ESP32 Varying PWM Frequency

[shawn_t]

I am trying to change the frequency of the PWM on the ESP32.

The frequency must be varied between 100Hz to 3KHz.

This will be used to dim lights in various rooms around the house.

I only found this library for Arduino.

Any advice on how to vary the frequency?

[J-M-L]

you don't need that library. Use what the ESP provides ( ESP32 LED PWM Controller with LEDC)

you have higher level functions:

    ledcSetup(pwmChannel, frequency, resolution);
    ledcAttachPin(pwmPin, pwmChannel);
    ledcWrite(pwmChannel, duty);

[shawn_t]

Thanks for the reply.

Please correct me if I am wrong, but the function

ledcSetup(pwmChannel, frequency, resolution);

only allows the frequency to be set once.

Will I have to call this function repeatedly to change the frequency?

[J-M-L]

yes, change it when needed

[shawn_t]

 // Send a GET request to <ESP_IP>/slider?value=<inputMessage>
  server.on("/slider", HTTP_GET, [] (AsyncWebServerRequest *request) {
    String inputMessage;
    // GET input1 value on <ESP_IP>/slider?value=<inputMessage>
    if (request->hasParam(PARAM_INPUT)) {
      inputMessage = request->getParam(PARAM_INPUT)->value();
      sliderValue = inputMessage;
      ledcSetup(ledChannel, (sliderValue.toInt()), resolution);
      ledcWrite(ledChannel, 127);
    }
    else {
      inputMessage = "No message sent";
    }
    Serial.println(inputMessage);
    request->send(200, "text/plain", "OK");
  });
  
  // Start server
  server.begin();
}

Changing the frequency does not change the brightness of my connected LED.

Any other suggestions?

[J-M-L]

you need to attach the pin into the channel with ledcAttachPin()

the brightness is typically not done by changing the frequency, just change the duty cycle..

you could use this analogWrite() for that

[shawn_t]

I'm using a Meanwell ELG-75-C500B, which needs a PWM Frequency of 100Hz - 3KHz to dim the connected LED's hence the reason why I need the frequency to change or am I misunderstanding the diagram from the datasheet above?

[shawn_t]

Just hooked it up to my Oscilloscope - can see the frequency changing.

[MicroBahner]

@shawn_t

am I misunderstanding the diagram from the datasheet above?

I would understand it as ' you can use any frequency between 100Hz and 3KHz'. But a PWM signal defines the brightness of the LED by its duty cycle, not by the frequency.

[Idahowalker]

PWM, Pulse Width Modulation.

A pulse of 10 Hz can have a duration of, say 50% of the duty cycle or 1% of the duty cycle. The longer time the pulse is high represents a longer on time and a higher brightness.

The ESP32 LEDC API is a very good API to use for LED's. Motors are better suited to the ESP32's MCPWM.

A link the the ESp3e2 API

[shawn_t]

Thanks all for the replies.

[J-M-L]

@MicroBahner

I would understand it as ' you can use any frequency between 100Hz and 3KHz'.

same here.

[ruilviana]

This driver LED allows any frequency between 100Hz and 3KHz.
But the adjustment is based on the duty cycle, as shown in the graph on the right.

RV mineirin

[shawn_t]

Thank you very much.