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How does this rotation control mechanism work? Answered

I've been trying to figure out a good technique to control the motor rotation in a split-flap display. I've found two methods that I want to compare. One is with a NEMA8 stepper motor (I want to try to keep things small and easy to replicate), the other technique is with a method I've only seen in one place, and I'm not exactly sure what's going on.

You can see the video here.

From what I gather, they have a DC Motor, that controls two discs. The right hand disc acts as your zero reference, and the left references each flap in the split-flap display.  I can faintly see a red light flashing that I think is on the left hand connector, that flashes every time a groove in the wheel spins past. The right hand wheel only has one groove in it, and when it's facing straight down, you'll see the LED turn on. I imagine the LED is turning on to let the programmer know that that sensor is picking up the groove, but I don't think it's the sensor. I also think those grooves are super important to the sensing, but I don't know how.

I know how ball mice work, but those require a IR emitter/receiver on each side of the wheel. I can't see that here (though it could be hidden).

So my question is, how does this work? Or, if it's a better question, what is the simplest/cheapest way to get precision accuracy (and the ability to zero if things shift out of place) out of a DC motor without programming the stopping points?

Any help is greatly appreciated.

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user
steveastroukBest Answer (author)2014-09-21

They're just using "slotted opto switches" Old photocopiers have loads of them inside.

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user

Okay. So it is the same thing you have in a mouse. Now I have a name for it, so thank you!

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