Gravity: SCD41 Infrared CO2 Sensor I2C Wiki - DFRobot

Introduction

CO2 is a key factor for indoor air quality as high levels compromise human’s cognitive performance and well-being.
This Gravity: SCD41 CO2 sensor is based on the SCD41 miniature CO2 sensor from Sensirion. SCD41 builds on the photoacoustic NDIR sensing principle and Sensirion’s patented PAsens® and CMOSens® technology to offer high accuracy at an unmatched price and smallest form factor. On-chip signal compensation is realized with the built-in temperature and humidity sensor, while temperature and humidity data outputs are also available.
SCD41 sensor detects the amount of energy that is absorbed by CO2 molecules. When pulsing the infra-red emitter, CO2 molecules absorb infrared light periodically. This causes additional molecular vibration resulting in a pressure wave inside the measurement chamber. The higher the CO2 concentration, the more light is absorbed, and thus the greater the amplitude of this acoustic wave becomes. A microphone inside the gas chamber measures this, from which the CO2 concentration can then be calculated.

SEN0536-1

Click to learn more about PAsens® technology.
Click to learn more about NDIR sensor.

Click to learn more about What types of NDIR sensors exist and how do they work?

Click to learn more about Design-in guide

Features

Application

Specification

CO2

Humidity

Temperature

Board Overview

Num Label Description
1 VCC +
2 GND -
3 SCL I2C Clock Line
4 SDA I2C Data Line

Arduino Tutorial

Requirements

Connection Diagram

Sample Code 1 - Period Measurement

Read data from SCD41 periodly.

/*!
 * @file  periodMeasure.ino
 * @brief  This sample shows how to configure period measurement mode, compensation and calibration.
 * @note  The actual compensation and calibration parameter should be changed according to the operating environment
 * @copyright  Copyright (c) 2010 DFRobot Co.Ltd (http://www.dfrobot.com)
 * @license  The MIT License (MIT)
 * @author  [qsjhyy](yihuan.huang@dfrobot.com)
 * @version  V1.0
 * @date  2022-05-11
 * @url  https://github.com/DFRobot/DFRobot_SCD4X
 */
#include <DFRobot_SCD4X.h>

/**
 * @brief Constructor
 * @param pWire - Wire object is defined in Wire.h, so just use &Wire and the methods in Wire can be pointed to and used
 * @param i2cAddr - SCD4X I2C address.
 */
DFRobot_SCD4X SCD4X(&Wire, /*i2cAddr = */SCD4X_I2C_ADDR);

void setup(void)
{
  Serial.begin(115200);

  // Init the sensor
  while( !SCD4X.begin() ){
    Serial.println("Communication with device failed, please check connection");
    delay(3000);
  }
  Serial.println("Begin ok!");

  /**
   * @brief set periodic measurement mode
   * @param mode - periodic measurement mode:
   * @n       SCD4X_START_PERIODIC_MEASURE : start periodic measurement, signal update interval is 5 seconds.
   * @n       SCD4X_STOP_PERIODIC_MEASURE : stop periodic measurement command
   * @n       SCD4X_START_LOW_POWER_MEASURE :  start low power periodic measurement, signal update interval is approximately 30 seconds.
   * @return None
   * @note The measurement mode must be disabled when configuring the sensor; after giving the stop_periodic_measurement command, the sensor needs to wait 500ms before responding to other commands.
   */
  SCD4X.enablePeriodMeasure(SCD4X_STOP_PERIODIC_MEASURE);

  /**
   * @brief set temperature offset
   * @details T(offset_actual) = T(SCD4X) - T(reference) + T(offset_previous)
   * @n T(offset_actual): the calculated actual temperature offset that is required
   * @n T(SCD4X): the temperature measured by the sensor (wait for a period of time to get steady readings)
   * @n T(reference): the standard reference value of the current ambient temperature
   * @n T(offset_previous): the previously set temperature offset
   * @n For example : 32(T(SCD4X)) - 30(T(reference)) + 2(T(offset_previous)) = 4(T(offset_actual))
   * @param tempComp - temperature offset value, unit ℃
   * @return None
   * @note When executing the command, the sensor can't be in period measurement mode
   */
  SCD4X.setTempComp(4.0);

  /**
   * @brief get temperature offset
   * @return The current set temp compensation value, unit ℃
   * @note When executing the command, the sensor can't be in period measurement mode
   */
  float temp = 0;
  temp = SCD4X.getTempComp();
  Serial.print("The current temperature compensation value : ");
  Serial.print(temp);
  Serial.println(" C");

