To charge an iPhone 3G / iPod Touch 2nd gen, usb data- (25) should be at 2.8v, usb data+(27) should be at 2.0v. This can be done with a few simple resistors: 33k to +5v (23) and 22k to gnd(16) to obtain 2v and 33k to +5v and 47k to gnd to obtain 2.8v. This is a "notification" to the iphone that it is connected to the external charger and may drain amps from the usb.
I'm assuming that D+ and D- in the minty boost are being taken from the battery feed which can be anywhere from 2.4v to 3 depending on the batteries used. I'm only a beginner on circuit diagrams so can someone verify this? Does it make more sense to pull that power from the nicely regulated 5v? So if my assumption is correct, and our feed to D+ and D- are from the 3v battery feed, that the suggestion above wouldn't work as they calculate the resistors based on a 5v feed? Would anyone here be able to tell me how best to modify the minty boost to get 2.8v to D- and 2v to D+?
I happen to have a store bought mobile battery pack that works with my iPhone 3Gs. I measured the data pins and get 2.8 and 1.99 so I think my hunch is correct. If we can get the data lines on the minty boost to those we should have success.
Thanks in advance.