Cordless light pen

Abstract

A cordless light pen for use with a cathode ray tube display screen as a data input for a digital computer. Contained within the exterior barrel of the pen is a depressible tip having a core made from a plastic which has been treated and whose index of refraction causes light entering in a direction parallel to the longitudinal axis of the core to pass through. The other end of the tip is operatively disposed relative to a light sensor. Also contained within the barrel of the cordless pen is a circuit card containing circuitry for amplifying, filtering and shaping the signals from the light sensor and to discriminate between signals due to the CRT sweep in the field of view of the tip and ambient noise. The so-called 'hits' occasioned by the passage of the CRT beam past the tip member when it is depressed cause an IR LED to be energized to produce a directed beam of IR energy. The IR energy is transmitted to a receiver positioned to detect it, provided the light pen is held on the face of the CRT screen. The receiver output is fed to the digital computer driving the CRT display causing the dot and line counts (refresh address coordinates) to be latched. With this latched information, the computer is able to determine the coordinate location on the face of the CRT screen where the hit occurred and is made to carry out a preprogrammed function as a result of the detected hit. The receiver is designed to provide a high degree of noise masking.