  /**
   * @brief set sensor altitude
   * @param altitude - the current ambient altitude, unit m
   * @return None
   * @note When executing the command, the sensor can't be in period measurement mode
   */
  SCD4X.setSensorAltitude(540);

  /**
   * @brief get sensor altitude
   * @return The current set ambient altitude, unit m
   * @note When executing the command, the sensor can't be in period measurement mode
   */
  uint16_t altitude = 0;
  altitude = SCD4X.getSensorAltitude();
  Serial.print("Set the current environment altitude : ");
  Serial.print(altitude);
  Serial.println(" m");

  /**
   * @brief set automatic self calibration enabled
   * @param mode - automatic self-calibration mode:
   * @n       true : enable automatic self-calibration
   * @n       false : disable automatic self-calibration
   * @return None
   * @note When executing the command, the sensor can't be in period measurement mode
   */
  // SCD4X.setAutoCalibMode(true);

  /**
   * @brief get automatic self calibration enabled
   * @return Automatic self-calibration mode:
   * @n        true : enable automatic self-calibration
   * @n        false : disable automatic self-calibration
   * @note When executing the command, the sensor can't be in period measurement mode
   */
  // if(SCD4X.getAutoCalibMode()) {
  //   Serial.println("Automatic calibration on!");
  // } else {
  //   Serial.println("Automatic calibration off!");
  // }

  /**
   * @brief persist settings
   * @details Configuration settings such as the temperature offset, sensor altitude and the ASC enabled/disabled 
   * @n  parameter are by default stored in the volatile memory (RAM) only and will be lost after a power-cycle.
   * @return None
   * @note To avoid unnecessary wear of the EEPROM, the persist_settings command should only be sent 
   * @n  when persistence is required and if actual changes to the configuration have been made. 
   * @n  The EEPROM is guaranteed to endure at least 2000 write cycles before failure.
   * @note Command execution time : 800 ms
   * @n When executing the command, the sensor can't be in period measurement mode
   */
  // SCD4X.persistSettings();

  /**
   * @brief reinit reinit
   * @details  The reinit command reinitializes the sensor by reloading user settings from EEPROM.
   * @return None
   * @note Before sending the reinit command, the stop measurement command must be issued.
   * @n  If the reinit command does not trigger the desired re-initialization, 
   * @n  a power-cycle should be applied to the SCD4x.
   * @n  Command execution time : 20 ms
   * @n When executing the command, the sensor can't be in period measurement mode
   */
  //SCD4X.moduleReinit();

  /**
   * @brief set periodic measurement mode
   * @param mode - periodic measurement mode:
   * @n       SCD4X_START_PERIODIC_MEASURE : start periodic measurement, signal update interval is 5 seconds.
   * @n       SCD4X_STOP_PERIODIC_MEASURE : stop periodic measurement command
   * @n       SCD4X_START_LOW_POWER_MEASURE :  start low power periodic measurement, signal update interval is approximately 30 seconds.
   * @return None
   * @note The measurement mode must be disabled when changing the sensor settings; after giving the stop_periodic_measurement command, the sensor needs to wait 500ms before responding to other commands.
   */
  SCD4X.enablePeriodMeasure(SCD4X_START_PERIODIC_MEASURE);

  Serial.println();
}

void loop()
{
  /**
   * @brief get data ready status
   * @return data ready status:
   * @n        true : data ready
   * @n        false : data not ready
   */
  if(SCD4X.getDataReadyStatus()) {
    /**
     * @brief set ambient pressure
     * @param ambientPressure - the current ambient pressure, unit Pa
     * @return None
     */
    // SCD4X.setAmbientPressure(96000);

    /**
     * @brief Read the measured data
     * @param data - sSensorMeasurement_t, the values measured by the sensor, including CO2 concentration (ppm), temperature (℃) and humidity (RH)
     * @n  typedef struct {
     * @n    uint16_t   CO2ppm;
     * @n    float   temp;
     * @n    float   humidity;
     * @n  } sSensorMeasurement_t;
     * @return None
     * @note CO2 measurement range: 0~40000 ppm; temperature measurement range: -10~60 ℃; humidity measurement range: 0~100 %RH.
     */
    DFRobot_SCD4X::sSensorMeasurement_t data;
    SCD4X.readMeasurement(&data);

    Serial.print("Carbon dioxide concentration : ");
    Serial.print(data.CO2ppm);
    Serial.println(" ppm");

    Serial.print("Environment temperature : ");
    Serial.print(data.temp);
    Serial.println(" C");

    Serial.print("Relative humidity : ");
    Serial.print(data.humidity);
    Serial.println(" RH");

    Serial.println();
  }
  delay(1000);
}

Expected Result 1

Sample Code 2 - Single Measurement

Read data after waking up the sensor, then let it enter sleep mode again.

