The big difference is that I decided I didn't want to destroy my ATX power supply in the conversion. Another advantage is that you can just plug in a new power supply if the old one goes caput.
Drill and bits
Screwdriver ( for taking project box apart)
Desoldering iron (optional)
Label maker (optional)
A lighted 12V switch
3/4" strain relief
ATX connector (purchased or scavanged)
Miscellaneous heat shrink tubing sizes
Some wire 14-20 Ga (colors matching standard ATX if possible)
Step 1: Obtain an ATX Motherboard Connector
Desoldering components can be tricky, so take your time. The easiest way I have found is to first flood all the pads with as much solder as they'll hold. This allows me to heat the entire pad and pin evenly with the desoldering iron. I use a simple Radio shack model with a squeeze blub.
Step 2: Connect the Neccessary Wires to the Connector.
Pinouts for the ATX connector can be found at:
The pinout is a little wierd, I think it was dreamed up by somebody who wasn't very familiar with electronics. Pin 1 and 11 are at the same end. Ditto for pins 10 and 20.
What I did to avoid confusion was to plug the connector into the power supply and note the color of the wires . Then I soldered wires to the following pins
Pin Standard Color My Color Use
1) Orange Orange +3.3V
7) Black Black GND
10) Yellow Yellow +12V ( I solderd two wires to this pin)
12) Blue Solid Grey -12V
13) Black Black GND
14) Green Green Switch on
18) White Grey/Red -5V
20) Red Red +5V
To finish off the connector I bundled the wires with some heat shrink tubing.
Step 3: Layout the Front Panel
I also had to drill an additional hole for the lighted switch. The beauty of using the lighted switch is that it can be both a power indicator and the load to keep the power supply on.
Step 4: Drill Cable Strain Relief Hole
Step 5: Assemble Hardware
I then soldered the leads to the posts. Looking from the front:
The center post is ground.
The leftmost posts is -5V.
The rightmost post is +5V.
The bottom post is 3.3V.
The top left post is -12V.
The top right post is +12V.
The switch has 3 terminals: +12V, GND, and the switched contact. When the switch is off, the switched contact will be open and the light will be off. When the switch is on, the switched contact will be grounded and the light will be on.
The other yellow wire goes to the +12V of the switch.
The second black goes to the switch ground.
Finally the power supply switch wire goes to the switched contact.
Step 6: Apply the Finishing Touches
One notable flaw with my design is that it relies on the overload circuitry of the power supply. It's hard to add a fuse without cracking open the power supply, and to fuse each output would have been more work. ATX power supplies are cheap. Some may have internal overload protection and some may not. I'll take my chances. That's the beauty of my design, I can just plug in another ATX power supply if the first one fails.
Another problem may be that the lighted switch won't pull enough current to keep the power supply running. If it didn't, you would have to add a load resistor to one of the outputs, or in series with the power to the lighted switch.