Noise on a2d / PWM BDC motor drive

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Noise on a2d / PWM BDC motor drive

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Seegoon
Contributor I
Hi to all.
A mc9s12c32 micro is used in this design. A brushed 24V dc motor is bieng driven
via a H-bridge , using 4 of the pwm Channels.
Basically the h-bridge drive is inducing noise in the a2d signals whenever there is a
transition , high to low or visa versa. At the moment I am filtering out noise in software.
Is there any way I can trigger the a2d convertor when the pwm "waveform" is in the middle
of its cycle , ie where there is no switching noise. If I look at a pwm "Bean" it shows a
pin can be used to externally trigger the a2d , but this pin is being used for something else.
I'm looking for some sort of internal trigger / software option.
Hope I'm not being to vague!!
Thanks
Robin
 
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Nabla69
Contributor V
Hello Robin,

I like this cheap solution.

When you initialize your PWM in the software, you can also use a Timer channel.
The timer channel will allow the rest of the software to be aware of when the levels are stables.
Either you use the timer channel interrupt to launch the ATD conversion sequence,
Or you wait on the timer channel flag to be set before starting the sequence if you don't want to use ISR (of course need to clear previous flags when starting to wait).

The good thing is that the timer channel can be used for other things as well.

Alfreda.
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Seegoon
Contributor I
Hi Alfreda , thanks for the reply.
I don't realy understand what you are trying to say/ do?
If I have the pwm running , at say 40% duty , how can I tell when the output is stable , either high or low.
I understand using a timer if I could trigger it on a transition to delay until the output is stable , but
how do I trigger it. I have no external pins available.
Robin
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