/*!
 * @file  singleShotMeasure.ino
 * @brief  This sample shows how to set single measurement mode, perform reset operation, and set sleep and wake-up mode.
 * @details Get 6 data from single measurement, take the average value, print it, enter sleep mode, wake up the sensor after 5 minutes, and repeat the above measurement process
 * @copyright  Copyright (c) 2010 DFRobot Co.Ltd (http://www.dfrobot.com)
 * @license  The MIT License (MIT)
 * @author  [qsjhyy](yihuan.huang@dfrobot.com)
 * @version  V1.0
 * @date  2022-05-11
 * @url  https://github.com/DFRobot/DFRobot_SCD4X
 */
#include <DFRobot_SCD4X.h>

/**
 * @brief Constructor
 * @param pWire - Wire object is defined in Wire.h, so just use &Wire and the methods in Wire can be pointed to and used
 * @param i2cAddr - SCD4X I2C address.
 */
DFRobot_SCD4X SCD4X(&Wire, /*i2cAddr = */SCD4X_I2C_ADDR);

void setup(void)
{
  Serial.begin(115200);

  // Init the sensor
  while( !SCD4X.begin() ){
    Serial.println("Communication with device failed, please check connection");
    delay(3000);
  }
  Serial.println("Begin ok!");

  /**
   * @brief set periodic measurement mode
   * @param mode - periodic measurement mode:
   * @n       SCD4X_START_PERIODIC_MEASURE : start periodic measurement, signal update interval is 5 seconds.
   * @n       SCD4X_STOP_PERIODIC_MEASURE : stop periodic measurement command
   * @n       SCD4X_START_LOW_POWER_MEASURE :  start low power periodic measurement, signal update interval is approximately 30 seconds.
   * @return None
   * @note The measurement mode must be disabled when configuring the sensor; after giving the stop_periodic_measurement command, the sensor needs to wait 500ms before responding to other commands.
   */
  SCD4X.enablePeriodMeasure(SCD4X_STOP_PERIODIC_MEASURE);

  /**
   * @brief perform self test
   * @details The perform_self_test feature can be used as an end-of-line test to check sensor 
   * @n  functionality and the customer power supply to the sensor.
   * @return module status:
   * @n        0 : no malfunction detected
   * @n        other : malfunction detected
   * @note Command execution time : 10000 ms
   * @n When executing the command, the sensor can't be in period measurement mode.
   */
  if(0 != SCD4X.performSelfTest()) {
    Serial.println("Malfunction detected!");
  }

  Serial.println();
}

void loop()
{
  /**
   * @brief Set the sensor as sleep or wake-up mode (SCD41 only)
   * @param mode - Sleep and wake-up mode:
   * @n       SCD4X_POWER_DOWN : Put the sensor from idle to sleep to reduce current consumption.
   * @n       SCD4X_WAKE_UP : Wake up the sensor from sleep mode into idle mode.
   * @return None
   * @note Note that the SCD4x does not acknowledge the wake_up command. Command execution time : 20 ms
   * @n When executing the command, the sensor can't be in period measurement mode.
   */
  Serial.print("Waking sensor...");
  SCD4X.setSleepMode(SCD4X_WAKE_UP);

  DFRobot_SCD4X::sSensorMeasurement_t data[6];
  memset(data, 0, sizeof(data));
  uint32_t averageCO2ppm=0;
  float averageTemp=0.0, averageHumidity=0.0;
  Serial.print("Measuring...");
  for(uint8_t i=0; i<6; i++) {
    /**
     * @brief measure single shot（SCD41 only）
     * @details  On-demand measurement of CO2 concentration, relative humidity and temperature.
     * @n  Get the measured data through readMeasurement(sSensorMeasurement_t data) interface
     * @param mode - Single-measurement mode:
     * @n       SCD4X_MEASURE_SINGLE_SHOT : On-demand measurement of CO2 concentration, relative humidity and temperature. 
     * @n                                   Max command duration 5000 [ms].
     * @n       SCD4X_MEASURE_SINGLE_SHOT_RHT_ONLY : On-demand measurement of relative humidity and temperature only.
     * @n                                            Max command duration 50 [ms].
     * @note In SCD4X_MEASURE_SINGLE_SHOT_RHT_ONLY mode, CO2 output is returned as 0 ppm.
     * @return None
     * @note When executing the command, the sensor can't be in period measurement mode.
     */
    SCD4X.measureSingleShot(SCD4X_MEASURE_SINGLE_SHOT);

