Arduino Code

You can easily wire this breakout to any microcontroller, we'll be using an Arduino. For another kind of microcontroller, just make sure it has I2C, then port the code - its pretty simple stuff!

  • Connect Vin to the power supply, 3-5V is fine. Use the same voltage that the microcontroller logic is based off of. For most Arduinos, that is 5V
  • Connect GND to common power/data ground
  • Connect the SCL pin to the I2C clock SCL pin on your Arduino. On an UNO & '328 based Arduino, this is also known as A5, on a Mega it is also known as digital 21 and on a Leonardo/Micro, digital 3
  • Connect the SDA pin to the I2C data SDA pin on your Arduino. On an UNO & '328 based Arduino, this is also known as A4, on a Mega it is also known as digital 20 and on a Leonardo/Micro, digital 2

The Si7021 has a default I2C address of 0x40 and cannot be changed!

Install Adafruit_Si7021 library

To begin reading sensor data, you will need to install the Adafruit_Si7021 library (code on our github repository). It is available from the Arduino library manager so we recommend using that.

From the IDE open up the library manager...

And type in adafruit si7021 to locate the library. Click Install

Also install the Adafruit Unified Sensor library in the same way:

We also have a great tutorial on Arduino library installation at:

Load Demo

Open up File->Examples->Adafruit_Si7021->si7021 and upload to your Arduino wired up to the sensor

Thats it! Now open up the serial terminal window at 115200 speed to begin the test.

You can try breathing on the sensor to increase the humidity. The sensor reacts very fast!

Library Reference

The library we have is simple and easy to use

You can create the Adafruit_Si7021 object with:

Download: file
Adafruit_Si7021 sensor = Adafruit_Si7021();

There are no pins to set since you must use the I2C bus!

Then initialize the sensor with:

Download: file

this function returns True if the sensor was found and responded correctly and False if it was not found

Once initialized, you can query the temperature in °C with

Download: file

Which will return floating point (decimal + fractional) temperature. You can convert to Fahrenheit by multiplying by 1.8 and adding 32 as you have learned in grade school!

Reading the humidity is equally simple. Call

Download: file

to read the humidity also as a floating point value between 0 and 100 (this reads % humidity)

This sensor also has a serial number which you might find handy! Call sensor.readSerialNumber() to read out the 8 bytes of unique ID. Then you can access them from sensor.sernum_a and sensor.sernum_b

This guide was first published on Sep 22, 2016. It was last updated on Sep 22, 2016. This page (Arduino Code) was last updated on Nov 21, 2018.