lamaPLC project: Sension SCD CO² measurement module

The main distinction between these Sensirion sensors lies in their measurement technology, which affects their size and power use. The SCD30 employs conventional NDIR (Non-Dispersive Infrared) technology, whereas the SCD40/41 series utilises a more recent, compact Photoacoustic principle.

Key Differences

• Form Factor: The SCD40/41 is approximately ten times smaller than the SCD30, making it well-suited for compact wearables or integrated smart home devices.
• Precision vs Size: The SCD30 generally offers slightly better accuracy and stability over extended periods, thanks to its dual-channel NDIR design, which naturally compensates for sensor drift.
• Power Efficiency: For battery-powered devices, the SCD41 is the preferred choice, featuring a “Single Shot” mode that significantly reduces power consumption compared to the SCD30 or SCD40.
• Mounting: The SCD40/41 is an SMD (Surface-Mount Device) component suitable for reflow soldering and mass production. In contrast, the SCD30 is usually hand-soldered or connected via pins.

The SCD30 is a high-precision, 3-in-1 sensor module from Sensirion that measures Carbon Dioxide (CO²), Temperature, and Relative Humidity. It is considered a “true” CO² sensor because it uses Non-Dispersive Infrared (NDIR) technology to directly measure CO² molecules, rather than approximating levels from other gases.

Key Features & Technology

• Dual-Channel Detection: It uses a dedicated reference channel to compensate for long-term drift, ensuring superior stability over its 15-year lifetime.
• Integrated Compensation: The module uses its built-in temperature and humidity data to internally calibrate and normalise the CO2 readings.
• Self-Calibration Options: Supports Automatic Self-Calibration (ASC), which resets the sensor's baseline when exposed to fresh air (~400 ppm) regularly, or Forced Recalibration (FRC) for manual setup.
• Adjustable Sampling: While the default interval is 2 seconds, it can be set to 1-1800 seconds to reduce power consumption in battery-powered projects.

Key Wiring Notes

• Internal Pull-ups: The module has internal 45 kΩ resistors connected to a 3V supply for the I²C lines.
• Voltage Warning: The module can be powered with 5V, but the SCL/SDA logic pins operate at 3V. When using a 5V microcontroller like an Arduino Uno, a level shifter is strongly advised to prevent damage to the sensor.
• Interface Selection: For I²C (the standard mode), leave the SEL pin floating or connect it to Ground. To use Modbus, connect the SEL pin to VDD via a voltage divider, ensuring the voltage does not exceed 4V.

To use the SCD30 with an Arduino, the SparkFun SCD30 Arduino Library and the Adafruit SCD30 Library are the most common choices.

#include <Wire.h>
#include "SparkFun_SCD30_Arduino_Library.h" //
 
SCD30 airSensor;
 
void setup() {
  Wire.begin();
  Serial.begin(9600);
 
  if (airSensor.begin() == false) {
    Serial.println("Sensor not detected. Check wiring!");
    while (1);
  }
  Serial.println("SCD30 detected!");
}
 
void loop() {
  if (airSensor.dataAvailable()) {
    Serial.print("CO2(ppm): ");
    Serial.print(airSensor.getCO2());
    Serial.print(" Temp(C): ");
    Serial.print(airSensor.getTemperature(), 1);
    Serial.print(" Humidity(%): ");
    Serial.println(airSensor.getHumidity(), 1);
  }
  delay(2000); // Sensor updates every 2 seconds by default
}

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