The SCD-40 and SCD-41 have the same pinouts.

Power Pins

• VIN - This is the power pin. To power the board, give it the same power as the logic level of your microcontroller - e.g. for a 3V microcontroller like a Feather M4, use 3V, or for a 5V microcontroller like Arduino, use 5V.
• 3Vo - This is the output from the onboard 3.3V regulator. If you have a need for a clean 3.3V output, you can use this! It can provide at least 100mA output.
• GND - This is common ground for power and logic.

I2C Logic Pins

The default I2C address for the SCD-4x is 0x62.

• SCL - I2C clock pin, connect to your microcontroller I2C clock line. There's a 10K pullup on this pin.
• SDA - I2C data pin, connect to your microcontroller I2C data line. There's a 10K pullup on this pin.
• STEMMA QT - These connectors allow you to connectors to development boards with STEMMA QT connectors or to other things with various associated accessories.

Status LED

There is a statis LED marked "on" when the sensor is powered (circled in green).

If you do not want this LED to light up (saving power or avoiding light), cut the circuit board jumper in the red box. If you ever want to reenable it, bridge the pads with a bit of solder.

Jumpers

The SCD-4x can run from 3 to 5V DC, for both power and I2C data/logic. Normally that would mean we wouldn't put a regulator and logic level shifter on the breakout. However, the SCD-4x also does best with a quiet power supply that can also supply ~200mA peak. Since that may or may not be the same as the logic power supply of the microcontroller, advanced users can customize the power/logic level setup for the sensor.

On the left is the level-shifted I2C logic level. Most of the time, Vin is the power and logic level for the microcontroller. However, if you are, say, powering from 5v because it's a better power supply source, but are using a 3V logic microcontroller, you can cut and re-solder this jumper.

On the right is the Sensor Power jumper. By default we power the sensor through the 3V regulator. If you happen to have a nice and quiet Vin power supply, you can cut and re-solder this jumper.