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Hi,

I'm working on a project to build an optical rain sensor using the same approach used in modern cars (automobiles) that reflect IR through the windshield/screen and measuring the small change in reflectance.

I was looking at the best emitter and detector pair for my purpose and could do with some advice on selection.  I've looked at the IR diodes usually used for remotes and break-the-beam sensors but I'm aware there are phototransistors etc.  However I'm guessing frequency and sensitive will be more important to me than pairs which are design to transmit data.

I could also do with some general advice on testing different components.  I have a basic multimeter but no oscilloscope.  Would one be of use?

I had thought of buying a car part for the purpose of reverse engineering it too.

Warm regards and thanks,

Steve.
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Manchester (England England)
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no oscilloscope.  Would one be of use?
It's like saying I have legs but no shoes would they be useful.

The matched pairs refer to the wavelength of the emitter / detector these must be the same for best sensitivity.
You need the IR to be modulated to prevent interference. A friend of mine made on of these in the 60s and the wipers went every time he drove under a lamp at night.
However, most modulated IR receivers are designed for remote control and as such need modulated IR that is pulsed. You don't want these, look for those receivers designed for beam breaking like the TSOP4038.
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I guess I meant would I get by with my multimeter or is a 'scope a must have;-)

Thanks for the advice, found and read the datasheet.  Very hand it has a preamp and isn't sensitive to voltage ripple and noise.  I'll need to look at a suitable emitter now modulated at 38 kHz.

S.
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Oscilloscopes as essential if anything goes wrong, otherwise you are guessing. If you plan to do more electronics then get one, if this project goes right I could imagine you could do it without but you can never know something is 100% right without one. Simple correct functionality does not mean it is right but it is a good start. smiley-wink
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Understood. Been looking at a Rigol DS1052E recently anyway.

On the project parts located and bought.  Worked up a circuit based on a 555 for the modulation.  Will get a breaking beam circuit working first.
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It sounds like you are on your way, best of luck with the project.
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What is your progress on this project? I've gotten used to the automatic wipers in my wife's Audi, and I'd like to integrate something similar into my Nissan Titan...
I'm at the beginning stage; still brainstorming on the idea.  I haven't a clue how to ensure the IR transmitter maintains a 45 deg angle to the windshield.  I am thinking some sort of suction cup with a piece of hard plastic mounted on the inside of it that the transmitter is glued to.  Thoughts?
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On the project parts located and bought.  Worked up a circuit based on a 555 for the modulation.  Will get a breaking beam circuit working first.

Recently completed a project using a DIY 38khz IR transmitter based on a 555 timer. Discovered that I had to use high tolerance parts (resistors and capacitors) and low value capacitors to maintain a good tolerance of the output frequency. I think that the next time around I'll be using an Attiny in lieu of the 555 and other components. - Scotty
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