Rain Sense

Posted on Friday 26 May 2006

car_rain_sensor2.jpg

Earlier this past spring(’06) I happened to visit my father in NJ an he had just traded up his older Buick for a recent model Buick LeSabre. Now what is interesting to me is that this luxury car came with many advanced features that were built in, OnStar, Electric seats, and most interesting were a plethora of sensors built in.

The one I want to focus on for now was the Rain Sensor, and following up after my most recent visit I have some video of a small test and have looked into who makes this sensor and how it works.

When I first looked at the behavior of the sensor from the outside I made an incorrect guess that it might work on detecting moisture, then responding. To my surprise the hardware portion was quite simple, an IR emitter and an IR detector pair work with light bounced off of the inside of the windshield. Simple huh? Well not so simple really, after all how often do shadows and other obstructions alter the reflective properties of windshield glass…

According to the documents found on the web by Opto-Electronic Design at http://www.raintracker.com/ promoting their own sensor to use in automobiles there is a process of “optical filtering” that deals with potential false trigering of the sensor. The Patents owned by the founder of the company, Rein Teder deal with optimizing the sensor to only respond to rain and to respond proportionally by moving the wipers with the appropriate frequency.

The company white paper is a website that explains much of this at: http://www.rainsensors.com

One more intriguing note is a patent that refers to algorithm that mimics human perception and response to rain. I hope in the future to speak directly to Mr. Teder more about this very interesting area of human behavior.

I did a simple test by spraying my Dad’s car with a hose in varying amounts. What I observed is that the wipers turn on not quickly, but certainly in a timely manor. The wipers stop as soon as the moisture is removed. Other tests I didn’t perform were spraying only portions of the windshield. If you would like to see the video I made you can go here: http://www.flashicon.com/ITP/car_rain_sensor.htm

I spoke to a very helpful company spokesman who will be sending me more documents to study and an offer for a test sensor for my experiments. I will probably be adding to this post in subsequent days but wanted to get this much up for now.


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