Adafruit SCD-40 User Manual

Adafruit SCD-40 and SCD-41

Created by Kattni Rembor

Last updated on 2021-09-15 03:29:06 PM EDT

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Guide Contents

Guide Contents Overview Pinouts

Power Pins I2C Logic Pins Jumpers

Python & CircuitPython

CircuitPython Microcontroller Wiring Python Computer Wiring Python Installation of SCD4x Library CircuitPython Usage Python Usage Example Code:

Python Docs Arduino

I2C Wiring Library Installation Load Example

Downloads

Files

Schematic and Fab Print

Overview

Take a deep breath in...now slowly breathe out. Mmm isn't it wonderful? All that air around us, which we

bring into our lungs, extracts oxygen from and then breathes out carbon dioxide. CO2 is essential for life

on this planet we call Earth - we and plants take turns using and emitting CO2 in an elegant symbiosis. But

it's important to keep that CO2 balanced - you don't want too much around, not good for humans and not

good for our planet.

The SCD-40 and SCD-41 are photoacoustic 'true' CO2 sensors that will tell you the CO2 PPM (parts-per-

million) composition of ambient air. Unlike the SGP30, this sensor isn't approximating it from VOC gas

concentration (https://adafru.it/PF7) - they really are measuring the CO2 concentration ! That means

they're bigger and more expensive, but they are the real thing. Perfect for environmental sensing,

scientific experiments, air quality and ventilation studies, and more.

Compared to the illustrious SCD-30 (https://adafru.it/QfK), this sensor uses a different measurement

technique, which allows it to be much smaller. The overall data quality should be very similar, however.

Like the SCD-30, this sensor has data read over I2C, so it works very nicely with just about any

microcontroller or microcomputer. There's both Arduino and Python/CircuitPython code so you can get

started in a jiffy.

There are two variants of this sensor - the SCD-40 and SCD-41

The SCD-40 is lower cost and is perfect for indoor/outdoor air quality and CO2 measurements. It has

a range of 400~2000 ppm with an accuracy of ±(50 ppm + 5% of reading)

The SCD-41 is more expensive, and while it can definitely be used for air quality, it's wide range

means it's best used for industrial or scientific CO2 measurements where the ppm can get very high.

It has a range of 400~5000 ppm with an accuracy of ±(40 ppm + 5% of reading)

Nice sensor, right? So we made it easy for you to get right into your next project. The sensor is soldered

onto a custom-made PCB in the STEMMA QT form factor (https://adafru.it/LBQ), making them easy to

interface with. The STEMMA QT connectors (https://adafru.it/JqB) on either side are compatible with

the SparkFun Qwiic (https://adafru.it/Fpw) I2C connectors. This allows you to make solderless connections

between your development board and the SCD-4x or to chain it with a wide range of other sensors and

accessories using a compatible cable (https://adafru.it/JnB).

This sensor can run from 3.3 to 5V, but it's more important for it to have a quiet power supply with low

ripple, than any particular voltage. For that reason, we've added a 3.3V regulator and level shifters: when

connecting to a 5V microcontroller like an Arduino UNO the 5V supply is often shared with other

electronic components that add noise. The onboard regulator will keep the voltage nice and quiet. For

advanced hackers, they can cut/solder the backtraces to change whether the regulator is enabled and

what I2C logic level is desired.

Pinouts

The SCD-40 and SCD-41 have the same pinouts.

Power Pins

VIN - This is the power pin. To power the board, give it the same power as the logic level of your

microcontroller - e.g. for a 3V microcontroller like a Feather M4, use 3V, or for a 5V microcontroller

like Arduino, use 5V.

3Vo - This is the output from the onboard 3.3V regulator. If you have a need for a clean 3.3V output,

you can use this! It can provide at least 100mA output.

GND - This is common ground for power and logic.

I2C Logic Pins

The default I2C address for the SCD-4x is 0x62.

SCL - I2C clock pin, connect to your microcontroller I2C clock line. There's a 10K pullup on this pin.

SDA - I2C data pin, connect to your microcontroller I2C data line. There's a 10K pullup on this pin.

STEMMA QT (https://adafru.it/Ft4) - These connectors allow you to connectors to development

boards with STEMMA QT connectors or to other things with various associated

accessories (https://adafru.it/Ft6).

Jumpers

The SCD-4x can run from 3 to 5V DC, for both power and I2C data/logic. Normally that would mean we

wouldn't put a regulator and logic level shifter on the breakout. However, the SCD-4x also does best with

a quiet power supply that can also supply ~200mA peak. Since that may or may not be the same as the

logic power supply of the microcontroller, advanced users can customize the power/logic level setup for

the sensor

On the left is the Sensor Power jumper. By default we power the sensor through the 3V regulator. If you

happen to have a nice and quiet Vin power supply, you can cut and re-solder this jumper.

On the right is the level-shifted I2C logic level. Most of the time, Vin is the power and logic level for the

microcontroller. However, if you are, say, powering from 5v because it's a better power supply source, but

are using a 3V logic microcontroller, you can cut and re-solder this jumper.

