Other article about ESP32, with using of development board of SunDuino ESP32 and temperature/humidity sensor Si7021 (HTU21).
I recommend the first article about ESP32 and SunDuino ESP32 which is available on https://time4ee.com/articles.php?article_id=43
Thanks dfrobot.com for ESP32 https://www.dfrobot.com/product-1559.html
For SunDuino ESP32 I thank designer of that http://www.sunduino.pl/wordpress/esp-wroom-32-czes...
Step 1: Installation of Si7021 (HTU21) Library
The installation of library for temperature/humidity sensor - Si7021 is very easy and you find it on https://learn.sparkfun.com/tutorials/si7021-humid... and github of SparkFun https://learn.sparkfun.com/tutorials/si7021-humid...
After installation of library for Si7021 you will see in File -> SparkFun Si7021 Humidity and Temperature Sensor, SparkFun_Si7021_Brekout_Example example code. I edited it. Edited code you find on my github https://github.com/petus/ESP32_SunDuino_Si7021/tr...
Step 2: Pinout of SunDuino and Connection
The pinout of SunDuino, ESP32 is below. I2C bus is connected to 21 (SDA) and 22 (SCL). Of course you connect to sensor GND and 3V3.
Step 3: Uploading of Code
During the uploading of your code you will see this warning message "WARNING: library Wire claims to run on [esp32] architecture(s) and may be incompatible with your current board which runs on [DFRobot_FireBeetle-ESP32] architecture(s)."
It's not important now.