Sensirion SCD30

Swiss I2C NDIS Sensor For CO2, Temperature And Humidity

The SCD30 is a digital carbon dioxide (CO2), temperature, and humidity sensor module developed by Sensirion, a Swiss sensor manufacturer.

It provides accurate and reliable measurements of CO2 concentration, temperature, and humidity in indoor air quality monitoring, HVAC systems, and greenhouse monitoring.

It can be interfaced using I2C or Modbus. A third option - PWM for CO2 concentration output - is experimental and may not be functioning yet.

Price variations are huge with this sensor. You can get it from local vendors for as much as EUR 90 (per piece), and from Asian sources for less than EUR 20 (including a base shield with voltage regulator).

Important Precautions

This is a highly sensitive precision device. Improper handling may damage the device or ruin its factory calibration:

  • Never touch or apply force to the optical cell (the black part on top of the green PCB).
  • Always touch the sensor module on the long side only. Avoid contact with the metallized parts of the optical cavity at all times.

  • Never expose the sensor to dust, grease, or dirt.
  • This sensor is ESD sensitive: wear grounding strips
  • Position the sensor board correctly in your sensor housing: use suffiencient openings in proximity to the inlets of the sensor module.

While electrostatic sparks can permanently destroy the device, touching the wrong parts (or a rough postal delivery) typically “only” void the factory calibration of the device, leading to wrong measurement results. A user calibration is recommended before you start using the sensor in production.

Overview

The SCD30 sensor module uses non-dispersive infrared (NDIR) technology to directly and specifically measure CO2 levels.

Since this technology is complex, the board is fairly expensive. Price ranges vary (EUR 90 - EUR 20, depending on source). Using the sensor is simple and straight-forward thanks to its I2C interface.

Parameter Value
Interfaces UART, I2C
DC supply voltage 3.3-5V
Average Current 19mA
max Current during measurement 75mA
I2C Input High 1.75 - 3V
I2C Input Low -0.3 - 0.9V
Modbus Input High 1.75 - 5.5V
Modbus Input Low -0.3 - 0.9V
Output High 2.4V
Output Low 0.4V
Sensor lifetime 15 years
Operating Conditions <95%RH, <50C
Size 35x23x7mm
Weight 3.4g
CO2 Sensor Value
Range 0-40.000ppm
Accuracy +- 30ppm + 3%
Temperature Stability +-2.5ppm/C
Response Time 20s
Operating Conditions 0-50C
Humidity Sensor Value
Range 0-100%
Accuracy +-2%
Response Time 8s
Temperature Sensor Value
Range -40 - +70C
Accuracy +-0.3C
Response Time >2s

Pins

The SCD30 sensor module can be used via its seven pins directly. It has seven pins. The pin-out is (from left to right as depicted):

Pin Number Label Description
1 VDD Supply voltage
2 GND Ground
3 TX/SCL Transmission line Modbus/I2C clock
4 RX/SDA Receive line Modbus/I2C Data
5 RDY Data ready pin, high when data is ready to be read
6 PWM PWM output of CO2 concentration (may not be functional)
7 SEL Interface select: connect to VDD for Modbus, floating or GND for I2C

Base Shield

There is a separate base shield available that is strongly recommended:

  • Voltage Regulator & Level Shifters: the base shield makes sure all voltages are translated to safe levels. While the raw sensor module does accept operating voltages from 3.3-5.5V, its I2C interface is limited to strictly 3V.
  • Safe Handling: the sensor module is highly sensitive. Touching it directly can damage it. The base shield is larger and can be handled easily without directly touching the sensor module.
  • Stemma Connectors: the base board comes with solder pins plus two Stemma QT/Qwiick/JST 1.0 connectors. This makes it easy to connect the sensor (and daisy-chain it with other I2C components like a display) without soldering.

The picture shows the (smaller green) sensor board on top, and the (larger pink) shield board underneath it. Both are connected via seven pins. The voltage regulator chip is covered by the mounted sensor board

Companies like Adafruit sell kits with sensor and base shield for around 60 EUR. The combo is available from Asian sources for 20 EUR.

Base Shield Connections

The base shield exposes the I2C interface only. If you want to communicate via Modbus or read the PWM output, you need to directly interface with the sensor module pins.

Solder Pins…

To connect the base shield with your microcontroller, you can either use the labeled solder pins:

Pin Label Description
1 VIN 3-5V
2 3Vo 3.3V output from internal voltage regulator
3 GND Ground
4 SCL I2C
5 SDA I2C
6 RDY High when data is ready to be read

…or Stemma QT / Qwiick / 1.0 JST

Or you use one of the two 4-wire QWIICK (Stemma QT) connectors.

Qwiick and Stemma QT are just brand names for the same thing: a JST 1.0 4-wire connector. You can get cables with these connectors from various sources for cheap. Note that the kits sold from Asian sources typically do not include these cables.

Generic JST 1.0 4-wire connectors use random colors, and colors may vary within a purchased batch. It’s strongly recommended that you carefully verify pin assignment and label your connections correctly.

Stemma QT/Qwiick connectors use this pin assignment (looking at the connector from the plug perspective, from left to right, see also labels in picture above):

Pin Description
1 GND: Ground
2 VDD: microcontroller voltage
3 SDA: I2C
4 SCL: I2C

When you use the base shield, VDD is your logic level (microcontroller) voltage. Supply 5V for Arduino and 3.3V for ESP32. This way, the base shield automatically uses the correct I/O voltage for your I2C bus.

