The cheap piezo elements I mentioned earlier just arrived, together with some minor bits and bobs (pic also has some locally produced custom knobs; experimenting with different colour schemes).
I guess I could do a bit of building, but my workbench is a mess; I decided to go through a couple of boxes with random stuff and put everything where it should be, but I keep finding unexpected things (a bunch of 4017s? why & when did I order these 4.3 V zeners? and ten 330k resistors?? etc) so now my workspace is full of random stuff too.