You can also check out page 134 of the May 13, 1998 issue of Electronic
Design, where is a simple design of a Rotation Counter, using no moving
parts, taking advantage of the momentary short created by the brush of a
permanent magnet motor.

Calvin
TGO Electronics


-----Original Message-----
From: Ron Fial <ron@FIAL.COM>
To: PICLIST@MITVMA.MIT.EDU <PICLIST@MITVMA.MIT.EDU>
Date: Lunes 22 de Junio de 1998 6:32 AM
Subject: Re: DC motor speed regulation


>Another (perhaps old fashiond) way to measure DC permanent magnet motor
speed is to measure the back EMF from the motor when the voltage to the
motor is momentarally off.  If you are doing PWM, then when the current is
off, if you read the back EMF voltage from the motor, it is directly related
to speed.  I have used this and the speed control is quite accurate -- You
are using the motor as a DC generator for an instant.
>
>This method takes more parts than measururing ON current, usually needs an
op-amp circuit, but way cheaper than a tach.  This is probably to complex a
method for an H bridge driver, but its quite easy for a PWM single direction
of rotation application.
>  Regards,
>     Ron Fial
>
>At 12:56 PM 6/22/98 +0200, you wrote:
>>Hi all,
>>
>>As a newcomer to the list, I am interested in speed regulation of a
>>small DC brush motor (e.g. as used in model trains) by using a PIC. Most
>
>
>Regards,
>  Ron Fial
>