Test Code

Connect SDA and SCL to the appropriate I2C pins of your microcontroller. ESP32 typically use GPIO21 for SDA, and GPIO22 for SCL.

Next, connect GND to one of the microcontroller GND pins, and for VDD use your logic level voltage (the voltage your microcontroller is using), i.e. connect it to pin 3V3 on ESP32, and pin 5V on Arduino.

Code

There are a number of libraries available for this sensor. The example below uses SparkFun_SCD30_Arduino_Library which works both for Arduino and ESP32:

#include <Wire.h>
#include "SparkFun_SCD30_Arduino_Library.h" 
SCD30 airSensor;

void setup()  
{
  Wire.begin();          // start I2C
  Serial.begin(9600);    // start serial terminal
  airSensor.begin();     // initialize sensor
}

void loop()  
{
  if (airSensor.dataAvailable()) 
  {
    // return CO2 in ppm (parts per million)
    Serial.print("CO2 (ppm): ");
    Serial.print(airSensor.getCO2());

    // return temperature
    Serial.print(", Temp (C): ");
    Serial.print(airSensor.getTemperature(), 1); 

    // return humidity
    Serial.print(", Humidity (%): ");
    Serial.print(airSensor.getHumidity(), 1); 

    Serial.println();
  }

  // wait for 2 seconds until measuring again:
  delay(2000); 
}

Libraries

If you use platformio, include the required library references into your platformio.ini file. Here is a sample platformio.ini for a ESP32 development board:

[env:esp32dev]
platform = espressif32
board = esp32dev
framework = arduino
monitor_speed = 115200
lib_deps = sparkfun/SparkFun SCD30 Arduino Library@^1.0.20

If you use Arduino IDE, in “Library Manager, add the library *SparkFun SCD30 Arduino Library.

Test Results

After you compiled and uploaded the sketch, new output is shown in your IDE serial monitor every 2 seconds:

CO2 (ppm): 937, Temp (C): 28.7, Humidity (%): 39.8
CO2 (ppm): 975, Temp (C): 28.7, Humidity (%): 39.7
CO2 (ppm): 930, Temp (C): 28.7, Humidity (%): 39.5
CO2 (ppm): 920, Temp (C): 28.8, Humidity (%): 39.5
CO2 (ppm): 922, Temp (C): 28.8, Humidity (%): 39.5
CO2 (ppm): 913, Temp (C): 28.8, Humidity (%): 39.5
CO2 (ppm): 901, Temp (C): 28.8, Humidity (%): 39.4
CO2 (ppm): 899, Temp (C): 28.8, Humidity (%): 39.4
CO2 (ppm): 901, Temp (C): 28.8, Humidity (%): 39.5
CO2 (ppm): 901, Temp (C): 28.8, Humidity (%): 39.4
CO2 (ppm): 900, Temp (C): 28.8, Humidity (%): 39.4
CO2 (ppm): 895, Temp (C): 28.8, Humidity (%): 39.4
CO2 (ppm): 892, Temp (C): 28.8, Humidity (%): 39.3
CO2 (ppm): 892, Temp (C): 28.9, Humidity (%): 39.4
CO2 (ppm): 894, Temp (C): 28.8, Humidity (%): 39.3
CO2 (ppm): 895, Temp (C): 28.9, Humidity (%): 39.3
CO2 (ppm): 894, Temp (C): 28.8, Humidity (%): 39.4
CO2 (ppm): 893, Temp (C): 28.9, Humidity (%): 39.3
CO2 (ppm): 892, Temp (C): 28.9, Humidity (%): 39.3
CO2 (ppm): 892, Temp (C): 28.9, Humidity (%): 39.3
CO2 (ppm): 891, Temp (C): 28.9, Humidity (%): 39.3
CO2 (ppm): 888, Temp (C): 28.9, Humidity (%): 39.3

Values may drift a bit at the beginning, and the very first CO2 reading is always 0. Wait a few minutes until the values stabilize.
[!CAUTION]
The sample sketch queries the sensor every 2 seconds. In real scenarios, query it much less often, i.e. every ten minutes (600000 seconds). This not only reduces energy consumption but also helps extend sensor life.

Calibration

The SCD30 supports automatic self-calibration (ASC). Sensirion recommends 7 days of continuous readings with >1 hour/dayday of fresh air’* for self-calibration.

ASC may be disabled. Make sure you enable it via I2C/libraries before you deploy the sensor.

How Self-Calibration Works

ASC assumes that the lowest CO2 concentration the SCD30 is exposed to corresponds to 400 ppm (fresh outside air).

It stores the seven most recent CO2 minima in volatile memory (first-in first-out) that are separated by at least 18 hours. Recalibration occurs when all seven recorded minima are within ± 50 ppm.

For ASC to succeed, the sensor needs to be exposed to fresh air at least every 18 hours for at least seven times in a row. Else, automatic recalibration is suspended until the prerequisites are eventually met.

Materials

Summary Information
Handling Precautions General Handling
Datasheet
Interface Description
Field Calibration
Design Guide
Low Power Mode
Adafruit Example
Manufacturer SourceCode
Calibration Certification

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(content created Jun 04, 2024 - last updated Jun 05, 2024)