USB differential transmission

The statement

> 17.78 mA of this current is returned on either the D+ or D- pin (the middle 2) of the keyboard's USB connector. Which pin carries the current is rapidly toggled between the two creating a high speed bitstream

is **wrong**. USB uses a differential, balanced transmission line with a nominal impedance of 90ohms. With high and full speed modes (the ones keyboards operate in) the differential I/O voltage level has a common mode voltage of 1.8V, and an design amplitude 1.65V; the differential voltage swing is designed for 3.3V, which against the 90ohm impedance of the cable equals to a momentary maximum loop current of about 25mA. The key word here is loop current, because as much current as goes into D+ is drawn from D- or vice versa. However in full speed mode (the one keyboards operate in) the ends of the transmission line are not terminated (i.e. reflections of the signal are designed into the system) and the receiver input impedance is on the order of kOhms, so the mean effective current flowing is measured in the µA order of magnitude.