 One potential application for this is to read a standard (4×3) 12-key numeric keypad using only 4 I/O lines.The traditional row-column scan method requires 4 + 3 = 7 I/O lines.Thus Charlieplexing saves 3 I/O lines; however it adds the expense of 12 diodes, (since the diodes are only free when LEDs are used).