Contamination sensor for transparent elements having a reflection light barrier and a working voltage controller

摘要

A circuit arrangement for detecting foreign bodies on a transparent element, particularly in a motor vehicle, including a dynamically driven reflection light barrier having a light emitting diode, a pulse generator connected electrically to the light emitting diode to produce light pulses and a phototransistor having a collector and an emitter. The phototransistor and the light emitting diode are positioned on the transparent element so the phototransistor receives reflected light produced by the LED. A resistor connects a power supply including a circuit, which can double an operating voltage in the motor vehicle, to the collector of the phototransistor. To neutralize the effects of stray light, e.g. from headlights of other vehicles, the circuit arrangement is provided with a working point controller connected electrically to the doubler circuit and to the collector of the photoresistor for controlling a voltage difference across the collector and emitter of the photoresistor as a function of an incident extraneous light intensity to compensate for the extraneous light intensity and to obtain an AC output voltage portion from the phototransistor substantially dependent only on the light reflected from the foreign bodies.