The source code has banner ads built in and you just need to enter in your AdMob adUnitID in the activity_temp_converter.xml file to get ad money. I give permission to anyone to put in their own adUnitId and receive their own ad money. I think this is still compliant with GPLv3 but let me know if that's not true. I'm pretty new to open source so please be patient with any mistakes.
App icons made with the open source Android Asset Studio (http://romannurik.github.io/AndroidAssetStudio/icons-launcher.html).