/* MQ9 Calibration modified on 19 Feb 2019 by Saeed Hosseini https://electropeak.com/learn/ */ void setup() { Serial.begin(9600); } void loop() { float sensor_volt; float RS_air; // Rs in clean air float R0; // R0 in 1000 ppm LPG float sensorValue; //Average for(int x = 0 ; x < 100 ; x++) { sensorValue = sensorValue + analogRead(A0); } sensorValue = sensorValue/100.0; //-----------------------------------------------/ sensor_volt = (sensorValue/1024)*5.0; RS_air = (5.0-sensor_volt)/sensor_volt; // Depend on RL on yor module R0 = RS_air/9.9; // According to MQ9 datasheet table Serial.print("sensor_volt = "); Serial.print(sensor_volt); Serial.println("V"); Serial.print("R0 = "); Serial.println(R0); delay(1000); }