Membrane keypad on pins 9 to 2, on an Arduino Uno

// A 4x4 membrane keypad: every key you press, printed.
//
//   keypad rows R1 to R4    -> pins 9, 8, 7, 6
//   keypad columns C1 to C4 -> pins 5, 4, 3, 2
//
// Sixteen keys on eight wires. Each key joins one row wire to one column wire
// when it is pressed. The Keypad library drives the columns low one at a time
// and reads the rows, so it can tell exactly which crossing closed.
//
// Click a key on the canvas.

#include <Keypad.h>

const byte ROWS = 4;
const byte COLS = 4;
char keys[ROWS][COLS] = {
    {'1', '2', '3', 'A'},
    {'4', '5', '6', 'B'},
    {'7', '8', '9', 'C'},
    {'*', '0', '#', 'D'},
};
byte rowPins[ROWS] = {9, 8, 7, 6};
byte colPins[COLS] = {5, 4, 3, 2};

Keypad keypad = Keypad(makeKeymap(keys), rowPins, colPins, ROWS, COLS);

void setup() {
  Serial.begin(9600);
  Serial.println("Mokxi Uno: keypad, rows on 9 to 6, columns on 5 to 2. Press a key.");
}

void loop() {
  char key = keypad.getKey();
  if (key) {
    Serial.print("key: ");
    Serial.println(key);
  }
}