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[DPRG] The quadrature blues, or - The Tale of two sensors

Subject: [DPRG] The quadrature blues, or - The Tale of two sensors
From: Jeffrey T. Birt ditto at ipa.net
Date: Tue Aug 28 21:39:35 CDT 2001

> Quick and dirty method of selecting encoder counts and placing detectors:
> Place the detectors on opposite sides of the shaft
> Use encoder wheels with an odd number of divisions.
> That way no matter how many encoder divisions you use, you will always
> optimal placement.  You can then change encoder wheels at will as long as
> they have an odd number of divisions.

I should have mentioned that I'm using a reflective type sensors, therefore
an even number of encoder divisions must be used.  I did have one other
thought on the way to work this morning though, which came from looking at
the encoder disk on a mouse a few weeks ago.  The slots were curved and the
two sensors mounted inline along a radii.  I occurred to me that with this
arrangement the bottom sensor was always 1/2 division off what the top was
seeing.  So, one could make wavey lined encoders or make the bottom half the
disk 1/2 division off the top, placing the sensors top to bottom on a radii
or 180 deg apart on looking at the top the other looking at the bottom.

Jeff Birt
Halfway, Missouri

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