Adafruit SCD-41 User Manual

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Adafruit SCD-40 and SCD-41

Created by Kattni Rembor

https://learn.adafruit.com/adafruit-scd-40-and-scd-41

Last updated on 2021-12-13 12:22:06 PM EST

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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

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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.

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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.

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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

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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,

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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)

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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(http

s://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.

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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

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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

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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.

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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

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pullup on this pin.

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

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pullup on this pin.

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

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development boards with STEMMA QT connectors or to other things withvariou

s associated accessories(https://adafru.it/Ft6).

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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.

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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(http

s://adafru.it/Ft4) connectors:

Board 3Vtosensor VIN (red wire)

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Board GNDtosensor GND (black

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wire)

Board SCLtosensor SCL (yellow

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wire)

Board SDAtosensor SDA (blue

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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)

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Board GNDtosensor GND (black

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wire)

Board SCLtosensor SCL (yellow

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wire)

Board SDAtosensor SDA (blue

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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).

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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)

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Pi GNDtosensor GND (black wire)

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Pi SCLtosensor SCL (yellow wire)

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Pi SDAtosensor SDA (blue wire)

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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)

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Pi GNDtosensor GND (black wire)

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Pi SCLtosensor SCL (yellow wire)

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Pi SDAtosensor SDA (blue wire)

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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

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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 c

ode.py file to your CIRCUITPY drive.

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

adafruit_bus_device/

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adafruit_scd4x.mpy

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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

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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.

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

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temperature - The current temperature in degrees Celsius.

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relative_humidity - The current relative humidity in %rH.

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

Python Docs

Python Docs(https://adafru.it/Uqa)

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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)

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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

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wire)toArduino GND

Connect board SCL (yellow

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wire)toArduino SCL

Connect board SDA (blue

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

wire)toArduino SDA

Connectboard VIN (red wire)

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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

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wire)toArduino GND

Connect board SCL (yellow

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wire)toArduino SCL

Connect board SDA (blue

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wire)toArduino SDA

Library Installation

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

in the Arduino IDE.

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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

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* 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(): ");

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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)

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

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

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Schematic and Fab Print

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

Adafruit SCD-41 User Manual

Adafruit SCD-40 and SCD-41

Table of Contents

Overview

Pinouts

Python & CircuitPython

Python Docs

Arduino

Downloads

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