Unlike most other ARM processors, this one comes in a 28 pin DIP package and works great on a breadboard. It does require 3.3V, but it is 5V tolerant on digital inputs (and, of course, a 3.3V ...

which was a bit too wide for common solderless breadboards. Since then I started over, having fixed the width problem, and ended up with a module that looks decidedly… cuter. To back up a ...