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While it’s a first-world problem that you don’t want to manually turn on your windshield wipers when it starts to rain, it’s probably one of those things that seems easier to solve than it actually is. After all, you can ask a four-year-old if it’s raining and expect a reasonable answer. But how do you ask that computer question? Especially a small, inexpensive computer that works pretty well on its own.
You may stop here and try to think how to do it. Measure the strength of the glass? Maybe the water on the glass affects the dielectric constant and you can measure the resulting capacitance? Neither do modern cars. The problem is complicated because you need a solution that works with the glass and is not prone to false positives due to dirt or debris.
Instead, they use infrared light shot at an angle against the windshield. The glass reflects most of the light back to the sensor, but water scatters the reflection. If the sensor sees less return light, it turns on the wipers. Where is the sensor? It depends on the car, though [Jeff] The video below shows the position very well on Toyota vehicles.
Typically, the assembly is located behind the windshield somewhere near the rearview mirror. Here’s a nice write-up and graphic on the Clemson Vehicular Electronics Lab website.
Of course, car companies aren’t designing these from scratch. They buy the technology from other companies such as Hamamatsu and other companies.
There was a time when you could buy a kit to add this to your car if you couldn’t stand doing your wipers by hand. If you’re so inclined, rolling your own shouldn’t be too difficult.
Of course, there are other ways to do the same thing. Some Tesla vehicles can use their cameras to easily detect rain. Also, if you don’t need to know the glass, it’s very easy to measure the effect of humidity on the PCB resistor.
It’s amazing how many things are easy for a human to figure out but very difficult for a computer. While we enjoy our automatic wipers, we don’t want to turn them on if we need to. We also occasionally get false positives.
There is a surprising amount of technology behind windshield wipers. Not to mention, potential, rhythm.
Banner Image: “Let the Rain Rain” by Basher Tome. Thumbnail: “Bank of America cash machines in a row, windshield wipers, rain, University Village, Seattle, Washington, USA” by Wonderlane.
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