Have you seen Audi, Lexus or Ford rain sensing wipers
and wondered how they work in these vehicles? They are handled by sensors at the center of the windscreen which detects rain water and turns on the wiper motor. Here is the working of rain sensitive wipers
with circuit schematic. The main component of this circuit is a 555 timer IC
that works in monostable mode. Two metal sheets fixed at a small distance apart are used as rain detector sensors
. From the working of a monostable 555 timer
, a negative voltage on the trigger pin will cause a high output. So when it rains, trigger pin gets a negative voltage. Output of one shot 555
(monostable) is connected to a relay through a transistor. The transistor acts as a switch for the relay to turn ON the wiper motor during rain.
- IC 555
- Transistor BC 548
- Diode (1N4007)
- Resistor (1K,10K,1M,)
- Relay (12V,10A)
- Rain sensor (Two metal sheets as figure)
How rain sensing wipers work?
Working of this circuit is same as the working principle of monostable multivibrator. Here the trigger to the second pin is given by rain sensors.
A small water drop on the rain sensor will connect the negative voltage to the trigger pin of 555 IC which in turn will turn the output pin of 555 high. 5
55 Output is connected to the base of transistor through a 1K resistor which forward biases the transistor. Thus relay gets negative and it switches ON the wiper motor. You can refer our previous post on how relay works for better understanding of relay.
Components Pin out