I chose to use the raw values returned from the web4robot i2c display as a model for all the keypads.
A normal keypad is laid out
12 Key (4x3)
| 1 | 2 | 3 |
| 4 | 5 | 6 |
| 7 | 8 | 9 |
| * | 0 | # |
16 Key (4x4)
| 1 | 2 | 3 | A |
| 4 | 5 | 6 | B |
| 7 | 8 | 9 | C |
| * | 0 | # | D |
| Key Pressed | Value returned by keypad() |
|---|---|
| 1 | 1 |
| 2 | 2 |
| 3 | 3 |
| A | 4 |
| 4 | 5 |
| 5 | 6 |
| 6 | 7 |
| B | 8 |
| 7 | 9 |
| 8 | 10 |
| 9 | 11 |
| C | 12 |
| * | 13 |
| 0 | 14 |
| # | 15 |
| D | 16 |