[werk_ag]

You did the right choice. The SHT31 sensor is a native 3.3V module (5.0v tolerant) while most of the the HTU21D modules are native 5.0V modules which also operate at 3.3V
The Wemos D1 mini, input / output is 3.3V

[Barrow4491]

Once the HTU21 can't be directly attached to the PCB (pinout on the PCB is for the SHT31) make sure the cables between the PCB and sensor are the shortest as possible.
The OLED display should be connected directly on the PCB.

I have just tested an unit with the HTU21 and latest software, and it is working fine. Double check if the installed HTU21 library is the one supplied with the software package.

Werk,
Back home after an extended absence, trying to solve the freezing problem but now have an issue with compiling, and have attached the relevant portion of the error message.
I am using IDE 1.8.9 and ESP 8266 board manager 2.4.2
I note that you recommend the SHT31 T/H sensor in lieu of HTU21D and am waiting for mine to arrive.
Regards
Jim
 

Code:

 
       In file included from C:\Users\JBA\Documents\Arduino\WeatherDuino_AQM_II\v120\software\WeatherDuino_AQM_ESP8266_ASK_v120_b006\WeatherDuino_AQM_ESP8266_ASK_v120_b006.ino:3:0:

C:\Users\JBA\Documents\Arduino\libraries\HTU21D/HTU21D.h:31:7: error: previous definition of 'class HTU21D'

 class HTU21D {

       ^

Using library ArduinoOTA at version 1.0 in folder: C:\Users\JBA\AppData\Local\Arduino15\packages\esp8266\hardware\esp8266\2.4.2\libraries\ArduinoOTA 
Using library ESP8266WiFi at version 1.0 in folder: C:\Users\JBA\AppData\Local\Arduino15\packages\esp8266\hardware\esp8266\2.4.2\libraries\ESP8266WiFi 
Using library HTU21D in folder: C:\Users\JBA\Documents\Arduino\libraries\HTU21D (legacy)
Using library Wire at version 1.0 in folder: C:\Users\JBA\AppData\Local\Arduino15\packages\esp8266\hardware\esp8266\2.4.2\libraries\Wire 
Using library ArduinoJson at version 5.13.2 in folder: C:\Users\JBA\Documents\Arduino\libraries\ArduinoJson 
Using library SoftwareSerial at version 1.0 in folder: C:\Users\JBA\AppData\Local\Arduino15\packages\esp8266\hardware\esp8266\2.4.2\libraries\SoftwareSerial 
Using library Timer in folder: C:\Users\JBA\Documents\Arduino\libraries\Timer (legacy)
Using library ESP8266HTTPClient at version 1.1 in folder: C:\Users\JBA\AppData\Local\Arduino15\packages\esp8266\hardware\esp8266\2.4.2\libraries\ESP8266HTTPClient 
Using library ESP8266WebServer at version 1.0 in folder: C:\Users\JBA\AppData\Local\Arduino15\packages\esp8266\hardware\esp8266\2.4.2\libraries\ESP8266WebServer 
Using library ESP8266mDNS in folder: C:\Users\JBA\AppData\Local\Arduino15\packages\esp8266\hardware\esp8266\2.4.2\libraries\ESP8266mDNS (legacy)
Using library TimezoneESP8266 in folder: C:\Users\JBA\Documents\Arduino\libraries\TimezoneESP8266 (legacy)
Using library Time at version 1.5 in folder: C:\Users\JBA\Documents\Arduino\libraries\Time 
Using library RadioHead in folder: C:\Users\JBA\Documents\Arduino\libraries\RadioHead (legacy)
Using library SPI at version 1.0 in folder: C:\Users\JBA\AppData\Local\Arduino15\packages\esp8266\hardware\esp8266\2.4.2\libraries\SPI 
Using library esp8266-OLED-SSD1306 at version 3.2.7 in folder: C:\Users\JBA\Documents\Arduino\libraries\esp8266-OLED-SSD1306 
Using library Adafruit_SHT31 at version 1.0.0 in folder: C:\Users\JBA\Documents\Arduino\libraries\Adafruit_SHT31 
exit status 1
Error compiling for board LOLIN(WEMOS) D1 R2 & mini.

[werk_ag]

Hello Jim,

WeatherDuino_AQM_ESP8266_ASK_v120_b006 compiles fine with IDE 1.8.9 and ESP 8266 board manager 2.4.2, for both types of supported T/H sensors (HTU21 or SHT31).
Please check again, software files and the used library.

Rgs

[Barrow4491]

Hello Jim,

WeatherDuino_AQM_ESP8266_ASK_v120_b006 compiles fine with IDE 1.8.9 and ESP 8266 board manager 2.4.2, for both types of supported T/H sensors (HTU21 or SHT31).
Please check again, software files and the used library.

Rgs

I am at a loss, I have re-downloaded the software and checked the libraries and board manager still to no avail.
Any ideas would be appreciated. I will have to reload the software to change the t/ h sensor when it arrives
Regards
Jim

[engolling]

C:\Users\JBA\Documents\Arduino\libraries\HTU21D/HTU21D.h:31:7: error: previous definition of 'class HTU21D'

I'm wondering why there is a backslash before the .h file.

I just compiled the package of werk and it compiles fine out of the box here. Could it be that you have some library twice or something like this.

Regards,
engolling

[Barrow4491]

C:\Users\JBA\Documents\Arduino\libraries\HTU21D/HTU21D.h:31:7: error: previous definition of 'class HTU21D'

I'm wondering why there is a backslash before the .h file.

I just compiled the package of werk and it compiles fine out of the box here. Could it be that you have some library twice or something like this.

Regards,
engolling

Werk / engolling
I have been trying to work the problem out an then finally decided to delete every file and download of anything to do with AQM II and start from scratch.
The file compiled first time as expected, an all i can put it down to is a recent upgrade of Windows 10 on my computer, because of the issue of no ongoing support for the previous version by Microsoft.
Thank you for your support and thoughts on the matter.
Regards
Jim