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4.2 - 4x4 Keypad

The 4x4 keyboard, also known as the matrix keyboard, is a matrix of 16 keys excluded in a single panel.

The keypad can be found on devices that mainly require digital input, such as calculators, TV remote controls, push-button phones, vending machines, ATMs, combination locks, and digital door locks.

In this project, we will learn how to determine which key is pressed and get the related key value.

Schematic

sch_keypad_ar

The rows of the keyboard (G2 ~ G5) are programmed to go high; if one of G6 ~ G9 is read high, then we know which key is pressed.

For example, if G6 is read high, then numeric key 1 is pressed; this is because the control pins of numeric key 1 are G2 and G6, when numeric key 1 is pressed, G2 and G6 will be connected together and G6 is also high.

Wiring

wiring_keypad_ar

Code

Note

You can open the file 4.2_4x4_keypad.ino under the path of euler-kit/arduino/4.2_4x4_keypad.
Or copy this code into Arduino IDE.
Then select the Raspberry Pi Pico board and the correct port before clicking the Upload button.
The Adafruit Keypad library is used here, you can install it from the Library Manager.

After the program runs, the Shell will print out the keys you pressed on the Keypad.

How it works

Including the Library

We start by including the Adafruit_Keypad library, which allows us to easily interface with the keypad.
```
#include "Adafruit_Keypad.h"
```

Keypad Configuration

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] = { 2, 3, 4, 5 };
byte colPins[COLS] = { 8, 9, 10, 11 };

The ROWS and COLS constants define the dimensions of the keypad.
keys is a 2D array storing the label for each button on the keypad.
rowPins and colPins are arrays that store the Arduino pins connected to the keypad rows and columns.

Initialize Keypad

Create an instance of Adafruit_Keypad called myKeypad and initialize it.

Adafruit_Keypad myKeypad = Adafruit_Keypad(makeKeymap(keys), rowPins, colPins, ROWS, COLS);

setup() Function

Initialize Serial communication and the custom keypad.
```
void setup() {
  Serial.begin(9600);
  myKeypad.begin();
}
```

Main Loop

Check for key events and display them in the Serial Monitor.

void loop() {
  myKeypad.tick();
  while (myKeypad.available()) {
    keypadEvent e = myKeypad.read();
    Serial.print((char)e.bit.KEY);
    if (e.bit.EVENT == KEY_JUST_PRESSED) Serial.println(" pressed");
    else if (e.bit.EVENT == KEY_JUST_RELEASED) Serial.println(" released");
  }
  delay(10);
}