All USB plugs run at 5v so need a way to make a portable 5v charging device. There are a few ways to do this. The way we are going to do it is to use a 9v battery and reduce its voltage to 5v with a 7805 voltage regulator. First, i like toggle switches and LEDs, the switch is placed first near the battery to ensure it's not running when not on. Then the LED (on indicator) and resistor before the regulator, but on ether side of the regulator a capacitor is placed to smooth out the current a bit.



For most USB charged devices this would be enough. Just attach the red and black wires from the USB and it should work, but Apples iDevices have a feature that tries to stop people like us from making our own charger or using most other non-Apple chargers. The iPhone or iPod Touch needs to "see" a 2v charge in each of the 2 USB data lines as a, "OK, this charger must be from Apple so it's time to start charging from the 5v." This is why you need the extra resistors to make a voltage divider to make the 2v because 22K / (22K+ 33K) * 5.0V = 2.0V. When I made mine I used the 22K and 33K values but you can also use 2 50K and 2 75K or 2 100K and 2 150K to also reach 2v. Let me know in the comments if those other values actually work, I think they will.



I have tested this charger with a few iDevices including an iPhone 4. For iDevises the charger will work until the 9v battery gets down to around 6v or 5v. Then you will get a message saying "Your iPhone does not recognize this charger." You may not get a whole charge out of a battery, so it is great to keep for emergencies. This charger can charge much more than iDecives. I have used it with other MP3 players, cell phones, cameras, and video cameras. Really anything that can be charged with a USB. That really was helpful when my kids were being cute and I wanted to video tape them but the recorder was dead. Just plug it in, carry it along, and catch those precious moments on video.