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3 Aspect Signal Control Circuits.

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British System
This Project describes how to use a rotary switch to control the 3 aspect lights on a layout. There are other projects using toggle switches and also an automatic system.
In the layout shown the train is approaching signal B1 which would be GREEN. This therefore would have A1 at Yellow, D1 at RED and C1 at GREEN. Once the train passes signal B1 the aspect will change to Red and all other signals should follow the sequence. The way to do this is to use a 4 way rotary switch so that one section of the 4 controls one signal. If all signals are wired to the one rotary switch they will all change in the correct sequence.
This circuit shows how B1 signal is wired to the B section of the rotary switch, you need to follow the table to wire up the other 3 sections to the same switch.
Please note the resistor is only used if you are using LED's, it should be omitted if you are using 12v filament lamps.
This shows the terminal end of the rotary switch with the letters and numbers printed into the plastic base. We have only shown signal B1 for clarity see the table for the wiring of all the other signals.
The switch positions are shown below with a table to show how each subsequent signal is wired. for realism C1 would be GREEN, B1 would be RED, (as the train has just passed signal B1 in Block B,  A1 would be YELLOW, and the next one would be GREEN
To wire the switch for this sequence follow the table below. Please note you can only get 4 signals on one rotary switch.
The Parts lists are shown for 3mm & 5mm LED's and 'Wheat Germ' bulbs. You could also use filament lamps.
Other Projects
Automatic Block Signalling
Toggle Switch control of Block Signalling
Points within Block Signalling layouts
Block Signalling Layout
Rotary switch wiring diagram
Back end of rotary switch