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I work at a computer repair shop in Marietta, Georgia and we have a lot of spare power supplies laying around. This tutorial will explain how you can take a generic computer PSU(power supply unit) and turn it into a power supply that will power your Arduino and give you all the amperage  you need as well as your standard 3.3 volts, 5 volts, and 12 volts for any accessories/electronics used on your breadboard .

Step 1: What You Will Need

1. A Standard Computer Power Supply Unit.
2. Scissors
3. Soldering Iron + Solder
4. Male Headers
5. A plug that fits into the Arduino's DC Jack (I got mine from an old keyboard power cord)
6. Heat Shrink Tubing (optional)

Step 2: Which PSU Suits Your Needs?

On the side of most PSUs there is a sticker detailing the maximum amount of amps for each rail. I chose a  random power supply because that did not matter so much to me, but some people might be picky.

Step 3: The Pinout

We will be cutting a Molex or a SATA("L" shape) power connector and splicing the wires

Black    - Ground
Yellow   - 12 Volts
Red       - 5 Volts
Orange  - 3.3 Volts

Step 4: Sata Vs. Molex

If you only have Molex connectors, you will notice two grounds, a 12 volt, and 5 volt wire. In the case that you only have Molex we will have to cut into the large cable you see here in order to get 3.3 volts.

If you have some SATA connectors on the other hand, those have two grounds and and 12, 5, and 3.3 volt wires. No need to cut into the large cable for 3.3 volts, unless you want extra. Otherwise skip this step

Step 5: Short the Green and Black Wires

Your PSU will only turn on if the green and black wires are shorted(as shown above).  You can use a small piece of wire or solder to short them or you can cut the two wires and solder them together.

Step 6: Solder on Your Male Headers

In my example I used cut up paper clips because they were all i had at the time, this was not the best idea because they are slightly to large for the breadboard.

Step 7: Solder on Your Plug for Arduino Power

This step is pretty self explanatory. One wire goes to 5 volts, one goes to ground.

Step 8: Finished Product

As the last step you can open up the PSU (while it is unplugged of course), cut the excess wires not in use, and electric tape them.

Step 9: Practical Use

Here is an example of me using the PSU to power the Arduino and a drill motor. I wouldn't be able to drive the motor on just the power from the Arduino due to amperage!
<p>many circuits show a capacitor between +5vdc and ground. Using a switching Power supply. is this necessary? A good idea? or don't do it?</p>
Its fine to do it. just remember the capacitor.<br><br>In reality, I wouldn't go directly from the power supply cable to electronics. too noisy. you would be better served to get either 7803/5/12 (&amp; caps), to clean up the voltage before hitting your circuit. maybe an LM317, also.
<p>Just a note to let you know I have added this instructable to the collection: <br>Encyclopedia of ATX to Bench Power Supply Conversion <br>&gt;&gt; <a href="https://www.instructables.com/id/Encyclopedia-of-ATX-to-Bench-Power-Supply-Conversi/" rel="nofollow">https://www.instructables.com/id/Encyclopedia-of-ATX-to-Bench-Power-Supply-Conversi/</a><br>Take a look at about 70 different approaches to this project.</p>
<p>An other easy solution is to get a cheap breadboard power supply that will give you 5v and 3.3v for your projects:</p><p><a href="http://voltatek.com/en/home/27-breadboard-power-supply-33v-5v-mb-102.html" rel="nofollow">http://voltatek.com/en/home/27-breadboard-power-su...</a></p>
Additional side note.. You needn't have to draw power from the supply, through the coaxial connector to the Arduino.. I found, after I unsoldered the power plug from an old, D-O-A, 3.5&quot; floppy drive, and straightened the pins, if you plug them into the breadboard, you _CAN_ run wires from +12V to Vin and +5V to the 5V pins of the arduino, and it will not effect it.. in fact, by adding the +5V, you're supplementing the arduino's 5v regulator..
Minor correction.. Someone on the Arduino forum said adding the +5V to the Arduino, from the supply, is a bad idea.. It has something to do with the switching circuit that changes between the USB +5V, and the regulator +5V, and has a problem of actually burning out the switching circuit on the MEGA 1280 &amp; 2650's. Though, you DO have the +12V.. On some projects, I've actually stepped that down.. I happened across a couple of old 16-bit sound cards, that actually had a 7809 regulator onboard.. I've unsoldered the regulator, and mounted them to a fairly big (1.5&quot; X 3&quot; X 1/4&quot;) heatsinks. <br>I've also used the regulators to charge a Sylvania Netbook and a portable DVD player that require a 9V supply to charge them. <br>
Is there any way i could get some of those from you?
I kept 1 floppy/HD 4-pin cable wired in, and added a 2X-SATA supply cable to one of my converted units. (I still connect external drives via a USB-to-ATA/SATA adaptor, for testing or re-formatting drives.) The Wattage, can usually compute out to the drive load.. about 25W per 4-pin drive connector. (give or take a molex connector.) But if you want the full wattage available to projects, You'd need to run EVERY wire from the supply, to the various voltage posts.. (including the drive connectors.) Technically, one 400W supply, is only good for 5 drives.. (1 3-plug, and 1 2-plug plus floppy.) .. But I ran EVERY wire from the ATX connector, to the binding post.

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