Gaz Man wrote in message . ..
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


If you have 3 conductors (I'm assuming you can steal power and ground
from the intercom), I'd go with a digital link. Connect a 3-8 decoder
to the 3 signal lines and the 6 relays (be sure the coils don't draw
more current than the decoder can supply--otherwise, a transistor or
op amp will serve as a buffer), and drive the line with an 8-3
priority encoder (like the 74F148) whose inputs are connected to the 6
buttons. You could use an 8-input NOR gate to activate an unused input
when all buttons are open.