A powered surgical tool (30) with a housing (32) that contains a power generating unit such as a motor (34). A control module (40) is disposed in a shell that is mounted in the housing. The control module contains a control circuit (64) for regulating the actuation of the power generating unit. The power generating unit emits a signal representative of the operating state of the unit that is transmitted through the structural material forming the shell. Also internal to the control module shell is a sensor (74,76) that monitors the signal emitted by the power generating unit. This signal output by the sensor is applied to the control circuit. The control circuit, based on the sensor signal regulates actuation of the power generating unit. Wherein the power generating unit is a motor, the signal emitted is the magnetic field that varies with rotor position. The sensor monitors the strength of this field.
