Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

How does a windshield tell the wiper to work?

  1. Jan 6, 2005 #1
    My dad has a Buick that has a windshield wiper system that senses somehow that it is raining and automatically starts the wipers working, then adjusts the speed and frequency to match the amount of rain hitting the windshield.

    How does this work?
  2. jcsd
  3. Jan 6, 2005 #2


    User Avatar
    Science Advisor
    Gold Member

    It's a switch!

    There are two parallel thin wires running very close to each other, these are coiled in on themselves, and placed somewhere on the outside of the car. When a water droplet bridges the gap between the two wires, a current can flow and this triggers the wiper circuit. I guess that there are a few of these 'switches' with different spacings in order to alter the speed and frequency of the wiper cycle.
  4. Jan 6, 2005 #3
    Thanks brewnog. I figured it had to be something like that. My dad thought it was a visual sensor, but I pointed out to him that it couldn't work in the dark.
  5. Jan 16, 2005 #4
    Isn't rain water pure and thus non-conductive? Or does all water have some conductivity. Or is rain water simply not pure.
  6. Jan 16, 2005 #5
    You live in NY and you think there's such a thing as pure rain water???

    With as much acid that's in the rain anymore I'm surprised that we all don't have windshields that etched so bad you can even see through them!

    The acid rain has definitely made a difference in my garden over the decades. I actually have to adjust for the ph after a heavy rain!!! And I live in the mountains! :yuck:
  7. Jan 16, 2005 #6
    Oh darn that's right, I forgot that we don't live in a clean enviroment anymore >_<
  8. Jan 17, 2005 #7
    Other methods include a piezo vibration sensor, as well as a multiband optical sensor to determine rain, vs other types of contamination on the windshield. Nissan used the piezo sensors for the last 20 years. The multiband optical was developed at TRW, so most likely it ended up on GM and or Chrysler.

  9. Jan 17, 2005 #8
    Where exactly are the rain detectors located? Windshield bottom I suppose? Are they easily visible?
  10. Jan 18, 2005 #9
    Peizo's are on the hood, typically under the heat shield. Multiband are typically in the defroster vents, not sure about the wire type.
  11. Jan 18, 2005 #10
    Pretty cool, I might go and have look later and see if my family's car h ave it.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook