This DIY gadget makes a highly satisfying project and is extremely useful for long road trips, mp3 players with tired batteries, plain neatness, and impressing your friends.
The idea is very simple: use a crank charge headlamp and re-route some of the power from the light to a USB port for charging USB devices. We rely on the battery to soak up the voltage peaks so that while you're cranking, it should be around 5v.
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Step 1: Materials
-Hand crank headlamp: http://www.leevalley.com/en/garden/page.aspx?cat=2,40731,58277&p=58277
-Female USB port single or double (you can get them out of old computers)
-Soldering iron & solder
This project is "do at your own risk". In other words, I'm not responsible if you fry or damage something in the process. Yada yada yada now let's get on with it.
Step 2: Construction / destruction
Unscrew the dynamo cover, remove it and take a good close inspection.
Cut out a square in the side of the dynamo case the size of your USB port. You can heat up your knife blade which might make it more tidy and or easier. Press the USB port into the socket you made for it and put a little glue in if necessary to keep it in place.
Step 3: Wiring
Now solder the other end of your USB port power wires to the headlamp power cord jack. Put the USB positive to the red one on the jack and the USB negative to the black. Be SURE to get the polarity correct.