posted on Mar, 30 2006 @ 05:13 PM
R1 = 56K
D1,D2 = 1N4001
Q1 = 2N3904
Ry = Relay, 12V
S1 = Momentary break (normally closed)
This relay driver is Self-Latching
which means that once it activates it will remain in that state until S1 is pressed and momentarily disrupts
power to the latch.
This circuit uses very little power when on. You could use batteries to power it and only use the mains to keep the batteries charged.
It would be the base for whatever other things you wanted to add to your system like a light beam or motion sensors, window and door switches.
All the parts should be available at Radio Shack, shouldn't cost much either.
The computer interface is quite a bit more technical than this circuit. Not a simple thing to build.
Do you want me to post it anyway?
[edit on 3/30/2006 by Beer_Guy]