(Yet Another 9 Volt USB Charger)
Step 1: Parts and Testing.
5v regulator (Lm7805)
Female USB port
Braided wire (20g)
Used 9v battery (Walgreen's brand)
5 minute liquid epoxy
Non-conductive epoxy putty
The circuit design is from http://ipod.hackaday.com/entry/1234000270029372/ All I did was add an LED so I could see if the battery was good. He's got nice diagrams of the USB and regulator to help you wire this together.
Step 2: Disassemble the Battery:
Pry the metal lip back from the bottom of the battery and straighten the edges as much as possible with pliers. Carefully pull out the plastic base and save. After that the innards should slip out without much trouble. Cut the negative lead going down the side and save the connector. Save the case.
I chose to use a Walgreens brand battery because it has nice thick plastic on the top and bottom. Duracell uses paper.
Step 3: Solder the Circuit Together:
For the USB I just drilled three holes in a row and cut out the rest of the rectangle with an Xacto knife. The USB should be mounted in the plastic before you solder the connections.
So the USB, LED, and resistor are on top and the regulator is on the bottom. The wire lengths are just to have enough room to epoxy the top in before the bottom, 2"-3".
Step 4: Prepare the 9v Case:
Sand the paint off the case with 400 grit sandpaper and rubbing alcohol. Carefully epoxy the LED and USB to the plastic base. Just use enough to tack it in place, don't get it in the USB.
Cut the case at about the 2/3 mark.
Score the inside of the case with a file or an awl to give the epoxy some kind of mechanical hold.
Step 5: Epoxy Putty the Top:
Put just enough epoxy putty to cover the components on top. Don't put it all the way to the edge, you want it to fit in the case.
Once the epoxy putty has cured (not fully, just enough that it doesn't deform when you push on it), put the top half into the case and seat it against the lip. While holding it against the lip drip a small amount of liquid epoxy around the edge to hold it in place.
After the top is held in place fill the remainder of the case with putty, leaving just enough room for the bottom to be pushed in. Push the wires into the case and force the top into the putty 1/16"-1/8" past the edge of the case.
Step 6: Close the Case:
While the epoxy starts to harden, cut 1/8" slots at each corner to help them fold over. When the epoxy has pretty much set up bend each edge over to close the case. Burnish or sand any sharp edges.
Step 7: Finished:
Test with a multimeter before plugging in your USB powered device.