An infrared touch input system is taught. Briefly stated, the system comprises a four-sided frame having an infrared transparent bezel (20) along the inside thereof and having infrared emitters (CR) along the bottom and one side of the frame with infrared detectors (Q) along the sides opposite the emitters. Darlington transistor arrays (U3, U4, U8, U9) are used as source and sink drivers for driving the LED's in an array. The l/O lines of a microprocessor (U2) in conjunction with the source and sink drivers are used to selectively energize each LED. Additional l/O lines (PB0-PB5, PC0-PC2) of the microprocessor in conjunction with BCD decoders are used to selectively energize corresponding infrared detecting phototransistors (Q) before, during and after LED turn-on. A host computer supplies a clocking signal for the microprocessor with programming in the microprocessor thereby automatically performing the selection and deselection of emitters and detectors. A serial data stream (DATA) is outputted from the microprocessor which indicates to the host computer the location of any broken light beams (22) thereby indicating a stylus (18) hit. Further, the optical power used with emitter-detector pairs (CR0-CR7, Q0-Q7) adjacent the corners of the bezel (20) is reduced with respect to emitter-detector pairs approaching the center of the bezel. In this manner, light which is reflected (26) after striking the side of the bezel adjacent the emitter-detector pair and which is received by the emitter is of low intensity or is ignored.
TOUCH INPUT DEVICE