This Strummer is a combination of my early Strumpad project with a piano keyboard. The Arduino software only needs to be minimally adjusted. The Strummer will be easy to convert to a right or a left hand guitar playing, this is why there are extra 4 holes for the piano keys. 

Today the PCB files are done and will be sent to a PCB house. All components are easy to find and standard. They should fit a 100mm x 100mm box that I already purchased. The 100mm x 100mm format is the best value for the price at the PCB houses.