> I have been experimenting with a Hall Effect device (UGN
> 3503U) trying to count the teeth on the sprocket that turns
> the shaft. Although promising, I only get a one millivolt
> difference between the tooth and the gap and the Hall Effect
> device has to almost tough the sprocket

The data sheet for the 3503 says "The sensor's output is
usually capacitively coupled to an amplifier that boosts the
output above the millivoilt level"

The sensor has a range of 0 to 900 gauss and outputs just
1.3mV per gauss, so you'd expect to need some amplification
for a linear sensor. If you want a digital output you should be
looking at a Hall Effect switch, eg the 31xx series

and, btw

Do you have a flux concentrator ? Is the sprocket ferrous ?

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