Minimizing wires!

[soundlight]

OK, here's one for the EE's or EE hobbyists out there. This one is brought to you by my ME major and EE hobbyist (who also works in the theater) friend.

So, we just recently installed a new direct control system for four circuits in our studio theater. It uses 4 SPDT toggle switches that are enclosed in a small remote. There are only FIVE wires going from the control box to the wall. How was this done, I ask you? We had only five wires to control four switches, and on the other end of each is a latching relay, and requires a signal to turn it on and a different signal to turn it off. So, this would imply 9 wires: one to send power to the remote, and 2 wires for each switch: one for off, and one for on. We enclosed no chips or complicated electronics in either end. It's very simple, hardly any more components, and we used no more than one other type of component.

We needed 9 wires, but only had 5. And somehow it worked! So, how'd we do it?

[Footer]

Used a common neutral....

[soundlight]

We just had one signal wire (+) running to the box. We had to send that signal out of four switches, and from each switch, it had to go two different places, one to turn the relays one, one to turn them off. The box is not a circuit in itself. It is just part of the circuit that powers the relay coils.

[n1ist]

Sounds like the trick I used back in high school to do do signaling between the booth and stage... The trick is to use a low-voltage AC supply and DC relays with steering diodes at both the switch and the relays; the switch selects between sending a positive or negative voltage to each relay.

[soundlight]

I thought that no one would ever figure it out.

Switch the voltage in to positive and negative waveform with diodes, hook both diodes up to the same wire, and send it down. "Decoder" diodes located at the other end. There was a spdt switch that switched between sending the positive or the negative waveform down the line. The positive waveform is hooked up to the relay input for turning it on, and the negative waveform to the relay input for turning it off. Simply amazing.

[Chris15]

We just had one signal wire (+) running to the box.

I was going to say the diode and AC method, but the quoted line, the (+) implies that it was a +ve DC line... Way to confuse me

[soundlight]

Oooops...my bad! Sorry 'bout that one.