I bought this charging adaptor from boxwave.com:
http://www.boxwave.com/products/iphonec ... e_2661.htm
It looks like a USB cable extension (male at one end, and female at other end). It works with all Ipod as the vendor claims.
As an experiment, I connect this adaptor to 4 NiMh AA cell in series (5.2 volts). With the male end toward the battery pack (pin 1 and 4 to battery), it will charge any Ipod connecting to the female end using the Ipod sync cable.
This is my measurement:
1/ D- line and pin 4 (ground): 2.4 volts
2/ D+ line and pin 4 (ground): 1.7 volts
With adaptor disconnected from battery, I measure impedance:
3/ D- and pin 4 ground: 345 ohms
4/ D+ and pin 4 ground: 234 ohms
At first, I thought inside this adaptor may be a voltage divider using resistors, but it is not true.
If I connect the female end of this adaptor (pin 1 and 4) to battery + and -, there is no voltage (0 volt) between D- and ground (or D+ and ground).
Also the impedance between D- (or D+) and ground is infinity.
So, inside the adaptor is some sort of circuit instead of resistors.
You can buy this adaptor to use with Mintyboot to solve the problem of charging Ipod touch/Iphone , or use the information above to modify R4 and R5 to make it work.
Iphone/Ipod touch charging adaptor
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