> -----Original Message-----
> From: Alan B. Pearce [SMTP:A.B.Pearce@RL.AC.UK]
> Sent: Tuesday, April 29, 2003 4:34 PM
> To:   PICLIST@MITVMA.MIT.EDU
> Subject:      Re: [EE]: PC mouse optical detectors.
>
> >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.
>
Not convinced about this.  The output would have the same mark/space
irrespective of direction.  With no reference to compare this signal to, how
would the direction be decoded?  In fact, you'd get the same output with
just one sensor AFAICT.

Mike


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