Dimmable Switch with RobotDyn AC Light Dimmer Module. https://help.sinric.pro/pages/tutorials/tutorials/dimmable-switch/robotdyn-ac-light-dimmer.html

RobotDyn-AC-Light-Dimmer.ino

#include <RBDdimmer.h> //https://github.com/RobotDynOfficial/RBDDimmer

const int ZC_PIN  = 0;
const int PWM_PIN  = 2;

int MIN_POWER  = 0;
int MAX_POWER  = 80;
int POWER_STEP  = 2;
int power  = 0;

dimmerLamp acd(PWM_PIN, ZC_PIN);

void setup(){
    Serial.begin(115200);
    delay(100);
    acd.begin(NORMAL_MODE, ON);
}

void loop(){
  for(power=MIN_POWER;power<=MAX_POWER;power+=POWER_STEP){
    acd.setPower(power);      
    delay(100);
  }

  for(power=MAX_POWER;power>=MIN_POWER;power-=POWER_STEP){
    acd.setPower(power);
    delay(100);
  }
}