When doing some electronics hacking it's a good idea to have a steady power source for testing your creations. You could (and probably should) just buy a decent variable power supply, but maybe you're doing things on the cheap, or you're using it for something else. If you have a free USB jack hanging around, you can get decent 5V power by stripping apart a USB cable, as in the second picture above. If you want something a little more convenient and versatile, you can put together a little mini breadboard power supply like the one here.

This power supply can run off a USB port in a computer or a phone charger, and you don't have to destroy a USB cable in order to make it. It also uses the handy MCP1700 to provide a 3.3V power option, which many components use.

Step 1: Parts

Here are the parts you'll need for this build:

USB-B jack
MCP1700 3.3V regulator
4x1 male header strip
10 uF capacitors (2)
slide switch

Step 2: Circuit Assembly

Assemble the circuit as shown in the diagram. I've included pinout diagrams for the USB jack and MCP1700 to help you along. As you can see in the last image, I like to make connections on the back of the board using component leads whenever possible.

Step 3: Operation

To use the power supply, plug a USB A/B cable into the USB jack on the supply and plug the other end into a computer's USB jack or a phone charger. Flip the switch to select the voltage you want, insert the power supply in your breadboard and run wires from the appropriate pins to the components you need to power.

There are many small modifications you could make to this circuit to suit your particular needs, and many other instructables showing you similar builds - make it your own! If I had it to do over, I would design it so the pins fit precisely into the power rails on my breadboard, and I would probably ditch the switch and just provide 3.3V to one rail and 5V to the other.