Here is a hobby/work bench power supply for those poor folks out there. It was taken from an old tower PC running Windows Millennium. For a size comparison, I put a Raspberry Pi next to it. It is completely free and only requires some electrical tape, a knife and a multimeter to get it going. I got this ATX power supply from the computer I pulled out of the garbage bin. Enjoy the hack!
Step 1: Slicing Wires
All of these ATX power supplys have connectors that would hook up to the computer's components. You will need to cut these off as close to the end as possible. When you're done, it should look like the picture above.
Step 2: Make It Turn On
That's right. You will see a green wire that you need to strip and twist together with a ground wire. If you don't do this, your power supply won't turn on.
Step 3: Tape It Up!
Now, take the electrical tape and sort out the wires according to color. When that is done, you need to tape the wires together. Look above for a visual aid. Tape the grey wire, purple wire and blue wire's off and make sure they don't touch any other wires. just keep them out of the way. I have found no use for them.
Step 4: Voltages
I've found with my multimeter that the voltages of the wires are this:
Red wire: 5 volts.
Orange wire: 3 volts.
Yellow wire: 12 volts.
Black wire: Ground.
Take your own multimeter and test the wires. You can follow my test results but remember, I'm not responsible if you fry your RPI using this result chart.
Step 5: Strip
Now take the knife or a wire stripper and cut off the ends of the wires. You can strip them all or just one wire of each kind. I find that by only stripping one wire of each kind, the others will stay away from that chance of short circuiting some stray wires.
Step 6: Make a Guide (Optional)
You can take the wires with a piece of cardboard and poke a hole in the cardboard for some wires. iThen write down the voltages below the wires for reference. I don't do this, I just remember what wire goes where when I test something. I don't mind the wires not being harnessed. (No photos because I didn't do this)
Step 7: Use Your Power
Just plug the power supply into a computer cord. It should start right up. Please note that it has been suggested that you should add a 200 ohm resistor between a 5 volt wire and ground to keep the supply from turning off. I've never had trouble with this. Test and power stuff with some aligator clips or extra wire. (Above I tested my tiny screen from the Simple Camcorder Viewfinder Hack) If you're feeling really geeky, you can even take an adjustable stereo volume knob to control the voltage coming from the supply. You may even wire a screen to display what voltage is being put out. Enjoy your new toy!