Patent ID: 8660443

Claim:
An electrophotographic image forming device, comprising: an optical emitter positioned to emit a light beam through a window into a reservoir of a toner cartridge holding toner toward a reflective surface in the reservoir as a paddle positioned within the reservoir rotates; and an optical receiver positioned to sense an amount of the light beam reflected by the reflective surface; and at least one processor configured to receive a signal related to the amount of light sensed by the optical receiver, the at least one processor including computer executable program instructions, including: instructions for calculating an average value for the signal for each of a plurality of sets of paddle revolutions; instructions for calculating a variation value for the signal for each of the plurality of sets of paddle revolutions; instructions for filtering each variation value to determine a plurality of short term variation values; instructions for monitoring whether at least one short term variation value exceeds a first threshold; and instructions for signaling that a toner level in the reservoir is low when the at least one short term variation value exceeds the first threshold.