Current through a motor is sensed to create a voltage which is amplified. The amplifier is followed by a high pass filter and a low pass filter. This recovers commutator pulses from the motor current, rejecting mains ripple and higher frequency noise. Commutator pulses are counted. Other arrangements could be used for injecting pulses into the motor supply, for counting at a remote position. Various techniques are described for controlling the motor in accordance with the result of counting,