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Auto 3 Aspect Signal Control & Isolation

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Previous projects have shown how to wire a 3 Aspect Signal using a toggle switch or a rotary switch, this project takes this one stage further and automates the signal. This time the train activates the signal and changes each aspect as it travels along the track. There are three sensors along the track which are activated by the magnet on the underside of the locomotive. The distance between sensors should be at least the length of your train, to create safe blocks between the sensors for the trains to travel in. (see below Automatic Isolation)
Basic Circuit

Because of the Latching properties of these relays, the signal should show a Green light, however it might show either no lights or a yellow light on initial switch ON. Easy to solve, you just need to reset both or one latching relay, do this by placing a magnet near SW3 sensor. Now you should have a green light showing.

Direction of Travel is from Left to Right. As the train passes over SW1 this will latch Relay 1 turning the Red light On and the Green Light Off. The train then passes over SW2 which switches Relay 2 On, this then turns the Red light Off and switches the Yellow light On. The train will then pass over SW3 which will reset both relays and switch on the Green light again.

Note 1: In automatic Isolation Mode the second set of contacts (T1) on Relay 1 can be used to Isolate a section of track prior to SW1. This Isolation will remain in force until the train has passed SW3.
Note 2: The drawings have been prepared using LED’s that require a dropping resistor. If your signal uses 12v filament lamps then the dropping resistor should not be used.
Automatic Isolation.
The following drawing tries to explain what happens when. Train 1 has just passed over SW2, this has just placed Signal 1 in the Yellow Aspect, and has removed power from the track in Isolation Area 1. Train 1 will continue forward and pass over SW3, this will put Signal 1 in the Green Aspect and Switch On Isolation Area 1. Train 2 is stopped at Isolation Area 1 because it is too close to Train 1. It will remain there until the Signal 1 goes to Green and the Isolation Area 1 has been reactivated. While Train 2 is in this position Signal 6 will be at Yellow and Isolation Area 6 has no power to the track, so any train coming around the curve at SW12 will be stopped at Isolation Area 6.
The above sequence can be repeated around the circuit and can be cascaded to the next Signal and so on.

Speed Control Connection
In this drawing we show how the DC speed controller is connected to the main section of the track. The isolated section will require the Positive feed from the speed controller to go first through the relay RL1 and then to the track. The Isolation fishplates are shown on both rails, but the Negative is fed directly from the speed controller. This system will work just as well on a DCC system, but I do recommend that both rails are switched On and Off, so a non latching relay should be used to switch both rails. This can be powered by the contacts 1 & 2 of T1 on Relay 1.

Note 3: The Latching relays can be purchased from Gaugemaster, Brimal, or a number of retails, as can the Magnetic Reed Switches, and magnets. The Isolation Fishplates and power connectors are by others.