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email Colin Mitchell: firstname.lastname@example.org
13 CIRCUITS as of 26-5-2012
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.
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.
This circuit flashes two red LEDs for a model railway crossing.
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.
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.
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.
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.
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.
FLASHING LIGHTS FOR MODEL
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.
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.
CAPACITOR DISCHARGE UNIT MkII (CDU2) -
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.
MAKE YOUR OWN POINT
MOTOR using a
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).
Since servos are made in huge quantities, they are very low-cost on eBay and you can get 4 for less than $10.00 post paid.
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.
The resistor in series with the motor is designed to limit the current and the electrolytic provides the short pulse of energy.
The circuit is very clever because it provides voltage-reversal and a pulse of energy from just two transistors.
When the switch is thrown in one direction, one of the transistors is activated and the electrolytic in the load is uncharged. It gets charged and this charging-current flows through the motor to produce activation. It only takes a very short time to charge and then the current drops to about 2 milliamps.
During this time the other electro is discharging and when the switch is thrown in the other direction, the motor receives a pulse in the opposite direction.
Note: Two versions of the circuit are shown to cover AC input and DC input.
If you have an AC transformer, the circuit produces both a positive supply and negative supply to reverse the motor.
If you have a DC transformer, you will need to produce an artificial "centre-tap" to get:
+v 0v –v by using two 100R 1watt resistors.
Supply for Servo Point Motor
using a DC Plug-Pack (wall wart)
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
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.
SERVO AS POINT MOTOR
This clever circuit will drive a servo and operate a set of points. The circuit operates from 6v to 12v but cannot be put on batteries as it consumes about 3mA when sitting around due to the reverse-bias conditions of the transistors.
You will need to open the servo and connect directly to the motor. The PC board is not needed.
Every time the switch is changed, the circuit provides a short pulse of energy to the motor. No limit-switches are needed as the output shaft only has a small travel as it moves the points. The 220R determines the "strength" of the motion. If you are worried about the 100u's becoming "depolarised" due to the reverse voltage, you can make non-polar 100u's by connecting two 220u's back-to-back.
These two c