    /**
     * @brief get data ready status
     * @return data ready status:
     * @n        true : data ready
     * @n        false : data not ready
     */
    while(!SCD4X.getDataReadyStatus()) {
      delay(100);
    }

    /**
     * @brief Read the measured data
     * @param data - sSensorMeasurement_t, the values measured by the sensor, including CO2 concentration (ppm), temperature (℃) and humidity (RH)
     * @n  typedef struct {
     * @n    uint16_t   CO2ppm;
     * @n    float   temp;
     * @n    float   humidity;
     * @n  } sSensorMeasurement_t;
     * @return None
     * @note CO2 measurement range: 0~40000 ppm; temperature measurement range: -10~60 ℃; humidity measurement range: 0~100 %RH.
     */
    SCD4X.readMeasurement(&data[i]);
    if(0 != i) {   // Discard the first set of data, because the chip datasheet indicates the first reading obtained after waking up is invalid
      averageCO2ppm += data[i].CO2ppm;
      averageTemp += data[i].temp;
      averageHumidity += data[i].humidity;
    }
    Serial.print(i);
  }
  Serial.print("\nCarbon dioxide concentration : ");
  Serial.print(averageCO2ppm / 5);
  Serial.println(" ppm");

  Serial.print("Environment temperature : ");
  Serial.print(averageTemp / 5);
  Serial.println(" C");

  Serial.print("Relative humidity : ");
  Serial.print(averageHumidity / 5);
  Serial.println(" RH\n");

  // Put the sensor from idle to sleep to reduce current consumption.
  Serial.print("Sleeping sensor...");
  SCD4X.setSleepMode(SCD4X_POWER_DOWN);
  delay(300000);   // Wake up the sensor after 5 minutes, and repeat the above measurement process
}

Expected Result 2

Main API Functions

/**
   * @fn enablePeriodMeasure
   * @brief set periodic measurement mode
   * @param mode - periodic measurement mode:
   * @n       SCD4X_START_PERIODIC_MEASURE : start periodic measurement, signal update interval is 5 seconds.
   * @n       SCD4X_STOP_PERIODIC_MEASURE : stop periodic measurement command
   * @n       SCD4X_START_LOW_POWER_MEASURE :  start low power periodic measurement, signal update interval is approximately 30 seconds.
   * @return None
   * @note The measurement mode must be disabled when configuring the sensor; after giving the stop_periodic_measurement command, the sensor needs to wait 500ms before responding to other commands.
   */
  void enablePeriodMeasure(uint16_t mode);

  /**
   * @fn readMeasurement
   * @brief Read the measured data
   * @param data - sSensorMeasurement_t, the values measured by the sensor, including CO2 concentration (ppm), temperature (℃) and humidity (RH)
   * @return None
   * @note CO2 measurement range: 0~40000 ppm; temperature measurement range: -10~60 ℃; humidity measurement range: 0~100 %RH.
   */
  void readMeasurement(sSensorMeasurement_t * data);

  /**
   * @fn getDataReadyStatus
   * @brief get data ready status
   * @return data ready status:
   * @n        true : data ready
   * @n        false : data not ready
   */
  bool getDataReadyStatus(void);

Raspberry Pi Tutorial

Requirements

Connection Diagram

Installation

  1. Enable the I2C interface of Raspberry Pi. If it's already enabled, skip this step. Open Terminal, type the following command, and press Enter:
    pi@raspberrypi:~ $ sudo raspi-config
    Then use the up and down keys to select "5 Interfacing Options" -> "P5 I2C" and press Enter to confirm “YES”. Reboot the Raspberry Pi.

  2. Installing Python dependency libraries and git (networking required). If it is already installed, skip this step. In the Terminal, type the following commands, and press Enter:
    pi@raspberrypi:~ $ sudo apt-get update
    pi@raspberrypi:~ $ sudo apt-get install build-essential python-dev python-smbus git

  3. Download DFRobot_SCD4X driver library. In Terminal, type the following commands, and press Enter:
    pi@raspberrypi:~ $ cd Desktop/
    pi@raspberrypi:~/Desktop $ git clone https://github.com/dfrobot/DFRobot_SCD4X

Sample Code

Sample Code 1 - Period Measurement (period_measure.py)

Sample Code 2 - Single-shot Measurement (single_shot_measure.py)

FAQ

For any questions, advice or cool ideas to share, please visit the DFRobot Forum.

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