My Story:
Build Your Own USB Charger

Has your phone or iPod ever died when you needed it the most? That's why I designed a quick little battery charger for your electronics! Just plug your device into its USB port, turn it on, and you're all set! Best yet, it all fits in an Altoids gum tin! My Story Phil Tang

The USB Plan

Lots of electronics are powered from a USB cable, so I figured that a powered USB port would be the most useful power source. I used a voltmeter to measure the voltage on each of the pins on my iPod AC Adapter, and wound up with +5.16V on the V+ pin, +2.06V on the D- pin, and +2.76V on the D+ pin. I'm using a 7805 voltage regulator to get +5V for V+, and am using two resistors for each data pin. I calculated the resistor values to minimize current loss (as not much current needs to go to each data pin).

Here's the schematic:

USB Charger Kit P/N 2136761

Parts You Will Need
Jameco P/N Qty. Description
151095 1 9V battery
109154 1 9V battery clip
51262 1 7805 voltage regulator
161024 1 USB socket
109171 1 Small switch
691180 1 22kΩ Resistor
691201 2 27kΩ Resistors
691243 1 39kΩ Resistor
36792 1 2 ft hook-up wire
285464 1 Electrical tape
1 Altoids Chewing Gum tin
1 Metal shears to cut Altoids tin


USB Project Assembly

For simplicity, I decided to just twist the leads together, as the circuit is pretty simple. You may want to solder them into a prototyping board for durability; see instructions for that below.

To twist the leads together, you'll need to solder wires to the switch, the regulator, and the USB socket. Then twist the red lead from the battery with one of the wires on the switch, and twist the other lead from the switch onto the left wire (with the regulator's metal part down) on the voltage regulator.

Then, twist the rightmost wire on the regulator with the 22kΩ and 39kΩ resistors and the lead from pin 1 of the USB socket. After that, twist the lead from pin 2 of the USB socket with the other end of the 39kΩ resistor and one end of one of the 27kΩ resistors. Then, twist the one end of the second 27kΩ resistor with the lead from pin 3 of the USB socket and the other end of the 22kΩ resistor. Finally, twist the lead from pin 4 of the USB socket with the remaining ends of the battery, the regulator, and the two 27kΩ resistors.

You should have a functional mess of twisted wires at this point, so test the circuit by plugging in a device or by using a multimeter. If it doesn't work, check the switch and your wiring.

Once it works, wrap each twist with a length of electrical tape. Then cut a USB sized hole in the Altoids tin with the metal shears. You only need to cut down twice, then just bend the metal repeatedly until it snaps. I'd suggest covering the edges with some electrical tape; it can be sharp! Then put the battery in the tin and push the USB socket through the hole. Then, push the rest of the circuit in the remaining space; it should fit pretty easily.

It looked pretty messy, so I covered up the guts of the device with some electrical tape. And voila! You have a working charger!

USB charger schematic
Figure 1. Schematic for the USB charger.



USB charger parts
Figure 2. All the parts you'll need to build the USB charger.



pin out diagram
Figure 3. USB Pin out Diagram, looking into the socket.



altoids can cutting
Figure 4. The Altoids tin, after cutting.



assembled charger closed
Figure 5. The finished product!
altoids charger open
Figure 6. The final product, opened up.

Going Further

If you want, you can put the circuit on a prototyping board; It'll be smaller and It'll look simpler, but It will be a little more complicated to make. It shouldn't be too much of a problem; there are just four resistors and a switch to put in. The USB socket's leads are 0.1" apart and will fit right into a proto board.

iPod is a trademark of Apple Inc. Altoids and the Altoids logo are trademarks of Callard & Bowser Inc.

Phil Tang is an engineering student at Tufts University and a summer intern at Jameco, working on new media and data integrity. He loves learning a little bit about everything and a lot about the interesting bits. He's a proficient roboticist and all-around computer guy, enjoying all kinds of electronic marvels. He can be reached at phil.sj.tang@gmail.com.