Auxiliary Throttle Controls

A variation on the walkaround throttle is in the next circuit. If extra wires are added to the control cable they can be put to use for operating accessories on the layout. For every extra wire 2 such loads can be controlled. Electromagnetic uncoupling ramps could be turned on and off, train whistles could be blown or a reverse loop switch can be thrown after the train has passed.

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Walkaround Throttle With Auxiliary Controls Schematic

By using 4N33 Darlington output Optoisolators as low power relays and adding two push buttons or a toggle switch to the hand held controller a wide variety of external devices could be operated with only a small current draw on the throttle circuit itself.
Unplugable operation would still be a feasible option even with six wires in the control cable. This would allow four auxiliary control outputs.
The optoisolator by itself can only handle a load current of 20 milliamps, larger load currents require adding another transistor. The next drawing is shows a more detailed view of the auxiliary outputs.

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Auxiliary Output Schematic

Push button switches are shown in the schematic but these could be replaced with a SPDT switch if desired. The only limit to the auxiliary outputs is that both loads can not be operated at the same time or a short circuit will occur. The 100 ohm resistor protects against this in the push button system. A little creative wiring or a second wire could provide a solution when needed. Any number of extra wires could be added for more control outputs.