MH-Z19B CO2 sensor with ESP32

Supply 5 V Bus GPIO Measures co2

Pins and ESP32 wiring

Pin	Role	ESP32 pin	Notes
VIN	Power	VIN	Needs 4.5 to 5.5 V: use VIN
GND	Ground	GND
TX	Output (the part drives it)	D25	UART: the part sends data here. Connect to an ESP32 RX pin (9600 baud, 3.3 V level)
RX	Input (the ESP32 drives it)	D26	UART: the part receives data here. Connect to an ESP32 TX pin
PWM	Output (the part drives it)	D27	PWM output, optional
HD	Not wired to the ESP32	—	Zero calibration: pulling LOW for 7 s calibrates to 400 ppm. Leave unconnected
VO	Analog output	D34	Analog output, optional (not on all versions)

Suggested wiring for the 30-pin ESP32 DevKit, avoiding flash, input-only and strapping pins. BoardPilot checks it for you as you wire.

This module is sold for 5 V. Its outputs may be 5 V: use a level shifter or a voltage divider on ESP32 inputs.

void setup() { Serial.begin(115200); }

void loop() {
  int mv = analogReadMilliVolts(34);  // VO on GPIO 34
  Serial.println(mv);
  delay(200);
}

Winsen MH-Z19B user manual, Pins Vin, GND, Tx, Rx, PWM, HD, Vo; UART 9600 baud, 3.3 V logic

Part data: CC BY 4.0, free to reuse with credit to BoardPilot.