Automatically controlled windscreen wiper drive with raindrop sensor

摘要

The device passes light from a diode (SD) through the windscreen to a photoreceiver diode (ED) earthed via a capacitor (C) in parallel with a transistor switch (T1). The output voltage (u) is compared (K) with a threshold (Uschw) produced by a microprocessor ( mu C). When the threshold is exceeded an output signal (A2) is produced which discharges the capacitor through the transistor. The microprocessor forms a measurement value corresponding to the time after which the threshold is exceeded. When the capacitor is recharged the LED is switched off by another output (A3) from the microprocessor to another switching transistor (T2).