Hi, I'm new to this forum, and I'll greatly appreciate your help. If I can get this electrical/computer engineering problem solved, I'll be that much closer in pursuing a career as a bio-physicist. With the help of my intor physics professor, I'm designing a juice delivery system in which the main components are a computer parallel port, a relay, a 12-volt battery, and a pump. As you can guess, once the computer sends the TTL signal, the relay switches to normally open, which triggers the 12V battery to turn on, which then causes liquid dispensation. Issues: 1.) The computer's parallel port sends out a TTL signal of 2.5 to 3.5 volts, though I was told that it's supposed to output 5V. 2.) The smallest relay I can find is a 5V mini relay that Radio Shack sells. If I cannot find a smaller relay, can anyone explain to me other alternatives? How is it that the parallel port's maximum signal is 3.5V? Again, any help will be greatly appreciated.