#define MQ2_NODE_ADDRESS 2 // I2C address of the MQ2 node module
#include <Wire.h>
const int MQ2_PIN = 4; // Analog pin connected to MQ2 sensor

int gasValue = 0;

void setup() {
  delay(20000); // allow the MQ2 to warm up
  Wire.begin(MQ2_NODE_ADDRESS); // Set the I2C slave address (0x43 for MQ2 gas sensor)
  Wire.onRequest(requestEvent); // Register the request event handler
}

void loop() {
  // Read gas sensor data
  gasValue = analogRead(MQ2_PIN);
  delay(2000);
}

void requestEvent() {
  Wire.write(gasValue);
}