and the term comes from the very beginning of supplying energy to houses when two rival companies had a war. One company supplied DIRECT VOLTAGE and the other supplied ALTERNATING VOLTAGE. The first was called DC and the second called AC.
The voltage at all power points of a house is ALTERNATING and to convert it to DC requires a transformer, a rectifier and a smoothing capacitor called an electrolytic.
We will not be concerned with any of these components but the three values we will be covering is: THE VOLTAGE    THE CURRENT and if the output is AC or DC.
A POWER SUPPLY plugs into your wall socket and delivers a VOLTAGE, a CURRENT and lets you know if the output is AC or DC. A Power Supply can also be called a Wall Wart, Plug Pack, Adapter or "Converter."

You will need at least 2 or 3 different power supplies for your layout. This is because a layout requires at least two different voltages.
Normally, these are very expensive, buy we are going to show how to use all sorts of "junk" and "discarded" power supplies from computers, shavers, toothbrushes, toys, printers, faxes, mobile phones, old electric drill chargers and anything you no-longer use, and convert them into a power supply.
They will cost you little or nothing and they will work PERFECTLY.
But you need to know what you are doing as there are lots of different options.
The Li-ion 4-cell power supply we will be describing is equal to $100 power supply (from a model railway supplier) and the $35 Power Supply (we will be describing)  using 5 Li-ion cells can be used as a BENCH POWER SUPPLY for all your testing and is equal to a $100 product. And some of the other power supplies we will be describing will cost you either nothing or just a few dollars.
Once you have a power supply, we will describe the next item on your list, a THROTTLE. (This is covered in Chapter 4 - halfway down). This is the module that connects between a power supply and delivers a voltage and current to the track to control the speed of the loco.

A typical "Wall Wart" or "Plug Pack" or "Adapter"

Power supplies are also called wall warts, plug packs, chargers or adaptors and must be of the type that is SAFE. In other words, you must be able to touch the output wires and the tap in the kitchen and not get killed.
This is not a joke. If the adaptor is only designed to be used with a fully plastic item, it may be lacking isolation as you cannot touch any of the wiring. This will only refer to very old devices where a simple capacitor was used to convert the household voltage to a situation where the output current and voltage was fairly low when you measured across the two output wires. But when you measured between either wire and the frame of a toaster, the voltage was 315 volts !!!
Throw out anything that you are not absolutely sure is safe.
Now we have a handful of say 10 different, old, unwanted, useless adaptors.
We are going to show how to connect two or three together to produce a voltage suitable for many of our railway projects.
Make 4 piles. The first will have current ratings from 100mA to 500mA.
The next will have current ratings from 600mA to 1 amp
The third pile will be 1 amp and higher.
And the fourth pile is for those adaptors that deliver AC.
From these piles you will be able to make a power supply using two adaptors by wiring the outputs IN SERIES.
Many of the CDU projects from Talking Electronics need an input of 20v DC to 25v DC.  The current can be as low as 100mA as the electrolytics in the CDU will take up to 1 amp if the the power supply can deliver this current, but if the available current is 100mA, the CDU will simply take longer to charge the electrolytic.
So, almost any power supply can be used and it is the voltage that is needed so the electrolytic charges to the maximum.
If you have two 12v DC adaptors with a current rating from 100mA to 1 amp, they can be combined together by connecting the output wires IN SERIES. If one adaptor is 100mA and the other 1amp, they can be combined and all that will happen is the output current will be limited to 100mA. You can even connect 3 adaptors in series to get a total voltage of 25v.
This is one way to use low-output-voltage adaptors to power the CDU project on your model railway.
Some adaptors are only 3v to 4v to 5v and they can
all be combined. 

You can also connect adaptors in PARALLEL - DC adapters. This involves connecting the negative output of one to the negative of the other and the two positives together.
Ideally, the output voltage of each adaptor should be the same as this will equalise the load-sharing.
But many adaptors have a high output voltage that drops as the load is applied.
For instance a 12v 500mA adaptor can be as high as 17v on no-load and this voltage will drop to 12v when 500mA is flowing.
The other adaptor may be 14v on no-load and 12v when 500mA is flowing.
These two adaptors can produce a 12v 1 amp power supply ONLY IF the actual sharing between the two is EQUAL. Otherwise the output voltage will be 17v on no-load and gradually drop to 12v as the current flowing to the load increases to 1 amp. And the current-sharing will change from 0:100 %  to something nearing 50:50 %
It is pointless placing a 12v and 5v adaptor in parallel as the 5v adapter will never deliver any current.
The two adapter share 50:50 when the output voltage is exactly the same. This will never be the case but no damage will be done as each adapter has a diode on the output that prevents one adapter passing any current to the other.

This is a good way to use up a box of old adapters.

Here is a typical 18v power supply for a model railway.  This is the ideal supply, but it is expensive and our aim is to show how to produce the same output voltage by using much cheaper items (Plug Packs etc.)

18v Power Supply

You can connect AC adapters in parallel, providing they produce the same output.
The only way to check this is to connect them together at one end and flick the other two leads to make them spark. If they produce a large spark, you need to change the leads from one adapter.
If you flick the leads and a small spark is created, they do not match perfectly and one or both will get hotter than normal as current will flow through the secondary windings.
It is very difficult to make any other tests without using a multimeter.
When you connect one end of each together and connect a multimeter (set to low AC voltage) to the other two leads, the meter should NOT SHOW any voltage. This means the output of each adapter is rising and falling at the same time and with the same amplitude. 

Here are two Plug Packs connected in series:

You can connect any TWO or THREE together and the output voltage will be the sum of all the voltages and the current will be determined by the lowest current of the 3 adapters.

This is very handy for CAPACITOR DISCHARGE UNITS as they need a voltage of approx 16v to 25v DC to fully charge the capacitors.

If you do not have any old Plug Packs, you can buy new ones on eBay for a few dollars.

You can buy 1Amp or 2Amp Plug Packs.
You will need:
1 x 12v adapter  and 1 x 5v  adapter for a THROTTLE.
2 x 12v 1Amp adapters for a Capacitor Discharge Unit.
Total of 4 Plug Packs.

Here are some examples:



The best DC adapter for all the CDU modules is a 24v or 30v supply made from two  12v adaptors in series of three 10v adaptors in series.
If the CDU module has an on-board regulator, the 30v supply is the best as it will charge the electros to a maximum of 27v.
For all the other CDU modules, you should use two 12v adaptors in series and the electros will charge to about 23v. 

note: Sometimes you will use a charger (wall wort) (or two in series) to charge a Capacitor Discharge Unit and the inrush current will be more than 1 amp and one of the chargers will "close-down" and fail to deliver its voltage. The solution is to add a 12 ohm resistor for 12v, 18 ohm for 18v or 24 ohm for 24v that is soldered to the positive lead. This will limit the current to 1 amp on turn-on. 

The $2.50 plug Pack above was purchased as 12v @ 1 amp.  It was easily opened-up via a screw and clip, to reveal the PC board shown below.
The output voltage is determined by the zener diode at the front of the board. The 12v zener was replaced with 15v and now the output is 15v DC. I would limit the current to 800mA, but a 15v supply can be connected to many of the throttle circuits covered later in this article to give 0v to 12v DC output.  The zener diode is "sitting high" to show the diode in this discussion and also to allow test chips to measure the voltage across it. It was then resoldered close to the board and the cover replaced. This module is LIVE when out of the case, so don't touch anything.

The new 15v zener converts this power adapter to 15v output.

You can also use a white LED in series with the
12v zener diode to get 15v output. Note the cathode of the zener is connected
to the cathode of the LED and the 1k current-limiting resistor is
linked with a jumper (it is not used).
Thus the 15v output drives the LED (3v drop) and the 12v
zener drops 12v. The anode of the zener is connected to 0v.
The result is 15v output.

36V !!
Some of the CDU projects can be supplied with 30v to 36v DC to fully charge the electrolytic(s).
You can make a 36v supply very cheaply by using 24v and 12v plug packs and these are available on eBay for less than $10.00 (for both) including postage.    
Simply connect the leads as shown in the following diagram to get 36v.
Some of these plug packs have a current detecting overload circuit and "shut-down" if the current is more than 1 amp (even for a millisecond).
To prevent this we add a 47 ohm resistor.
This "trick" only applies when you are using the plug packs for our CDU modules as the high current is only required for a few seconds and then falls to a very low value and the resistor will not get warm when used for this particular application.  

Because a Wall Wort producing 13v AC or 27v DC is fairly difficult to obtain (almost impossible) Talking Electronics has produced a number of CDU modules that accept almost any voltage (AC or DC or DCC) from 9v to 15v (either AC or DC) and the on-board voltage generating circuit will produce an output of exactly 27v DC.
The latest module to have this feature is JIM's CDU MkII and it has a mini trim pot to adjust the output voltage from 13v to 27v DC to cater for all different types of solenoid points. 
This module has on-board push-switches to control the position of the point and each module is designed to be connected to a single point or two or three points that ALL need to be activated AT THE SAME TIME.   You can see the project
This is just one way to get around the problem for the moment, but at some point in your plans to produce a large layout, you will need a POWER SUPPLY. You can spend a lot of money on a POWER SUPPLY but Talking Electronics is always aiming to show the cheapest and best way to get something at the lowest cost.

Let's look at what we are talking about:

A Bench Power Supply is the name given to a power supply that looks like the following images:

They come in all sorts of arrangements and offer current limiting and output voltages from 0v  to 35v (or higher) at 1 amp to 10 Amp or more.
But these cost a lot and you can build a similar "instrument" (a piece of test gear is called an INSTRUMENT) for less and since it will be "out of a case" you will be constantly reminded of how it has been put together.

Power Supply MkII
0-12v DC(voltage adjustable)   0-1Amp(current adjustable)
Power Supply MkII
kit from
Talking Electronics for $20.00 plus $7.50 postage. 
Click HERE for details.
(see the full article HERE)

The following project is a 0v to 12v BENCH POWER SUPPLY  with current limiting and has an output of 1 amp. This is sufficient for all types of testing and you can increase the values by referring to the circuit.
The whole idea is to create projects at the lowest cost and have them open for viewing so you can remember how they were assembled.      

This is the cheapest, safest Power Supply you can get.
It will deliver 0-12v at 1amp and you can limit the current to a few milliamp so you will not damage a project you are designing.
It has 14v at 5 amp  - called an AUXILIARY OUTPUT  - that connects directly to 4 cells and you need to be careful as the Li-ion cells are capable of delivering up to 50 amps if the wires are shorted.
This project is called a BENCH POWER SUPPLY as it is a handy piece of TEST EQUIPMENT that is designed to deliver a controlled voltage for a project you are developing.
It is not a continuous power supply as the cells need to be charged (when the indicator LED does not illuminate).
The Li-ion cells are available on eBay for a few dollars each and you can buy a single-cell charger for a few dollars. These chargers are microcontroller based and they stop charging when the cell is fully charged. You cannot charge the cells from a "battery charger."
You can also get a single-cell charger PCB that connects to your laptop USB socket and it will charge a cell very quickly. But you will only be able to charge one cell at a time.
All these things are covered later in the article.

You can use 2 x 470R @ 0.25watt or 1 x 1k @ 0.5watt

The new PC board uses 1k (in place of 220R shown above as the
current limiting resistor for the white LED) to keep the
brightness low to stop blinding you.


Power Supply MkII

$20.00 plus $7.50 postage. 
Click HERE for details

4 - 1R      0.25 watt resistors
1 - 4R7
1 - 100R
1 - 220R to be replaced with 1k
(the old board shows 220R - new board uses 1k)
2 - 470R (or use 1k @ 0.5watt resistor)
1 - 1k (as shown in circuit above)
1 - 22k
1 - 150k

2 - 500R trim pots
2 - knobs to suit

1 - 3v9 zener
1 - 6v2 zener
1 - 9v zener
1 - BC338 transistor
1 - TIP31 transistor
1 - BD679 transistor
1 - 3mm white LED
4 - 2-screw terminal blocks
2 - heat fins

4 - sets of nuts and bolts and 5 washers
4 - hook-up wire for battery boxes (to replace
     the rubbish on the battery boxes)
2 - side-view panel meters and 2 stickers and   
     foam tape to hold them in position
1 - toggle switch
10cm 0.5mm tinned copper wire for meters
30cm fine solder
Backing card and 4 feet and foam tape
1 - Power Supply MkII PC Board

Trickle Charger Components are included:
2 - 180R
4 - 3v9 zeners
2 - 9v zeners
3 - 3mm white LEDs
Trickle Charger PCB

Single-cell charger kit $7.00:
1 - USB voltage/current monitor module
1 - single cell charger PC board
1 - single cell battery box
1 - 1R0  5-watt wire wound resistor

These parts are not included in the kit:
5 - 18650 Li-ion cells
1 - 4-cell battery box
1 - single cell battery holder
1 - 4 cell charger
1 - single cell charger
USB charger module and single cell battery box
These items can be bought on eBay.


