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2.1.8 Keypad¶

Introduction¶

A keypad is a rectangular array of buttons. In this project, We will use it input characters.

Required Components¶

In this project, we need the following components.

It’s definitely convenient to buy a whole kit, here’s the link:

Name	ITEMS IN THIS KIT	LINK
Raphael Kit	337	Raphael Kit

You can also buy them separately from the links below.

COMPONENT INTRODUCTION	PURCHASE LINK
GPIO Extension Board	BUY
Breadboard	BUY
Jumper Wires	BUY
Resistor	BUY
Keypad	-

Schematic Diagram¶

Experimental Procedures¶

Step 1: Build the circuit.

Step 2: Open the code file.

cd ~/raphael-kit/python-pi5

Step 3: Run.

sudo python3 2.1.8_Keypad_zero.py

After the code runs, the values of pressed buttons on keypad (button Value) will be printed on the screen.

Code

Note

You can Modify/Reset/Copy/Run/Stop the code below. But before that, you need to go to source code path like raphael-kit/python-pi5. After modifying the code, you can run it directly to see the effect.

#!/usr/bin/env python3
from gpiozero import DigitalOutputDevice, Button
from time import sleep

class Keypad:
    def __init__(self, rows_pins, cols_pins, keys):
        """
        Initialize the Keypad with specified row and column pins and keypad layout.
        :param rows_pins: List of GPIO pins for the rows.
        :param cols_pins: List of GPIO pins for the columns.
        :param keys: List of keys in the keypad layout.
        """
        # Initialize row pins as DigitalOutputDevice
        self.rows = [DigitalOutputDevice(pin) for pin in rows_pins]
        # Initialize column pins as Buttons
        self.cols = [Button(pin, pull_up=False) for pin in cols_pins]
        self.keys = keys  # Set the keypad layout

    def read(self):
        """
        Read the currently pressed keys on the keypad.
        :return: A list of pressed keys.
        """
        pressed_keys = []
        # Scan each row and column to identify pressed keys
        for i, row in enumerate(self.rows):
            row.on()  # Enable the current row
            for j, col in enumerate(self.cols):
                if col.is_pressed:  # Check if the column button is pressed
                    # Calculate the key index based on row and column
                    index = i * len(self.cols) + j
                    pressed_keys.append(self.keys[index])
            row.off()  # Disable the current row
        return pressed_keys

try:
    # Configure rows, columns, and keypad layout
    rows_pins = [18, 23, 24, 25]
    cols_pins = [10, 22, 27, 17]
    keys = ["1", "2", "3", "A",
            "4", "5", "6", "B",
            "7", "8", "9", "C",
            "*", "0", "#", "D"]

    # Create an instance of the Keypad class
    keypad = Keypad(rows_pins, cols_pins, keys)
    last_key_pressed = []

    # Continuously read the keypad and print newly pressed keys
    while True:
        pressed_keys = keypad.read()
        if pressed_keys and pressed_keys != last_key_pressed:
            print(pressed_keys)  # Print the list of pressed keys
            last_key_pressed = pressed_keys
        sleep(0.1)  # Short delay to reduce CPU load

except KeyboardInterrupt:
    # Handle a keyboard interrupt (Ctrl+C) for a clean exit
    pass

Code Explanation

Imports the DigitalOutputDevice and Button classes from the gpiozero library, and the sleep function for delays.

#!/usr/bin/env python3
from gpiozero import DigitalOutputDevice, Button
from time import sleep

Defines the Keypad class. The __init__ method initializes the keypad with given row and column pins and keys. The read method scans the keypad and returns a list of pressed keys.

class Keypad:
    def __init__(self, rows_pins, cols_pins, keys):
        """
        Initialize the Keypad with specified row and column pins and keypad layout.
        :param rows_pins: List of GPIO pins for the rows.
        :param cols_pins: List of GPIO pins for the columns.
        :param keys: List of keys in the keypad layout.
        """
        # Initialize row pins as DigitalOutputDevice
        self.rows = [DigitalOutputDevice(pin) for pin in rows_pins]
        # Initialize column pins as Buttons
        self.cols = [Button(pin, pull_up=False) for pin in cols_pins]
        self.keys = keys  # Set the keypad layout

    def read(self):
        """
        Read the currently pressed keys on the keypad.
        :return: A list of pressed keys.
        """
        pressed_keys = []
        # Scan each row and column to identify pressed keys
        for i, row in enumerate(self.rows):
            row.on()  # Enable the current row
            for j, col in enumerate(self.cols):
                if col.is_pressed:  # Check if the column button is pressed
                    # Calculate the key index based on row and column
                    index = i * len(self.cols) + j
                    pressed_keys.append(self.keys[index])
            row.off()  # Disable the current row
        return pressed_keys

Sets up the GPIO pins for rows and columns and defines the keypad layout.

try:
    # Configure rows, columns, and keypad layout
    rows_pins = [18, 23, 24, 25]
    cols_pins = [10, 22, 27, 17]
    keys = ["1", "2", "3", "A",
            "4", "5", "6", "B",
            "7", "8", "9", "C",
            "*", "0", "#", "D"]

Creates an instance of the Keypad class with the specified configuration.

try:
    ...

    # Create an instance of the Keypad class
    keypad = Keypad(rows_pins, cols_pins, keys)
    last_key_pressed = []

Continuously reads the keypad for pressed keys, prints any changes in the key state, and introduces a short delay to reduce CPU load. Catches a KeyboardInterrupt (like Ctrl+C) to allow for a graceful exit from the script.

try:
    ...

    # Continuously read the keypad and print newly pressed keys
    while True:
        pressed_keys = keypad.read()
        if pressed_keys and pressed_keys != last_key_pressed:
            print(pressed_keys)  # Print the list of pressed keys
            last_key_pressed = pressed_keys
        sleep(0.1)  # Short delay to reduce CPU load

except KeyboardInterrupt:
    # Handle a keyboard interrupt (Ctrl+C) for a clean exit
    pass