Noise-insensitive, photoelectric transceiver including a digital

Abstract

This invention provides a photoelectric transceiver (10) for detecting the presence and absence of objects (16) in a selected region (12). The transceiver (10) includes a light source (18), a light sensor (22), and electronic circuitry (13). The transceiver (10) generates a timing signal (MDCLK) that synchronizes its operation. In synchrony with the timing signal, the transceiver emits pulses of light (14) into the selected region (12) and senses light (24) coming from the selected region. When an object (16) is present in the selected region (12), the emitted light pulses (14) are reflected back to the transceiver (20). Based upon the light sensed, the transceiver generates an output (OUTOD) indicating whether or not an object is present. The transceiver includes three features that reduce the effect of interfering noise on the output (OUTOD). First, the output (OUTOD) is generated by a digital count hysteresis process to reduce the effect of random noise. Second, the transceiver timing signal (MDCLK) is modulated between two frequencies to reduce the effect of repetitive noise. Third, the transceiver timing signal (MDCLK) is interrupted when interfering noise is detected to further reduce the effect of noise. The transceiver includes a digital stability indicator (42) that indicates whether the transceiver operation is stable.