SDC40 from aliexpress

[ardunoxo]

hello forum

i got a SCD40 sensor from aliexpress but i can't get the CO2 value out of it...
https://www.aliexpress.com/item/1005006068980609.html

this is the module used:

with the DFRobot_SCD4X library and demo script "periodMeasure.ino"
i get the following result:

Begin ok!
The current temperature compensation value : 4.00 C
Set the current environment altitude : 540 m
Carbon dioxide concentration : 0 ppm
Environment temperature : 27.61 C
Relative humidity : 37.73 RH

code used:

DFRobot_SCD4X/examples/periodMeasure at main · DFRobot/DFRobot_SCD4X

same with sparkfun
CO2(ppm):0 Temperature(C):25.6 Humidity(%RH):37.2
code used:

SparkFun_SCD4x_Arduino_Library/examples/Example8_SCD41SingleShot at main ·...

(compiles and uploads without issue)

Sensirion:
Waiting for first measurement... (5 sec)
Invalid sample detected, skipping.

hm, does anyone have an idea why it shows 0 ppm?

(one possibility is that the CO2 sensor is fake, that occured to me, but i think then it would show a random value)

[6v6gt]

The SCD40 module looks tiny and maybe it does not have any I2C pull up resistors on board.
Maybe try adding 4.7k pull up resistors to SDA and SCL.
Provide links to the code samples you have used.

[ardunoxo]

i edited the main post and added the links and the picture of the sensor board.

it's not the sensor alone but has 2 resistors and one capacitor in addition to your picture.

[TomGeorge]

Hi, @ardunoxo
Welcome to the forum.

@ardunoxo

i edited the main post and added the links and the picture of the sensor board.

Please do not go back to old posts and edit them.
Always add new info in new post so the flow of the thread is not confusing.

Please post your code in code tags, some platforms do not like off site links.

How to get the best out of this forum

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Thanks.. Tom...

[ardunoxo]

hi tom

oke, will do that!

the codes:

DFRobot/DFRobot_SCD4X/blob/main/examples/periodMeasure/periodMeasure.ino

/*!
 * @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);
}

Blockzitat

and the second one:

sparkfun/SparkFun_SCD4x_Arduino_Library/blob/main/examples/Example8_SCD41SingleShot/Example8_SCD41SingleShot.ino

/*!
 * @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);
}

[xfpd]

What value are you using for VCC?

[6v6gt]

Well, the DFRobot code has no difficulty reading temperature and humidity from that SCD40 sensor so it is unlikely to be a code or I2C issue.
The device does need quite a high current of around 200mA. How have you connected it ?

[ardunoxo]

i don't see a code or I2C issue (I2C scanner finds the module)

it's connected to an arduino nano (5V/GND + I2C) that is fed by USB
some small oled screen is attached too