Introduction: App Inventor + Arduino Analog Voltmeter
There are many arduino voltmeter project on the net.
Im upgraded little, and replace the lcd to the android phone.
In the android app, the scale is for 8Volt, but that not the max.
The app inventor part is based on imagesprite rotating. Every volt is 22.5° (180/8)
App is in the video, arduino code download link in video description as always.