====== lamaPLC project: Sension SCD CO² measurement module ======
{{ :sensor:scd30.png?120|SCD 30 Modul}}

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. 

|< 100%>|
^Feature^SCD30^SCD40^SCD41|
^ |{{:sensor:scd30.png?100|SCD 30 Modul}}|-|{{:sensor:scd_41.png?100|SCD 41 Modul}}|
^Technology|NDIR (Dual-Channel)|Photoacoustic|Photoacoustic|
^Size|35 x 23 x 7 mm|10.1 x 10.1 x 6.5 mm|10.1 x 10.1 x 6.5 mm|
^CO² Range|0 – 40,000 ppm|400 – 2,000 ppm|400 – 5,000 ppm|
^Accuracy|±(30 ppm + 3% MV)|±(50 ppm + 5% MV)|±(40 ppm + 5% MV)|	
^Voltage|3.3V – 5.5V|2.4V – 5.5V|2.4V – 5.5V|
^Power (avg)|~19 mA|~15 mA|~0.5 mA (Low Power Mode)|
^Interface|[[com:basic_i2c|I²C]] (Address **0x61**), [[com:basic_uart|UART]], PWM|[[com:basic_i2c|I²C]]|[[com:basic_i2c|I²C]]|
^Operating Temperature|0°C to 50°C|||

**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.

{{page>:tarhal}}

===== SCD30 =====
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.

==== SCD30 Pinout ====
{{ :sensor:scd30_pinout.png|}}
^Pin^Name^Description^Logic Level|
^1|VDD|Supply Voltage (3.3V – 5.5V)|—|
^2|GND|Ground|—|
^3|TX / SCL|Modbus Transmit / I²C Clock|3.0V (internal pull-up)|
^4|RX / SDA|Modbus Receive / I²C Data|3.0V (internal pull-up)|
^5|RDY|Data Ready (High when new data is available)|3.0V|
^6|PWM|Pulse Width Modulation output|3.0V|
^7|SEL|Interface Select (Floating/GND = I²C; High = Modbus)|< 4.0V|

**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.

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

<code c>
#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
}

</code>

===== SCD41 =====
{{ :sensor:scd_41.png?120|SCD41 Modul}}
The SCD41, developed by Sensirion, is a compact, highly precise sensor for measuring CO₂, temperature, and humidity. As the second generation of their optical CO² sensors, it employs photoacoustic NDIR (Non-Dispersive Infrared) technology. This approach enables the sensor to be much smaller than conventional CO₂ sensors while maintaining high accuracy, making it perfect for indoor air quality (IAQ) monitoring.

**Key Features**

  * 3-in-1 Sensing: Measures CO2 concentration, relative humidity, and temperature simultaneously.
  * Miniature Form Factor: Its extremely small size (10.1 x 10.1 x 6.5 mm³) enables easy integration into compact devices.
  * High Accuracy: Offers a precision of ±(40 ppm + 5% of reading) across the range 400 to 5,000 ppm.
  * Low Power Modes: Includes a "single-shot" mode that reduces average current consumption to <0.4 mA for battery-operated applications.
  * Standard Interface: Communicates via I2C, making it compatible with microcontrollers such as Arduino, ESP32, and Raspberry Pi. 

**Technical Specifications**

^Parameter^Range / Value^Accuracy (Typical)|
^CO² Concentration|400 – 5,000 ppm (up to 40,000 ppm output)|±(40 ppm + 5%)|	
^Relative Humidity|0 – 100% RH|±6% RH|	
^Temperature|-10°C to 60°C| +-0.8 °C (at 15-35°C)|
^Supply Voltage|**2.4V – 5.5V**|N/A|
^I²C Address|0x62|N/A|

==== SCD41 Pinout ====
Most breakout boards use a standard 4-pin or 5-pin arrangement for easy connection to microcontrollers like Arduino or ESP32.

{{ :sensor:scd_41.png?200|SCD41 Modul}}
^Pin Name^Type^Description|
^VIN / VCC|Power|Connect to (2.4V – 5.5V) (depending on your board's logic level).|
^GND|Ground|Common ground for power and logic.|
^SCL|I²C Clock|Serial clock line for I²C communication. Usually has a 10k pull-up.|
^SDA|I²C Data|Serial data line for I²C communication. Usually has a 10k pull-up.|
^3Vo|Output|(Adafruit boards only) 3.3V output from the onboard regulator.|

==== SCD41 Arduino example ====
Search for "Sensirion I2C SCD4x" and install it. The example below initialises the sensor and outputs CO², Temperature, and Humidity readings every 5 seconds. 

<code c>
#include <Arduino.h>
#include <SensirionI2cScd4x.h>
#include <Wire.h>

SensirionI2cScd4x scd4x;

void setup() {
    Serial.begin(115200);
    while (!Serial); // Wait for serial monitor

    Wire.begin();
    scd4x.begin(Wire);

    // Stop potentially running measurement
    uint16_t error = scd4x.stopPeriodicMeasurement();
    if (error) {
        Serial.print("Error stopping measurement: ");
        Serial.println(error);
    }

    // Start periodic measurement (updates every 5 seconds)
    error = scd4x.startPeriodicMeasurement();
    if (error) {
        Serial.print("Error starting measurement: ");
        Serial.println(error);
    }

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

void loop() {
    uint16_t co2 = 0;
    float temperature = 0.0f;
    float humidity = 0.0f;
    bool dataReady = false;

    // Check if data is ready to be read
    uint16_t error = scd4x.getDataReadyStatus(dataReady);
    
    if (dataReady) {
        error = scd4x.readMeasurement(co2, temperature, humidity);
        if (!error) {
            Serial.print("CO2: ");
            Serial.print(co2);
            Serial.print(" ppm\t");
            Serial.print("Temp: ");
            Serial.print(temperature);
            Serial.print(" °C\t");
            Serial.print("Humidity: ");
            Serial.print(humidity);
            Serial.println(" %");
        }
    }
    delay(1000); // Check status every second
}
</code>

**Key Functions to Note**

  * **startPeriodicMeasurement():** Sets the sensor to measure every 5 seconds.
  * **getDataReadyStatus():** Use this to avoid reading "stale" data until the next 5-second interval.
  * **measureSingleShot():** Available only on the SCD41 (not the SCD40). It allows manual measurement to save power, making it ideal for battery-powered projects. 
===== Communication topics on lamaPLC =====
{{topic>communication}}

{{tag>SCD30 SCD40 SCD41 IAQ NDIR sensor I2C arduino_code}}

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