How to have Speed Control in an AC Fan using a GPIO AC Dimmer?

Question

We are using a XIAO Seeed ESP32S3 board as a microcontroller. We have managed to make the fan run but it only runs in either 0 speed or 100% speed (the speed control is not working). The D2 Pin of the XIAO board connects to the Z-C pin in the AC Dimmer GPIO and the D3 connects to the PWM pin. We are not using the RBDDimmer.h library as it gives too many errors.

This code snippet runs but only in binary (0 or 100% speed).

const int zeroCrossPin = D2; // Zero-cross pin
const int adcPin = D3;       // AC dimmer control pin

void acdimmer(int pm25)
{
  Serial.print("Adjusting fan speed based on PM2.5: ");
  Serial.println(pm25);

  if (pm25 < 15) {
    fan = 40; // Very low fan speed
  } 
  else if (pm25 >= 15 && pm25 < 30) {
    fan = 60; // Low fan speed
  } 
  else {
    fan = 100; // Maximum fan speed
  }

  // acd.setPower(fan); // Set power 0 to 100% 
  // int actualPower = acd.getPower(); // Fetch the power level the dimmer is applying
  analogWrite(adcPin, 10);
  Serial.print("Fan Speed Set To: ");
  Serial.print(fan);
  Serial.print("% (Actual Power: ");
  Serial.print(100);
  Serial.println("%)");
}

This code written for an AC powered fan does not work at all

#include <Arduino.h>

// Pin Definitions
const int zeroCrossPin = 2; // Zero-crossing detection pin
const int dimmerPin = 3;   // Dimmer control pin (PWM output)

volatile int dimming = 128; // Initial dimming level (0-255 for PWM duty cycle)
volatile bool zeroCross = false; // Zero-crossing detected flag

void zeroCrossHandler() {
  zeroCross = true; // Set zero-cross flag on interrupt
}

void setup() {
  // Initialize serial monitor for debugging
  Serial.begin(9600);
  Serial.println("Fan Speed Control Initialized");

  // Initialize pins
  pinMode(zeroCrossPin, INPUT);
  pinMode(dimmerPin, OUTPUT);
  
  // Attach interrupt for zero-cross detection
  attachInterrupt(digitalPinToInterrupt(zeroCrossPin), zeroCrossHandler, RISING);

  // Start with fan off
  analogWrite(dimmerPin, 0);
  Serial.println("Dimmer initialized.");
}

void loop() {
  // Example: Read an analog value (0-1023) and map it to dimming level (0-255)
  int sensorValue = analogRead(A0); // Assume a potentiometer connected to A0
  dimming = map(sensorValue, 0, 1023, 0, 255);

  // Debugging output
  Serial.print("Sensor Value: ");
  Serial.print(sensorValue);
  Serial.print(" -> Dimming Level: ");
  Serial.println(dimming);

  // Adjust fan speed if zero-cross detected
  if (zeroCross) {
    zeroCross = false; // Reset zero-cross flag
    delayMicroseconds(dimming * 65); // Delay proportional to dimming level
    digitalWrite(dimmerPin, HIGH); // Trigger triac gate
    delayMicroseconds(10); // Allow time for triac to latch
    digitalWrite(dimmerPin, LOW); // Turn off gate signal
  }
}