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

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17 CIRCUITS as of  1-10-2016

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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:

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.

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.

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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 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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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)

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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.
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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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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.
The 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.
But 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.


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.

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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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.

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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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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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.  
 HERE to buy kit

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. 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
$15.50 plus $6.50 postage.  
 HERE to buy kit

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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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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

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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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)

25-1-2014  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.