here is a bit about them:http://en.wikipedia.org/wiki/Stylophone
By following this circuit diagram:
My god, thats a tiny diagram.
Click on it, and you will get a larger version.
Right-click on it, open it in a new tab or window, and then change the part of the url that says MEDIUM to LARGE (it is case sensitive), and you will get a larger one.
It is now!!! Here is my design which should be easy to make. https://www.instructables.com/id/A-Stylophone/
I'm not certain (I only had the original diagram because I have a Stylophone). You might be better posting that as a fresh question.
I bought one of those mini stylophones from thinkgeek... it's really cool and tiny. I've always wished it had buttons though...
Or the 21st century equivalent ;¬)