Hi all. Thanks in advance for any help you can give. Please note my
email address is invalid - this is to stop spam. Reply to gazman at
pobox dot com to email me directly.

Here's my problem :

My front gate is 150M from the house and I will have an intercom and
system to open the gates, turn on the lights, etc etc.

I ran two Cat 5E cables (total 16 conductors) underground. Somehow one
of the cables has been cut, so I have only 8 conductors left. The
intercom requires 5 of these, so I have just 3 conductors to control
the gates, lights, fountain etc as well as send a signal back to the
house to indicate what position the gate is in.

So I need a circuit that can send a coded signal down the wire, which
is decoded at the other end to open or close a relay.

My suggestion is this : At the house, each of 6 control buttons sends
a signal down the wire at a unique frequency. At the gate a circuit
detects the signal, and according to its frequency, toggles one of 6
relays. That way, multiple relays can be activated using just a pair
of wires.

It would NEVER occur that two control buttons are pressed at the same
time.

There are other ways of coding the signal (pulse count for example)
and I have used frequency just as an example.

Does anybody know where I can find a circuit to do this sort of thing?
I have searched the web without success.

Thanks in advance.

Gaz