I've been asked to bring an old ROLLS midi pedalboard into 2017. It needed to send midi note on and midi note off, whereas the original circuit only sent program change.
the board was really old fashion, 90's maybe. No microcontroller, all digital logic.
A cheap STM32f0 was perfect for that very low end application. The board was designed with 0805 SMD packages.
When PCBs are order form China they come by 5 or 10 pieces. The cost is lower that way. To avoid waste, I designed the PCB to be able to use it for any other MIDI related applications. Therefore all the unused pins are available. This went handy for another project, a small midi controller.
Another important factor was the price, I wanted the pcb to cost the less possible. Hence the use of 0805 package.
Designing the board was a bit tedious as I needed to take exact measurements to place correctly the 7segment displays and the power connector.
Overall the result is what I wanted and work wonderfully.