From: James Burkart <james@burkartstudios.com>
To: Microcontroller discussion list - Public. <piclist@mit.edu>
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Date: Wed, 29 Jul 2020 07:46:41 -0700
Subject: Re: [PIC] How to properly set PWM duty cycle
Thread-Topic: [PIC] How to properly set PWM duty cycle
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Thanks, Nicola.

Human bean, it's a compliment. It is someone who, though might be a little
jaded, is willing to help someone for the greater good.

On Wed, Jul 29, 2020, 8:04 AM Nicola Perotto <nicola@nicolaperotto.it>
wrote:

> Hi James,
>
> On 29/07/2020 14:35, James Burkart wrote:
> > "What am I not getting?" Is very useful. It tells you that I don't
> > understand, possibly not even enough to know what information you need =
to
> > help me.
> My bad, I misunderstood the sentence, I speak better Asm than English ;-)
>
> >
> > What library? I did say I'm using MCC generated functions. Do you mean
> you
> > would like to know what version of MCC?
> I never used MCC so for me is not significant but for other people can be=
:
> version of tools and libraries is often important.
>
>
> >
> > PR2 is calculated by MCC. I'll dig through the generated code and see
> what
> > it is set to. There is something wrong with MCC: it's not showing the
> > proper PWM frequency.
> This was another missing information item :-)
> With PWM you have to check:
> - there is "something" in the pin;
> - the frequency is correct or if it's wrong is an integer (sub-)multiple
> of
> required frequency;
> - the duty is correct.
> If something is wrong the first step is to obtain a pwm, with a fixed and
> known
> duct cycle.
> Than I work with frequency, usually with a very minimal program to exclud=
e
> other
> causes.
>
> >   My last question to the PIC list was about that
> > problem.
> >
> > Thanks, Nicola, for pointing me in the right direction. You're a
> wonderful
> > human bean!!
> Bean, beam... maybe but human?!?!?! Are you sure? ;-)
> Happy to help
>        Nicola
>
>
>
> >
> > -- James
> >
> >
> >
> > On Wed, Jul 29, 2020, 1:12 AM Nicola Perotto <nicola@nicolaperotto.it>
> > wrote:
> >
> >> Hi James,
> >> find attached a small spreadsheet to do calculations.
> >> It confirm (part of) your calculations.
> >> I don't know the library you are using.
> >> Some info are missing:
> >> - code snippet, including PWM initialization
> >> - PR2 value (the period is calculated from this, not the inverse), my
> >> value is 155
> >> - "What am I not getting?" is actually useless... describe with detail=
s!
> >> Regards
> >>          Nicola
> >>
> >>
> >> On 29/07/2020 06:07, James Burkart wrote:
> >>> Hey, everyone!
> >>>
> >>> I am trying to figure out how to properly set the duty cycle for a PW=
M
> >> on a
> >>> PIC16F1503. I'm sure I am missing something obvious.
> >>>
> >>> System clock is the internal oscillator at 16MHz.
> >>> TMR2 prescaler is 1:64, period is set to 2.496 ms.
> >>> This gives the PWM a 9-bit resolution.
> >>>
> >>> The PWM frequency is 400 Hz. My goal is to be able to adjust the puls=
e
> >>> width from 1 ms to 2 ms (controlling an ESC).
> >>>
> >>> I'm using the MCC generated function:
> >>>
> >>> void PWM2_LoadDutyValue(uint16_t dutyValue)
> >>>
> >>> I was assuming that making dutyValue 512 would give me a 100% duty
> cycle,
> >>> instead I get a duty cycle of around 82%.
> >>> A dutyValue of 624 gets me 100%, 312 gets me 50%.
> >>>
> >>> What am I not getting?
> >>>
> >>> --
> >>> Sincerely,
> >>>
> >>> James Burkart
> >>> *925.667.7175*
> >> --
> >>
> >> Nicola Perotto - NP Engineering
> >> Sistemi Informatici ed Elettronici
> >> skype: nicolap
> >>
> >> --
> >> http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
> >> View/change your membership options at
> >> http://mailman.mit.edu/mailman/listinfo/piclist
> >>
>
> --
>
> Nicola Perotto - NP Engineering
> Sistemi Informatici ed Elettronici
> skype: nicolap
>
> --
> http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
> View/change your membership options at
> http://mailman.mit.edu/mailman/listinfo/piclist
>
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