Python & CircuitPython

It's easy to use the SCD-4x with Python or CircuitPython, and the Adafruit CircuitPython

SCD4x (https://adafru.it/UzE) module. This module allows you to easily write Python code that reads CO2,

temperature, and humidity from the SCD-4x sensor.

You can use this sensor with any CircuitPython microcontroller board or with a computer that has GPIO

and Python thanks to Adafruit_Blinka, our CircuitPython-for-Python compatibility

library (https://adafru.it/BSN).

CircuitPython Microcontroller Wiring

First wire up a SCD-4x to your board exactly as shown below. Here's an example of wiring a Feather M4 to

the sensor with I2C using one of the handy STEMMA QT (https://adafru.it/Ft4) connectors:

Board 3V to sensor VIN (red wire)

Board GND to sensor GND (black wire)

Board SCL to sensor SCL (yellow wire)

Board SDA to sensor SDA (blue wire)

You can also use the standard 0.100" pitch headers to wire it up on a breadboard:

Board 3V to sensor VIN (red wire)

Board GND to sensor GND (black wire)

Board SCL to sensor SCL (yellow wire)

Board SDA to sensor SDA (blue wire)

Python Computer Wiring

Since there's

dozens

of Linux computers/boards you can use, we will show wiring for Raspberry Pi. For

other platforms, please visit the guide for CircuitPython on Linux to see whether your platform is

supported (https://adafru.it/BSN).

Here's the Raspberry Pi wired to the sensor using I2C and a STEMMA QT (https://adafru.it/Ft4) connector:

Pi 3V to sensor VIN (red wire)

Pi GND to sensor GND (black wire)

Pi SCL to sensor SCL (yellow wire)

Pi SDA to sensor SDA (blue wire)

Finally here is an example of how to wire up a Raspberry Pi to the sensor using a solderless breadboard :

Pi 3V to sensor VIN (red wire)

Pi GND to sensor GND (black wire)

Pi SCL to sensor SCL (yellow wire)

Pi SDA to sensor SDA (blue wire)

Python Installation of SCD4x Library

You'll need to install the Adafruit_Blinka library that provides the CircuitPython support in Python. This

may also require enabling I2C on your platform and verifying you are running Python 3. Since each

platform is a little different, and Linux changes often, please visit the CircuitPython on Linux guide to get

your computer ready (https://adafru.it/BSN)!

Once that's done, from your command line run the following command:

pip3 install adafruit-circuitpython-scd4x

If your default Python is version 3, you may need to run pip instead. Make sure you aren't trying to use

CircuitPython on Python 2.x, it isn't supported!

CircuitPython Usage

To use with CircuitPython, you need to first install the SCD4x library, and its dependencies, into the lib

folder on your CIRCUITPY drive. Then you need to update code.py with the example script.

Thankfully, we can do this in one go. In the example below, click the Download Project Bundle button

below to download the necessary libraries and the code.py file in a zip file. Extract the contents of the zip

file, and copy the entire lib folder and the code.py file to your CIRCUITPY drive.

Your CIRCUITPY/lib folder should contain the following folder and file:

adafruit_bus_device/

adafruit_scd4x.mpy

Python Usage

Once you have the library pip3 -installed on your computer, copy or download the following example to

your computer, and run the following, replacing code.py with whatever you named the file: python3

code.py

Example Code:

# SPDX-FileCopyrightText: 2020 by Bryan Siepert, written for Adafruit Industries # # SPDX-License-Identifier: Unlicense import time import board import adafruit_scd4x

i2c = board.I2C() scd4x = adafruit_scd4x.SCD4X(i2c) print("Serial number:", [hex(i) for i in scd4x.serial_number])

scd4x.start_periodic_measurement()

print("Waiting for first measurement....")

while True: if scd4x.data_ready: print("CO2: %d ppm" % scd4x.CO2) print("Temperature: %0.1f *C" % scd4x.temperature) print("Humidity: %0.1f %%" % scd4x.relative_humidity) print() time.sleep(1)

If running CircuitPython: Once everything is saved to the CIRCUITPY drive, connect to the serial

console (https://adafru.it/Bec) to see the data printed out!

If running Python: The console output will appear wherever you are running Python.

Here is a quick explanation of the code and library features.

First, you import the necessary modules and library, and initialize the I2C connection with the sensor.

Next, you print the serial number.

Then, you start measuring data with start_periodic_measurement() .

Now you're ready to read values from the sensor using these properties:

data_ready - Check the sensor to see if new data is available .

CO2 - The CO2 concentration in PPM (parts per million).

temperature - The current temperature in degrees Celsius.

relative_humidity - The current relative humidity in %rH.

That's all there is to using the SCD-40 and SCD-41 with CircuitPython!

Python Docs

Python Docs (https://adafru.it/Uqa)

Arduino

Using the SCD4x with Arduino involves wiring up the sensor to your Arduino-compatible microcontroller,

installing the Adafruit SCD4x (https://adafru.it/Uxc) library written by Sensirion, and running the provided

example code.

