This is something I wanted to show because it uses the Pololu screwless terminals - which I think are the cat’s meow. For those who don’t know those little green come apart and you can make them any size you want. I use an exacto knife and a small screwdriver to pry them apart and make larger or smaller sizes than the 2,3,4,5,6 size they come in.
This project has five cat5 wires coming into this radio shack phone box. My PC talks to a Parallax Propeller microprocessor ( parallax.com/propeller/ ) and that sends a 3.3v signal (via a shift register) down a long stretch of cat5 wire (I’ve tested it out to 8000 feet round trip for the power signal but I think the camera video signal will only go 500 feet or so) and that in turn turns on the transistor which allows 12v power to go to the cctv camera.
I’m setting up computer controlled cctv system and this allows me to turn various cameras on or off whenever and whereever I want. Everything on this is redundant too - double wiring, double transistors, double signal paths, etc. so if any one item fails on the board or in the wiring the whole thing will still continue to work. This one box will actually control two different cameras.