Alan B. Pearce wrote:
>>For now, I only have to worry about one finger - but
>>need to track position in 3 dimensions with a resolution
>>of about 5mm over an area of 1 cubic meter.  Also,
>>the device cannot use a reflective method (such as ir
>>or ultrasonic).

Why not? Ultrasonic emitters on the tips of the fingers would be
tiny and using time-of-flight measurements, and 4 receivers,
easy to decode.
Use multiple frequencies if you need simultaneous multiple tracking.

What sample rate do you need?

>>    So far, I have investigated using
>>accelerometer chips, but these are still fairly expensive
>>and I would like a lower-cost alternative.

HUH? $25 for 3 axis 1G (ADXL 303JE) is pretty darned cheap.
But they probably won't give you the kind of accuracy you want.
And you've said nothing about tracking orientation.


> I suspect that accelerometers will have long term drift. What sort of long
> term accuracy do you need?
> 
> One thought I had was to use one of those sensory gloves that are used for
> virtual reality type things. You would need to have the person sitting to
> get a reference point, or some other method of reference.

These gloves use magnetics, (Flock of birds, 6 DOF) for gross position
and fibre optics to detect bending of the fingers.

Stay away from the Polhemous stuff. It's AC and suffers from big issues
with reflections (eddie currents).

Robert
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