topic Re: I Want Generate 20Hz PWM? in MCUXpresso IDE

I Want Generate 20Hz PWM?

velmurugan2educ — Mon, 29 Oct 2018 08:34:23 GMT

Dear sir/madam,

i need 20Hz PWM Generate using FTM-> Single PWM Example , i simply change 24000U to 20U and Compile and Debug, then Measure PWM Frequency is 83.33Hz, Where is Change any Setting or any Mode

Kindly Help me

Regards & Thanks,

V. Velmurugan

Re: I Want Generate 20Hz PWM?

Alice_Yang — Tue, 30 Oct 2018 08:03:41 GMT

Hello V. Velmurugan,

Please tell use which part number you used.

And which code do you used, SDK ?

Alice

Re: I Want Generate 20Hz PWM?

velmurugan2educ — Tue, 30 Oct 2018 10:16:29 GMT

Hi Alice_Yang,

I'm using MK22FN512VLL12 Processor.

Thanks

Re: I Want Generate 20Hz PWM?

Alice_Yang — Wed, 31 Oct 2018 06:25:44 GMT

Hello Velmurugan V,

20Hz frequency is too low .

As to the PWM frequency = PWM clock source (or FTM clock source) / MOD,

PWM frequency * MOD = PWM clock source

the maximum of MOD is 0xFFFF, please check the FTM clock source in your code.

So even if MOD configure to 0xFFFF, if PWM frequency = 20hz, then PWM CLOCK source should almost

less than 2MHz.

Hope it helps,

Have a great day,
TIC

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Re: I Want Generate 20Hz PWM?

velmurugan2educ — Wed, 31 Oct 2018 12:01:39 GMT

Hi Alice_Yang,

Thanks For your Reply, i will try and Reply.

Thanks & Regards,

Velmurugan V

Re: I Want Generate 20Hz PWM?

velmurugan2educ — Wed, 31 Oct 2018 13:37:21 GMT

Hi Alice_Yang,

Thanks, it is Working Fine.

Re: I Want Generate 20Hz PWM?

Alice_Yang — Thu, 01 Nov 2018 02:15:11 GMT

Hi,Velmurugan,

Ok, welcome!

Have a great day,
TIC

Re: I Want Generate 20Hz PWM?

velmurugan2educ — Thu, 01 Nov 2018 04:19:42 GMT

Hi Alice_Yang,

i need Find RPM,

i'm using one revolution how time tick taken and calculate RPM

My Method

Home Pin Interrupt Occur First time -> Load Timer Value & Start timer.

Home Pin Interrupt Occur Next Time -> Current Timer Value Read & Stop Timer.

My Formula

Calc_RPM = ( 60.0* (Timer Clock Source / (Load Timer tick value - Current Timer tick value )))

What is My method is wrong and Where is corrected My method

Please Help Me!

Advance Thanks,

Velmurugan V

Re: I Want Generate 20Hz PWM?

gunnarbohlen — Fri, 02 Nov 2018 09:22:59 GMT

Hello,

the formula is correct, but you have to make sure that you clock source matches the expected measuring range.

e.g. if your timer is 16bit, you need to set the clock source to a frequency that you have at most 65535 timer ticks per revolution. Otherwise you have to check for timer overruns and add up these overruns (sometimes tricky in case the overrun happens between 2nd irq event and code execution for this event)

Another point: If it is possible that you system suddenly stops, and all you do is waiting for an interrupt, you might never get the second interrupt and therefor never notice the stop condition. In this case you should have a timer interrupt that creates an event at the slowest rpm that you want to measure. (e.g. if you want to measure 60 rpm this time is set slightly larger than to 1sec., for min. rpm=600 timer woud be set to ~100ms.