Evaluation circuit for photoelectrically read traces - has variable gain amplifier and trigger circuits reducing signal variation with paper speed and contrast

摘要

A circuit for evalution of marked recording media is partic. suitable for recordings of traces read by a photo-electric sensor. It is designed to reduce variation of the output signal with the speed of the recording medium, contrast, trace width, and the tolerances of the time and threshold detection components. The circuit distinguishes between markings of relatively high and low intensity. An amplifier receives an input from a light sensitive sensor and adjuster circuit. The amplifier gain is adjustable and its output feeds two trigger circuits. The higher trigger voltage circuit has an adjustable trigger point whilst the lower trigger voltage circuit has a fixed trigger point.