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  1. #1
    150+ Forum Groupie mach7's Avatar
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    Another Interface board question..

    Next question…regardless of interface board choice. Will these boards accept an input from a switch transistor (2N3704)…or the NTE85? Or are they limited to regular toggles, rockers, and pushbuttons?

    My plan is to have these transistors send a switch closed message for 15 to 20 seconds to an interface board to simulate engine starter engage operation. After 20 seconds the transistors would revert to a switch open signal...

    also...thanks to Mounty for the last response thread!

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    It depends on how the input card is scanning its inputs. If it does not multiplex its inputs (i.e. doesn't require diodes) then you probably can tie the transistor collector to the switch input. The transistor emitter must be tied to the switch card ground.

    If the input card does multiplex its inputs, things get dicey. Multiplexed inputs don't have a ground side for the switch connection. What would have been the switch ground is now an enable-low signal. You can still use a switching transistor on the input, but the circuitry gets a little more complex. One approach is to use an opto-isolator.

    A low tech approach is to use an electro-mechanical relay. This will work on both multiplexed and non-multiplexed inputs. There are some nice reed relays with low current 5 volt coils that work well in logic circuits.

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