I love the Mintyboost power supply/charger Instructables, but wanted to look for something a little readily available that doesn't see much use anymore and that was a little easier to customize. Going through a few stores of odds and ends, I came across an old cassette tape collection, and there it was! I tossed in a $1.69 Radio Shack 7805 5 volt regulator (they have virtually every type of protection built in, including thermal overload, spiking, reverse polarity, etc.), and came up with this! It's easy, fast, and a great little charger that you can use with just about any DC power source to charge your cellphone, or, with a little extra effort, your USB! A big thanks to JDurban for his advice on this project!
You couldn't ask for an easier part. It requires no additional components to work, and you only have to solder to three pins. The DC power leads attach to pins 1 and 2 (2 is the common ground for both input and output), and pins 2 and 3 for the output... what could be simpler?
The simplest means of setting up and using this regulator is to simply take the cellphone connector wire from a broken wall charger and solder the red(positive) lead to pin 3, and the black/white(negative) lead to pin 2 (ground). You can then cut the end off of any used DC wall wart (make sure that the milliamps is AT LEAST the same, or more than what's listed on your original cellphone wall wart), and solder the positive wire to pin 1, and the negative wire to pin 2.
I went ahead and used an old leftover female USB port (leftover from a motherboard add-on) instead of wiring directly into my cellphone wire, as I had a USB charger adapter readily available. I also used alligator clips which would allow me to attach any available DC power power supply, including batteries, instead of wiring directly to a DC wall wart.
Here you can see that I'm actually charging my cellphone from a 9 volt battery! 4-6 AAs also work, and even a cordless drill battery...
Now, one word of caution... if you plan on hooking this onto something like a 12 volt car battery or anything with serious amps, you'll definitely want a heat sink attached to the regulator. I drilled a small hole in the bottom and ran a bolt through alternating small and large washers on the underside of the case to make a "fanned" heatsink, then placed two small washers inside to hold the regulator up off the plastic case, and then the nut to tighten everything in place. It works well without getting too hot, even with a 2-3 amp, 12 volt power supply.
I took it a step further by adding an LED with a 1K ohm resistor attached to the positive LED pin, and soldered the LED to pins 2 and 3 of the regulator. This would serve as a nice indicator light to show that I had the polarity correct on the alligator clips before plugging anything into the USb port, which I also mounted inside the cassette case. I finished the whole thing off by making a custom case cover in Photoshop and printing it out on a sheet of photo inkjet paper, which I then cut down and glued to the top!
I've tested this with several USB devices, including MP3 players, and it works great! I'm not guaranteeing this will work with everything, as some devices might use the lower amp 3 volt signal present in a full USB to computer interface. I could even use it on my USB powered Mutant Furby!