Here is a set of 4 Li-ion cells. Just use the 4 lower cells in a 4-cell carrier. The top cell is just to increase the voltage slightly so the project will produce slightly more than 12v at 1 amp.

You can buy Li-ion cells for about $2.50 each on eBay. They have a capacity of about
2 Amp-hour to 3 amp-hour.

The 4-cell carrier can be bought on eBay for about $2.50

The following 4-cell charger can be bought on eBay for about $3.50.
This will charge the cells at about 70mA to 150mA and it will take about 24 hours to fully charge a depleted set of cells. 

The charger below will charge a single cell at about 500mA to 700mA and connects to your USB port on a laptop. You can only charge one cell at a time with this arrangement.

The 1 ohm resistor will discharge the cell quickly. The cell voltage must not go below a minimum voltage of 2.8v. You need to place a voltmeter across the resistor while discharging to make sure you do not discharge the cell below its recommended minimum.  The module in the photo charges the cell quite quickly and at 4.2v the cell is charged to 90% (or more) and the circuit turns OFF.
You must use a charger that turns OFF when the cell is charged as this type of cell cannot be left charging on a "trickle charger" as the cell will produce internal "whiskers" and it will get damaged.

More details of the project shown above can be found HERE.  It describes a 1 amp adjustable POWER SUPPLY that can be used to power your locos or as a BENCH POWER SUPPLY for all your testing. 

How much current do you need?  That is: how many AMPS do you need?
A small loco takes 300mA to 600mA and you need a 1AMP supply to make sure the necessary current can be supplied as the motor will take 800mA to 900mA when starting and accelerating and when hauling a number of coaches.
For a DC layout, you will generally only be running one loco at a time and a 1-Amp supply will be sufficient.
The current values mentioned above apply when the supply is 12v.
If the supply drops to say 10v, the current will be less and if the supply increases to 14v, the current will increase by a considerable amount (when the same motor is connected). It is impossible to state the actual values because
the current taken by a motor increases and decreases due to the load and this load is not only the velocity of the train, but the acceleration and inclination of the track and also the rpm of the motor (as it takes more energy to rotate at higher rpm) and lots more current when the motor is "loaded."

Before we finish, there is a bit of theory that needs to be understood.
We have mentioned the AC voltage and DC voltage on (or for) many of the projects.
The two values are a little bit different and you may be wondering why.
The technical reason is this: When you deliver 10v AC to a circuit that has diodes and capacitors (electrolytics) that convert the voltage to DC, the output is 40% higher than "10" because the 10v AC is actually 14v at the instant when the voltage is rising to a maximum and the capacitors get charged to this value. 
There is a loss of about 1.5v across the diodes in the circuit and the output becomes 12.5v
Quite often the manufacturer of the 10v AC transformer will add a few extra turns and the voltage will be 13v AC (under no load).  This is done because the output drops when full current is delivered (because the transformer is very poor quality) and this will ensure the output never goes below 10v AC. It drops from 13v to 10v - under full load.
However the 13v AC will produce 18.2v AC minus 1.5v = 16.7v DC when unloaded and if you deliver more than 13v AC, the resulting unloaded voltage may be too high for some of the electronic components - especially IC's.

You need to buy or make 2 POWER SUPPLIES:
15v to 17v  @ 1 amp POWER SUPPLY for a throttle (to drive a loco - suitable for 1 or 2 locos).
24v POWER SUPPLY for a Capacitor Discharge Unit. (less than 100mA needed)
Cost will less than $15.00 for up to 4 Plug Packs. (see above for details of the Plug Packs you need to buy.
If you build a Bench Power Supply (see
Power Supply MkII) you will have an adjustable output voltage (0v to 12v DC) and you will be able to limit the current (from 30mA to 1 amp) so the project you are testing will not be damaged.

When you have the 2 Power Supplies, you can decide on the Capacitor Discharge Units and the Throttle module.

Under NO circumstances should you build a power supply with soldered wires or bare joints or bare leads going to the mains or any wiring with bare MAINS connections. One day a child may come and play with your equipment and touch exposed wires and get thrown across the room.
Always use Plug Packs (Wall Warts) or Power Supplies in a professional case. They are called "double insulated" and that means they do not have an earth lead. It also infers they do not have a metal case and this makes them extremely safe.  

You may find instructions or a circuit on the web for a CAPACITOR-INPUT POWER SUPPLY.
This is a power supply with just a single or even 2 capacitors connected to the mains, followed by a bridge and an electrolytic. There is no transformer in this type of power supply and although you think the capacitor separates the mains from the 12v output, IT DOES NOT.
It does reduce the voltage of the mains to say 12v DC after the bridge, but if you touch either of the output wires and a water tap or kettle or toaster, you will get a jolt of 240v AC and although the current may be less than 100mA, you only need 15mA to kill you. It's the duration of the electric shock that is finally fatal and if you are under a railway layout and cannot remove your hand fast enough, you will get fried.
Another point to remember. This has NEVER been mentioned before. The output of a cap-fed power supply is only 12v when the diode bridge and 12v zener is connected. If any of these wires are cut, the "12v section" becomes
336 volts !! The 12v zener is called the LOAD and when you connect your project to this power supply, the current passing through the zener is now diverted from the zener and to your project. But if the zener "blows up" and then your project "blows up" you will have 336volts on your project.
This type of power supply is illegal in many countries and hopefully you will never see one. BUT this comment is to inform you: NOT TO BUILD A CAPACITOR-INPUT POWER SUPPLY.  

     to Index


Using a motor to control a point

This is PART "A"  of our discussion on controlling a point.
(see PART "B" to control a point containing a solenoid)


Talking Electronics makes 8 different modules to assist and change and active the points in your layout (to suit different voltages and different situations). That's why you have to read
Part "A" and Part "B"

A Point Controller is a "device" or "MOTOR" or "SOLENOID" that changes the point from "ahead" to "Siding."
The ACTUATING MECHANISM can be a double-acting solenoid to move the rails from one position to the other. Or it can be done with a motor and gearbox or a micro motor and gearbox or a SERVO or even a LINEAR ACTUATOR. These all come in different sizes and at different costs.
That's why there is a number of different projects.
This section does not cover the SOLENOID POINT. See Chapter Three to control a SOLENOID POINT with a CAPACITOR DISCHARGE UNIT. 

All layouts need a point or lots of points so you can make an impressive layout and have the trains leave and enter the main line and provide shunting yards and loops and interconnecting lines.
There are so many choices for a point and so many different expenses that we have simplified everything and created the best control modules on the market at the lowest cost for all the different situations.


Start by buying the cheapest left or right hand point FOR MANUAL OPERATION. This is the  version we will convert to either remote or automatic operation.


If you have a solenoid operated point, we will cover it later:
This is a point with a solenoid actuator to move the rails. We will cover this later in the article. We will firstly cover a MOTOR to activate the point.

This module converts a manual point into a remotely controlled point.
There are a number of modules available and the differences will be cost, size, and fast or slowing changing of the point.
The first choice is: POINT CONTROLLER using 3v MOTOR and WORM GEARBOX for $20.50
Here to order.

We connect a motor and worm gearbox as shown in the following image to the actuating lever on the point:

Image shows the control rod on the gearbox is
bent to fit the push-bar of the point.
The movement of the control rod will activate the point.
You have to provide some "springyness" to the push-bar so that a train coming
in the wrong direction will (from the right) will separate the
rails and not be derailed. 

The arm (lever) on the output of the gearbox
is activated about 90 but will move less than this when
restricted by the "throw" of the lever connected to the point.
Cut the arm to length and bend it carefully by using a pair
of pliers to hold the arm and don't let it move where it is held
by the plastic output gear.
Mount the motor and gearbox with double-sided tape when
adjusting its position and finally use glue to hold it in place.
The two 500R pots on the latest PC board (not shown) allow you to adjust the
strength of the "throw" of the arm.

The following image is the module that controls and limits the motor's operation. It allows the motor to be connected to a 9v to 16v AC or DC supply.

The module with motor/gearbox is available from Talking Electronics
for $25.00 including postage.

You get a micro motor with worm gearbox and module and DPDT push-push switch and the position of the point is shown on the red and green LEDs on the module. The movement of the point is fairly rapid. There are other modules with slow movement.

The circuit above uses a 3v micro motor with worm gearbox. The latest PC board has a number of improvements with two 500R pots to adjust the strength of the throw of the arm. 


In place of the micro motor and worm gearbox shown above, you can use a converted servo, as shown in the following image. The servo is converted to a MOTOR and GEARBOX.
This module is called
POINT CONTROLLER using converted SERVO  for $19.00 plus $6.50 postage. 
Here to order.

The activating module comes with a push-push switch and knob, that clicks when pushed and unclicks when pushed again.
The module limits the output arm of the servo to less than 45 degrees
and the position of the point is shown on the red and green LEDs. A length of gold wire is included for the linkage.
The movement of the point is fairly rapid. There are other modules with slow movement.


This module is identical to Choice Number 2, but this has two mini trim pots to adjust the amount of travel of the arm on the servo..

This choice is: POINT CONTROLLER using converted SERVO ver 4 for $21.50
Here to order.

The Printed Circuit Board has 2 x 500R mini trim pots to adjust the amount of travel of the output arm.


This module is called
POINT CONTROLLER using 555 IC  for $18.00 plus $6.50 postage
Here to order.
The on-board toggle switch changes the point via a servo fairly slowly and this is the main difference from the other modules.  The servo and gold-wire linkage are included with the module. The module outputs a PWM signal to the servo to provide a limit-to-rotation in both directions and this is adjustable on the new version via mini trim pot (not shown on photo).

The on-board LEDs show the position of the point.     


This module is called
POINT CONTROLLER using 555 IC with mini trim pots Ver4 for $20.00. (plus postage $6.50).   Click  
Here to order.

Click  Here to order.
This is the latest version with mini trim pots to adjust the end positions of the converted servo


If you want the servo to move slowly to produce a realistic effect, we have a module called JIM's SLOW SERVO
for $xx0.00 including module, servos and  extension lead.
Here to order.  This module allows the servo to move very slowly. (PC Boards are currently being produced)




If your layout has a number of points that need controlling, we have a 5 SERVO Controller module that controls 5 servo's separately with very slow action.
This module is called
5 POINT CONTROLLER  for $45.00 including module with microcontroller, 5 servos and 5 extension leads. The servos provided with this module are the small 9g version as these servos are guaranteed to work very very slowly from a particular manufacturer. The servos are $2.50 each and the extension leads for the servos are $1.50 each. You can also get aluminium brackets to hold the servo under your layout for $2.50 each. 
The 5 POINT CONTROLLER  costs $20.00 if you have your own servos, but remember we test all modules with the very small servos before posting, to make sure they all respond to the PWM signals. The new module uses a PIC16F628 microcontroller as it has more input/output lines and the on-board LEDs show the position of each point. 

Here to order.


The on-board tactile buttons need to be pressed for about 1/2 second for the program to recognise the button and activate the servo to set the point to the correct position. You need to set each point so that the PC board reflects the correct position of the point. Do this will all 5 points and you are ready to drive the loco.


A manual point costs between $15.00 and $25.00. (you can buy these from any model railway shop) The modules above cater for all sorts of different requirements (such as speed of activation, cost, 1 or 5 points) and this means a remotely activated point can be added to your layout for as little as $40.00

But there are other options, so keep reading.
And there are a number of options for a point that has SOLENOID OPERATION - and this is covered next. 

     to Index


Controlling a SOLENOID point
using a CDU module

This is PART "B"  of our discussion on controlling a point.
This Part uses a Capacitor Discharge circuit to control a solenoid on your point to prevent it "burning out."
You must read all of this discussion as some modules can be wired to operate many points (one after the other) while some modules can only be connected to ONE POINT.

[Here is the module to operate a KATO point motor.]

(see PART "A" to control a point with a motor)

The most common type of point motor is a solenoid that moves the rails from one position to the other.
It is also called  a TURN-OUT MOTOR:

This is s PL-11 Point Motor

Here is the inside of a PL-11 POINT MOTOR.
It must be activated for less than 1 second. 
It was activated for 4 seconds and it MELTED !!
The plastic core melted and bubbled through the coil
and the activating rod is FROZEN.
That's what this article is all about.
If you add a CDU module to activate these
POINT MOTORS they will not get damaged.

and the 3 wires needed to activate the two solenoids.
They are called PULL SOLENOIDS because the core is not a magnet.

