HiLetgo RS485 SHT20 Temperature Humidity Sensor Module High Precision Temperature Humidity Monitor Transmitter Sensor Probe Compatible to Modbus with 1M Lead

Seems to work fine, but if you have it on constant power (and FYI it works on 5V), it generates and measures heat: 81F reading in a 77F environment, with relative humidity skewed acccordingly. You can compensate in software or in its registers, but for accurate measurements it may need to be on switched power (eg mosfet), only on when measuring.

Red wire is supply (+) Black wire is supply (-) Yellow wire is data(+) White wire is data(-) Relative addressing is fine unless/until the implementation is wrong. Frankly it's MUCH less time consuming overall to give the MB addresses in both absolute and relative terms, as is done in virtually all professional data sheets. Register 0 (relative) is defined by the Modbus standard as (read code x04) 30001 for input registers and (read code x03) 40001 for holding registers. Register 1 (relative) is 30002 or 40002 and so on. To clarify - in *absolute* addressing terms: Register 30002 = Temp in C x10 (divide by 10 for correct value) Register 30003 = Humidity % x 10 (divide by 10 for correct value) MB addr. node is register 40258, valid values 1-247 Baud rate is register 40259, valid values 9600, 14400, 19200. Temp. comp. is register 40260, valid values +/- 100 (i.e. +/- 10.0 deg. C) Hum. comp. is register 40261, valid values +/- 100 (i.e. +/- 10.0%) Thankfully, once you get past the derp, the sensor works just fine.

Use function address 0x04 (read input register) register 0x01 (2 bytes) is temperature register 0x02 (2 bytes) is humidity both registers need to be divided by 10 (ex. 215 means 21.5C)