My main problem was the poor connection due to used jumper wires.
After replacing the Arduino Uno by an Nano and replacing all the jumpers it is working.
Posts made by JohanG
Connecting two identical sensors.
I discovered recently Arduino and Domoticz.
I installed Domoticz on a Windows 10 laptop, build a serial gateway, a light sensor and a temp sensor.
Everyting is working perfect.
I made another temp sensor , but in domoticz I cannot find it.
I used for both temp sensors the sketch the My Sensors site.
The only difference is: the first one has an Arduino Nano, the second an Arduino uno.
What am I doing wrong ?