The SOLENOID Point Motor consists of two coils of wire that alternately pull a metal rod into the middle of the solenoid and at the same time change the position of the point.
It is also called a double-acting solenoid because it will both PUSH and PULL.
The "core" or "plunger" is not a magnet and it will only PULL into a solenoid. The solenoid will accept AC or DC and it can also be called an ELECTROMAGNET.
Because an electromagnet only "pulls," you need two to produce PUSH and PULL motion.  It is really PULL-PULL motion. The core only PULLS into a solenoid. (When the core is a magnet, you can get push-pull action with a single winding)
But because the core in the solenoid point motor is classified as a SOFT IRON CORE,  you need 2 coils.
But the problem is the coils have very low resistance.
The resistance of the coil is about 4.5 ohms for some types and 11 ohms for others and when connected to 12v, the current will be nearly 1 to 3 amps. They must only be activated for less than half a second and if the 12v is connected for more than 10 seconds, the plastic case will start to smell and melt. In a few more seconds the solenoid will be completely damaged. The photo above was damaged in 4 seconds !!
To prevent this from occurring, you need an electronic module that delivers the current for a very short period of time (so that nothing gets warm).
This module is called a CAPACITOR DISCHARGE UNIT and it contains 2 or more 1,000u (or 2,200u or 4,700u) electrolytic capacitors that deliver the required energy.
These capacitors get charged slowly and when they are fully charged, you can press a switch and operate the point. It does not matter how long you hold the switch because the capacitors are drained in less than a second.

If you operate some of the solenoid point motors DIRECTLY from the 12v train supply or the 16v AC supply from the train transformer, some  will take more than 3 amps and produce a more than 30 watts of heat.  This is equal to a small soldering iron and it will quickly melt the plastic case.
If you already have a PASSING SWITCH or a "spring return toggle switch" with a centre-off position, it will work perfectly, but if you have visitors working the control panel, they may leave the switch ON or change it very slowly and it can cause the solenoid to heat up.
To prevent any of these catastrophes, we have designed a number of CDU - CAPACITOR DISCHARGE UNITS to operate the points safely. These CDU modules are connected between the
PASSING SWITCH and the power supply to give you double protection.


The simplest and cheapest CAPACITOR DISCHARGE UNIT MkIIB is shown in the following image:  CDU MkIIBM  $14.50 plus $6.50  (BM means built and tested - made up)
Click  Here to order.

This is CDU MkIIBM  $14.50 plus $6.50   fully assembled

The screw terminals make it easy to fit to your layout.
Here are the connections to the Power Supply and point:

The two push switches in the wiring diagram above are also shown in the two following diagrams:

The PECO Passing switch only makes contact when the red lever
touches and pushes the contact. This occurs when the lever is in the
 "12 O'Clock" position and you must move it past this position
to prevent the point motor

The green wire is called the COMMON

A single CDU can be used to operate 2 or more point
motors provided you allow a few seconds
been each activation, for the CDU to re-charge.

Our CDU module fits between the Power Supply and the switch or switches to a SOLENOID POINT MOTOR. It is designed to deliver a short pulse of energy to the solenoid to change the position of the point. A Passing Switch will deliver a pulse of energy but if it gets stuck in the mid-position, our CDU will prevent the point motor "burning out."
If you do not include a Capacitor Discharge Unit, and you activate any type of switch for more than 10 seconds, the flow of current will heat up the solenoid and "burn it out." The CDU prevents this.
To go over it again, the CDU module can be used with a PECO PASSING SWITCH so that if the lever is moved too slowly or kept at "12 O'clock" too long, the CDU will only allow a short pulse of energy. And you have
double protection !! 

If your transformer does not supply 15vAC to 16vAC, you can increase the input voltage by adding a 100u to 220u electrolytic and 1N4004 diode to the input to create a voltage doubling arrangement. You can also change one or both the 1,000u electrolytics for 2,200u. This will deliver a much larger pulse to the point-motor and guarantee operation.

By adding one power diode and 220u electrolytic, the 16v AC input will be "doubled."  You need to ask for 35v electrolytics before you do this as the final voltage on them will be very close to 30v to 35v DC

If you ask for 35v electrolytics, you can supply the module with 35v from one or two plug packs.
You cannot get a single 35v plug pack but you can get 12v and 24v  or use 3 x 12v plug packs.
Here is the authors solution to providing 36v:

The image shows a 24v plug pack and 12v plug pack from this supplier:

Universal EU US Plug Switching Adapter AC 220V-240V To 5 V 12 V 24V Volt Power Supply DC 5V 12V 24V 1A 2A 3A 5A Power Adapter Output Voltage 12v   Current 1A   $2.30

Universal EU US Plug Switching Adapter AC 220V-240V To 5 V 12 V 24V Volt Power Supply DC 5V 12V 24V 1A 2A 3A 5A Power Adapter   Output Voltage 24v US Plug  Current 1A   $3.60

The adapter costs less than $1.00 (you need 2) and you need to order the type to suit your wall socket:

This gives you a 36v supply for less than $10.00  You just need to wire the outputs in series.
If one of the plug packs does not turn on when connected to a Capacitor Discharge Unit, it will be due to the high in-rush current being detected by the over-load section.
The answer is to add a 22 ohm or 27 ohm resistor in series. This will limit the current to 1 amp and the resistor will not get warm because the current reduces to a very small value within 5 seconds.


If you want to use a toggle switch and 2 LEDs to show the position of a point, this
POINT MOTOR CONTROLLER Module offers these features.
  $13.50 plus $6.50
Click  Here to order.
You can also buy the module fully built and tested with toggle switch on an extension lead for $20.50 plus $6.50 postage.

Note: The common to the solenoid is fitted to the top screw terminal. 

The amount of energy delivered to the solenoid depends on the voltage delivered to the module. For 12v DC supply, the solenoid will work very delicately and will be suitable for small solenoids used in "Z-scale." Supplying 16v AC will deliver FOUR times more energy and will be suitable for larger scales and can operate 2 points.
The 100R resistor determines the amount of energy delivered. Increasing the 100R to 150R or 220R increasing the timing and thus the amount of energy delivered.

See the full article: HERE



Talking Electronics has an In-line version that takes up less space on your console. This In-line CDU module has two LEDs that show the position of the point. It is fitted to your control panel and the LEDs show the position of a point. This very handy for a point that cannot be seen from the control area.
The module is very slim and more than one can be placed side-by-side to control all the points in your layout. Each module is connected directly to a point.
It is called CDU In-Line and costs $12.50  plus $6.50 postage. It is shown in the following image:
Click  Here to order.

The input voltage needs to be 12v to 16v AC or DC and you may need two adaptors in series to get this voltage. See Chapter 1 for the Plug Packs (or Choice Number 11).


For layouts that need 2 or more points changed at the same time, a larger version is available with 2 x 4700u electro's:
It is CAPACITOR DISCHARGE UNIT MkIII  and is shown in the following image:
CDU MkIII fully built and tested $16.50 plus $6.50 postage
Click  Here to order.

CDU MkIII fully built and tested $16.50 plus $6.50 postage

Connecting CDU MkIII to 24v DC supply

Connecting CDU MkIII to 14v - 16v AC supply

You can use the "accessories" output of a train transformer if it is DC (14v DC to 24v DC) or if the accessories output is AC (14v AC to 18v AC). The module has been tested up to 20v AC but it is best to keep to 18v AC max.


A larger CDU is also available from Talking Electronics, to change up to 8 points at the same time:

It is CDU 18,000u Flat version (built and tested) and costs $18.50  plus $6.50 postage. It is shown in the following image:
Click  Here to order.

CDU Module 18,000 fully built and tested $18.50  plus $6.50 postage

 This Capacitor Discharge Unit is easy to connect to your layout with screw terminals.
You need two push switches to change the position of the point. The LED on the board shows the electrolytics are charged.
Input voltage can be AC or DC. But you MUST use the correct set of terminals. It did not work for one customer because he connected DC to the AC terminals. There is a 100u electrolytic on the AC terminals and "it will not let the DC in."  The 100u is for a voltage-doubling network at the side of the board as shown in the image above. 
Three sets of input terminals are provided.
8v to 12v AC
13v to 20v AC
12v to 30v DC
The project comes with instructions for connecting to a plug pack (wall wart) plus information to connect two plug packs (in series) to get the required voltage.
The CDU 18,000u has zener diode regulation to prevent over-charging.





A slimline version of CDU 18,000u is available from Talking Electronics, to change up to 8 points at the same time:
It has the same capacity (4 x 4700u electrolytics - the same storage capacity as choice number 12) but only one input option: 15v AC. 

It is CDU 18,000u Slimline and costs $19.00  plus $6.50 postage. It is shown in the following image:
Click  Here to order.


A NEW version off CDU 18,000u Slimline MkII has both AC input and DC input and you can decide which input to use. The DC input can be 12v DC to 16v DC and the AC input can be 15v AC from a train transformer.
The circuit on the underside of the PC board DOUBLES the DC voltage and the chip has a maximum operating voltage of 18v. But we do not want to exceed 15.5v as the chip will be damaged if it sees more than 18v. The on-board zener regulator limits the voltage on the electro's to 25.5v  and 15.5v will deliver 25v, due to 5v losses in the circuitry. 
CDU 18,000u Slimline MkII costs $19.50  plus $6.50 postage. It is shown in the following image:
Click  Here to order.

The DC input voltage for CDU 18,000u Slimline MkII
must be 16v MAXIMUM and each module comes with a VOLTAGE REDUCER module so you can adjust the voltage on the module to 15.5v


The VOLTAGE REDUCER MODULE consists of a 3-terminal block and 4 power diodes and screws into the 3-terminal block on the module.
This is how the Voltage Reducer Module works:  Each diode reduces the incoming voltage by 0.75v, making a total of 3v.
When you get CDU 18,000u Slimline - MkII, check the voltage of your power supply (before touching the module) and make sure it is less than 18v. The voltage reducer module only works for voltages: 16v, 17v and 18v.
If it is 18v, connect the VOLTAGE REDUCER to CDU 18,000u Slimline - MkII as shown in the following image:

If the input voltage is 17v, you can remove one of the diodes by soldering a link across one of the   diodes (to short it out), as shown in the following image:

If  the input voltage is 16v you can remove 2 diodes and if it is 15v, you do not need the VOLTAGE REDUCER MODULE.

If you want to deliver 15.5v DC to CDU 18,000u Slimline - MkII with two plug packs, here is the circuit:

An easy way to get 15.5v for CDU 18,000u Slimline - MkII
 is with two plug packs - 5v and 12v.  
You can also use three 5v plug packs and you will find many of these
in your parts-bin from old mobile phones !!!!



1,000u Capacitor Discharge Unit
with SPDT Switch SLIM
Click HERE  to buy.

Fully built and tested for $10.60 plus $6.50 postage.

We are constantly updating and improving and adding to our range of modules and this one combines three features at a LOWER COST -  amazing  !!

The name: Capacitor Discharge Unit with SPDT Switch - SLIM has been chosen to identify it from all the other CDU modules made by Talking Electronics. 
It combines a number of features with a clever circuit to allow a single 1,000u to be charged to 35v and produce sufficient energy to operate a point. It also has an on-board mini toggle switch and two indicator LEDs - this reduces your wiring.
The circuit also includes a voltage doubling arrangement for 12vAC to 15v AC - (from a train power supply) and two indicator LEDs to show the position of the point.
The mini toggle switch can be easily fitted to your console and small holes on each side of the switch used for the LEDs to shine through the console.
All these features are in this narrow PC board so that a row of these modules can be aligned on a panel to show the position of the points.
This module reduces your wiring considerably as only 3 wires are needed for each point and a common "bus" of positive and negative to the modules.  

A close-up of the switch, showing the leads soldered to the tabs on the switch

All the components fit on the PC board and the module comes with 2 x 1,000u electrolytics. The input can be 12vAC to 15vAC or 20vDC to 35vDC.

You can make a 12v 24v or 36v supply very cheaply by using 24v and 12v plug packs. These are available on eBay for less than $10.00 (combined) including postage.    
If you are making 36v, simply connect the leads as shown in the following diagram.
Some of these plug packs have a current detecting overload circuit and "shut-down" if the current is more than 1 amp (even for a millisecond).
To prevent this we add a 47 ohm resistor.
This only applies when you are using the plug packs for our CDU modules (like this project) as the high current is only required for less than a second and then falls to a very small value.   The resistor will not get warm when used in this particular application.  

At first inspection, this switch may not appear to be suitable. But here is the secret of its operation.
When you slide the switch to the left or right NOTHING HAPPENS.
You need to push the switch for 0.5seconds for it to make contact and the energy from the CDU changes the point.
If you push the switch for more than 1 second, all the energy from the CDU will pass to the point in less than 1 second and the extended time of pressing will not damage anything.


