I am currently trying to learn how to use my MQ 7 CO Standalone to read CO in the air around the sensor. Currently Im using this circuit using my Arduino Uno. I get results of 900-1000. Here's a Fritzing Schematic on my setup. enter image description here

Currently this is the code I am using on the arduino:


int mqx_analogPin = A0; // connected to the output pin of MQ-X

void setup(){
  Serial.begin(9600); // open serial at 9600 bps

void loop()
  // give ample warmup time for readings to stabilize

  int mqx_value = analogRead(mqx_analogPin);

  delay(100); //Just here to slow down the output.

I'm following the setup from this Instructables: http://www.instructables.com/id/Smoke-Detector/?ALLSTEPS

However his readings are around 150-200ppm outside. I'm unsure how to reach these values since im following basically everything from the guide. Does anyone any experience with a MQ7 sensor?

I've been reading I need to preheat the sensor but I can't find any circuit that clearly shows how to preheat an MQ7 sensor or find any code for the arduino.

  • 1
    You are following a flawed tutorial which does not correctly operate the heater - see the comment by "Gregory0" part way down the page. Apr 23 '16 at 0:55
  • I believe you just leave it running for 5 minutes before taking a reading. Apr 23 '16 at 18:51

Using of this sensor is a bit more complicated than that. You must cycle through 60 seconds of heating and 90 seconds of measurement cycles, during heating you need to provide 5V on its heater pins, during measurement you need to provide 1.4V, so you'll need transistor or some other PWM-controlled current limiter (Arduino pin can't provide enough current for sensor heating). I've tried to explain all details and calibration process here: https://www.instructables.com/id/Arduino-CO-Monitor-Using-MQ-7-Sensor/


Yes, it is not easy, lot of details to MQ-7 is here: http://www.arduinohobby.euweb.cz/ in the section "Analysator CO"

  • While this may theoretically answer the question, it would be preferable to include the essential parts of the answer here, and provide the link for reference. Nov 18 '20 at 15:49
  • Yes, thank you. That link can helps. A foreign text can transform Google. MQ7 is element for stable enviroment and continuous ranning. Long brake of Vcc influences of the sensor sensitivity and it takes time to return it. Basically, the MQ7 is for observing of a hygienic limit CO as 100ppm continuously with a compatator. That limit should be adjusted with a calibration gas and RL resistance. Any other application is comlicated, see that link. Josef
    – Josef
    Dec 7 '20 at 23:17

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