An opto-matrix touch input device which samples and compares beam readings is taught. Briefly stated, phototransistor readings (Q) which sample ambient light as well as light from an associated light emitting diode (CR) are compared with preset values. if the readings from the phototransistor are below a certain level, then the phototransistor/LED pair are flagged as bad. If the readings are within preset limits, yet below nominal values, then the phototransistor/LED pair are flagged as indicating a marginal beam. In this manner a trouble report may be generated for the purpose of repair or investigation as well as providing a vehicle for keeping a history of the opto-matrix frame condition and thereby a method of early fault detection.
EARLY FAULT DETECTION