Hello,
When installing APP Inventor 2, I got a message saying that AIT STARTER could not be installed on my machine.
So I downloaded the latest version of AIT STARTER but, when I launch the emulator, I have the message attached.
Is it a location problem and if so,in which directory should I install AIT STARTER?
Jean-Michel
Hello Loco
App Inventor is the right choice to work with your Arduino applications - but it is not installed, it is a "web App" that runs in your Browser (Firefox or Chrome).
AI Starter runs the Emulator, but even if perfect it would be of little use because you cannot communicate with micro-controllers such as Arduino from the Emulator. It is in fact best to generate an APK (phone App) and test your project directly on your phone, but App Inventor also has a phone App, the "Companion" that enables you to test your App while modifying it in App Inventor.
So, remove the Emulator from your thoughts and work with the hardware 
Are you thinking of using Bluetooth to communicate with your Arduino?
I don't quite understand the answer.
To test the APP, there are 3 solutions: Companion, Emulator and USB.
I already use Companion and I wanted to test Emulator but it doesn't work because of AIT Starter.
When I use APP Inventor to make my APP, it does not know that I am going to address an ARDUINO.
Otherwise, indeed, I dialogue with the ARDUINO in Bluetooth and besides I have, at the moment, a big problem, I think of parasites (due to the motors) which blocks me the serial link.
Jean-Michel
Jean-Michel -to test your App, there is the Companion App, the Emulator and simply generating an APK (the installable version of your App).
USB is simply a way to connect your PC to your phone but it is generally not necessary as you can scan instead.
If your App Project uses Bluetooth or other external communications it is not going to work in the Emulator. The Emulator is anyway better used for testing snippets of code rather than a whole App. There are 3rd Party Emulators such as BlueStacks, that can perform the basics fairly well, but honestly the best way to test your App is on your Android device.