====== 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|
^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>

===== Communication topics on lamaPLC =====
{{topic>communication}}

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