a circuit for reducing noise and increasing the reliability of touch panels involves the use of a supplemental noise or electromagnetic interference pickup lead which extends generally coextensively with the parallel connected outputs from a series of successively coupled photodetectors and a high pass filter for substantially reducing the noise signals created by variations in the level of ambient light . when the photodetectors output is connected to one of the inputs of a differential operational amplifier , and the compensating pickup lead is connected to the opposite polarity other input , the noise is substantially cancelled out , and a cleaned - up photodetector pulse is provided . a pulse forming circuit squares up the photodetector output signal pulse ; and a hysteresis type storage or buffer 15 circuit is employed to indicate the presence or absence of photodetector output signals , from successive photodectors , thereby indicating whether or not the light beams are interrupted either fully or partially .