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This section will cover using the AR-2 Automatic Reversing Circuit with Adjustable Delay. This setup was used during the 2008 season to
have the train travel back and forth from the tree base to the end of the Toy Factory. The circuit worked flawlessly
and provided a nice delay at each end of the track. I have also used this same circuit, without the relays, on a HO scale train
set that goes back and forth on our fireplace mantel during the holidays. The main circuit is only designed to
handle 5 AMPS of power at 12 volts. If you are using a motor that uses less than 5 AMPS you will not need the extra
relay and wires. You will be able to connect the circuit board directly to your motors. If however, you need to
switch a larger motor then keep reading to find out how it is done.
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The AR-2 provides a 5 amp reversing capacity and also incorporates an adjustable time delay circuit that will stop a
train at each reversing point for a set period of time before reversing the direction. This time delay is adjustable
from 0 to over 1 minute. In addition, a terminal is provided for external activation of the time delay circuitry without
reversing direction. This terminal can be connected to a panel pushbutton to permit stop and delays at any point.
Up to 4 intermediate stopping points. This is ideal for trolley or switching setups where you would like to have a
train shuttling between end points, making various stops along the way. The AR-2 is constructed on a 3" square printed
circuit board and requires a 12-18 volt AC or DC power supply for proper operation. Can be purchased
at http://www.bakatronics.com.
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You will need 4 Automotive Relays and sockets. You can use any DC 12V relay for this as long as the AMP
rating exceeds your motor AMP rating. You can get them online from Radio Shack, JC Whitney, or All Electronics just to name
a few places. They are a very common automotive relay. You will also want to buy the sockets that fit the relay. It will
make wiring much easier and if you need to change out a relay then it will be a simple plug and play procedure.
12V SPDT 30 AMP AUTOMOTIVE RELAY - $2.40 each (CAT# RLY-351)
Relay Link
SOCKET FOR AUTOMOTIVE RELAY - $2.00 each (CAT# SRLY-2)
Socket Link
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This circuit requires 2 diodes to block the back flow of current when reversing the positive and negative terminals.
This is what you will need.
RECT DIODE 1AMP/50PIV - 15 for $1.00 (CAT# 1N4001)
Diode Link
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Terminal Strip
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Barrier Strip
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This is what the circuit board looks like mounted in the engine.
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This is what the relays and wiring looks like.
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Connecting power to the circuit board. The (-/+) terminals on the bottom of the board are used to power the AR-2 circuitry.
We then add a jumper wire up to the “IN” terminals to also power our relays with 12 volts. Obviously, do not connect the
battery power while you are working with the circuit, this just shows how it will be done.
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This next step we are going to use the barrier strip and two diodes to build the logic of our system. The circuit board is
going to be reversing the “OUT” (-/+) terminals to perform its forward/reverse functionality. The R1’s and R2’s stand for
Relay set one (Forward) and Relay set two (Reverse). This part will control which set of relays will be activated depending
on the -/+ output of the AR-2. If built like the diagram, the diodes will have their silver stripe oriented at the top like this.
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Now we are going to connect the barrier strip to the coils of the four relays. The numbers on the relay pictures correspond
to the numbers that appear on the bottom of the actual relays. If you have your relays in hand this will make perfect sense, but
if you do not, then the picture on the right will help. Just make the connections shown below and now your circuit will either
activate the Forward OR the Reverse set of relays.
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This final step shows the completed circuit. We have now connected the relays to the terminal strip. The terminal strip will
then be connected to the battery and the motor. Note that terminal 87a on each relay is not connected to anything. Just tape
or cap off this wire to make sure it does not touch anything.
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Now we need to add some magnetic reed switches (dry contacts) to our AR-2 and our train track.
The contacts will replace the optical sensors that come with the AR-2. They need to be Normally Closed (NC)
contacts with an operating gap of 1/2 inch. Here is what they look like.
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Here is what the contacts look like when mounted under the train. There is also a push button switch in the middle of the
magnets. I planned to put a wedged shaped piece of wood at the very ends of my track just in case the magnets did not work
and the train kept going. The push button would be activated by the train passing over the small ramps and thus cut the
power off to my motor. I did not get around to adding the ramps on the track and I did not need them. The magnets
worked 100% of the time.
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Here is one of the magnets mounted to my track. (small white box on track)
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Here is a diagram to show the AR-2 circuit wired up to use magnetic reed switches (dry contacts) instead of the
optical sensors that come with the circuit board. It is assumed the circuit would be mounted on the train and
powered by 12-volts and be running a max 5 amp motor. The two magnets appear to be wired together because they
are sharing the common green wire. I did it this way just to save on the number of wires I had to run from the circuit.
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