It’s a freeform circuit that synthesizes sound using 555 timers. The circuit has been ... standard materials of 3D-printed plastic and FR4 PCB. Go forth and explore what you can do!

And of course, if an ATtiny was used, there should have simply been a 555 timer ... circuits. This comes at a great cost, however. The 555 chips take up an unnecessarily large area on the PCB ...