If they use an Arduino, it should have been an ATtiny. And of course, if an ATtiny was used, there should have simply been a 555 timer. This time, however, [Tim] decided to actually show how this ...

[R-B] designed a 555 timer circuit to scan a keypad. Keypads are common interfaces for small projects and require row and column scanning by a microcontroller. [R-B’s] setup allows you to reduce ...