I’ve been able to connect my Arduino Uno to my RPi 3 over USB and finally to Cayenne. All you have to do is run the “cayenne-ser.sh” shell script on the Pi while the Arduino is connected and have the CayenneSerial.h library running on your Arduino. My Arduino sketch looks something like this:
I believe, upon first running the script, the command line will prompt you with a command to install a utility called “Socat.” Once you have installed Socat, run the script again and it should give you this:
Here, all you have to do is type in the address of your USB-Arduino connection (which it should give you in the brackets). So in my case, it is /dev/ttyACM0, so i would type it after the colon.
If all goes well, your terminal should look something like this:
Hopefully this is what you’re asking and hopefully this helps!
-Ken