It turns out that the power supply unit, or PSU, of a standard desktop computer is the perfect device to energise most of your DIY electronics projects. With rails for 12, 5 and 3.3 volts, it suits a wide range of hobbyist gadget demands. The following guide will show you how to transform a decommissioned PSU into a tweakable DIY power source.
Instructables user "l19bal" took the time to put together a thorough tutorial on performing a PSU conversion. Before you do dive in, it's important to note that cracking open a power supply and playing around with its guts is not recommended unless you completely understand the dangers involved. So if you're not entirely confident of your sparkie credentials, you might want to give this a miss.
What makes this build particularly neat is that it incorporates and Arduino and LCD screen, allowing you to alter the output and monitor each rail. This requires a bit of programming to get up and running, but l19bal includes the scripts you need. There are also wiring schematics to handle hooking everything up.
While you can use an old PSU for this, depending on how often you're going to use it, it might be worth investing in quality hardware. The last thing you want is to fry your DIY projects because you cheaped out on a $50 unit.
Bench PSU Power Supply from Old ATX with Arduino and LCD Monitor [Instructables]