Power Pins:

• Vin - this is the power pin. Since the sensor chip uses 3 VDC, we have included a voltage regulator on board that will take 3-5VDC and safely convert it down. To power the board, give it the same power as the logic level of your microcontroller - e.g. for a 5V micro like Arduino, use 5V
• 3Vo - this is the 3.3V output from the voltage regulator, you can grab up to 100mA from this if you like
• GND - common ground for power and logic

SPI Logic pins:

All pins going into the breakout have level shifting circuitry to make them 3-5V logic level safe. Use whatever logic level is on Vin!

• SCK - This is the SPI Clock pin, its an input to the chip
• SDO - this is the Serial Data Out / Microcontroller In Sensor Out pin, for data sent from the MAX31856 to your processor
• SDI - this is the Serial Data In / Microcontroller Out Sensor In pin, for data sent from your processor to the MAX31856
• CS - this is the Chip Select pin, drop it low to start an SPI transaction. Its an input to the chip

If you want to connect multiple MAX31856's to one microcontroller, have them share the SDI, SDO and SCK pins. Then assign each one a unique CS pin.

Additional Pins

There's two more pins that are available for advanced usage

• FLT - This is the Fault output. If you use the threshhold-notification capabilities of the MAX31856 you can monitor this pin, when it goes low there's a fault!
• DRDY - This pin is used for advanced uses where you tell the sensor to begin a reading and then wait for this pin to go low. We don't use it in our library code because we keep it simple with a delay/wait, but it is available in case you need it!