Clever idea! I think that printed magnets with hall sensors would work as well as an analog quadrature disk.

Good call. 

Even, maybe a regular-ol' disk-magnet, assuming its poles are both in the same plane. At some point, of course, those magnetic position-sensors designed for the task would probably give much higher resolution (and accuracy)... Though those things promise resolutions in the thousands per revolution, I wonder how accurate they can really be considering a tiny bit of misalignment would completely change the fields entering the sensor. Can't recall who it was, off hand, but someone 'round here set up a nice jig to test one of those out with good results.

Although, now that you mention it, another decent sensor idea for e.g. linear tracking might be just to record a sine-wave on an audio-cassette tape and stretch it out. Hmmm... I wonder if hall sensors can detect those tiny fields, 'cause I think a regular pick-up would only work if it was moving (and its amplitude would change with speed?).

Mind if I thank you for the skull, here? I think I've spammed your profile page a bit. ;)

You welcome! I am always grateful for your skulls!

Hmm, got me thinking a bit more... A triangle-wave (printed or magnetic) would remove the need for anaQuad altogether, a simple *single* ADC-reading (and comparison to the prior) would be all that's necessary to determine direction. Only confusing-factor software-wise would be what happens when the sensor is "too large" and averages out the high-to-low transition... Might look identical to a fast-reverse. Guess two sensors are still a good idea.

Hrm.. by which, of course, I meant sawtooth-wave, or a right-triangle, maybe...