The computer parallel port is the easiest way to control devices outside the PC, like LEDs, lights and even home appliances. In this tutorial we will teach you how to use the computer parallel port to control circuits outside your computer.

The greatest thing about printers nowadays is that they use USB connection. Thus, on the majority of modern PCs the parallel is not used, so it is available for us to use it to control circuits outside the computer box.

In fact the idea behind parallel port is really simple. It is an 8-bit parallel interface, so you have eight bits available there. Simple put, since each data bit can be set as either “0” (“turned off”) or “1” (“turned on”), we can directly turn on or off up to eight devices, like LEDs, lights and even home appliances. You can connect LEDs direclty to the parallel port and play with them – actually that is exactly what we are going to do in this tutorial, since this is the best way to learn how to use the parallel port. But for “heavier” circuits like lights and home appliances, you will need to build a power circuit, because the computer parallel port is not capable of driving enough current to deal with such devices. We’ll explain how to build this kind of circuit as well.

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Figure 1: Connecting LEDs to the parallel port.