You can hack some parts you probably have lying around into a cable that will let you power electronic projects from a PC.
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These two pictures show the finished product. A PC power plug with long extension wires that reach the breadboard. |
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This is my ARM Cortex M3 breadboard. You can see the evaluation board with the graphic display and a button connected to one of the I/O pins. The PC provides +12 and +5 VDC. The Evaluation board has a +3.3 VDC supply which it regulates from the USB interface. |
First let me say that this is dangerous. Your PC power supply should have protection from shorts but you are sure to loose any open files not if, but when you make a mistake on your breadboard. Also the PC power supply can output a great deal of current so things can get out of hand quickly. In fact, the more I think about this, the more I realize it is a bad idea.
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I found this old PC fan in a junk box. We can sue the long red and black wires and the male power connector to make our cable. I dug up a long piece of yellow wire to extend the +12V. |
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PC drive connectors have 4 connections, 1 Red = +5V, 2 Black = GND, 1 Yellow = +12V. |
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Notice that the wires are cut at different lengths. This is an old trick; each wire is cut to prevent shorts. The red wire splice will be in a different place then the black or yellow connections. When you tape up the splices you can wrap around all the wires which is easier and ultimately safer then trying to protect each splice when they are all side by side. |
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I wrapped the wires together then soldered each connection. The two black wires are ground and were wrapped together along with the black extension wire. |
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All the connections are complete in this picture. Next I loosely braid the wires together then tape the connections as well as wrap some tape every 8 inches or so just to keep it all together. Once you have taped up the cable, you can connect it to your PC. Remember that if you have any shorts your PC will instantly shut down. Any files you have open will likely be lost. |
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Caution: An ATX PSU can supply a large amount of current, enough to burn those hook-up wires in a flash. You should really fit fuses near to the PSU end (e.g. 1 - 2A) in each of the supply lines to prevent a potential fire.
I agree Bill, I am thinking about designing some active current limiters. The fuses will protect the wires but the current limiter might protect the circuits better and maybe the PC will not be forced to shut down when you accidentally short something.
Good idea..
This would actually be a good thing to do with a spare power supply (not necessarily powering your computer). That way you’re not going to damage your PC. You’d just have to make sure you’re drawing enough load to power it on (most don’t supply without some significant load).
Thanks Jonathan.
The PC power supply does have short circuit protection and I use a current limiter to further protect things. My post after this one describes the current limiter which you would want to use even with a standalone PC supply.
Aside from the current limit considerations, the Molex connectors are notoriously unreliable under any sort of physical movement. If you’re hacking along with the side of your PC open, as I envision being the case using such a cable, you’re liable to jostle the connection and glitch your project’s power.
Hi, i want to use an old PC power unit to give me around 4A/12V DC for hobby use. Can it be done safely?
I’d recommend using a current limiter circuit on each voltage, which is easily made with an inexpensive power mosfet and a pot, to protect your circuits. it’ll also save you having to buy so many fuses.
Playing with a power supply this powerful without a current-limiter can lead to fires and explosions- be careful out there!
I agree. I did make a current limiter and described it in this post. http://www.uchobby.com/index.php/2006/11/12/current-limited-pc-power/
This is a smart idea! It will really come in handy when Im hacking something and need a quick line. Ill have to get a spare PS for this.
“We can sue…”
Only if something bad happens!
Me,
Let me put it this way. Messing with electronics as a hobby can result in all manner of injuries. Everything from a simple burn to total dismemberment without death is possible. If you do any experiment you see on the web you must accept any and all of the possible consequences. The projects on this web site may cause spontaneous combustion of your naughty bits in addition to any one of the other possible things that can happen. Please for the love of your soul and the sake of all other responsible hobbyist, do not repeat any experiment you find anywhere if you can not accept the possible consequences of your actions.
Check the link below for a simple way to convert computer power supplies into a lab supply. Had written this about a year ago.
http://www.wikihow.com/Convert-a-Computer-ATX-Power-Supply-to-a-Lab-Power-Supply
Naturally AT/XT power supplies are a whole lot easier and often fall into the category of “toxic waste” in many places and so can be had for free. A real power switch, possibly passthrough, in best cases with an isolation transformer and fair amount of beef.