Hi, everyone. Just registered to post my findings on the Touchpad's charging circuit.
It's a relatively basic resistor divider. The Data pins in the middle are shorted out and there's a 250K pull-up resistor to the 5V power supplied as well as a 300K pull-down to Ground.
The schematic is attached, and on the actual circuit board, the resistors are marked 304 (meaning 30 plus 4 0s) and 39D(? very small, couldn't figure out with a magnifying glass, so just used a multimeter.), respectively.
Unfortunately, there is no way I can think of to modify other chargers without breaking them open and putting in the resistors in yourself. This may render apple chargers incompatible with the iDevices they were designed for.
A little bit of playing around with another USB source (my computer) tells that the data pins are used for nothing more than signaling in the first second or so that the touchpad is connected to the official AC adapter.
It does not initially appear that the voltage on the data pins affects the charging speed, but I need to mess around more with other chargers and the setup and see if I'm wrong.
Right now, I think the touchpad sucks in power until the load forces the power on the 5V pin to hit some threshold, which appears to be ~4.5V.
[Of course, nothing is free, and my AC charger had to be disassembled and sacrificed at the altar for this knowledge.
]
I'll be sure to post any later findings, but right now I'm happy having my touchpad take 1.5A from my solar panel setup
. If anyone else on here is of the EE inclination and can confirm, please post!