Thursday, March 19, 2009

Homemade USB multi-charging

USB is quickly becoming the worldwide standard for battery charging. Most new small electronic devices come with a USB cable that will charge it. This is a great feature to look for when buying a new device. It's more convenient for you and better for the environment when you use a single cable and power adapter to charge multiple devices. Unfortunately due to myopic designers and legacy devices, many of us own devices that don't have USB connections. Luckily it's not hard to fix many of these devices.

I wanted to travel with a minimal charging equipment, and have convenient charging for multiple devices at home. I had 2 mobile phones, an iPod, a GPS, 2 digital cameras, and a number of other devices that used AA and AAA batteries. Except for the cameras I can now charge everything from a single USB hub. I plan to make this a high priority next time I buy a camera.

This is what I used:
  1. USB power adapter (search ebay for "usb charger"). They are cheap and small and you can get one for your home and car.
  2. a USB hub (also cheap and small on ebay)
  3. USB AA battery charger (ebay again, also charges AAA bateries)
  4. a few old USB cables
  5. a soldering iron, solder and heat shrink tubing

For small devices (like mobile phones) check the markings on the chargers. The ones that output 5VDC (that's 5 Volts of DC power) can be converted to USB. All you need to do is cut off the cable and replace the wall brick with a USB plug. When you solder the USB plug just make sure the pins 1 and 4 match the polarity of the power adapter for your device. A basic multimeter and the USB pinout will help.

For my phones I cut the plugs from the original charger and an old USB cable then soldered them together. The GPS was new enought to charge with USB, but the iPod was more involved.

You'll probably find out that iPods, and many other devices that use Mini USB charging cables only charge from the original cable. This is because they have added extra resistors and designed the device to only charge when it detect them in the original "charger" cable. The iPods have the resistors in the power brick so you need to make a special USB cable for it and add some resistors to convince the iPod to charge (four 47K resistors work well). Motorola put the resistors in the end of the mini-USB plug, so you can just cut the original cable and use the original plug.

Have fun and don't forget good ventilation when you are soldering.

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