Jim's CDU MkII

Buy a kit:  Jim's CDU MkII $24.50 plus $6.50 post
Fully assembled and tested: $30.50 plus $6.50 post

This project combines a number of features from three of the projects we have previously designed for Model Railway Hobbyists.  It is available as a kit or fully built and tested.
Now you can have 3 features in one module.
The first feature is the power supply. This module connects to your track and you don't have to provide 15v AC or a higher voltage to charge the electrolytics. The module has an on-board charging and voltage generating section that accepts almost any voltage and charges the electrolytics to a maximum of 27v.
The next feature is the variable voltage (or maximum voltage) for the electro's. You can reduce the voltage to as low as 13v for those solenoid points that do not need a large amount of energy for their activation.
The third feature is the reed switch inputs. This allows the module to be used automatically to control a solenoid point so the point gets changed correctly when the train approaches from the other direction.
And lastly, the kit comes with a TRACK-PICKOFF MkII connector that fits between the sleepers and connects to the rails with springy connectors.     

All the work is done with the microcontroller.
The charging of the electro's - the timing to activate the solenoid and the detection of the reed switches.
The rail voltage is passed to the project via a bridge and this allows AC, DC or DCC to be converted into DC and stored to a small extent in the first 100u. The 100u on the output of the 78L05 provides a small amount of reservoir for the micro and we are assuming the train will be moving most of the time to maintain supply for the micro.
The micro drives a BC 338 transistor with short pulses to allow current to flow into (through) the inductor and produce magnetic flux. When the transistor turns OFF, the magnetic field collapses and produces a very high voltage spike. This spike passes through the high-speed 4004 diode and into the 4,700u electros. The spike is really about 50v but the energy in the spike is converted into charging current and the electros would charge to more the 40v. But they will explode if the voltage rises above 30v so the voltage on the electros is monitored by the 100k resistor and 10k pot.
The PIC micro detects a HIGH when an input is 2.2v and the 10k pot can be adjusted produce a voltage from 13v to 27v.
The project takes a very small amount of energy from the track during the charging process and this will not be noticed when powering a train around the layout.
The indicator LEDs on pins 2 and 5 are output devices as GP2 and GP5 are constantly changed from input to output lines. They normally illuminate one of the LEDs, but every 100mS, the program converts the lines to input to detect if a reed switch has been activated.  
When they are input lines, we want them to have 0v on them and the 10k resistors across the LEDs provide this feature. Without the 10k resistors, the impedance of the LEDs is very high and the input lines can "float" and if a white LED is used as an indicator, this "float" voltage can be as high as 3.3v. The micro sees any voltage above 2.2v as a HIGH and the circuit would not work correctly.
If a reed switch is activated, the line will be HIGH and the program will respond accordingly.

                                         JIM's CDU MkII circuit
Soldering these kits is simple if you have a bit of experience in soldering small components because all the parts are identified on the PC Board. You will need tweezers for the surface-mount components. We supply solder THAT IS NOT CHINESE SOLDER. Do not use Chinese solder as it does not contain the correct percentage of tin and lead and it does not "run" or melt or flow properly and does not produce a shiny joint. It did not work for me and I threw it in the trash. The frustration of trying to get a shiny joint was enormous.
The first things you add to the board are the 13 surface mount resistors. Add a small amount of solder to one land for each resistor and pick them up with tweezers with the numbers showing and solder one end with the solder that is already on the land. Then go around and solder the other ends by adding a small amount of solder to each resistor. Watch the solder "click" onto the resistor and it will look a little bit like a skateboard ramp. 
The rest of the components are through-hole and it does not matter if you start at one end of the board or with the small components first.
Every component is identified on the board and most of the parts have to be fitted around the correct way - so look at the legend on the board.
The LEDs must be soldered very quickly otherwise they will be damaged.
The mark of a well-designed PCB is being able to put it together with a handful of parts and no other reference.
And the mark of a well-designed circuit is 100% operation with every board. You cannot afford to be messing around, "adjusting" the component values and trying to work out why it does not work. 
That's why every value has a reason and a purpose. This can only be gained by working on hundreds of circuits and gaining the experience, knowledge and understanding. 
The circuits are provided with all the projects to give you this experience.
And to help you fix something, if it "blows up."

 The photo's above show the complete module (before all the leads are connected). The electro's will be bent over and laying flat above the top of the board on modules pre-built and posted through the mail as they are too tall to be posted when they are upright.
The mini trim pot can be adjusted from 13v to 27v so the electros hold the right amount of energy for the point you are using. This is the first module on the market to provide this adjustment as some points bounce too much if the voltage is too high.
The power for this project can come from a power supply 9v to 15v AC or DC or DCC. In fact it can be ANYTHING !!
You can also connect the project to the track with a very small THIN PC board that fits between the sleepers. It is called Track Pick-Off MkII.  It has two springy clips that touch the inner parts of the rails and make electrical contact. .
The PC board comes with the two springy clips soldered in place and you need to remove the plastic from between two sleepers to allow the board to fit (as shown in the photo below). Twist the board into position and give the spring clip a twist with a pair of pliers so it pushes against the rail.

This track pick-off is called BETWEEN SLEEPERS

A close-up of the springy gold wires and the
fine screened lead

Alternatively, you can ask for Track Pick-off "using Rail Joiners." You will need to get to the track, remove the rail joiners that presently connect the rails, and fit the track jointers as shown in the following image:

This track pick-off is called "using Rail Joiners"


Jim's CDU MkII
$24.50 plus $6.50 post
Order a kit

1 - 22R  surface mount
2 - 100R
1 - 220R
2 - 1k
3 - 2k2
1 - 5k6
2 - 10k
1 - 100k

1 - 100k mini trim pot

1 - 100n monoblock
1 - 22u
2 - 100u
2 - 4,700u 25v electrolytics

4 - 1N4004 power diodes
1 - UF4004 high speed 1amp diode

1 - 78L05 5v regulator
1 - BC338
2 - BD679 transistors
1 - PIC12F629 micro with "JimCDU"

1 - 3mm red LED
1 - 3mm green LED
3 - 2-way screw terminal blocks
1 - 3-way screw terminal block
1 - slide switch
2 - tactile switches
1 - 10mH choke

1 - 8 pin IC socket
30cm very fine solder

1 - Jim's CDU MkII PCB

extras  $4.50:

2 - 2-way screw terminal blocks
2 - reed switches
2 - super-magnets
2 - 1.2m screened lead for reed switches
1- Track Pick-off MkII PCB with springy connectors called "Between Sleepers"
1- Track Pick-off called "Between Sleepers"  (tell us the one you want)
1m - fine screened power lead for above
2 - tactile switches for remote operation
1 - PCB to mount the 2 tactile switches
1 - 3m flat lead for switches (4 core)

This is a very interesting project to convert a
solenoid operated point into semi-automatic operation by adding the two reed switches so the train will set the point correctly when entering the point from the opposite direction.
The module shows the position of the point via a red and green LED and it's very easy to set-up with the Power Connector and extension switches.


This module operates a SERVO very slowly. All the other modules operate the servo fairly quickly.

Buy  Jim's Slow Servo $31.50 plus $6.50 post
Fully assembled and tested with servo and leads

The original circuit used two 555 IC's. The new and improved circuit uses a microcontroller and 15 fewer components !!  That's why some of the components are no longer required.
The top terminal block on the left connects to a reed switch and this activates the servo slowly to change the position of the point to allow the train to come back into a point with the rails in the correct position. 
The other terminal block on the left connects to a switch on your control panel to activates the point manually so you can send the loco to the siding.
The top terminal block on the right connects to a reed switch to allow the train to come to a point with the rails in the correct position.  
The other terminal block connects to your control panel.
The module comes with a servo, extension lead for the servo, gold push-rod for servo, leads to your panel for the Main and Siding switches, 2 reed switches on 1200mm leads and two very strong rare-earth magnets: 10mm diameter x 1mm thick.
There are many ways to mount the servo and one customer asked about "N Scale code 55 track."  Here is the solution:

The shortest arm (supplied with the servo) can be cut with one hole remaining and the gold 0.7mm wire wound around the arm with plenty to fit into the lever on the point. Allow the 0.7mm wire to produce a "spring tension" to keep the point, in each direction, with a little bit of tension and this will allow the arm to rotate about 70 degrees. 


Automatic Point

Automatic Point is available as a kit from:
Talking Electronics for $29.50 incl reed switches
and servo. 
Click HERE for details.

Turn your manually-operated point into an automatically operated point.
Here is a typical turn-out.

You can convert it to an automatic point, with over-ride via two push-buttons and it will cost less than buying a solenoid actuator for the point, plus a CDU module.
AUTOMATIC POINT project comes with 2 reed switches and a motor/gearbox and when the train approaches the point from the siding or via the other rail entering the point, the loco is detected and the circuit changes the point to accept the train. This prevent derailments and saves you having to remember to constantly change the point.
You will have to manually choose when to send the train to the siding.
The project only prevents a derailment when returning.

AUTOMATIC POINT is powered by the track voltage and will operate on a voltage between 9v and 16v DC. It has a 100u storage capacitor to allow the circuit to work when the rail voltage is intermittent.
The servo takes less current and less voltage than a solenoid operated point and that makes it ideal for remote points. You can use thin cable for the wiring.

Turn your manual point into an AUTOMATIC POINT
When a train comes from direction A or B, the
point gets automatically set to prevent a derailment.

Click for large image

There are many ways to position the servo to allow the lever to control the point.
Placing the servo on its side will give better alignment, as shown below:


The image on the left is just an example to show the connection of the servo to the point. The servo can lay down to take up less room.





The servo rotates less than 70 and the gold wire is called the "linkage."
Any electro-mechanical device (motor, solenoid, servo) that operates a point is called a SWITCH MACHINE.
This project will only operate a normal (unconverted) SERVO as the circuit sends PWM signals to the servo to set its angle of rotation.
Talking Electronics has other projects that operate a motor and gearbox or a solenoid, but this project is specially designed to turn a manual point into an automatic point at the lowest cost.
The servo can be placed under your layout or in a plastic model such as a Platelayers Hut.

A platelayers hut can be used to hide the servo

There are many ways to connect the servo to the "switching lever" and here's one way that adjusts the movement of the arm on the servo to the travel needed by the switching lever.
It consists of a machine pin fitted to your layout and another machine pin fitted into it. This forms a  pivot and you can adjust the travel by providing the correct ratio for the gold wire before the pivot and after the pivot.
This arrangement also puts a small amount of tension on the rails, allowing the loco to pass if the point is not set correctly.  

The following images clearly show how the 3.7g SERVO is connected to the point via a LINKAGE:

The Machine pin in the centre of the linkage acts as a pivot and the "crank" in the lever is simply to align the activating arm to the slider on the track.
The gold wire is soldered to the pin so it does not change alignment.

The supply for this project is 9v to 16v DC - but it is best to deliver a maximum of 12v. A voltage higher than 12v will make the 470R and BC338 slightly hotter.
You can deliver 12v AC as the diode and 100u will convert this to a DC voltage and the BC338 will smooth the output with the aid of the 6v2 zener diode.
Nothing in the circuit is susceptible to a small amount of ripple, so AC input is not a problem.

Assembly of the PC board is straightforward.
Fit the resistors first and then the electros, transistors, LEDs and diodes. The last parts to fit are the terminal blocks and switches.
You will need wiring to a 12v supply and you will need to connect the mini reed switches to the screened audio cable and add metal ends to the wires so they can be fitted to the screw terminals.
All these parts are included in the kit as well as 2 very strong super magnets. These are to be fitted under two locos.

Everything fits neatly on the board

All the components are clearly identified.

The two reed switches are carefully soldered to the
leads (very fine screened audio lead).
2 very strong rare-earth magnets
operate the reed switches at 2-3cm
(reed switches separately with 2 magnets cost $4.00)

The kit comes with 2 x 10mm super magnets about 1mm thick and to get the best magnetism from these magnets, place them on the bench about 5mm apart with one magnet having the North pole up and the other South pole up.
Don't worry yet.   When the opposite poles are up,  the reed switch will activate when it is lowered over the magnets at 10mm distance. If no reaction, flip one magnet over. The response will be dramatic. Now glue the magnets to the underside of a loco with N-pole up and the other S-pole up.
One up and one down creates a circular magnetic path through the "leaves" of the  reed switch and makes one leaf "N" at the tip and the other "S" at the tip and the two leaves click together.

