A control circuit having a drive circuit and a controller adapted for use in optical mice is disclosed. The drive circuit is connected between first and second ports and passes a current between those ports having an amplitude determined by a control signal that is generated by the controller. The first port is connected to an illumination device and the second port is connected to a power rail. The control circuit also includes a potential measuring circuit that generates a signal indicative of a drive circuit potential between the first and second ports. The controller records the drive circuit potential for a predetermined current when the first port is connected to an illumination device. The controller sets the control signal based on the recorded drive circuit potential. The control circuit can record the drive circuit potential when the controller is powered.