Have you ever wanted to control devices from your computer. With this circuit you will be able to do all that through an interface connected to the parallel port and a program written in Qbasic. The program will give you the basic idea of how to control devices and how to monitor events. By modifying the program you can have the computer turn lights on while you are away from home or you could use it as a alarm system and have the computer dial a phone number. The possibilities are endless.
Lets start with the circuit first and then discuss the program to control it.
The chart shows all the pins of a parallel printer port. Below is the actual circuit to control output devices. I have shown how to interface a relay and a light. You could have hooked up a motor or control a DC circuit. This is a Quick Basic program to control the interface circuit.