Fit the two reed switches near the point but give the servo time to change the point before the loco gets to the point.
Connect the 12v supply and one of the LEDs will illuminate. It indicates the position of the point.
Press the other button and the point will change.  Drive the train through the point (from left to right) and when you return from the siding, the point will be ready for the train.


Automatic Point

$29.50 including reed switches
and servo. 
Click HERE to buy the kit.

1 - 470R
4 - 1k
2 - 2k2
4 - 10k
1 - 47k
1 - 120k
1 - 2M2

1 - 22n ceramic capacitor
2 - 10u electrolytics
2 - 100u electrolytics
1 - 1N 4148 diode
1 - 1N 4004 diode
1 - 6v2 zener

2 - BC547 transistors
2 - BC557 transistors
1 - BC338 transistor
1 - 555 IC
1 - 8 pin IC socket
1 - 3mm white LED
1 - 3mm blue LED
2 - 40cm lengths twin hook-up flex
3 - 60cm lengths screened lead
2 - reed switches
2 - rare-earth magnets
3 - 2-screw terminal blocks
2 - large push buttons with caps
1 - servo with "arms" and 2cm gold wire
1 - 3-pin 90 male connector for servo
30cm fine solder
1 - Automatic Point PC Board

The next module changes the point automatically and has 3 other features so you can design a layout with a loop.
This module is called: LOOP with 2 RELAYS and MOTOR.
You can use either a 3v micro motor and gearbox or a SERVO or a converted SERVO.
You need a loop at the end of your layout and you can select either a SERVO or a converted SERVO to do the activation. The project also comes with a 2-aspect signal. 

Loop with 2 Relays and Motor costs $xx.50  plus $6.50 postage. It is shown in the following image:
Click  Here to order.

There is another COMPLETELY DIFFERENT type of Point Motor. It is used for a KATO point - to change the direction of the point.
Kato point motors operate completely differently and you need a different type of circuit to operate it.
It has a magnetic PUSH ROD. In other words, the plunger is MAGNETIC.  And this means the single solenoid is classified as DOUBLE ACTING. The single solenoid consists of a single winding and has just 2 wires and it operates by reversing the supply. Reversing the supply reverses the magnetic lines of force and this causes the plunger to be attracted or repelled. 
We have designed a module to operate up to 4 points.
You can get the module for 1 point, 2 points, 3 points, or 4 point.
Only the components for 1 point will be fitted for $10.00
The components for 2 points will be fitted for $15.00
The components for 3 points will be fitted for $20.00
And the components for 4 points will be fitted for $25.00
These points are operated separately and individually by toggle switches (4 switches).


 Modules are available for this project from
Talking Electronics for $25.00 plus $6.50 postage.

This module controls 4 Kato points.
(It does not work with any other type of point
because KATO points work by REVERSING THE SUPPLY. All
other points work by alternately pulsing one or the
other coils to get two-way operation.)

Connect the supply to the terminals (at the end of the module).
The Supply can be a Plug Pack (wall wart) or from your train transformer.
It can be AC or DC. 
The AC wires can be connected either way around.
The DC wires will not work if connected the wrong way so you will soon find your mistake. 
Connect the Kato Point Motor to the terminals at the top of the module with the wires either way around.
The module will work with voltages in the range 10v AC to 12v AC 
 or  12v DC to 15v DC and even higher.
The 1,000u electros are 35v so you can use a supply up to 35v.
But 35v may be too much for your Point Motor. 
If the Point Motor "bangs" too hard in each direction, you can reduce the voltage.
Switch all the toggle switches to the UP POSITION so that none of the electros get charged at the moment and none of the Point Motors operate.
Now change any of the points to "main,"  allowing half a second for the circuit to do its job.
If all the toggle switches are DOWN when power is applied, it will put a lot of strain on your power supply as all the Point Motors will try to get activated at the same time. 

The KATO solenoid

The KATO Point Motor Circuit.
This is multiplied 4 times on the PC board.

The circuit is very simple, but it is very clever. The electrolytic gets charged when the toggle switch is in the "down position" and the charging current flows through the solenoid from the supply to the electro.
This makes it change the point to the siding.
When the switch is in the "up position," the energy in the 2,000u electrolytic (this is 2 x 1,000u electrolytics) flows out and through the solenoid, from the lower wire to the wire connected to the supply. This is in the opposite direction to previously and is actually a VOLTAGE REVERSAL. And because the voltage is reversed, the current flows in the opposite direction.
This activates the solenoid in the opposite direction and the point changes to the main line.
This very simple circuit does TWO THINGS. It supplies a pulse of energy so the solenoid does not get hot and creates a voltage reversal so the solenoid activates in both directions.
The LEDs on the board show the position of the point.  
The power diode
does two things. It allows AC to be connected and although only the positive cycles charge the 1,000u electrolytic, this is sufficient for the circuit to operate perfectly. The diode also prevents DC connection around the wrong way. DC around the wrong way will not illuminate the LEDs and the 2,000u will leak when voltage is applied in the wrong direction and not charge properly.
The 1,000u also reduces the impedance of the supply so the 2,000u can charge quickly and operate the point motor. 
Getting a Point Motor to activate depends on the voltage you deliver to the module.
Kato Point Motors are very delicate and do not require a lot of energy for their activation, and you should start with a 12v supply.
If you think the Point does not respond and "click" strongly, you can increase the supply by adding a 5v plug pack in series with the 12v plug pack to get 18v.
If you are operating 2, 3 or 4 points at the same time, you will need to increase the supply voltage, maybe up to 24v. The maximum voltage is 35v - 36v and this is obtained by connecting a 24v and 12v plug pack in series.
You can use AC from any source, but remember, any AC voltage will be converted to the voltage marked on the supply PLUS 50 PERCENT MORE!!!!
Only use the minimum voltage needed and this is found by decreasing the voltage until you do not get reliable operation, then increasing the voltage by an extra 3v to 6v.
None of these voltages will damage or over-heat the point motor, they will simply make the point "click" or "bang" loudly in each direction. 

Connecting the Kato points to the module
The module is supplied with the components soldered to the PC board,
but the toggle switches are supplied separately as they are too tall for the
posting box.  This allows you to solder them to the PC board
or fit them to your control panel.

You can buy this module for 1, 2, 3 or 4 Point Motors and only the
necessary components will be fitted.

 Modules are available for this project from Talking Electronics for $25.00 plus $6.50 postage.


Some of the modules and power supplies come with free wire and switches and terminal blocks to make connection easy.
Hook-up wire and stranded wire is very expensive by the metre and the length we supply will get out out of trouble.
The spring-terminals connector block are very cleverly designed. But you have to be an Einstein to work out where to put the wire.
When you push the lever (button) on the top, the metal spring produces a gap just below the button and when released, the spring digs into the wire and you cannot remove it. You will get some of these FREE when you buy the modules. The wire will be different colours and different thickness.

Here is another clear picture of how to fit the wires
into the terminal block.
The wires go above the metal spring and just below the "push-button."
When you push the lever on the top of the terminal block, the spring is depressed and a it creates a space for the wire. Releasing the lever grips the wire very tightly by the edge (end) of the flat spring.

Let's look at the 20 choices and describe the differences.
You will see some choices turn a manual point into a remotely-operated point and some prevent a solenoid point: "burning out."
These choices are classified as the BASIC DESIGNS.
They are the simplest designs to do the simplest job.

Later, we will explain modules that change the point slowly and modules that automatically change the point when the loco approaches and modules that show the position of the point on your control panel. 
For a simple layout and those who are just starting to improve their layout, the choices above will provide the answer to remotely control a point and also show its position on your control panel. 
Read the features of each module and make sure you have the required voltage available. You can get almost any voltage (and current) from one or two PLUG PACKS. These provide safety and security and prevent you being able to touch the 110v or 240v MAINS.
Under NO circumstances should you make your own POWER SUPPLY with soldered wiring and leads around your control panel carrying MAINS VOLTAGES. One day a young visitor may come in and be looking and feeling around your wiring and touch something LIVE !!!

   to Index
Point Motors take a high current when they are operated for the very short time they are intended to work.
Most point Motors have a coil resistance of about 3.8 ohms and when operated on a supply of 12v, this will allow 3 amps to flow.
Normally, wiring for 3 amp will require medium duty hook-up wire because the current will be flowing for a long period of time and thick wire prevents it getting hot. But with a solenoid-type Point Motor, it is only activated for less than a second.
This means thin hook-up wire is perfectly suitable.
3 metres of thin hook-up wire will have a resistance of about 1 ohm and if 3 amps flows, the voltage drop across the wire will be 3 volts.
But most Capacitor Discharge Units are charged to a voltage higher than 12v and can be 24v.
If we take 24v, the current will be 5 amps and the voltage drop will be 5v.
This gives the solenoid 19v.
The Capacitor Discharge Unit is designed to give 24v at the beginning of the pulse and gradually drop to almost zero after less than 1 second.
This give the solenoid Point Motor an initial kick to start moving and then the current gradually reduces so the "end clunk" is not so strong.
This means the wiring to the Point Motor can be almost any thickness as it has very little effect on the operation of the solenoid.
  to Index



Talking Electronics has produced a number of different TRAIN THROTTLES.
These need either AC or DC input and produce 0v to 12v DC output.
If you have an AC supply such as: 10v AC to 12v AC, the Throttle Circuit below will produce an output of 0v to 12v DC - that is what it is designed to do.
If you have a 12v DC supply, the voltage-drops across the input power diodes and the control circuitry, will reduce the output to about 10v DC. 
This means you need an input voltage of 14v DC, to get 12v out, and this will require 2 adaptors in series or a set of 4 Li-ion cells.
The POWER SUPPLY project described above uses 4 Li-ion cells to provide a voltage of about 14.2v DC to 14.8v DC and is adjustable. It can be used as a TRAIN THROTTLE.

Most locos take about 300mA to 500mA and need a voltage of about 12v for full speed.
A 1Amp power supply or 1Amp THROTTLE will just be capable of operating two loco's.  

There are two types of TRAIN THROTTLE:
TypeA produces an output 0v to 12v DC and you need a reversing switch to reverse the train.
TypeB has a control with 0v in centre-position and "left" reverses the train at a gradual increase and "right" drives the train forward at an increasing velocity. No change-over switch needed.
This type of Train Throttle can be PWM and provides pulses of energy. It "kicks" the motor in bursts of about 600Hz and allows it to start the train very slowly. The "kicks" are very rapid and sometimes you can hear the "buzz" from the motor.
These circuits require an input voltage of 14v DC, so the full 12v DC can be delivered to the motor (as up to 2v DC is lost in the circuitry).

Here is a circuit and photo for typeA and the wiring for the reversing switch:

Two Amp Power Supply circuit diagram. It is also called 2-amp THROTTLE

The completed project, showing the placement of the parts

The input voltage can be AC or DC. 
The DC voltage needs to be at least 16v6 to get 12v DC out. If you supply 17v to 20v DC, nothing will be damaged.  Just the 470R resistor will get slightly hotter when the input voltage is above 18v.

The 2-Amp POWER SUPPLY project is HERE
Kits come with 0-2 Amp meter to show the current. The ammeter is not a square meter as shown above but a side-meter as shown in the POWER SUPPLY project.  But it is FREE, so don't complain. 
$12.50 USD plus $6.50 USD postage.
Click  Here to order.

You will need a double-pole double-throw toggle switch to reverse the train. Ask for it.  $2.50 extra.

Connecting a reversing switch


TRAIN THROTTLE No2.  (kit:   $18.00 with leads) Click  Here to order.
See the project: HERE
This circuit connects an AC transformer (or a DC supply) to a track to provide a voltage from 0v to max voltage (depending on the voltage of the transformer). 
The transformer can be AC or DC and any voltage from 12v to 18v.
The throttle handle connects to the 1k pot.
The diode on the output protects the transistors from reverse polarity (if  another controller is also connected to the rails).
The circuit is limited to about 1amp due to the 1N4004 diodes.

Here are two controllers that may be available from Model Railway suppliers and hobby shops. They are expensive but look really nice.
In this article we are showing you everything because some hobbyists want to build it themselves and others want to buy a ready-made item.

Transformer with 12v AC output and 18v AC

An impressive throttle can be built by using the following circuit and the THROTTLE PC Board in the kit (the
lever handle shown above is not available).

   Train Throttle Circuit

The 8 power diodes are now replaced by 4 x 1N5404

AC plug packs are very difficult to buy, but 12v 1-amp DC or 2-amp DC can be
purchased at very low cost.
You can increase the output by 1.5v if you connect the positive and negative leads of the DC plug pack to the following points on the PC:

The layout of the PC Board.
You can connect the plug pack directly to the points shown
on the diagram above. You do
not have to remove the diodes.

