SCD30 — Photoacoustic / NDIR CO2, Temperature, and Humidity Sensor

Overview

The SCD30 is a dual-channel Non-Dispersive Infrared (NDIR) true $\text{CO}_2$ sensor module manufactured by Sensirion. Unlike eCO2 VOC sensors (such as SGP30 or MQ-135) that estimate carbon dioxide indirectly via proxy hydrogen/VOC gases, the SCD30 measures true atmospheric carbon dioxide molecules using infrared light absorption at $4.26\text{ }\mu\text{m}$ .

The module incorporates a dual-channel NDIR optical absorption cell (one channel for $\text{CO}_2$ sensing, one reference channel to compensate for optical drift), an integrated Sensirion SHT31 humidity and temperature sensor, and automatic self-calibration (ASC) logic.

Quick reference


Operating Voltage (`VDD`)	3.3 V to 5.5 V DC
Measurement Range ( $\text{CO}_2$ )	400 ppm to 10,000 ppm
Accuracy ( $\text{CO}_2$ )	$\pm (30\text{ ppm} + 3\%\text{ of reading})$
Temperature Range / Accuracy	$-40^\circ\text{C}$ to $+70^\circ\text{C}$ ( $\pm 0.4\text{ }^\circ\text{C}$ accuracy)
Relative Humidity Range / Accuracy	0% to 100% RH ( $\pm 3\%\text{ RH}$ accuracy)
Communication interfaces	I2C (address `0x61`, clock stretching required), Modbus over UART
Onboard Self-Calibration	Automatic Self-Calibration (ASC) & Forced Recalibration (FRC)
Average Supply Current	19 mA (2-second interval) / 75 mA peak during IR lamp pulse

Pinout

Standard 7-Pin Header Interface

Pin	Name	Type	Description
1	`VDD`	Power Input	Supply voltage (+3.3 V to +5.5 V DC)
2	`GND`	Power	Ground (0 V)
3	`TX` / `SCL`	Digital I/O	UART TX (Modbus mode) / I2C Serial Clock `SCL` (I2C mode)
4	`RX` / `SDA`	Digital I/O	UART RX (Modbus mode) / I2C Serial Data `SDA` (I2C mode)
5	`RDDY`	Digital Output	Data Ready pin (`HIGH` when new sample measurement is ready)
6	`PWM`	Digital Output	PWM output pin (proportional to CO2 concentration)
7	`SEL`	Digital Input	Interface Select (`LOW` or Unconnected = I2C mode, `HIGH` = Modbus UART mode)

Specifications

Parameter	Symbol	Min	Typ	Max	Unit	Conditions
Supply Voltage	$V_{DD}$	3.3	5.0	5.5	V	DC
Peak Current	$I_{PEAK}$	—	75	95	mA	IR optical lamp pulse
Average Current (2s rate)	$I_{AVG}$	—	19	25	mA	Default 2-second interval
Repeatability ( $\text{CO}_2$ )	$REP$	—	$\pm 10$	—	ppm
Response Time ( $t_{63\%}$ )	$\tau$	—	20	—	s	Natural convection
Temperature Compensation	$T_{COMP}$	—	Onboard	—	—	Automatic SHT31 compensation

Communication Registers (I2C Address `0x61`)

Each I2C read/write command uses a 16-bit command word followed by 16-bit data words with an 8-bit CRC byte (CRC-8 polynomial $x^8 + x^5 + x^4 + 1$ ):

Command Hex	Description
`0x0010`	Start Continuous Measurement (Parameter: Ambient pressure in mbar or `0x0000`)
`0x0104`	Stop Continuous Measurement
`0x0202`	Set Measurement Interval (2 to 1800 seconds)
`0x0207`	Read Data Ready Status (Returns `1` if new reading available)
`0x0300`	Read Measurement (Returns 18 bytes: 4 bytes CO2, 4 bytes Temp, 4 bytes Humidity + CRCs)
`0x5306`	Enable / Disable Automatic Self-Calibration (ASC)

Wiring

SCD30 Pin	Microcontroller (Arduino Uno / ESP32)	Notes
`VDD`	`5V` (or `3.3V`)	5V recommended for stable IR lamp pulse
`GND`	`GND`	Ground
`SCL`	`SCL` (A5 on Uno, GPIO22 on ESP32)	Requires I2C Clock Stretching!
`SDA`	`SDA` (A4 on Uno, GPIO21 on ESP32)	$10\text{ k}\Omega$ pull-up resistor
`SEL`	`GND`	Selects I2C protocol mode

Warning

I2C Clock Stretching & Power Peak Guidance:

Clock Stretching: The internal microcontroller of the SCD30 holds the SCL line LOW for up to 150 ms while reading the optical IR cell. Software MUST enable hardware I2C clock stretching or use a generous timeout setting.
IR Lamp Peak Current: The internal IR lamp pulses at 75 mA. Ensure the power rail can supply steady current without dropping below 3.3V.

Common mistakes

Covering the white PTFE optical membrane: The white filter membrane on top of the SCD30 protects the optical cell from dust. Touching, puncturing, or sealing this membrane prevents air exchange.
Orientation tilt: The optical cavity in the SCD30 is factory calibrated in a vertical orientation. Mounting the module upside down or sideways can shift calibration by 20–50 ppm.
Disabling Automatic Self-Calibration (ASC) without outdoor fresh air exposure: ASC assumes that the sensor is exposed to fresh outdoor air ( $\approx 400\text{ ppm }\text{CO}_2$ ) at least once every 7 days. If deployed in a permanently sealed, occupied room without fresh air exchange, ASC will miscalibrate.

Notes

Includes ambient pressure compensation inputs (0x0010) to adjust $\text{CO}_2$ readings for barometric pressure changes at high altitudes.

Interface	I2C, Modbus (UART)
Supply	3.3–5.5 V
Package	Optical Module (35 x 23 x 7 mm)