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Arduino > Si7021 > GY-21-Si7021.JPG

GY-21 Si7021 (with voltage regulator) AliExpress: 2$

Arduino > Si7021 > Si7021.jpg

AliExpress: 6$ (for 2)

Arduino > Si7021 > Adafruit-Si7021.JPG

Arduino > Si7021 > Adafruit-Si7021-back.JPG

Adafruit Si7021 (with voltage regulator) Amazon: 7$+4$ + tax

Compatible with SHT2x by address and protocol

AliExpress: 3.5$

Lib: https://github.com/adafruit/Adafruit_Si7021

Demo: https://github.com/adafruit/Adafruit_Si7021/blob/master/examples/si7021/si7021.ino

Datasheet: https://www.silabs.com/documents/public/data-sheets/Si7021-A20.pdf