GY-21 Si7021 (with voltage regulator) AliExpress: 2$
AliExpress: 6$ (for 2)
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
Sensors test examples:
Test 1 with SD datalogging 2 mux 20 hours
Test 5 v5 saturated salt solution
Test 4 v6 Saturated NaCl solution
Test 2 v7 room RH12 low humidity
Test 3 v7 balcony RH15-92 changing humidity
Test 4 v8 RH12 to RH94#Si7021vsSHT85SensorsHumidity
Test 1 v8b Balcony high to mid RH
