I bit banged a PWM routine (several bits of sample code available on
piclist.com under I/O routines) then immediately before turning on the
output transistor I measured the voltage at the motor using the A/D module.
I used this measured value to adjust the duty cycle up or down.  Worked
pretty well.  All I did for a feedback circuit was a 10k resistor from the
drain of the transistor to the RA0 input with a 6.8k to ground to divide the
voltage down and a .33uF cap to ground to smooth out the waveform.  I was
running at about 150 Hz so I had lots of time to measure and do
calculations.

-----Original Message-----
From: Justin Grimm [mailto:Justin.Grimm@SOUTHCORP.COM.AU]
Sent: Monday, August 26, 2002 2:03 AM
To: PICLIST@MITVMA.MIT.EDU
Subject: [EE]: DC motor control


Does anyone know the best way to control the speed of a 12v DC motor without
losing too much torque? Would pwm work or just varying the voltage?

Thanks
Justin

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