Wiring the pot, power input wires and reversing switch to the PC board

The control knob for the Throttle kit

The $2.50 plug Pack above was purchased as 12v @ 1 amp.  It was easily opened-up via a screw and clip, to reveal the PC board shown below.
The output voltage is determined by the zener diode at the front of the board. The 12v zener was replaced with 15v and now the output is 15v DC. I would limit the current to 800mA, but a 15v supply can be connected to many of the throttle circuits to give 0v to 13v DC output. 

The new 15v zener converts this power adapter to 15v output.

You can also use a white LED in series with the
12v zener diode to get 15v output. Note the cathode of the zener is connected
to the cathode of the LED and the 1k current-limiting resistor is
linked with a jumper.

This gives you a very low cost throttle.


 THROTTLE WITH PWM   Kit: $28.50 plus $6.50 postage. 
Click HERE to buy a kit.
Built and Tested: $35.00 plus $6.50 postage. Click HERE to buy a module. 
This is our latest design with forward and reverse via the yellow CONTROL POT. This project does not need a reversing switch as the pot provides zero speed when at 12 O'clock and reverse when turned to the left and forward when turned to the right. The output is Pulse Width Modulated (PWM) to give the loco smooth starting.
By this we mean the motor gets pulses from the throttle that allow it to start very slowly.
The module is capable of delivering 3 amps (due to the thickness of the tracks) and the power diodes are 5 amp. Additional heatsink fins will be needed for currents above 2 amp. But we suggest a 1-amp supply for most loco's.
The 4 FETs on the output bridge are capable of handing more than 10 amp and the trackwork on the board can be modified to handle 5 amps by soldering tinned copper wire along the tracks identified with additional solder pads.  This means the controller can be used for garden layouts where the loco will draw 5 amps. If you want to control more than 5 amps, you will need to connect the supply directly to the MOSFETs in the bridge and by-pass the 5 amp diodes.
The switch at the right is the on-off switch. The two LEDs on the board indicate forward and reverse, in case you cannot see the loco on a large layout.

All the digital signals are controlled (and generated) by the microcontroller and the pot determines the timing of the waveform and the activation of the H-bridge.
The two lower MOSFETs turn ON or OFF to take one or other of the output leads to 0v.  At the same time the top, opposite, MOSFET is switched ON and OFF at a fairly low frequency (about 600Hz) to provide pulses to the motor.
The ON-time is increased, compared to the OFF-time to increase the speed of the loco.
The THROTTLE WITH PWM module comes with connectors that are fitted in place of rail joiners to deliver the voltage from the throttle to the track.

Connect a plug pack and the throttle project is ready. 


This type gives better current capability.

You can request the following type if you do not want to use the rail joiners:

It will just pass 1 amp.

The following images of controller are called DC CONTROLLERS. They increase and decrease the DC voltage and most have a reversing switch. There is nothing wrong with these controllers, but if you want to start the train very slowly, and have a controller-knob that has both forward and reverse, THROTTLE WITH PWM is the upgrade.
If you have one of the controllers shown below or a similar type that has a 0-100 scale AND a reversing switch, you can connect its output to the input of
THROTTLE WITH PWM and get the new features.


Connect your throttle to the mains and turn the knob or lever to maximum.
Measure the voltage coming out of the throttle and make sure you identify the positive lead.
Now turn it off and connect the positive lead to the "+" DC screw terminal on
Now connect the other lead to the "-" DC terminal on
Put your throttle under your layout, making sure you do not touch the handle or the reversing switch.
Now connect your track to the two screw terminals marked "to track" on the
THROTTLE WITH PWM module will use your throttle as a power supply and deliver PWM to your layout via the forward/reverse knob on THROTTLE WITH PWM.

The above 7 controllers are suitable for adding to THROTTLE WITH PWM module


Some of the following controllers deliver just 7v and some are up to 16v AC output and/or 16v DC output. They all have forward/reverse on the control handle so the only improvement you will get by connecting to the THROTTLE WITH PWM module above is PWM.

Here is the wiring from your controller to THROTTLE WITH PWM module
to provide PWM and forward/reverse via yellow control knob.
The module also comes with track connector as shown above.
When everything is connected, the voltage to the track will be
slightly less than the output voltage of the Athearn controller,
due to the voltage drop across the diodes on the PWM module.

The Transformer
You can find suitable transformers in the oddest of places. Here is a 12v,  4-amp transformer from a 50 watt down-light. The light was replaced with a 10 watt LED light and it produced 3 times more light !!
The 50 watt transformer makes an ideal supply for a throttle and at 4 amps, it has enough current for other items too.
The 12v2 AC produces 18v DC after rectification minus 2v to 3v drop across the diodes in the bridge.
The circuitry in the throttle drops another 2v and the output was measured as 13.5v DC.
All our down-lights were replaced with 5watt or 10 watt LED lights and the rooms are much brighter, with a whiter light and the wattage is less than 25% than before.  Now we have 6 transformers.
Transformers like this can be found in all sorts of equipment and they are ideal for the throttles we have described. You just have to check everything.

Servo Speed
(slow) Controller


Buy a Module
Fully Built $25.00 plus $6.50 postage


Sometimes you want a servo to rotate slowly to produce animation that is realistic for the scale model you are designing.
This project provides different speeds.
It also has a repeat feature that activates the servo back-and-forth at the speed you have chosen.
It allows you to ANIMATE things.

The output of the servo moves about 70 degrees as this will give the greatest "throw." You can select the hole on the arm to produce the travel you want.
The repeat feature allows you to produce models with "pumping action" or "see-saw" action as a servo is smaller and cheaper than buying a motor and gearbox.

You can use it to control a point or a set of boom gates as well as swing-gates or a drawbridge or crane or a "see-saw" action.  It has so much potential. You can get a smaller servo or a linear-movement servo for very tight spaces, but there is nothing cheaper than the standard 9G servo.

Here is a set of gates controlled by 4 servos.
Our module can be used to control this:

All the functions are in the PIC12F629 microcontroller

The module comes with 2 Test Switches and extension lead for servo, plus the servo and 0.6mm and 0.7mm push rods. You just need a 8v to 12v supply.  .

All the complex electronics in the project above can be reduced by using our module and a servo.

Theory, Test Gear 
& More Projects

Talking Electronics has produced a lot of matrix board in all sorts of sizes and shapes so the board is ready and neat for the layout of components. These boards cost just $2.00 for the small boards, $2.50 for the medium size and $3.00 for the larger boards.
Simply email Colin with the number and size and they can be sent to you.
Click  Here to order

SMALL BOARDS $2.00 each
MEDIUM BOARDS $2.50 each
LARGE BOARDS $3.00 each
Click  Here to order

     to Index

I test all my projects with a $5.00 multimeter !!
Because an analogue multimeter puts a load on a circuit and the reading MUST be genuine.
Secondly, an analogue multimeter will show fluctuations in a circuit and show when a certain part of a circuit is not maintaining stability.
And thirdly, an analogue multimeter will respond to changes and pulses much faster than a digital meter.
Lastly, if I can design and test a circuit with a cheap meter, everyone else should be able to do the same when using a more-expensive meter.
Finally, an analogue meter lasts a lifetime. And if you damage it, the cost is only $5.00
And you get 500mA range, a digital meter gives 200mA.
Analogue Meters are on eBay
I have digital meter when I want to read voltages accurately.

If you buy two multimeters, you can test currents up to 1 amp by placing the multimeters in PARALLEL as shown in the following diagram:

The red and black probes go to the positive and negative terminals of the project you are testing and you simply ADD the current readings (shown by the pointer on each meter) to get a final value (up to one amp). 

Current flows through the multimeter from the positive probe to the negative probe and the arrow on top of the meter above shows this direction.
This is how we arrive at that statement:
When taking a measurement of CURRENT, the voltage on the positive probe will be very slightly higher than the voltage on the negative probe, because a very small voltage will be dropped across the CURRENT RESISTOR inside the meter. The meter is actually measuring the voltage across this resistor and you are reading the pointer where the scale says 0-500mA
We know that current flows from positive to negative and when you trace the circuit above, you can see the meter is part of this circuit.
When measuring CURRENT, you use exactly the same reasoning as when you are measuring voltage.
Look at the circuit or project and work out which point will have the (slightly) higher voltage. The red probe goes to this point.
When measuring CURRENT, even the wires will have a slightly higher voltage at one end. This is the end for the red probe.
When measuring CURRENT, the circuit has to be CUT and the probes inserted into the CUT.  You cannot measure the current taken by a component by placing the probes "across it." You have to cut a wire or a track or desolder one of the wires.

If you cannot remember how to connect a multimeter when testing CURRENT, tilt it slightly so the positive terminal is higher than the negative terminal and lay the red probe on the bench, HIGHER than the black probe.
Now connect the red probe to the positive terminal of the battery and the black probe to the positive "input" of the project. Use another jumper to connect the negative of the battery to the negative (0v) of the project.

See how the current has to flow across the meter (from left to right) to make the pointer read "up-scale". The probes are connected to the battery as shown in the diagram above. 
But don't be surprised if a project does not work perfectly when a multimeter is connected like this. The meter changes the "impedance of the supply" and the project may be relying on a "low impedance supply" - equal to a NEW - FRESH - battery.
The meter turns it into an OLD - WEAK - battery and not only will the project fail to work, but the current reading will be incorrect. 

     to Index

There are many different types of SERVOS on the market. Some are very cheap while others are very expensive. The main difference in cost is due to plastic gears Vs metal gears.  We only need plastic gears.
We have simplified the requirement and come to the conclusion that there are two types suitable for controlling a point. The "normal" size is called "9g" and the "Micro" size is called "3.7g." You can see by the dimensions above that the difference is only very slight.
But you have to be careful.
There are many different manufacturers with the same plastic body and the same appearance. Some will work in our applications and some will not. The program in the "electronics" (the PCB inside the case) is slightly different.
In some of our projects, we slow-down the rotation of the arm to make the movement "realistic."
All the Micro SERVOS work in this "slow-down" application, but only 30% of the 9g models work successfully  - some jitter when travelling slowly and there is no way to determine the faulty ones without testing each servo.
In addition, some of the 9g models can rotate 360 because there is no "stop" on the output shaft. This is not a problem in any way.
All it means is this: the shaft cannot get jammed against the "end-stop."  You cannot digitally rotate the shaft any more than about 180 to 270, as the electronics is only designed to allow this much rotation. But if you position the shaft at the exact "dead-spot," the servo will not know "which way to turn" and you have to activate it twice and it will swing around to the correct position. Under normal operating conditions, the servo will never land on the "dead-spot" and you will never have a problem.
In all other respects, the two servos are identical. The Micro version is slightly more expensive and ideal for controlling a point as it can easily be housed in a PlateLayers hut. (see image up further)

There is another SERVO on eBay called TENSTAR ROBOT 9g and it has no "end-stops." This is a vast improvement as the servo will not get "jammed" at the end of its travel.
The servo has a "pot" as the feedback but it does not have any "stops" and thus the wiper passes the end of the curved track. 
I tested this servo by trying to find the "dead spot" where the servo did not respond to a position that would normally be past either of the "end-stops." The program in the servo detects when the wiper is not on the track and sends the arm to a starting position  -  proving this servo is the best one to buy. 
"No stops" means the servo will not get jammed if it is forced (by an outside force). Sometimes, when these servos are used in a Robot-Fighting situation, they get forced to move (when in a collision) and this jams the gears.  This servo does not have that fault.
This servo also operates slowly (when connected to some of our modules) and does not "jitter" when used in our projects.

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The reed switch only detects a magnet when the magnet is in  positions A and C.  This is because the magnetic flux produced by the magnet "hits" the left or right reed and magnetises it in a process called TEMPORARY MAGNETISM or INFLUENCED MAGNETISM and since the other reed is not magnetised, the two reeds "stick together." When the magnet is in the centre of the reed, both reeds get magnetised by the North pole of the magnet and they do not make contact.
This means the reed switch MUST be placed "along the track" (parallel with the rails) so the magnet has the greatest opportunity to activate the reed. It does not matter if the north or south pole is near the reed switch - you need the magnet to sweep across the reed switch from one end to the other to make sure the reed switch activates.

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Hall Device
The Hall Device must be connected the right way to the circuit.
Here is a close-up the Hall device with the output lead connected to the first lead. These two are connected to the white lead of the screened audio cable. The middle wire is the ground connection and it goes to the screening wires. 
This is very unusual way to wire a Hall device, and is just another clever trick by Colin Mitchell to show how you can do just about anything with electronics.

Connecting the screened lead to the Hall device

This is the circuit for the Hall Device

This is just one way to connect it to a circuit when you want to be able to connect a Hall Device or a reed switch to the same input terminals of a project.

