SCD40 with ESP32

Specifications

Power and logic levels

3.3 V: safe to connect directly

ESP32 pins, including those on a display board's connectors, work at 3.3 V and are not 5 V tolerant. Modules differ, so if in doubt, measure the signal before you connect it.

Wiring

Arduino code

#include <Wire.h>

const int SDA_PIN = 8, SCL_PIN = 9;   // use your board's I2C pins
const uint8_t SCD40_ADDR = 0x62;

void command(uint16_t cmd) {
  Wire.beginTransmission(SCD40_ADDR);
  Wire.write(cmd >> 8);
  Wire.write(cmd & 0xFF);
  Wire.endTransmission();
}

void setup() {
  Serial.begin(115200);
  Wire.begin(SDA_PIN, SCL_PIN);
  command(0x21B1);   // start periodic measurement
}

void loop() {
  delay(5000);       // a new value about every 5 s
  command(0xEC05);   // read measurement
  delay(1);
  if (Wire.requestFrom(SCD40_ADDR, (uint8_t)9) != 9) {
    Serial.println("SCD40 not responding");
    return;
  }
  uint16_t raw[3];
  for (int i = 0; i < 3; i++) {
    raw[i] = (Wire.read() << 8) | Wire.read();
    Wire.read();     // CRC byte, not checked in this short example
  }
  Serial.printf("%u ppm  %.1f C  %.1f %%\n", raw[0],
                -45.0 + 175.0 * raw[1] / 65535.0, 100.0 * raw[2] / 65535.0);
}

No extra library needed. Compiled for ESP32-S3 with arduino-esp32 3.x. Not yet tested by us on a physical sensor. Change the pins to match your board.

On a display

Read the value in your sketch and pass it to a label, or send it over MQTT and show it with an MQTT value in the editor.

Boards with a ready connector

Only boards whose connectors we have surveyed. Others may still work on free GPIOs.

Good to know

• Peaks reach 205 mA. Use a solid supply.
• A new value arrives about every 5 seconds, and the response time is 60 s.
• The example skips the CRC check to stay short. Add it in a product.
• Accuracy is specified from 400 to 2000 ppm.

What it is good for

• Indoor air quality displays
• Meeting room CO2 traffic lights
• Ventilation control

FAQ

Sources

• https://sensirion.com/products/catalog/SCD40

Related parts

• BME280
• SHT31 / SHT3x