Re: Recommendations for a Quadrature Decoder IC or MicroController

On Tue, 29 Jul 2008 23:18:06 -0700 (PDT), benn <benn686@xxxxxxxxxxx>
wrote:

I have an atmega16 that interfaces to a motor with a quadrature
encoder sensor. Turns out the frequency of the pulses are much more
than my little 4Mhz can handle (the micro does other things as well!)
As a result, the motor control isn't very accurate, nor does it react
very fast.

You haven't mentioned much about your situation, such as the motor's
rate, the number of A/B transitions per revolution, etc. You might be
okay with what you have, but just need to think more closely about the
details to make it work cleanly. Hard to do anything more than accept
your conclusion, though, without more info.

SO.. I'm looking for either a quadrature decoder IC that can take the
load off (will calculate position/velocity and interface to a host
micro via serial/parallel bus), OR, a beefy microcontroller with built-
in decoders (and pwm output). 32-bit with lots of GPIO is ideal if
going the microcontroller route.

There is (or was) an expensive HP part that I've used in the past, as
well, the HCTL-2020. It is designed for the purpose and works well,
but you pay for it when you find it. A separate micro would be
cheaper, I think, but you've have to code it up. I'll leave the
do-all micro recommendations to others.

Jon


P.S. I've handled motors running at 250 RPM (actually, I controlled
the motor speed, too, and 250 RPM was the max), coupled to optical
encoders with 10000 A/B transitions per rotation (medical pumps.)
There is a cam attatched to the motor, so there was also analog
conversion of that and a real time graphics display set up to display
the home and certain key pulses other than A and B, along with the cam
height, so that the workman could adjust the optical encoder relative
to the cam shaft to calibrate the motor while spinning (requirement.)
I mapped the timing in a hand-drawn paper diagram before attempting
the coding. By the time I was writing code (and I did use assembly
for some critical parts of it), I'd already resolved the mechanism to
use and knew it was sufficient.
.

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