75 Model Railway Project

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

email Colin Mitchell: talking@tpg.com.au

19 CIRCUITS as of 1-6-2017

CONTENTS
Arc Welder Simulator Capacitor Discharge Unit MkII Capacitor Discharge Unit MkII - modification CDU - discussion Flashing Railroad Lights Flashing Lights LED Tester Make your own Point Motor using a servo Model Railway Time Over-Current Detection Point Motor Driver Reversing A Motor Servo as Point Motor Track Tester Traffic Lights Train Throttle 4-Way Traffic Lights	27MHz Link

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INTRODUCTION
This e-book presents some 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:
The projects in these books can be found on Talking Electronics website in the left-hand column.
Since releasing these two books, we have designed some extra projects and more are being released all the time.
The projects will be presented in this eBook and you will need to come back on a regular basis to see the updates.

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:
http://www.dccconcepts.com.au/

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.
We will not be covering any projects for DCC so it's best to visit the DCC website.

NOTE:
Many of the projects and circuit and ideas in this eBook are available from Talking Electronics as complete kits, fully assembled, or as components or on the web at very low prices.
Email: Colin Mitchell and ask for assistance before launching out on your own.

THEORY & PROJECTS

The POWER SUPPLY
Every project needs POWER. Power 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 and the 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, 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."

A POWER SUPPLY FOR YOUR MODEL RAILWAY
You will need at least 2 or 3 different power supplies for your layout. This is because a layout requires at least to 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 ill 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 the module that connected 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 was fairly low current.
Throw out anything that you are not absolutely sure of its safety-factor.
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 and 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.

It is difficult to combine AC adaptors as the voltage from each adapter is rising and falling and if the rise-and-fall from one is not identical to the other, the output voltage will be unknown. You can try connecting two in series and see if the voltage and current is as expected.
AC adaptors are very uncommon. In general you can expect the output to be DC.

USING ADAPTORS IN PARALLEL
You can also connect adaptors in PARALLEL. This involves connecting the negative output of one the 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.
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 prevent one adapter passing any current to the other.

This is a good way to use up the 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

USING ADAPTORS IN SERIES
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:

BENCH POWER SUPPLY
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 to 35v or more 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.

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 or viewing so you can remember how they were assembled.

Here is a set of 4 Li-ion cells. Just use the 4 lower cells in a 4-cell carrier:

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.

CURRENT
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 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. 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 and also the rpm of the motor as it takes more energy to rotate at higher rpm.

CONCLUSIONN
You need to buy or make 2 POWER SUPPLIES:
16v 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 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.

CAPACITOR DISCHARGE UNIT
The next item we will cover is the CAPACITOR DISCHARGE UNIT.

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

It consist of two solenoids that alternately pull a metal rod into the middle of the solenoid and at the same time change the position of the point.
These solenoids have a small number of turns of wire and take a high current when connected to a train power supply. The resistance of the coil is about 4.5 ohms and when connected to 12v, the current will be nearly 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.
To prevent this from occurring, you need an electronic module that delivers the current to it 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 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.
The simplest and cheapest CAPACITOR DISCHARGE UNIT is shown in the following image:

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:

This module fits between a Power Supply and the solenoid on a point. It is designed to deliver a short pulse of energy to the solenoid to change the position of the point.
If you do not include a Capacitor Discharge Unit, you may leave the switch connected to the point for more than 10 seconds and the flow of current will heat up the solenoid and "burn it out." The CDU prevents this.

For layouts that need 2 or more points changed at the same time, a larger version is available with 2 x 4700u electro's::

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

Connecting CDU MkIII to 24v supply

Up to 8 points can be changed at the same time with the largest CDU::

CDU Module 18,000 fully built and tested $22.00 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.
SPECIAL FEATURES
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.

Talking Electronics has produced 8 different modules to operate a point and you need to look at all the different designs before deciding.
If you want to convert a manual point to automatic, 4 of the modules cover this.
The old way to change a point is via a solenoid, but these are expensive and need a CDU to make them reliable and safe from overheating.
The new way is to use a micro motor and gearbox and these change the point slowly and the motor/gearbox and electronics is much cheaper.
One module changes the point automatically and has 3 other features so you can design a layout with one or two loops and a signal.
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 to loop at the project and then contact Colin Mitchell for final details of which actuator you want as the program in the PIC micro has to be burnt to suit the actuator. The project also comes with a 2-aspect signal.

We will start with the solenoid POINT CONTROLLER.
This is the most common of all the controllers and consist of two solenoids that pull a metal rod into the middle of the solenoid and at the same time change the position of the point.
These solenoids only have a small number of turns of wire and take a high current when connected to a train power supply. The resistance of the coil is about 4.5 ohms and when connected to 12v, the current will be nearly 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.
To prevent this from occurring, you need an electronic module that delivers the current to it 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 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.
The simplest and cheapest CAPACITOR DISCHARGE UNIT is shown in the following image:

CAPACITOR DISCHARGE UNIT
The next item we will cover is the CAPACITOR DISCHARGE UNIT
This is the module that fits between a 24v Power Supply and the solenoid on a point. It is designed to deliver a short pulse of energy to the solenoid to change the position of the point.
If you do not include a Capacitor Discharge Unit, you may leave the switch connected to the point and the flow of current will be very high and either the point will start to heat up or the power supply will be overloaded and "burn out."

