Newsgroups: comp.robotics
Path: brunix!sgiblab!sdd.hp.com!hp-cv!hp-pcd!hpcvca!hpcvcec.cv.hp.com!abrown
From: abrown@hpcvcec.cv.hp.com (Allen Brown)
Subject: Re: DC motor speed control
Message-ID: <1993Sep12.005547.18206@hpcvca.cv.hp.com>
Sender: nobody@hpcvca.cv.hp.com
Nntp-Posting-Host: hpcvcec.cv.hp.com
Organization: Hewlett-Packard Company, Corvallis, Oregon USA
References: <dkj-110993093923@kip-87.apple.com>
Date: Sun, 12 Sep 1993 00:55:47 GMT
Lines: 16

dkj@apple.com (Dave Johnson) writes:
: In the past I have rolled my own PWM with a 555 and a power transistor.
: I want to control the speed with an analog voltage rather than a
: pot, and ...
: Dave Johnson, dkj@apple.com

You can use the sawtooth waveform off of the capacitor attached to the
555.  Compare that against an analog voltage with a simple comparator.
The output is PWM and roughly linear to the input voltage.  You should
constrain the input voltage to correspond to the sawtooth limits of
the 555.
--
  Allen C. Brown  abrown@cv.hp.com or hplabs!hpcvca!abrown or "Hey you!"
      Not representing my employer.
    Everything should be made as simple as possible, but no simpler.
    --- Albert Einstein
