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. This is done using solder jumpers on the back of the breakout.

On the left is the I2C logic level jumper. By default, this is set to 3.3V which should work for both 3.3V and 5V logic level boards. Power at Vin can be 5V even if using a 3.3V logic level board, since the I2C logic will be 3.3V. The only reason (should be rare) to change this jumper is if a 5V logic level board does *not* work with the 3.3V I2C logic levels. In that case, this jumper can be cut and soldered to change I2C logic to Vin, which should be 5V when using a 5V board.

On the right is the Sensor Power jumper. By default, power comes from whatever is connected to Vin. This allows using 5V power if desired. To use the onboard 3.3V voltage regulator, cut and solder this jumper.

If the above description is still confusing, checkout the schematic available at the end of this guide. The jumpers are very simple and it may be easier to just read the schematic to determine what they do.