Talking Electronics has produced 8 different modules to operate a point and you need to look at all the different designs before deciding.
If you want to convert a manual point to automatic, 4 of the modules cover this.
The old way to change a point is via a solenoid, but these are expensive and need a CDU to make them reliable and safe from overheating.
The new way is to use a micro motor and gearbox and these change the point slowly and the motor/gearbox and electronics is much cheaper.
One module changes the point automatically and has 3 other features so you can design a layout with one or two loops and a signal.
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 to loop at the project and then contact Colin Mitchell for final details of which actuator you want as the program in the PIC micro has to be burnt to suit the actuator. The project also comes with a 2-aspect signal.

Here are two CDU (CAPACITOR DISCHARGE UNITS) from Talking Electronics:

The input voltage needs to be 16v DC to 25v DC and you will need two adaptors in series to get this voltage.

When you have made a 25v power supply for the CDU modules, (to change the points), you will want to make a POWER SUPPLY for a THROTTLE to power your loco's.
Most locos take about 500mA and need a voltage of about 12v for full speed.
For a throttle to deliver 12v, it needs an input voltage of 14v to 16v as about 3v to 4v is lost in the bridge diodes and the electronics.
It is very difficult to get 16v DC from any plug pack, and that's why you need to follow our discussion.

POINT CONTROLLERS
The next set of projects we will cover are called POINT CONTROLLERS.
A Point Controller is a "device" or "MOTOR" or "SOLENOID" that changes the point from "ahead" to "Siding."
The ACTUATING MECHANISM can be double-acting solenoid to move the rails from one position to the other. Alternately this 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.
We will now cover the 6 different projects from Talking Electronics, including the cost of the electronics.

The following image is a typical manual point. The spigot is moved sideways to alter the position of the rails.

A Manual Point that will be converted to remote operation by the projects described below:

In the following projects we will cover projects that convert a MANUAL POINT into an AUTOMATIC POINT (or remotely controlled point).
All these projects are cheaper than getting a solenoid for the point shown above and adding a CDU module.
In place of the solenoid, these projects use a SERVO or MOTOR and GEARBOX or a MICRO MOTOR and GEARBOX.
And some of the projects include additional features such as automatic operation of the point and reversing the voltage to the track so that loops can be included in your layout.
You have to go through each of the projects carefully and work out the features you want.

TRAIN THROTTLES
There are a number of different TRAIN THROTTLE circuits.
The type(s) we are considering need either AC or DC input and produce 0v to 12v DC output.
If you have an AC supply 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. You can lose up to 2v DC.
This means you need an input voltage of 14v DC and this will require 2 adaptors in series or a set of 4 Li-ion cells.
The following project uses 4 Li-ion cells to provide a voltage of about 14.2v DC to 14.8v DC and this is ideal for many types of TRAIN THROTTLE.

There are two types of TRAIN THROTTLE:
Type1 produces an output 0v to 12v DC and you need a reversing switch to reverse the train.
Here is the circuit and photo of the completed project and the wiring for the reversing switch:

Two Amp Power Supply circuit diagram.
The ammeter is also included in the kit

The completed POWER SUPPLY, 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.

The 2-Amp POWER SUPPLY project is HERE
Kits come with 0-2 Amp meter to show the current.
$12.50 USD plus $6.50 USD postage.

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

Here is a set of 4 Li-ion cells. Just use the 4 lower cells in a 4-cell carrier:

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 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. This is very critical.
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 damage the cell.

The second type has a throttle 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. This design "kicks" the motor and allows it to start the train very slowly. The "kicks" are very rapid and sometimes you can hear the "buzz" from the motor.
All 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).

PROJECTS
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TEST EQUIPMENT
LED TESTER
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 Project

The 3 button cells are held in place with narrow heatshrink
after soldering fine tinned copper wire over the cells.
You can then cover the cells with duct tape.

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TEST EQUIPMENT
TRACK TESTER
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.

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FLASHING RAILROAD LIGHTS
This circuit flashes two red LEDs for a model railway crossing.

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FLASHING LIGHTS FOR MODEL RAILWAY CROSSING:
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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TRAFFIC LIGHTS
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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4 WAY TRAFFIC LIGHTS
This circuit produces traffic lights for a "4-way" intersection. The seemingly complex wiring to illuminate the lights is shown to be very simple.

