I find this page recentely, and it’s seems very easy and interesting !
A clone of the famous Drum machine with only an ARDUINO
Schematic and code by Jan Ostman .
the page with info and schematic :
and the code :
Do you know this project ? what do you think about it
Can we make a module with trigger input for each sound with some little modifications ?
another schem with clock and reset out (that is in the code)
His GitHub with others projects (2 others drums and string)