How do automatic windshield wipers know when to wipe?


How do automatic windshield wipers know when to wipe?

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Normally there is a rain sensor near your rear view mirror. The sensor measures how much rain is on your windshield wiper using rays of science.

I am sure someone can give a more scientific answer.

When a ray of light goes between glass and air, it will “refract”. Change the angle it travels at. You might see this effect making a straw in a glass of water appear bent.

If the angle is sharp enough, the refraction means the light gets reflected inside the glass. This is what happens normally. We have an infra red light, and a sensor that expects to detect the reflected light.

However, if there’s a drop of rain on the glass, we aren’t looking at light going from glass to air. It’s going from glass to water. This causes a much smaller amount of bending. The light doesn’t get reflected back. The sensor detects it’s not receiving light and tells the wiper to activate.

There is a sensor embedded in the windscreen.

It could be electrical (like how a phone senses that you have touched the touchscreen) or it could be optical (it senses how raindrops on the glass refract light)

The sensor then tells the wipers to activate