Understanding PWM (stm32,Esp32,Arduino)

What is PWM

By dividing an electrical signal into discrete pieces, pulse-width modulation (PWM) or pulse-duration modulation (PDM) is a technique for lowering the average power produced by an electrical signal. By rapidly flipping the switch between the supply and the load on and off, the average amount of voltage (and current) provided to the load is managed. The total power provided to the load increases while the switch is on for a longer period of time compared to when it is off.

Calculations

Available duty cycle = (2^bit)-1

Maximum frequency = clock frequency/2^bit

example : bit=10,clock frequency=8Mhz

Available duty cycle = (2^10)-1 = 1023

Maximum frequency = 80000000/2^10 = 78.125khz

PWM in stm32

HardwareTimer timer(1);  //select timer 

void setup() {
pinMode(PA8, PWM);  //set PA8 as pwm pin
timer.setPrescaleFactor(1);   //select prescaler
timer.setOverflow(1024); //set duty cycle from calculation 
}

void loop() {
pwmWrite(PA8,pwm_value);  //write the pwm value to PA8
}

PWM in Esp32

const int ledPin = 16;  // 16 corresponds to GPIO16

// setting PWM properties
const int freq = 5000; //set the maximum frequency from calculating max frequency avalible for the resolution you selected from formula
const int ledChannel = 0;
const int resolution = 8; //set resolution 
 
void setup(){
  ledcSetup(ledChannel, freq, resolution);  // configure 
 
  ledcAttachPin(ledPin, ledChannel); // attach the channel to the GPIO to be controlled
}
 
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);
  }
}

PWM on Arduino

//Initializing LED Pin
int led_pin = 6;
void setup() {
  
  pinMode(led_pin, OUTPUT); //Declaring LED pin as output
}
void loop() {
  //Fading the LED
  for(int i=0; i<255; i++){
    analogWrite(led_pin, i);
    delay(5);
  }
  for(int i=255; i>0; i--){
    analogWrite(led_pin, i);
    delay(5);
  }
}

How to configure fast PWM on Arduino

pinMode(3, OUTPUT);
pinMode(11, OUTPUT);
TCCR2A = _BV(COM2A0) | _BV(COM2B1) | _BV(WGM21) | _BV(WGM20);
TCCR2B = _BV(WGM22) | _BV(CS22);
OCR2A = 180;
OCR2B = 50;

Output A frequency: 16 MHz / 64 / (180+1) / 2 = 690.6Hz

Output A duty cycle: 50%

Output B frequency: 16 MHz / 64 / (180+1) = 1381.2Hz

Output B duty cycle: (50+1) / (180+1) = 28.2%

A good explanation of setting fast PWM on Arduino is provided in the Arduino website

https://docs.arduino.cc/tutorials/generic/secrets-of-arduino-pwm

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