Pwm input capture mode in stm32H7 MCU

[Edwin kaus]

Posted on April 22, 2018 at 05:41

HELLO..

I want to measure the frequency and duty cycle of the external signal. I have gone through some example available , and suggestions on website. Everywhere they are using either channel 1 or channel 2 in any of timer , unfortunately in my case signal is given to channel 4 ,  Is it still possible to measure duty cycle and frequency by using channel 4 , if so how to configure the same in stm cubemx ..

Can anybody suggest please , I am fully stuck with this issue ..

Thank you

#pwm-input #stm32h7 #cubemx

[Tesla DeLorean]

Posted on April 22, 2018 at 16:06

The PWM Input mode pairs Channel 1 and 2.

You could use Input Capture with Channel 4, and Channel 3 (Indirect) to time stamp TIMx_CH4 along the timeline of TIMx and interrupt. You could then delta measurements in an interrupt (or sample with DMA), to measure the period and duty of an input signal.

[Edwin kaus]

Posted on April 22, 2018 at 16:45

Hello ..

Thanks for response ..

I am just confused , Can you please give me some more explanation, suggest some example project if possible . In stm example project they used TIM1 channel 1 as direct & channel 2 as indirect mode .  I am using TIM 8 CHANNEL 4 for frequency capture and duty cycle measurements.

Suggest me how to configure the tim8 and how calculate duty cycle .

[Tesla DeLorean]

Posted on April 22, 2018 at 17:33

Use a free-running timer, use CH3 and CH4 to time-stamp different edges, and subtract values, or prior values.

[Edwin kaus]

Posted on April 22, 2018 at 19:12

Hello ...

Thanks for the information ..

As per my understanding I need to set channel 4 for input capture mode (direct mode) with rising edge , and channel 3 for falling edge(indirect mode) . 

With the above configuration once rising edge detected i will read both channel capture values, then once falling edge detected (so this difference gives active pulse time) , and then next rising edge value give full cycle period .

Is my understanding is right , can I get both duty cycle and period with this configuration.

[Tesla DeLorean]

Posted on April 22, 2018 at 19:26

>>Is my understanding is right , can I get both duty cycle and period with this configuration.

The math and concept here should not be confusing.

If you time 3 consecutive edges A, B, C starting with a rising edge

C - A describes ticks for period

B - A describes ticks for high time

C - B describes ticks for low time

((B - A) * 100) / (C - A) describes high duty in percent

A clock ticking at 1 MHz will have ticks describing micro-seconds