[oopic] Re: H-Bridge issue...maybe.

--- In oopic@yahoogroups.com, Shaggy <charrington@...> wrote:
>
>
> Then I will go with the Sabertooth.
>
> Thanks for the information.

Until I read the documentation at

http://www.dimensionengineering.com/Sabertooth2X5.htm I was concerned
that the device would only work with R/C pulses. That would seriously
limit resolution due to the manner in which the OOPic generates the
pulses. The .pdf is here:

http://dimensionengineering.com/datasheets/Sabertooth2x5.pdf

But the good news is that the H-Bridge will also work in analog mode
and you can use the oPWM objects to control the motors.

You may want to deal with the issue of 2.5V being the OFF condition.
When the OOPic first starts up, the IOLine is an input and floating.
The motor may run away briefly. I might put a 20k resistor between the
input and +5V and another 20k resistor between the input and Gnd in an
attempt to bias the input to 2.5V until the oPWM object takes over.

Obviously, you want to start with the oPWM at 50%, then establish the
IOLine and finally set the operate property. Hopefully, you will get a
bumpless transition into the stop condition.

Thinking about the OOPic.Delay = 500 as the first executable statement
(and it is HIGHLY recommended) the motor could run away for a very long
time.

If the bias idea doesn't work, put a suitable SPST relay in series with
the motor power and control it via the OOPic and a trasistor of MOSFET.

One way or the other, you need to deal with this bias situation.

Oh, and read the note on filtering the PWM signal on page 10 of
the .pdf. If you use the bias resistors, the resistor at the pin needs
to be a lot smaller (maybe 1k or less) to allow the pin to pull the
signal all the way up or down. The 1k resistor is working in series
with the bias resistors and forms a voltage divider. Given that the
resistor is much smaller, the capacitor should be much larger - say 1
ufd (probably electrolytic).

I suspect there will still be a little tinkering to do...

Richard

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