I have a set (3) of switches (bell pushes) that are a considerable number of years old. They are connected up to a four core cable, one for each switch and one common. The common side of the switches however, are connected to the plate in which the switches themselves sit.
This is a problem as it means I can't simply supply the common with a voltage and use it to switch the rest of my circuit.
As I see it my options are:
- Bring the voltage way down (switching regulator) and limit the current (resistor) and go ahead and drive the common and detect the small voltage at the other end.
- Drive the switched lines and put common to ground, and then use an IC like the 74LS04 to invert the output.
I don't really like either (1) because even though its a tiny amount of power it just feels wrong driving any large, exposed metal surface high, (2 (and 1 really)) because the the inverter and all the other circuitry get to sit around consuming power waiting to detect a push which will be very very rare, whereas before the switches could disconnect the entire circuit from the power supply completely until it was needed.
Have I missed something? Is there another way to utilise by board?