I have a few 12 V motors and other sensors/electronics that require anywhere from 3-12 Volts. I usually use a battery pack but did not want to continue to go through batteries. For prototyping, I decided to convert an old ATX power supply into table top power supply. This generally will allow you to have terminals for +12V, +5V, +3.3V and potentially a -5V and -12V. These voltages are pretty common for anyone who works with micro-controllers and sensors.
This project uses:
-x2 mounted LEDs
-ATX Power supply
-Various heat shrink sizes
-x2 5 watt resistors
-x2 330 ohm resistors
Step 1: Preparing an Old ATX Power Supply
There are a bunch of references for building them. First thing I did was find a supply laying around I could use. You can reference the diagram below for the color coding of the ATX supplies.
ATX supplies can put out a good amount of current. If the maximum amount of current were to be pulled I recommend using all the wires at a given voltage to withstand max current draw. It may be 12 ground wires and 4 +3.3V wires etc...
**WARNING!!!! BEFORE CUTTING WIRES, USE A MULTIMETER TO CHECK THE CAPACITORS TO ENSURE THEY ARE NOT STORING ANY ENERGY. IT WOULD ALSO BE A RECOMMENDATION TO LET THE SUPPLY SIT FOR SEVERAL DAYS FOR ANY CHARGE TO DISSIPATE"
Remove the cover and cut the adapters off of the wires coming from the supply. You should be left with a large amount of wires that will need to be stripped.
Step 2: Preparing You Project Box
I went ahead and purchased the box from Radioshack for a few dollars. You may find other tutorials that modify the power supply box. In my case, the supply had a fan on top which limited the room I had for terminals, switches and LED's. I used INKSCAPE to layout what I wanted my box to look like. I printed it out actual size and used it as a template to drill the project box out. I had one swtich, 2 LED's and 5 termianls for my wires. I drilled a large hole in the back to thread all the wires through.
Step 3: Wiring the Power Supply Up
The same color lines should be soldered together for wiring the supply to get the max amount of current the supply can provide. Once you get the ground and voltage wires together you are a left with a few others. My supply did not have a -5 V. The BROWN wire is the +3.3V sense with needs to be tied in with the +3.3V line. The GREEN wire is soldered to the switch on my supply. The PURPLE wire attaches to the red LED and the GRAY wire attaches to the green LED.
All the solder connections should utilize heat shrink in the event a connection comes lose and to ensure you get no shorts in the system.
The schematic would be as follows. I did not utilize the fuses in line. The resistors are required for the LEDs and I bought a round switch. Wiring for all other components is correct. I used 2 5 Watt resistors in series in place of the one 10 Watt. Some supplies require an initial load in order to turn on. Before turning your supply on you should CHECK ALL YOUR CONNECTIONS TO ENSURE THE SYSTEM WAS WIRED CORRECTLY.
The red led will turn on when the ATX supply is plugged in. The green led will signify the switch is turned on, supplying power to the rails. Everything worked great and I was very pleased with how everything turned out.
I have a few references on my blog site that have some additional detail.