You have a Due, not a Duemilanove. The names are sort of similar but these are two very different boards.
You need to do this:
- Tools > Board > Boards Manager
- Wait for the downloads to finish.
- Click on "Arduino SAM Boards (32-bits ARM Cortex-M3)"
- Click "Install"
- Wait for installation to finish. If you are prompted to install a driver, confirm.
- Click "Close".
- Tools > Board > Arduino Due (Programming Port)
Make sure you have the USB connected to the Programming Port on the Due:
ardxx1:
I get an 'Serial port COM 1 (port busy) error when I run the Serial monitor to view the sensor output.
It's unlikely (though possible) that your Due is on COM1. Please make sure you have the port of the Due selected from the Tools > Port menu. The correct port should be labeled as "Arduino Due" in the menu.