The HTU21D-F is a I2C sensor. That means it uses the two I2C data/clock wires available on most microcontrollers, and can share those pins with other sensors as long as they don't have an address collision. For future reference, the default I2C address is 0x44 and you can also select address 0x45 by connecting the ADDR pin to a high voltage signal.
- Vin - this is the power pin. The chip can use 2.5-5VDC for power. 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. For a 3.3V controller like a Raspbery Pi, connect to 3.3V
- GND - common ground for power and logic
- SCL - I2C clock pin, connect to your microcontrollers I2C clock line. This pin has a 10K pullup resistor to Vin
- SDA - I2C data pin, connect to your microcontrollers I2C data line. This pin has a 10K pullup resistor to Vin
- STEMMA QT - These connectors allow you to connect to development boards with STEMMA QT connectors, or to other things, with various associated accessories.
- ADR - This is the I2C address selection pin. This pin has a 10K pull down resistor to make the default I2C address 0x44. You can tie this pin to Vin to make the address 0x45
- RST - Hardware reset pint. Has a 10K pullup on it to make the chip active by default. Connect to ground to do a hardware reset!
- ALR - Alert/Interrupt output. You can set up the sensor to alert you when an event has occured. Check the datasheet for how you can set up the alerts