[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 ...

If you’re not familiar with the 555 timer, suffice it to say that this ... total propagation delay (~ 5.2 ns) plus some small R and C of the circuit itself. When used with typical RC values ...