ESP32 changing frequency instead of duty cycle

Question

Using this code on an ESP32 allows varying the duty cycle of the PWM with a fixed 5000 Hz frequency; it is working fine.

How do I vary the frequency and keep the duty cycle at a fixed value?

// the number of the LED pin
const int ledPin = 16; // 16 corresponds to GPIO16
// setting PWM properties
const int freq = 5000;
const int ledChannel = 0;
const int resolution = 8;
 
void setup(){
 // configure LED PWM functionalitites
 ledcSetup(ledChannel, freq, resolution);
 
 // attach the channel to the GPIO to be controlled
 ledcAttachPin(ledPin, ledChannel);
}
 
void loop(){
 // increase the LED brightness
 for (int dutyCycle = 0; dutyCycle <= 255; dutyCycle++) { 
 // changing the LED brightness with PWM
 ledcWrite(ledChannel, dutyCycle);
 delay(15);
 }
 // decrease the LED brightness
 for (int dutyCycle = 255; dutyCycle >= 0; dutyCycle--) {
 // changing the LED brightness with PWM
 ledcWrite(ledChannel, dutyCycle); 
 delay(15);
 }
}

• lucian_v: const int freq = 5000; - this is the frequency
• Eugene Sh.: Hm. Right, sorry
• Eugene Sh.: Use ledcWriteTone ?
• Tono Nam: Why remove points on the question? changing the frequency will be helpful if you are working with a stepper motor for example.

Answer 1

If you want to change the pwm frequency during runtime there is a function ledc_set_freq() for this purpose. I'm not sure if your duty cycle will remain valid, but I guess it does as long as the resolution does not change. You will have to try that on your own and eventually implement a compensation.

• lucian_v: I tried using ledc_set_freq but the issue is that if do it very quickly then is not set it anymore. If I do this on a normal arduino using pwm library i can change pin frequency each 50ms and is fine.