The MCP9808 is a very straight-forward sensor, lets go thru all the pins so you can understand what you need to connect to get started
- VIN (VDD on header-only version) - This is the positive power and logic level pin. It can be 2.7-5.5VDC, so fine for use with 3 or 5V logic. Power VIN (VDD) with whatever logic level you plan to use on the i2c lines.
- GND - this is the ground power and logic reference pin.
- SCL - this is the I2C clock pin. There's a 10K pull-up already on the board, so connect this directly to the i2c master clock pin on your microcontroller
- SDA - this is the I2C data pin. There's a 10K pull-up already on the board, so connect this directly to the i2c master data pin on your microcontroller
- STEMMA QT - These connectors allow you to connect to development boards with STEMMA QT connectors, or to other things, with various associated accessories.
These are pins you don't need to connect to unless you want to!
- Alert - This is the interrupt/alert pin from the MCP9808. The chip has some capability to 'alert' you if the chip temperature goes above or below a set amount. This output can trigger to let you know. It is open collector so you need to use a pull-up resistor if you want to read signal from this pin.
- A0 (as well as A1 and A2 on the original version) - These are the address select pins. Since you can only have one device with a given address on an i2c bus, there must be a way to adjust the address if you want to put more than one MCP9808 on a shared i2c bus. The A0/A1/A2 pins set the bottom three bits of the i2c address. There are pull-down resistors on the board so connect them to VDD to set the bits to '1'. They are read on power up, so de-power and re-power to reset the address
The default address is 0x18 and the address can be calculated by 'adding' the A0/A1/A2 to the base of 0x18
A0 sets the lowest bit with a value of 1, A1 sets the middle bit with a value of 2 and A2 sets the high bit with a value of 4. The final address is 0x18 + A2 + A1 + A0.
So for example if A2 is tied to VDD and A0 is tied to VDD, the address is 0x18 + 4 + 1 = 0x1D.
If only A0 is tied to VDD, the address is 0x18 + 1 = 0x19
If only A1 is tied to VDD, the address is 0x18 + 2 = 0x1A
If only A2 is tied to VDD, the address is 0x18 + 4 = 0x1C