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MODEL RAILWAY TIME
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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REVERSING A MOTOR-4 (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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THE CDU (Capacitor Discharge Unit)
TALKING ELECTRONICS has produced a number of CDU projects and they all have slightly different features. They all supply a lot of energy to a POINT MOTOR for a short period of time and this prevents the Pont Motor getting hot.
Some of the CDU's have LEDs on the PC board that show the position of the point and others control up to 4 points.
Approximately 2,000u is needed to activate the solenoid to change the point and some projects have 2 x 1,000u to meet this requirement.
One project has 2 x 4,700u and this CDU will activate 2 - 5 points at the same time.
Our largest CDU has 4 x 4,700 and is called 18,000u. This is for a very large layout.
Talking Electronics also produces a remotely controlled CDU for a point that is distant from the control panel. It takes a small amount of current from the track to charge 2 x 1,000u capacitors and does not need any wiring back to the control panel. The transmitter is 315MHz and the receiver detects a coded signal to activate the point. The project comes with 1, 2 or 3 remotely controlled CDU's.
Two more projects use a servo to activate the point and this is similar to the Turtle Point Controller.
Our project is cheaper and easier to install as you don't have to get under the layout to install the controller.
One project is remotely controlled and the other uses a toggle switch. There are three versions of this using different switches.

LET's START AT THE BEGINNING with an explanation:

Here is a diagram to show a CDU is connected to a Point Motor:

A Point Motor is a double-solenoid as show in the image below. It is also called Side Mounted Turnout Motor.
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.
That's why you need 2 coils.
But the problem is the coils have very low resistance.
If you operate them from the 12v train supply or the 16v AC supply from the train transformer, they 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.
You need to use a switch that only delivers a voltage (and current) to them for less than 1 second. This is called a PASSING SWITCH or a "spring return toggle switch" with a centre-off position.
If you use this type of switch carefully, the operation will be successful. But if you have visitors working the control panel, they may leave the switch ON or work 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.

Here is a list of the 7 CDU projects from Talking Electronics

Talking Electronics also has projects that convert a manual point into a remotely controlled point. (This is a point that does not have a Turnout Motor ).
The movement of the rail is done with a servo and this is a cheaper alternative to buying a point motor and CDU unit.

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

The servo moves the track via the springy-brass wire. The servo is controlled by the project to have less than 90° movement and the project reverses the servo.

Talking Electronics has 3 projects using a servo to control a point.
All the projects are easy to install and you don't have to get under the layout or create any cut-outs.
The following set of projects covers some of the kits available from Talking Electronics.
More kits are listed on the front index of Talking Electronics website and more projects are being developed.

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CAPACITOR DISCHARGE UNIT MkII (CDU2)
This project is available as a kit for $10.80 plus $6.50 post. email Talking Electronics for details.

This circuit will operate a two-solenoid point-motor and prevent it overheating and causing any damage. The circuit produces energy to change the points and ceases to provide any more current. This is carried out by the switching arrangement within the circuit, by sampling the output voltage.
If you want to control the points with a DPDT toggle switch or slide switch, you will need two CDU2 units.

HOW THE CIRCUIT WORKS
The circuit is supplied by 16v AC or DC and the diode on the input is used to rectify the voltage if AC is supplied. If nothing is connected to the output, the base of the BD679 is pulled high and the emitter follows. This is called an emitter-follower stage. The two 1,000u electrolytics charge and the indicator LED turns on. The circuit is now ready.
When the Main or Siding switch is pressed, the energy from the electrolytics is passed to the point motor and the points change. As the output voltage drops, the emitter-follower transistor is turned off and when the switch is released, the electrolytics start to charge again.

The point-motor can be operated via a Double-Pole Double-Throw Centre-Off toggle switch, providing the switch is returned to the centre position after a few seconds so that the CDU unit can charge-up.

The Capacitor Discharge Unit can also be purchased with screw-terminals for the input and output leads:

See the full article: HERE.

CDU MkIIB with 2 x 2,200u electrolytics and screw terminals
$12.50 plus $6.50 postage.
Click HERE for details

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CAPACITOR DISCHARGE UNIT MkII (CDU2) - modification
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.

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POINT MOTOR DRIVER
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

Point Motor connected to track

See the full article: HERE

CDU with SPDT switch
$13.50 plus $6.50 postage.
Click HERE to buy kit

Here is a video showing a point motor connected to a set of points, from the Rail Video Channel:
http://www.youtube.com/watch?v=aW67CFSWGzU&feature=related

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MAKE YOUR OWN POINT MOTOR using a SERVO
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. We do not need this feature. The PC board needs to be removed. Open the servo and remove the PC board and signal wire. The pot can be left in position but the wires need to be removed.
The two remaining leads are connected directly to the motor.
Our circuit drives the motor and gearbox with a short pulse of energy to provide clockwise or anticlockwise movement.
No limit switches are needed because the railway track provides the limits-of-travel and the motor effectively stalls when the end-of-travel is reached. The gearing produces adequate torque (or effort) to move the rails and a current of about 50mA is sufficient to operate the motor to provide this effort.

See the full article HERE

Point Controller
for Motor/Gearbox
PARTS LIST $15.50 plus $6.50 postage.
Click HERE to buy kit

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TRAIN THROTTLE
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.

Transformer with 12v AC output and 18v AC

An impressive throttle handle

Train Throttle Circuit

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

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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 $21.50 plus postage.

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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.

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These two c

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If 3rd band is gold, Divide by 10
If 3rd band is silver, Divide by 100
(to get 0.22ohms etc)

25-6-2018 Colin Mitchell

You can copy and use anything for your own personal use.
Direct copying to other websites is not allowed as these projects are updated and too many
websites have copied my eBooks and not given credit to me.