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I am working on the RPI-CM4 board with raspbian buster OS.

I am trying to generate the 38KHz PWM wave using pigpio the library. My code is as follows.

#include <pigpio.h>
#include <unistd.h>

#define PWM_PIN 18

int main(int argc, char *argv[])
{
   gpioCfgClock(1, 0, 1);

   if (gpioInitialise()<0) return 1;

   gpioSetPWMfrequency(PWM_PIN, 38000);

   gpioPWM(PWM_PIN, 128);

   while (1) { sleep(1); }

   gpioTerminate();
}

At the output, I am getting the PWM wave generated @27.63 KHz. pwm_wave

Will you please help me to know, How do I set up a PWM clock to get a 38KHz resolution?

1 Answer 1

1

pigpio supports two types of PWM.

  1. DMA timed PwM on GPIO 0-31. This has a limited number of frequencies and duty cycle resolution. See gpioSetPWMfrequency for the permitted frequencies.

I am not sure why you seem to be getting 27 kHz, I'd expect 40 kHz from the way it is being setup.

  1. Hardware timed PWM on GPIO 12-13, 18-19. This is fully hardware PWM. See gpioHardwarePWM.

As an aside I would use waves to generate IR carrier. There is a Python example.

3
  • Using the gpioHardwarePWM I am able to generate the PWM waves > 50KHz after that the wave gets displeased 50% duty cycle. I want to drop down it up to 30KHz. will you please help me to know, how can I achieve this?
    – shiv patil
    Mar 28, 2022 at 5:11
  • Spent some time on this & found that the gpioHardwarePWM will work only on PWM channel-1 (gpio 19-13). ( referance link ) I am able to get the 38KHz wave on channel1 (gpio 19), but in between some pulses are missed. Now, will you please help me to know, 1. how do I configure channels to the hardware PWM? 2. Why the pulses are get missed in-between?
    – shiv patil
    Mar 29, 2022 at 12:56
  • I have solved this problem by using gpioWaveAddGeneric
    – shiv patil
    Mar 30, 2022 at 11:12

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