Thanks for the reply
re i2c and SPI enabled in raspi-config? yes
Is there anything different between the units that work and the units that don’t? no, same os, same firmware
Do the Python examples work? I just use the C examples. I will try but I am not sure that it is different.
Have you updated the operating system? No. I want to keep the same OS
(That can cause issues)
Have you tried re-installing the Dexter libraries? No but I think this will be my next step. Actually I am a teacher and I use these kits for lab courses. My next session will be Tuesday the next week and I will re-install the dexter libraries.
Have you tried exchanging modules/Raspberry Pis/SD cards between the working units and the ones that don’t work? Yes, I switch r-pi and and modules dexter and clearly the problem seems to come from the module. Maybe the module have been hardware issues. But i do not know how to check.
Thanks for you help