I need to measure the amount of carbon-dioxide in parts per million (ppm) within a closed environment. Currently, I am using a MQ-135 gas sensor which has some sort of concentration on Carbon-dioxide. Unfortunately, that sensor does not provide accurate values.

What gas sensor can I get to obtain precise data?

The cost should not be more than USD 30. The MQ-135 has a very slight concentration on CO². The value it returns has a high fluctuation rate. Within the difference of seconds the value changes from 450 ppm to 700 ppm. I want a digital sensor that should give accurate data like Carbon Dioxide Meter PCE-WMM 50.

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2 Answers 2


Sensor Used: MH-Z19 CO² Sensor.
It is a common type, small size sensor, using non dispersive infrared (NDIR) principle to detect the existence of CO² in the air, with good selectivity, non-oxygen dependent and long life.

Output Modes: UART and PWM wave I personally find this useful and used the same in a project. Also you can take help of the following github link to setup with NodeMCU.

Details of the sensor can be found in this user manual (PDF).


Air Quality Sensor : ams IAQ-CORE C

The iAQ-Core sensor module is used to measure VOC levels and provide CO² equivalent and TVOC equivalent predictions. It can measure 450 to 2,000 ppm CO² equivalents. It has a dimension of 15.24 x 17.78 mm. The data is available via I²C bus.

Key Benefits

  1. Direct correlation to CO² and TVOC levels
  2. High sensitivity and fast response
  3. Micro size for convenient installation
  4. Long-term stability
  5. Low power consumption

Applications : Smart Home, Internet of Things, HVAC, Thermostats

Personal Review : Fluctuation rate is very low. Data is very accurate and precise. It is possible to integrate this sensor with Arduino, NodeMCU and Intel Edison.

Implementation : Arduino library for the iAQ-core indoor air quality sensor module with I2C interface from ams. The code has been tested with NodeMCU(ESP8266), Arduino pro mini and Arduino nano.

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