Datasheet: http://www.ti.com/lit/ds/symlink/hdc2080.pdf
Programming HDC20x0: http://www.ti.com/lit/an/snaa312/snaa312.pdf
aliexpress 3$
Source code example: https://github.com/tinkeringtech/HDC2080_breakout
Sensors test examples:
Test 4 v6 Saturated NaCl solution
Test 2 v7 room RH12 low humidity
Test 3 v7 balcony RH15-92 changing humidity
Test 3 v8 Humidity absorber RH12