Sensor to measure Hydrocarbon(HC) levels compatible with Arduino UNO

I want to make a project which will measure the Carbon monoxide & Hydrocarbon levels of the vehicle exhaust, and want to display the same on an LCD screen and whenever the values crosses threshold, I want to light up an LED and also send notification.
My idea behind this project is to make a system that can replace our current vehicle PUC system.

Problem is:
I am not able to find a sensor that can measure HC levels.

Looking forward for some suggestions, Thank you…

Use the given below list to find your sensor

  • MQ-2 - Methane, Butane, LPG, smoke
  • MQ-3 - Alcohol, Ethanol, smoke
  • MQ-4 - Methane, CNG Gas
  • MQ-5 - Natural gas, LPG
  • MQ-6 - LPG, butane gas
  • MQ-7 - Carbon Monoxide
  • MQ-8 - Hydrogen Gas
  • MQ-9 - Carbon Monoxide, flammable gasses
  • MQ131 - Ozone
  • MQ135 - Air Quality (CO, Ammonia, Benzene, Alcohol, smoke)
  • MQ136 - Hydrogen Sulfide gas
  • MQ137 - Ammonia
  • MQ138 - Benzene, Toluene, Alcohol, Acetone, Propane, Formaldehyde gas, Hydrogen
  • MQ214 - Methane, Natural gas

according to me the best you can go with are MQ 138 or MQ135.
MQ135 is preferred in this situation as you want it for CO as well as smoke


You cannot use one sensor to detect both. But you can use MQ9 for Carbon Monoxide levels and MQ2 for Hydrocarbon levels.

Thanks Brother.
I will bring MQ 2 Sensor, but I already have MQ7 sensor, can I use that instead of MQ 9 ?

Yes! you can. But MQ9 is a successor of MQ7. It can detect CO(carbon monoxide), CH4(methane-hydrocarbon) and LPG. Upto you.

So, even if you don’t get yourself MQ2, MQ9 should do the job for the simplest HC in environment.

Hey, can you tell me, How to send the data from Bolt to Server. I have sent MQ7 Sensor data from arduino UNO to bolt cloud via UART communication, I need to get that data on the server becase I want to send notification, when the sensor crosses Threshold.

What’s wrong in the below code ?

I’m getting the below error

Have you done serial communication before? Are you familiar with serial monitor and how Master and Slaves communicate?

Yes, I’ve done serial communication, last time also you were the one who guided me.
But I don’t know anything about Master and Slaves

Check your newly created topic.

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