# NH3 and CO Gas Sensor, MQ-137, Ammonia, Analog and Digital, 5V

> MQ-137 gas sensor module for detecting ammonia (NH3) and carbon monoxide (CO), with analog output 0-5V and digital TTL output via LM393 comparator. Adjustable sensitivity threshold via potentiometer, response time under 1s, measurement range 10-300ppm. Power supply 5V DC, dimensions 28 x 20mm, compatible with Arduino, ESP32 and Raspberry Pi. LED indicator for power and signal.

- Page: https://sigmanortec.ro/en/nh3-and-co-gas-sensor-mq-137-ammonia-analog-and-digital-5v
- Price: 174.88 RON
- Availability: In stock; 1-2 zile
- Reference: 88165 · EAN: 5944832002267
- Category: Mechatronics and IoT > Sensors and Modules > Gas and Air Quality Sensors
- Specifications: Supply Voltage: 5; Input Voltage Type: “DC” in Romanian can mean **“de ce”**, which translates to **“why”** in English.
- Package (shipping data): 0.02 kg
- Updated: 2026-09-14
- Shop: [Sigmanortec.ro](https://sigmanortec.ro/en/llms.txt)
- Prices: RON, VAT included; prices and stock as of 2026-09-23 17:04 (Europe/Bucharest)

## Description

MQ137-based sensor module for detecting ammonia NH3 and carbon monoxide CO, ideal for air monitoring projects and security systems. It offers 0-5V analog output for concentration estimation and TTL digital output with LM393 comparator, has adjustable threshold from potentiometer and fast response under 1s, operates at 5V and is compatible with Arduino, ESP32 and Raspberry Pi.
The MQ137 module, compatible with Arduino and other development boards, is designed for the detection of ammonia (NH3) and carbon monoxide (CO), ideal for air quality monitoring and environmental safety projects.
The capsule has a SnO2 element in its component that changes its resistance when exposed to ammonia gas (or other amine gases).
The sensor has analog and digital (TTL) output, being fully compatible with microcontrollers such as Arduino, Raspberry Pi or ESP32. It can operate both in analog mode, for concentration measurements, and in digital mode, for simple detection of the presence of gas.
The sensor has a wide detection area, fast response (under 1 second) and high sensitivity, with an integrated potentiometer for adjusting the sensitivity threshold. It uses an LM393 voltage comparator to generate the logic signal. Its compact housing and reliability recommend it for gas leak detectors, safety alarms, air monitoring or medical and industrial applications.
Specifications:
Model: MQ137
Detected gases: ammonia (NH3), carbon monoxide (CO)
Measured concentration: 10 - 300ppm
Supply voltage: 5V DC
Response time: <1s
Sensitivity: approximately 3%
Analog output: 0 – 5V (proportional to gas concentration)
Digital output: 0V or 5V (TTL logic)
Signal: digital active low level (LED on when detected)
Sensitivity adjustment: via integrated potentiometer
Compatible with: Arduino, Raspberry Pi, ESP32
LED indicator: for power and signal
Dimensions: 28 x 20mm
Use:
Power the module with 5V and connect the analog or digital outputs to the desired microcontroller. The digital output can be connected directly to a 5V relay module (on signal only).
When powered on, the power LED lights up.
Wait a few minutes for the sensor to preheat.
In the absence of gas, the digital output remains at 0V and the output LED is off.
Expose the sensor to the target gas (NH3 or CO). If detected, the LED lights up and the digital output becomes active.
If the sensor does not respond immediately, adjust the potentiometer until the output LED activates.
For more accurate concentration measurements, use the analog output and interpret the voltage using a microcontroller.
Avoid prolonged exposure to very high gas concentrations to maintain sensor accuracy and lifespan.
Pinout: