// other
MQ-135
Air quality (NH3, NOx, CO2, alcohol)
€10.00
avg eur
Analog
Digital
Pins
4
Specs
3
Libraries
1
Protocols
2
// wiring → esp32 devkit v1
3V3
EN
GPIO36
VP
GPIO39
VN
AOUT
GPIO34
DOUT
GPIO35
GPIO32
GPIO33
GPIO25
GPIO26
GPIO27
GPIO14
GPIO12
GND
GND
GPIO13
ESP32
WROOM-32
devkit v1
USB
VIN
5V
VCC
GND
GPIO23
GPIO22
SCL
GPIO1
TX0
GPIO3
RX0
GPIO21
SDA
GPIO19
MISO
GPIO18
SCK
GPIO5
SS
GPIO17
TX2
GPIO16
RX2
GPIO4
GPIO2
GPIO15
sensor pin (left)
sensor pin (right)
unused
// pinout → esp32
| Sensor Pin | ESP32 Connection |
|---|---|
| VCC | 5V (VIN) |
| GND | GND |
| AOUT | GPIO 34 |
| DOUT | GPIO 35 (opt) |
// technical specs
Detects
NH3, NOx, alcohol, benzene, CO2
Heater
5V
Voltage
5V
// github libraries
// notes & warnings
Not a real CO2 sensor. For accurate CO2 use SCD30 / SCD41 / MH-Z19.
// related sensors · other
Submitted by caio.ricciuti@outlook.com
· Apr 26, 2026