Peak detecting bar code reader

摘要

A signal processor for reading a bar code symbol having alternating dark and light portions includes a photodetector for receiving light reflected from the bar code symbol and for forming a sense signal representing the intensity of the reflected light. A differentiator circuit coupled to the photodiode generates a first derivative of the sensed signal, and an offset circuit generates an offset signal which is displaced slightly from the first derivative. An output circuit generates an output signal which indicates changes in the intensity of the reflected light when the first derivative signal and the offset signal have approximately equal amplitudes.