Connecting the Hall wires to the module

The internal circuit of the 3144 contains a number of "Building Blocks"

The Hall device is being used in an unusual way in this project, with the output connected to the "supply lead."
The circuit above shows some of the "building blocks" inside the 3144 and one of the features is the amplifier block that detects a signal from the Hall block to turn ON the output transistor.   Some of the other Hall devices turn-on-slowly as a magnet is brought closer to the detecting face. Make sure you do not use one with this feature, as we have not checked it and it may not turn on hard enough to start the module flashing. The main reason for it not working may be the low impedance of the input line (on the Flashing Lights Module) - due to the 220R load resistor.

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This project tests LEDs and tests for continuity and tests for other things as well.
It's a very handy piece of test gear.
See the full project HERE

The LED Tester Circuit

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Track Pick-offs are available  from Talking Electronics for $2.00 plus postage.
This Printed Circuit board is fitted between the sleepers and has contacts to touch the rails so the voltage on the track can be monitored or delivered to a project.
If the current taken from the track is very small, it will not interfere with the operation of the train(s) on the layout and is called LEACHING.
A little bit of power is taken from the track and this saves running wires all the way back to your control panel.
Talking Electronics has designed 2 of these TRACK PICK-OFF boards:

Track Pick-Off MkI has two track joiners soldered to the board and this is fitted between two sections of your layout.
The images below show this board and how it it fitted to the track: 

Twin lead or screened lead can be used for the
Track Pick-off PC board

Here is the module connected to a project:

If it is not easy to connect the track joiners to your layout, we have:

Track Pick-Off MkII.  It has two springy clips that touch the inner parts of the rails and make electrical contact.
The board comes with the two clips soldered in place and you need to remove the plastic from between two sleepers to allow the board to fit. Twist the board into position and give the spring clip a twist with a pair of pliers so it pushes against the rail.

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This project tests the voltage on your track.
It's another very handy piece of test gear.
See the full project HERE
The Track Tester kit costs $10.00 AUD plus $4.50 AUD postage.
The Track Tester is also available ready-made for $16.50 USD (posted)
It alerts you to the presence of DCC via the piezo diaphragm and the voltage of your track at all parts of the layout. 
Click  Here to buy a Track Tester.

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Requested by William Hicks:
This circuit detects when the tracks are overloaded by too many trains.

Note:  Each 1R resistor needs to be 0.5watt   0R22 needs to be 5watt!!
The circuit will drop 1.4v when full detection-current is flowing.

Here is the simplest over-current circuit:

The reed switch closes when about 1.5 amps flows for 3 turns wrapped around the centre of the reed switch. 2 turns will detect about 2 amps.
Keep the reed switch at least 6cm from the mechanical buzzer as the magnet inside the buzzer will turn the circuit ON all-the-time.
The sensitivity of reed switches vary enormously and the ones we are using require 19 turns to detect 1 amp then tapped at 7 turns, 2 turns, 2 turns and the final winding is 8 turns. Nothing is linear with the turns and magnetic flux  because the turns are at different locations across the reed and have differing effect.
You cannot get a simpler circuit and it only drops 22 millivolts when 2.5 amps flows.
It is ideal for detecting SHORT CIRCUITS. If something falls across the tracks, the buzzer will sound.

The Overload Alarm Module is fitted between the Train Power Supply and the Controller

Kits are available for this project from
Talking Electronics for $8.00 plus $4.50 postage.
The reed switch and coil with tappings is already fitted to the board as this has to be calibrated with a 3-amp power supply and load.




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This circuit flashes two red LEDs for a model railway crossing.
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A flashing LED is used to create the timing for the flash-rate and the transistor provides the alternate flash for the second set of LEDs. The first circuit comes off the web, but Colin Mitchell doesn't think it will work. See his circuit below.

The top two 1k resistors are current-limiting resistors and can be increased if you want the LEDs to be dull.
The 2k2 makes sure the two LEDs are completely turned-off because the flashing LED draws a small current when it is off and this shows in the two LEDs. The lower 1k may need to be reduced to 470R to completely turn the transistor OFF. The other circuit does not have any of these features. The flashing LED has to be an ON-OFF flashing red OR green LED.  Not a red-green flashing LED or a RED-GREEN-BLUE flashing LED. The flashing LED actually has an in-built resistor and will work on 2v to 5v. But we are using its feature of "taking a small current" when illuminated and then "taking almost zero current" when not illuminated, to "switch the transistor."  
You can get the CROSSING LIGHTS plastic mouldings from Talking Electronics. They will take 3mm LEDs.
Cost: $6.00 for 2 Crossing Lights with 4 LEDs and 2 metres of fine 0.25mm enamelled wire. .
You need to "push-out" the red lens and fit the 4 x 3mm red LEDs and carefully solder wires to the LEDs.

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Here's a clever circuit using two 555's to produce a set of traffic lights for a model layout.
The animation shows the lighting sequence and this follows the Australian-standard. The red LED has an equal on-off period and when it is off, the first 555 delivers power to the second 555. This illuminates the Green LED and then the second 555 changes state to turn off the Green LED and turn on the Orange LED for a short period of time before the first 555 changes state to turn off the second 555 and turn on the red LED. A supply voltage of 9v to 12v is needed because the second 555 receives a supply of about 2v less than rail. This circuit also shows how to connect LEDs high and low to a 555 and also turn off the 555 by controlling the supply to pin 8.  Connecting the LEDs high and low to pin 3 will not work and since pin 7 is in phase with pin 3, it can be used to advantage in this design. 
Here is a further description of how the circuit works:
Both 555's are wired as oscillators in astable mode and will oscillate ALL THE TIME when they are turned ON. But the second 555 is not turned on all the time!
The first 555 turns on and the 100u is not charged. This makes output pin 3 HIGH and the red LED is not illuminated.  However the output feeds the second 555 and it turns on.
Output pin 3 of the second 555  turns on the green LED and the second 100u charges to 2/3 rail voltage and causes the 555 to change states. The green LED goes off and the orange LED turns on.
The second 100u starts to discharge, but the first 100u is charging via a 100k and after the orange LED has been on for a short period of time, the first 555 changes state and pin 3 goes LOW.
This turns on the red LED and turns off the second 555.
The first 100u starts to discharge via the 100k and eventually it changes state to start the cycle again.
The secret of the timing is the long cycle-time of the first 555 due to the 100k and the short cycle due to the 47k on the second 555.
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This circuit produces traffic lights for a "4-way" intersection. The seemingly complex  wiring to illuminate the lights is shown to be very simple. This circuit is used in the next article.  
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 4-Way Traffic Lights

 Kits are available for this project from
Talking Electronics for $20.00 for the parts and PCB plus
$5.00 for each overhead light (4 needed) plus $6.50 postage.
The project is also available fully assembled and tested for $25.00 plus postage.

This project adds realism to your layout with functioning traffic lights at an intersection.
You can use column signals or overhead signals.
The PC board shows the condition of the lights and you only need to extend leads from the board to the signals, to complete the project.
The supply MUST be 12v as the voltage of the LEDs adds up to about 10v and any voltage below 12v will not allow some of the LEDS to illuminate AT ALL - and you will think the project is faulty.


This image shows how to connect the very fine wires from the end of the post to the screw terminals. The kit contains fine screened lead and two of these leads are used for each overhead signal to the terminals. Two overhead signals are joined in parallel to the first set of four screw terminals and two overhead signals are connected to the second set of four screw terminals.

This wiring diagram shows how the LEDs are connected in the over-head light. All the anodes are connected to the black wire and the cathodes emerge as Green, Orange and Red. The 4-screw terminal block is looking at the where the wires enter the terminals and this is clearly shown in the photograph above.

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Jim's Crossing Lights MkIV

Kits are available
Talking Electronics for $18.00 plus $4.50 postage.
See the FULL PROJECT HERE with more details of the Hall Device
The kit is the latest module for type-A lights and type-B lights
Fully built and tested modules come with 2 reed switches (1200mm leads) and 2 super magnets for $25.00 usd  plus $6.50 usd postage

This project operates crossing lights automatically when the train enters the crossing and turns them off automatically. The flash-rate can be adjusted as well as the brightness of the lights and the overall length of time for the flashing. No other module on the web offers these features.
The latest module is version #5 and has a change-over switch for Common Anode lights and Common Cathode lights.  This is called Type-A and type-B lights

Two LEDs on the module indicate when the lights are flashing and the module comes with 4 extra LEDs for those who have bought crossing signals without the LEDs installed. 

Jim's Crossing Lights MkIV circuit

The circuit has a number of very clever features. .
It is
Jim's Crossing Lights MkIV

It uses two 555 ICs to provide all the functions. The signal diode on the first 100u discharges the 100u quickly when the circuit turns off so the timing can restart again with full duration.
The flash-rate can be adjusted because everyone says "the flash-rate is not right."
The "duration of the event" can be adjusted to suit your layout. 
The brightness of the LEDs can be adjusted to suit the type you are using.
The circuit will take 12v DC as the ideal voltage. Do not go below 10v DC as the voltage drops across the various components gives the second 555 less than 5v because the power diode drops 0.7v, the 47R drops about 1.5v and the first 555 outputs a voltage and current via pins 3 to the second 555 for all the rest of the circuit. There is about another 1.5v drop in doing this.
The circuit will work perfectly up to 15v DC and when you supply a DC voltage higher than 15v, the 15v zener comes into action and any voltage above 15v, will be dropped across the 47R resistor. If you supply 16v, the voltage drop across the resistor will be 1v and the current that will flow through the 47R will be
I=V/R =  1/47 = 20mA. This current will also flow through the 15v zener and is called the REGULATION CURRENT or wasted current and the wattage dissipated by these two components will not be noticed at the moment. But if the supply voltage is raised to 20v, the "wasted current" will be 100mA and the wattage dissipated by the 15v zener will be 15 x 0.1 = 1.5watts. The zener is 1watt and it will burn out at 1.5watts, so the limitation of input voltage is 18v.
The zener in this circuit is NOT called a zener regulator but a ZENER LIMITER.   It prevents voltages higher than 15v because the 555 IC's are limited to 18v operation. 
The circuit is designed to take either two reed switches OR two Hall effect devices (switches).
The Hall switches are connected in a very clever way. They are connected so that they sit with a load resistor of 220R and due to the small current they require, the voltage at the "pick-off" point is about 9v for a 12v supply.
When any of the input devices detects magnetic flux, the circuit switches ON and the output lead effectively goes LOW. The voltage goes to 0v for the reed switch, but the Hall device is different. This "pulls" the "pick-off" point lower and as it gets lower, the voltage to the Hall device drops too. As the voltage across the device reduces, its capability to keep the output low is reduced and thus the output does not drop to 0v, but stops at about 2-3v. At this voltage the device is still working and pulling the output as low as possible, (with the current that is available at this low voltage).
You can combine one reed and one Hall device as the 220R will cover the requirement of either/both devices.    
The voltage at the "pick-off" point is detected by Pin2 of the 555. This pin only detects a LOW and when the voltage drops to 33% (or less) of the voltage on pin 8 of the chip, it starts to "time the event."
The timing of the event is done by charging a 100u via a resistor(s) and when Pin6 detects 66% of the voltage on the Pin8, the output Pin 3 goes HIGH and the project turns OFF. The only component taking current when the project is not flashing, is the first 555 and this takes up to 10mA. 
To reduce the brightness of high-brightness red LEDs, it takes up to 10k via a mini trim pot. This will allow all different types of LEDs to be used.

Everything is identified on the PC board  

The module is available fully-built and only needs to be connected to 12v DC. Connect the reed switches or Hall devices to the input terminals and switched ON.
Bring the magnet up to the reed switch or Hall device and work out the distance at which it is detected.
The magnet must be around the correct way for the Hall device as it detects just the North or South pole, according to the way the Hall device is placed.
The detection range is about 5mm for the tiny super-magnets we supply in the kit
This will help you place the reed switch or Hall device in the centre of the track and glue the magnet under the loco, and have the gap small enough to make sure the circuit responds every time. 

There are many different types of crossing lights and most of them have three wires.
The black and red wires are shown in the diagram below. 

