Abstract: Apparatus for controlling vibratory machines of the type having at least one electromagnetic drive coil to drive a member at a resonant frequency includes a DC power supply; a programmable controller that produces PWM control signals that when applied to the drive coil cause vibrating motion; a switching driver circuit that applies a drive waveform to the drive coil by switching DC power to the drive coil in response to the PWM control signals; and a motion sensor that detects vibration amplitude; the controller tracking resonant vibration frequency as a function of an amplitude signal related to the drive waveform. The motion sensor preferably produces a signal related to vibration velocity.