Reading an encoder using counters or TV hardware?

Graham Stabler

I am sure I remember someone came up with a super clever way of reading quadrature encoders at lightning speed using either counters or the TV hardware but I can't remember any other details, am I imagining this?

Cheers,

Graham

Phil Pilgrim (PhiPi)

Graham,

How fast are are the pulses that you need to decode and count?

-Phil

Graham Stabler

I need to monitor six encoder with peak frequencies of around 400khz.

I wrote code in assembly for tracking a single encoder which is about as fast as can be coded I think (uses a look up table stored in a single long and some shifting) and could extend this but I just remember that someone posted something really clever that I think could track several encoders at a very high frequency. Can't believe I have lost it.

Graham

p.s. my code which was someone else's idea implemented by me is here:

http://forums.parallax.com/showthread.php?p=617168

It does a single encoder at 1.3Mhz including write to hub memory.

Post Edited (Graham Stabler) : 8/4/2009 11:22:01 PM GMT

Timmoore

You can change Jeffs version to speed it up for 6 encoder only by unrolling the loops. It does most of the encoder processing at the same time and you only have to unroll and interleave the +/- and hub access. I estimate you can get 350K on a 80Mhz or 440K on 100Mhz. Heres a partial hack so you can see what I mean, I didn't fix the initialization code.

Graham Stabler

Thanks for that, I might try that or do something similar with my code.

What is bugging me is that I am sure I read about some clever method for doing it with counters or something and I am starting to think I am going mad. Particularly as I was sure Phil wrote it and even emailed him.

Graham

Phil Pilgrim (PhiPi)

Graham,

You may be thinking of this thread: http://forums.parallax.com/showthread.php?p=742749. It uses the counters to generate quadrature output.

-Phil