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Date:	Wed, 21 Dec 2011 13:16:54 -0500
Message-Id:	<201112211816.pBLIGsaf016475@envy.delorie.com>
From:	DJ Delorie <dj AT delorie DOT com>
To:	geda-user AT delorie DOT com
In-reply-to:
	<CALSZ9godJsJDhBd_PaCiWPx9M8GyKz8PW1wVUs6NxVgtrOS-Fw AT mail DOT gmail DOT com>
	(message from Rob Butts on Wed, 21 Dec 2011 12:11:24 -0500)
Subject:	Re: [geda-user] Design suggestions...
References:	<CALSZ9godJsJDhBd_PaCiWPx9M8GyKz8PW1wVUs6NxVgtrOS-Fw AT mail DOT gmail DOT com>
Reply-To:	geda-user AT delorie DOT com

Search for "motor controller" on digikey - I keep tripping over
i2c/spi motor controllers that do what you want, each time I search
for bldc drivers.

If that doesn't work out, it's possible to drive the output pins via
software (bit bang) in what I call a "pulse dithering modulation"
mode.  I use it for LED brightness control, it might be good enough
for your purposes.  In summary: in your timer interrupt, add your
"speed" value to a counter.  If the counter overflows, turn on the
motor, else turn off the motor (i.e. the pin is the carry bit).  You
need an interrupt frequency only a few times your effective PWM cycle
time to get something that "works" (although faster is better :)

For more info, see "Bresenham's line algorithm" in Wikipedia :-)

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