>One pin to GND
>One pin (via a inductor) to power
>One pin to the IC

I suspect your sensor may not be two photo diodes, but rather two
photoresistors in series across the supply, and the input on the chip is
actually an analogue one measuring the voltage of the divider. This way it
would be easy for the micro to see the "black stripe" of the spoke in the
wheel move past and trigger an interrupt at midpoint, and then figure out
which way the bar is moving by determining if the voltage moves up or down.

It may not be CDS type sensors, but that was what I had in mind, but I don't
think they are fast enough response for this. Anyone remember the dance arm
sensors on reel to reel tape drives ????

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