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Low cost Carbon Monoxide meter

Today Carbon Monoxide (CO) meters are available in different forms. Overall, Carbon Monoxide meters sense CO fast and display the amount to the user and trigger alarm if it reaches a critical level. Compare with most of the DIY Carbon Monoxide meters, the project which we described in this article does not need any development platform or MCU / firmware. The Carbon Monoxide meter in this project design around using general-purpose ICs, such as NE556 and LM3914.

Prototype version of Carbon Monoxide meter
Prototype version of Carbon Monoxide meter

The main component of this meter is the FC-22 CO Gas sensor module. This module consists of the MQ-7 sensor and can use to detect CO gas concentrations, anywhere from 10 to 10,000ppm.

Apart from the sensor, this module consists of the LM393 comparator to detect the trigger level.

In this design, we use both analog and digital output of the sensor module. The analog output use by the LM3914 LED driver and alarm system is drive using the digital output.

Home made PCB with alignment holes.

The PCB of this meter designs as a single side PCB with dimensions of 102mm × 39mm. All the components used in this design are through-hole type components with generally available values.

After assembling the circuit, the trigger level of the alarm needs to adjust using the preset potentiometer available at the sensor module. The sensitivity of the LED array can change using the preset potentiometer (RV1) on the PCB.


This meter design to power using a 5V power supply unit. Before taking any measurements, run it for a few minutes to heat the sensor. For the testing and calibration, we use exhaust fumes coming from the tailpipe of the motor vehicle.

Schematic and PCB design of this project are available to download at EasyEDA and Google drive.
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