Something that I think would work well and be very low power (and simple)
would be to make a small one shot timer out of a 555 (the monostable setup)
thas is triggered by the first RS232 '0' bit in the byte (which would be a
+5 to +17 or so DC). So you could set up the timing so once this '0' bit is
recieved, it would start the 555 timer triggering the relay. Then, when ever
you wanted to turn on the relay, you'd just send any byte out (as long as it
has a '0' bit in it) on the serial port. You wouldn't need a RS232 converter
either, just hook up the RX pin directly to the 555 with a resistor and
(probably) some protection diodes, similar to the way the PICs do it on
their pins.

Aaron

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