Overview

The MH-Z19B is an NDIR (Non-Dispersive Infrared) carbon dioxide (CO2\text{CO}_2) gas sensor manufactured by Winsen Electronics. It utilizes infrared absorption spectroscopy to accurately measure atmospheric CO2\text{CO}_2 concentration from 400 ppm to 5,000 ppm (with optional 10,000 ppm variant).

The gold-plated optical chamber houses an internal IR light source, a narrow bandpass optical filter, an IR detector, and temperature compensation. It outputs concentration data via UART serial (9600 baud) and a PWM duty cycle output line.

Quick reference

Operating Voltage (Vin)4.5 V to 5.5 V DC (5.0 V nominal)
Measurement Range400 ppm to 5,000 ppm CO2\text{CO}_2
Accuracy±(50 ppm+3% of reading)\pm (50\text{ ppm} + 3\%\text{ of reading})
Warm-up Time3 minutes (180 seconds)
UART Interface9600 baud, 8 data bits, 1 stop bit, no parity (9600,N,8,1)
PWM Cycle Period1004 ms (PPM=5000×TH−2ms1000ms\text{PPM} = 5000 \times \frac{T_H - 2\text{ms}}{1000\text{ms}})
Average Current<40 mA< 40\text{ mA} average / 150 mA peak during IR heating

Pinout

Standard 7-Pin Gold Module Header

PinNameTypeDescription
1Vout / VOAnalog OutputAnalog voltage output (0.4 V to 2.0 V, optional)
2NCNot ConnectedUnused
3GNDPowerGround (0 V)
4VinPower InputSupply voltage (+4.5 V to +5.5 V DC)
5RxDigital InputUART Receive line (3.3V TTL logic level input)
6TxDigital OutputUART Transmit line (3.3V TTL logic level output)
7PWMDigital OutputPWM output pin (pulse width proportional to CO2 PPM)

Specifications

ParameterSymbolMinTypMaxUnitConditions
Supply VoltageVINV_{IN}4.55.05.5VDC
Average CurrentIAVGI_{AVG}—4060mAActive operating mode
Peak CurrentIPEAKI_{PEAK}—150200mAIR lamp pulse
Preheating Timetwarmupt_{warmup}—180—sInitial stabilization
Response Time (t90t_{90})τ\tau—<120< 120—sNatural convection
Temperature DriftΔT\Delta T—±0.2\pm 0.2—% FS/°CInternal temp compensation

UART Command Protocol (9600 Baud)

Send a 9-byte packet to read CO2\text{CO}_2 concentration:

  • Request Command: 0xFF 0x01 0x86 0x00 0x00 0x00 0x00 0x00 0x79
  • Response Packet (9 Bytes): 0xFF 0x86 HIGH LOW TT 0x00 0x00 0x00 CS

CO2 Concentration (PPM)=(Byte2×256)+Byte3\text{CO}_2\text{ Concentration (PPM)} = (\text{Byte}_2 \times 256) + \text{Byte}_3

Check Byte 8 Checksum (CSCS): CS=0xFF−(Sum of Bytes 1 to 7)+1CS = 0xFF - (\text{Sum of Bytes 1 to 7}) + 1.

Wiring

MH-Z19B Module Pin→Microcontroller (Arduino / ESP32)Notes
Vin5VRequires 5V supply for internal IR lamp
GNDGNDGround
TxRX (e.g. GPIO16 / D2 for SoftwareSerial)3.3V TTL output
RxTX (e.g. GPIO17 / D3 for SoftwareSerial)3.3V TTL input
PWMGPIO Pin (optional for PWM reading)Pulse width proportional to PPM
Warning

Automatic Zero Calibration (ABC) Warning: By default, the MH-Z19B has ABC (Automatic Baseline Calibration) enabled. Every 24 hours, the module assumes the lowest CO2\text{CO}_2 concentration it recorded during that period was 400 ppm400\text{ ppm} (fresh outdoor air). If used continuously in an unventilated bedroom or greenhouse, ABC will miscalibrate. Disable ABC via UART command 0x79 for indoor environments.

Common mistakes

  • Powering from 3.3V: Operating the sensor from a 3.3V rail causes incomplete IR lamp heating and erratic UART timeouts. Always supply 5.0 V DC.
  • Inverted RX/TX lines: Connecting module Tx to MCU TX.
  • Forgetting 3-minute warm-up: Reading data immediately upon cold boot outputs invalid readings (400 ppm400\text{ ppm} or 5000 ppm5000\text{ ppm}). Wait 180 seconds after applying power.

Notes

  • Fully supported in ESPHome via the dedicated mhz19 component.

Assets & downloads