Picture of Make a USB breadboard power supply for close to nothing!
This is how to make a USB power supply for a breadboard without breaking the bank. The reason I made this instructable is because when I make projects on my breadboard, my batteries would keep on dying. So I thought to myself and I came up with the idea to use a USB to power my breadboard indefinitely. NOTE- I am not liable if your circuit backfires and destroys your computer.          


Step 1: Obtain a USB cord

Picture of Obtain a USB cord
 This is pretty straightforward. Just use a USB that you don`t use anymore, or you could buy one for about $3-6 USD
MrSgg3 years ago
You can use a LM317 set up as a voltyage regulator. That would provide protection for your system.

Here is some information from the data sheet for the LM117/LM317A/LM317

The LM117 series of adjustable 3-terminal positive voltage
regulators is capable of supplying in excess of 1.5A over a
1.2V to 37V output range. They are exceptionally easy to
use and require only two external resistors to set the output
voltage. Further, both line and load regulation are better
than standard fixed regulators. Also, the LM117 is packaged
in standard transistor packages which are easily mounted
and handled.
In addition to higher performance than fixed regulators, the
LM117 series offers full overload protection available only in
IC's. Included on the chip are current limit, thermal overload
protection and safe area protection. All overload protection
circuitry remains fully functional even if the adjustment terminal
is disconnected.

please refere to:
prrgg149354 years ago
This is a cool project! I'm just concerned that a USB port can't supply enough current to drive H-Bridges/DC Motors. I've heard of stories where people have tried driving DC motors from USB ports, and the port died! Do you think you can improve this project by adding some current limiting hardware?
newwarhammer2 (author)  prrgg149354 years ago
yes, step 5 tells you all about that.
verence4 years ago
Very nice! (and will work as long as you don't need more than 100mA)


Ever tried, what happens to the device powering your USB-cable (I guess, it's a PC or laptop), when you short the circuit? Well, on a breadboard, you will find out in a short enough time.

You have any idea, what happens, if your circuit inadvertently creates a higher-than-5V voltage (as can happen when switching a relay or with any other coil) and the over voltage feeds back into the supplying device? Nor do I.

I would just use a simple wall-wart - if you want 5V regulated, try to get a wall-wart-USB-charger. Any brand will do. You'll get more than 100mA, the chance that you blow up something is minimal, and even if, it's just a wall-wart, not a multi 100$ PC.
I agree.
Actually, I've heard that USB ports can support up to 500mA MAX. However, I've been breadboarding for years, and accidental shorting happems relatively often, dispite being careful. Accidents happen. If you draw more than the maximum current, the computer will tell you. A UI will pop up and tell you that the port has been damaged. I've had this happen when using a bad SD card adapter. The port is still unuseable.

Yes, if you could find a fuse small enough that would burn out at say 5v@450mA, then you may be good. However, in the micro seconds it would take to burn out the fuse, the damage could already be done.

Good call on the spikes. If anyone is going to use this to activate a mangetic actuator of any kind, it should truly be protected by a diode.
100ma is a normal output, you supposed to request that the port be put in a 500ma mode, but I dont think anyone today actually bothers with it since everything has a usb plug on it now