Newsgroups: comp.robotics
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From: sasrer@unx.sas.com (Rodney Radford)
Subject: Re: PWM motor control
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Date: Tue, 17 May 1994 14:05:02 GMT
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References: <1994May17.102942.26485@imada.ou.dk>
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zaphod@imada.ou.dk (Anders S. Soerensen) writes:

>If you are interested in easy PWM control of DC motors, then 
>check out the LM629 IC.
>It takes care of everything!

Including any spare cash you may have lying around....!

The last time I checked the price of an LM629 was about $75 EACH and I
need at least 4 in my current project!

So since my current project is supposed to be a learning exercise anyway,
I decided to build my own LM629-equivalent circuit.  I originally started
with using several PIC 16c54s (one for doing open loop PWM, the other closed
the loop by monitoring optical encoders and sending new PWM value to the
first), but I scrapped this idea when I saw the specs on the 87c752 part.

This one part has a hardware PWM (replaced one PIC), A/D (for sensing motor
current to detect stall), I2C interface for communication, and enough
processing power for the PID calculations. I am still very early in the
design process, but I hope to have something ready soon (of course, I said
the same thing about the PIC before I decided to scrap it). 

I also lucked out and had a friend loan me an 87c752 ICE for realtime
code emulation - this will certainly make the job *MUCH* easier.

So, if everything pans out, I will have the equivalent of an LM629 plus the
advantage of a serial link and A/D for sensing motor current/voltage - all
in a $15-20 package!  

However, if anyone knows of a cheap supplier for LM629 parts, I will gladly
scrap my current design (again), and just buy the LM629....  ;-}

--
---
Rodney Radford,     Senior Systems Developer,  Image Technology Group
sasrer@unx.sas.com  SAS Institute, Inc, Cary, NC 27513  (919) 677-8000 x7703

