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Message-ID: <4EF229B4.8050008@ecosensory.com>
Date: Wed, 21 Dec 2011 12:47:16 -0600
From: John Griessen <john AT ecosensory DOT com>
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To: geda-user AT delorie DOT com
Subject: Re: [geda-user] Design suggestions...
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On 12/21/2011 12:16 PM, DJ Delorie wrote:
>   You
> need an interrupt frequency only a few times your effective PWM cycle
> time to get something that "works" (although faster is better:)
>

That, and add a little capacitance to the DC motors/potentiometers so
PWM of them effectively creates a sigma delta DAC with an output smoothing filter.

When you say potentiometers, are they carrying the full DC motor current?
or is there some kind of motor control there already?

On 12/21/2011 11:11 AM, Rob Butts wrote:
 > The documentation for that microprocessor says the pmw can be set up for one, two or four channels but it has just one pwm module.

That probably means, "every interrupt, set each PWM channel pin high or low according to its stored duration and state."
So, it's not limiting you.  Two DC motors is easy for it timing-wise.
Maybe one channel for forward, one for reverse -- where
the logic for which leg of an H-bridge gets the PWM signal comes from which channel it is also.  might need an inverter
or just select pfets and nfets to get that effect from the PWM signal polarity you have.

You would use all 4 PWM channels, (fwd1, rev1, fwd2, rev2 ), but minimize external parts needed.

Each PWM requires external power FETs in a H-bridge for forward reverse and  stop, right?

John