2.1.5 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.

Schematic Diagram¶

Experimental Procedures¶

Step 1: Build the circuit.

Step 2: Open the code file.

cd ~/davinci-kit-for-raspberry-pi/python-pi5

Step 3: Run.

sudo python3 2.1.5_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 davinci-kit-for-raspberry-pi/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