The Crossing Light above is available from Talking Electronics for $5.00
You will need 2 of these.  (HO scale)

This crossing Light is on eBay

Jim's Crossing Lights
plus $4.50 postage
Kits are available

1  - 47R   all 0.25watt
1  -  220R
2  -  1k
1  -  2k2
2  -  4k7
1  -  10k
1  -  100k
2  -  10k mini trim pots
1  -  100k mini trim pot

3  -  100u electrolytic

1  -  1N4148 diode
1  -  1N4004 diode
1  -  15v 1watt zener diode
6  -  3mm red LED

2  - 555 ICs
2  -  8 pin IC socket 
1  -  BC547 transistor

2m  -  2-core cable for input devices
2  -  mini reed switches  or
2  --  Hall effect devices
2  -  10mm x 1mm super-magnets
1  -  2-way terminal block
2  -  2 pin sockets - round pins
2  -  4 pin sockets - round pins (called
                                machine pins)
1  -  mini slide switch
1  -  20cm very fine solder 

1  - Jim's Crossing Lights MkIV PCB

You will need 2 x Crossing Lights as
shown in the images above

TWO versions of this project are now available because some 2-aspect lights have a black wire that goes to the anode of each LED via a resistor and some are wired with the black lead to the cathode of the two LEDs.
The difference between the two PC boards can be clearly seen by the white frame around the output pins.

The wrong type of Crossing Light will NOT work with the wrong module.
You can test each Crossing Light with a 6v battery and 1k resistor or use the LED Tester project.
With the ver2 PC board, the LEDs must illuminate when the positive of the 6v battery is connected to the black wire and the red wire is connected to the 0v of the battery. You will need a 1k resistor to prevent the LEDs burning out, just in case the Crossing Light does not have an internal resistor.
But when the Crossing Lights are fitted to either module, the PC board has current limiting resistors under the board and a 10k pot to reduce the brightness to any level.


A new version of JIM'S CROSSING LIGHTS (called ver5) has been produced for customers who cannot work out which type of lights they have installed. It has a change-over switch and works with both types - very clever !!!

The image above shows the fully built and tested module. It comes with 2 reed switches on 1200mm leads and 2 super magnets for $25.00 usd  plus $6.50 usd postage.  Order a module:  Jim's Crossing Lights for TypeA&B lights

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 Jim's LEDs is available  from
Talking Electronics for $18.00 plus $4.50 postage.

This is another module requested by Jim Hamilton who supplies Z scale signs, houses and lighting to hundreds of modellers. His website is: Scaleworkshop,  South Australia, Mob 0412111152

The module is a DISTRIBUTION BOARD capable of illuminating 30 LEDs across your layout.
There are 4 separate brightness controls. Two controls have shafts that can be easily adjusted and two controls are via mini trim pots.
The Distribution Board comes fully built and has sample LEDs to show the brightness.
6 flying leads can be fitted into the JST 2mm sockets and 12 sets of LEDs can be fitted into the screw terminals.
The end of the module has 12 sets of female machine pins and you can insert 0.5mm wire into them.  
The input voltage can be 9v AC or DC up to more than 20v as the 7805 regulator delivers 5v to all the LEDs. As you add more LEDs, the regulator might get warm and you can add a heatsink if you cannot hold it in your fingers.   
These modules are very popular as they solve the problem of illuminating stations, roads and scenes with the appropriate level of brightness. You can use any colour LEDs as each section is individually protected with a current-limiting resistor.

6 SIGNALS is available  from
Talking Electronics for $19.00 plus $4.50 postage.
Plus $4.00 for the two reed switches

This project adds interest to your layout by providing SIGNALING

The timing for this project starts when the loco passes over one of the reed switches and the train strops at the first signal.
On the 6 SIGNALS module you need to program the time for the first signal via pot #1 through to the sixth signal via pot #6.
On the PC board you will find the timing for each pot - from a few seconds - to about 15 seconds.
The first signal remains red for say 6  seconds and then you can progress to the next signal.
The second signal will remain red for your second programming time and then you can advance to the third signal.
The first 3 signals will be activated by the reed switch at the bottom of the diagram (see diagram below)
And the next set of 3 signals will be activated by the second reed switch.
The second reed switch will start the timing when the train passes over the switch and this will allow you to obey signals 4, 5 and 6.

The signals on the left are the authors prototypes to test the module and are not part of the items for sale.
You will need to buy signals shown in the images below to suit your layout.
There are many different types of signals on eBay.




The layout shows the two reed switches and the 6 signals. The loco travels from the bottom of the diagram to the top.
The timing of the lights is designed to make you stop at each control-point and this adds a bit of activity to each circuit of the layout.

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To-Fro Module (built)  $35.00USD
post $6.50USD

To buy:
To-Fro Module


This module uses an opto-coupler to turn ON each transistor.  It is an AUTOMATIC REVERSER and will accept AC or DC input from 12v to 15v DC or up to 12v AC (this becomes 17v DC via the module).
It also has a THROTTLE CONTROL to produce very slow travel via PWM with increments from just about zero to nearly full speed. The PWM ensures the loco will start at a very low setting.

You only need an isolated section of track. Simply connect the two alligator clips to the rails around either way.
Fit the
Set the speed to the lowest value and the time to the shortest number of seconds. Increase both values to suit the length of track you are using. This will allow the train to constantly shuttle from one end to the other.
Ideally you can use a small track-maintenance vehicle for this.

Turn the module ON and the train will move slowly towards the reed switch in short bursts until the reed switch is reached. The loco will stop and move in the other direction and then detect the speed and time you have set on the two pots.
The speed of the train will depend on the setting of the SPEED pot and it will continue to move for the number of seconds as determined by the TIME setting.
The train will then stop at the other end of the track and reverse at the same speed and for the same number of seconds back to the starting position.
It will then "inch" towards the reed switch and start the cycle again.
It will take a few adjustments to get the speed and time adjusted correctly for the length of track you are using.
The reed switch is designed to provide REGISTRATION. In other words it sets the train for the same number of seconds and the same distance on each cycle.
If this does not occur, the "inching" towards the reed switch re-starts the cycle and removes any discrepancies in the distance travelled. 

The reed switch is now included with the module.
The TIME pot and the SPEED is set (and adjusted)   so
the train reaches the end of the track - then stops - then
returns to the starting position.
This will take a while to set-up.

The reed switch is fitted along the length of the track
because the centre of the reed switch is not sensitive.
Allow 15cm of track past the reed switch to prevent
the train running out of track.

The module comes fully built and tested for $35.00 as we build them 10 at a time and test them with a 300mA motor and 12v DC supply to make sure everything works. You can buy a kit for $25.00 and if you want a kit, you will need to email Colin Mitchell: for all the details. 

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The double-sided board has two chips
and very small surface-mount
Two 0805 LEDs come on 30cm leads

This project is available from Talking Electronics for $5.00 plus $4.00 post.
Buy A Kit It uses surface mount parts on a double-sided board 15mm x 15mm. Two very bright LEDs are mounted on the tips of the wings of your model aeroplane and the LEDs flash twice then delay 2 seconds before the next double flash.

You can also add the module to the front of a loco, as shown in the following animation:

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Here is a circuit that will convert any clock mechanism into Model Railway Time.
For those who enjoy model railways, the ultimate is to have a fast clock to match the scale of the layout. This circuit will appear to "make time fly" by turning the seconds hand once every 6 seconds. The timing can be adjusted by changing the 47k. The electronics in the clock is disconnected from the coil and the circuit drives the coil directly. The circuit takes a lot more current than the original clock (1,000 times more) but this is one way to do the job without a sophisticated chip. 

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(see 1, 2, 3 in 200 Transistor Circuits)
In this example the power is applied via the start switch and the train moves to the away limit switch and stops. The 555 creates a delay of 1 minute and the train moves to the home limit and stops. Turn the power on-off to restart the action.

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One of the first things (you will want) when expanding a model railway is a second loop or siding.
This needs a set of points and if they are distant from the operator, they will have to be electrically operated. There are a number of controllers on the market to change the points and some of them take a very high current. (You can get a low-current Point Motor).
The high current is needed because the actuating mechanism is very inefficient, but it must be applied for a very short period of time to prevent the point motor getting too hot.
Sometimes a normal switch is used to change the points and if the operator forgets use it correctly, the Point Motor will "burn-out" after a few seconds.
To prevent this from happening we have designed the following circuit. It operates the Point Motor for 5mS to 10mS (a very short time) and prevents any damage.
You can use a Peco switch (PL23 - about $10.00!!) or an ordinary toggle switch (change-over switch - SPDT - single-pole double-throw).
You can connect to either side of the Point Motor and both contacts of the other side go to 14v to 22v rail.

Point Motor mounted
under the track.

The Point-Motor shaft moves left-right to change the points.

Wiring a Point Motor
The white wire is the "common" because it goes to the start of the two windings.
The red wire move the point to the left and the brown wire moves the point to the right.

Point Motor connected to track

Here is a video showing a point motor connected to a set of points, from the Rail Video Channel::
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Point Motors can be expensive. You can save over 75% by making your own.
Point Motors (or switches) are also known as Turnouts or Points.
A point Motor can be made from an RC Servo (Radio Control Servo).

Servo and Horns

Connecting the push-rod

Mounting the Servo on a bracket

Fitting the Servo to the track

All servos come with a variety of attachments for the output shaft. These are called "Servo Horns" or "Servo Arms" and are "single leg horn, (or servo arm), double servo horn, circular horn (wheel) and others.
They convert circular motion into straight-line motion with the aid of a push-rod.
That's exactly what we want, to move the track-rails.  Any of the horns can be used for this project as you only need a very short travel. The push-red needs to be spring-steel and you can unwind a small spring to get this item. 
Servos have 3 leads. Positive, Negative and Signal. The Signal wire is connected to a PC board containing a chip that detects pulses to activate the motor.
Normally the arm on the output of the servo rotates up to 270 degrees. But this is too much for our application and so we need a module to reduce the angular rotation to less than 70 degrees.

That's what the Point Controller using 555 IC project does.
See the full project

The kit comes with different arms and lengths of different 0.5mm diameter wire so you can connect the output of the servo to the activating lever on the point.
The wire should have a certain amount of "springyness" so the point is kept in either position and that's why different types of wires are provided. 

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Arc Welder Simulator

This project adds reality to a work-site. It produces realistic flickering from an arc-welder.
The full project can be viewed HERE.  A full kit is available from Talking Electronics  for $21.20 plus  $4.50postage.

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27MHz link for about $10.00

These two modules are available from Talking Electronics for about $10.00 plus post.
They produce 2-channel transmission and can be used for all sorts of communication on your layout.
You may want to control something at the far-end and running cables may be practically impossible.
Or you may want to control something that moves around the layout.
This is an ideal way to solve the problem.
The range is about 10 metres.
The modules come with whip antennas.
See more of this project: HERE

Note: Only one motor is connected to the chip.

The two outputs can be used to reverse a motor or each output can be used to turn on a device.
When there is no transmission (reception) both outputs have zero volts.
For Forward, one output goes high and the other goes low.
The voltage lost across the output FETs is only a few millivolts (about 3 to 5mV).
The output FETs can handle about 200mA to 300mA. 
Each output can be used to turn on a separate motor:

You don't have to buy these modules. You can use the transmitter/receiver from a toy car that no-one wants any-more. (some of them are 4 channel). 
You can operate sound modules, lights, gates, points and anything up to 6v and 200mA. 
Every module is different with different circuitry and chips. This article is just to give an approximate idea of how to use the modules. 

More projects are being added and up-dated all the time.


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The first resistor in row 1 (brown-black-silver and the last band will be gold) is one-tenth of an ohm
If 3rd band is gold, Divide by 10
If 3rd band is silver, Divide by 100 (thus 10 becomes 0.10ohms or 0.22ohms etc)

In the following table I have included some of the common values and some very uncommon values to show how careful you have to be when reading the value of resistance. Some surface-mount resistors have letters and you have to look up a chart.
A clever trick is to measure the value with a digital meter to get some idea of the resistance and most of the time a reading such as 9680 ohms will be a 10k resistor with the surrounding components making the value slightly lower than 10k. Sometimes, reversing the leads will give a different value.

This is only a starting point. Eventually you may have to remove the resistor to get the true value, but try and avoid this at all costs. Resistors rarely give any problems and you should look at capacitors first, then transistors and diodes.
The biggest problem will be reading the resistor and think it has changed value.
Don't forget, a substitute value may have been used.
Before removing it, you can solder the same value across it to effectively get a reduced value and see if it alters the operation of the circuit. 

"0"  or "000" on a resistor indicates it is a LINK. It is zero ohms.

"R1"  or  "R01" or  "R001"  indicates the resistor is a CURRENT SENSING resistor (because it is such a low value). A high current through the resistor will produce a voltage across it and this voltage is detected and passed to the rest of the circuit.
The biggest mistake is thinking "100" is one hundred ohms. It is ten ohms.


Surface mount capacitors are unmarked and their size does not indicate the capacitance. The only way to determine the value is via a capacitance meter. These are available on eBay for less than $20.00 and the instrument can include inductance readings as well as resistance.
Alternatively you can replace the capacitor with a leaded value and see if the circuit works the same. 

15-7-2019  Colin Mitchell   

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