Position encoder help

Brian Carpenter

I have a project where i have a motor with a 20 tooth sprocket connected to a #25 chain driving a 30 tooth sprocket on a 3/4 steel shaft (business end).
The motor turns pretty slow as it is at about 60 rpm but then with the gearing... well, we are not talking about high rpms hear.

I want to be able to count how many revolutions the large sprocket makes in one direction so that i can ensure that it makes the same revolutions on the way back so that i know it is in the right position. The sprocket is solid and black, so my idea is to paint white marks on it in a circular fashion and use a reflective IR switch? Is this what you would do?

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It's Only A Stupid Question If You Have Not Googled It First!!

erco

Brian: You can use reflected IR just fine. I like the little self-contained Hamamatsu sensors, but you can also make your own using an IR LED and a phototransistor. Your particular black/white marks may reflect/absorb IR different, so you may have to·adjust your sensor distance and LED intensity by changing the resistor value. The unit I used has lots of internal circuitry that gives it a real nice digital output signal:

http://forums.parallax.com/showthread.php?p=874406

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·"If you build it, they will come."