A system driven by a DC motor (11) having two pairs of FETs (29, 32 and 30, 31) which form a bridge commutating circuit so that the motor can be driven in both directions. In each pair of FETs, one is driven by a pulse duration modulated control signal while its partner is conducting. There is a sensor (24) for the motor current and another (33) for the supply voltage for the commutating circuit. There is an estimator for the motor voltage based on the commutating supply voltage and the control signals. A sensor detects the rotation of the motor, based on the current drawn and estimated terminal voltage.
