Electronics Question

[Conkers]

I'm looking for a way to operate two switches, common ground and two switched wires (three in total), using only two wires.

I'm thinking along the lines of multiplexing.

Basically, I have a switch in a remote location and I only have two wires running to it. I've had to install another switch in the remote location and don't want to re-cable if possible.

Any thoughts on if this is even possible ??

[wadgey]

you could try a solution with a small microcontroller (eg PIC) at either end to do the multiplexing. prolly easier and quicker to run some more cable.

[procode]

Donkey's years ago, before multichannel radio control came within the reach of the general public, a system was in use that only used one frequency carrier that was either on or off.

This sounds like the sort of thing you may be able to use.

Basically, it's a rotating multi-contact switch. Every time power is applied, the switch moves round by one switch position.

You gave very little detail as to the task you wish to solve so I'll give my own example.

If you want to switch three items on and off, there will be eight options of which will be on and which will be off at any one time.

I'm going to use a traffic light set of red, yellow and green bulbs,
These are the options.
1 None on
2 Red
3 Red + Yellow
4 Red + Green
5 Red + Yellow + Green
6 Yellow
7 Yellow + Green
8 Green

Clearly, a switch with eight positions is required, the number of banks will depend on the use. In my example case, a three bank, one pole switch would surfice.

A solenoid would need to pull a pawl with 15° separation (I'll draw and post it if you don't know what it is).
This complete item can be bought, or made.

A bleep sequence could be emmitted as a refinement, so that you know the current position.
The old analogue telephone exchanges had hundreds of thousands of uniselectors in them to select different customer lines and links.

Getting/deciding on the components is the difficult bit, after that it should be faster than building a PCB for a 16F84, and programming it.

[procode]

Maybe I should have included how this would work.

Everytime you pass (or pulse) power down the two wires, the switch will rotate one position.

In the worst senario, if only the red light is on, and you want no lights on, you will have to pulse the switch seven times to get it to the required position.

If some options are more likely, you could wire the switch up in such a way as to allow this combination to occur twice or more.
Any options that are never required can simply be omitted from the original calculations.

Hope this helps M8

[cobalt]

You could do it by setting up an astable which you run to two switches with one of them having a frequency divider inbetween it and the switch. you then have two frequencies (call them high and low) and you can send them down the wire.

at the other end you have a high pass filter and a low pass filter, these are then connected to the relevant ends

not sure if this would work for your needs as you could only send one down the wire at the time. if you give more details of your situation/what you need to do it'd be easier to help

[philo]

Could try a 4 to 16 demux, tie two inputs high or low then use your two wires to control the outputs. If you need to drive the switches (if the output from the demux is not strong enough) feed the output from the demux into a uln2003, they have quite a drive capabillity and if more power is required parallel them. Hope this helps