Abstract: A monitoring system for a display unit includes phototransistors for detecting light emitted from a plurality of selectively energizable light-emitting diode (LED) segments in an energized state and for generating a voltage which is representative of the light emitted from the LED segments in the energized state. A glass filter filters ambient light from the phototransistors and passes the light emitted from the LED segments in the energized state. A comparator for each of the LED segments generates a comparison signal, with the comparison signal being representative of a comparison between a predetermined reference voltage and the voltage for each of the LED segments. A conditional power supply conditionally energizes the LED segments in response to an energizing signal. A routine of a central processing unit generates display data.