A controller for a haptic actuator is described. The controller includes a driver which has an output configured to be coupled to a linear resonant actuator in a first mode and a frequency detector having an input configured to be coupled to the haptic actuator in a second mode. The frequency detector is configured to detect a signal generated on the terminals of the haptic actuator in response to an externally applied force and to determine a resonant frequency of the haptic actuator from the generated signal.