Pinout

4×4 matrix membrane keypad (8-pin ribbon) pinout

Pins

1: ROW 1 — the 1 2 3 A row (the keypad is a passive switch matrix: no VCC, no GND, no polarity and no electronics, so a wrong connection cannot damage it — it just reads the wrong key)
2: ROW 2 — the 4 5 6 B row
3: ROW 3 — the 7 8 9 C row
4: ROW 4 — the * 0 # D row
5: COLUMN 1 — the 1 4 7 * column
6: COLUMN 2 — the 2 5 8 0 column
7: COLUMN 3 — the 3 6 9 # column
8: COLUMN 4 — the A B C D column (scan by driving one column LOW at a time and reading the four rows with INPUT_PULLUP — no external resistors needed; because there are no diodes in the matrix, three keys held together can ghost a fourth)

Keys	16 (4 rows × 4 columns)
Type	Passive switch matrix, no diodes
Power	None needed
Connector	8-pin female header, 2.54 mm pitch
Contact rating	24 V DC, 30 mA max (typical listing)
Contact bounce	≤ 5 ms
Scanning	4 outputs + 4 inputs with pull-ups
Pad size	≈69 × 77 mm (typical)