Newsgroups: comp.robotics
Path: brunix!sgiblab!swrinde!elroy.jpl.nasa.gov!decwrl!netcomsv!netcom.com!nagle
From: nagle@netcom.com (John Nagle)
Subject: Re: How do I control a hobby servo from a microcontroller?
Message-ID: <nagleCKEo1x.5Gn@netcom.com>
Organization: NETCOM On-line Communication Services (408 241-9760 guest)
References: <CKCs40.7nE@SSD.intel.com>
Date: Sat, 29 Jan 1994 19:13:08 GMT
Lines: 19

stupak@ssd.intel.com (Mike Stupak ) writes:
>  I have several hobby servos (remote control glider type) that I would
>like to run from a microcontroller.  I'm not sure what type of signals
>it needs on which wire.  My understanding is that these are PWM controlled
>such that the position is proportional to the pulse width.  What pulse
>width (and frequency) is necessary?  What are appropriate voltage and 
>current levels?  Is any additional power source required?  Is any additional
>circuitry required?

      Black is ground, red is power (+5 or so), and the third wire is 
control.  The control signal is a square wave with a low duty cycle;
0.5ms to 1.5ms on, 13ms or so off.  The on time controls the servo; the
off time isn't critical.  Make sure you have good filtering on the power
line to isolate the motor noise from any electronics on the same supply.
Voltages aren't critical.  The control signal is 0/+5, and a CMOS driver
is enough to drive most servos.  Timer outputs from a 68HC11 run these
things very nicely.  Lots of people have done this.

					John Nagle