I2C Wiring

Here is how to wire up the sensor using one of the STEMMA QT (https://adafru.it/Ft4) connectors. The

examples show a Metro but wiring will work the same for an Arduino or other compatible board.

Connect board VIN (red wire) to Arduino 5V if you

are running a 5V board Arduino (Uno, etc.). If your

board is 3V, connect to that instead.

Connect board GND (black wire) to Arduino GND

Connect board SCL (yellow wire) to Arduino SCL

Connect board SDA (blue wire) to Arduino SDA

Here is how to wire the sensor to a board using a solderless breadboard:

Connect board VIN (red wire) to Arduino 5V if you

are running a 5V board Arduino (Uno, etc.). If your

board is 3V, connect to that instead.

Connect board GND (black wire) to Arduino GND

Connect board SCL (yellow wire) to Arduino SCL

Connect board SDA (blue wire) to Arduino SDA

Library Installation

You can install the Sensirion I2C SCD4x library for Arduino using the Library Manager in the Arduino IDE.

Click the Manage Libraries ... menu item, search for SCD4x , and select the Sensirion I2C SCD4x library:

If asked about dependencies, click "Install all".

Load Example

Open up File -> Examples -> Sensirion I2C SCD4x -> exampleusage

/* * Copyright (c) 2021, Sensirion AG * All rights reserved. * * Redistribution and use in source and binary forms, with or without * modification, are permitted provided that the following conditions are met: * * * Redistributions of source code must retain the above copyright notice, this * list of conditions and the following disclaimer. * * * Redistributions in binary form must reproduce the above copyright notice, * this list of conditions and the following disclaimer in the documentation * and/or other materials provided with the distribution. * * * Neither the name of Sensirion AG nor the names of its * contributors may be used to endorse or promote products derived from * this software without specific prior written permission. *

* * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE * POSSIBILITY OF SUCH DAMAGE. */

#include <Arduino.h> #include <SensirionI2CScd4x.h> #include <Wire.h>

SensirionI2CScd4x scd4x;

void printUint16Hex(uint16_t value) { Serial.print(value < 4096 ? "0" : ""); Serial.print(value < 256 ? "0" : ""); Serial.print(value < 16 ? "0" : ""); Serial.print(value, HEX); }

void printSerialNumber(uint16_t serial0, uint16_t serial1, uint16_t serial2) { Serial.print("Serial: 0x"); printUint16Hex(serial0); printUint16Hex(serial1); printUint16Hex(serial2); Serial.println(); }

void setup() {

Serial.begin(115200); while (!Serial) { delay(100); }

Wire.begin();

uint16_t error; char errorMessage[256];

scd4x.begin(Wire);

// stop potentially previously started measurement error = scd4x.stopPeriodicMeasurement(); if (error) { Serial.print("Error trying to execute stopPeriodicMeasurement(): "); errorToString(error, errorMessage, 256); Serial.println(errorMessage); }

uint16_t serial0; uint16_t serial1; uint16_t serial2; error = scd4x.getSerialNumber(serial0, serial1, serial2); if (error) { Serial.print("Error trying to execute getSerialNumber(): "); errorToString(error, errorMessage, 256); Serial.println(errorMessage); } else { printSerialNumber(serial0, serial1, serial2); }

// Start Measurement error = scd4x.startPeriodicMeasurement(); if (error) { Serial.print("Error trying to execute startPeriodicMeasurement(): "); errorToString(error, errorMessage, 256); Serial.println(errorMessage); }

Serial.println("Waiting for first measurement... (5 sec)"); }

void loop() { uint16_t error; char errorMessage[256];

delay(5000);

// Read Measurement uint16_t co2; float temperature; float humidity; error = scd4x.readMeasurement(co2, temperature, humidity); if (error) { Serial.print("Error trying to execute readMeasurement(): "); errorToString(error, errorMessage, 256); Serial.println(errorMessage); } else if (co2 == 0) { Serial.println("Invalid sample detected, skipping."); } else { Serial.print("Co2:"); Serial.print(co2); Serial.print("\t"); Serial.print("Temperature:"); Serial.print(temperature); Serial.print("\t"); Serial.print("Humidity:"); Serial.println(humidity); } }

After opening the demo file, upload to your Arduino wired up to the sensor. Once you upload the code,

you will see the CO2, temperature, and relative humidity data values being printed when you open the

Serial Monitor (Tools->Serial Monitor) at 115200 baud, similar to this:

Downloads

Files

SCD-4x datasheet (https://adafru.it/Uxd)

EagleCAD PCB files on GitHub (https://adafru.it/Uxe)

Fritzing object in the Adafruit Fritzing Library (https://adafru.it/Uxf)

Schematic and Fab Print

Fab print shows SCD-41 - the SCD-40 is the same!

Adafruit SCD-40 User Manual

Specifications and Main Features

Frequently Asked Questions

User Manual