The keypad circuit's output pulse drives the external interrupt input, RA 2, of a Microchip 16F630 microcontroller. Listing 1 presents an interrupt routine for the 16F630 that measures the pulse width ...

Any X-Y switch matrix can be considered with this circuit, which simplifies decoding of the common 4x4 keypad matrix and eliminates having to scan rows or columns.

Using eight digital inputs, this circuit simplifies decoding of the common membrane 4x4 keypad matrix and eliminates the traditional requirement of scanning rows or columns. Any X-Y switch matrix ...