AVR-Chat

Larry Barello said:
>       Don't use the enable line for PWM input.  Use the complementary PWM
> outputs
>  to drive the A & B side of the H-Bridge and use the enable line to,
> well,
>  enable the driver.
>


Larry,

Thank you for the feedback.  I hadn't thought of using PWM on the A and B
lines.

I'm having a tough time visualizing what'll be happening though.

Here's the mental picture I had of my original "PWM on the Enable Line"
scenario:  I can easily picture what happens when I set A=1 and B=0 for a
motor.  It'll go clockwise.  Similarly, set A=0 and B=1, and I get reverse
(counter clockwise).  And the PWM signal on the Enable line then turns the
motor on for only small snippets of time, as defined by the duty-cycle.
Also in this scenario, I can set A=B and get braking mode.


Now I'm trying to picture Larry's suggestion of using complementary PWM on
A & B lines.  Firstly, I can easily picture the Enable line now.  Its now
used simply for enable/disable, with no "rapid" switching like PWM.  Then
my vision gets cloudy of what's happening on the A & B pins.  My limited
understanding is that pin A will experience an average voltage
proportional to the duty-cycle of the PWM signal.  Pin B will experience
the complementary average voltage.  But what does this actually do for me?
 Doesn't it cause the direction of motor motion to switch really rapidly
(at the PWM frequency)?

I would love it if you would take tht time to explain intuitively what's
happening.

Ethan
www.bufbotics.org