Mike Keitz wrote:

> If you connected both ends of the motor through resistors to the ADC,
> then turning on the right transistor would always result in a positive
> voltage.

  Clarification:  You connect both ends of the motor through resistors
to the same ADC input; you get half the voltage (which is probably the
scaling you wanted anyway) but by switching the lower transistors in the
H-bridge, the voltage is always positive and ground-referenced.
--
  Cheers,
        Paul B.