Tutorial 4- Matrix Keypad

In this tutorial, we will learn how to connect a matrix keypad to the Raspberry Pi 5 and receive the input characters.

Introduction #

A keypad is a rectangular array of buttons. In this tutorial, we’ll learn how to connect a matrix keypad to the Raspberry Pi 5 board. We’ll write a Micropython program that reads the different character inputs.

Components Needed #

Fritzing Diagram #

Connect the Keypad to your Raspberry Pi as shown in the following diagram.

Code #

from gpiozero import DigitalOutputDevice, Button
from time import sleep

# 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"]

# Initialize row pins as DigitalOutputDevice
rows = [DigitalOutputDevice(pin) for pin in rows_pins]
# Initialize column pins as Buttons
cols = [Button(pin, pull_up=False) for pin in cols_pins]

def read_keypad():
    """
    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(rows):
        row.on()  # Enable the current row
        for j, col in enumerate(cols):
            if col.is_pressed:  # Check if the column button is pressed
                # Calculate the key index based on row and column
                index = i * len(cols) + j
                pressed_keys.append(keys[index])
        row.off()  # Disable the current row
    return pressed_keys

# Main loop to continuously read the keypad and print newly pressed keys
last_key_pressed = []

print("Press keys on the keypad. Press Ctrl+C to exit.")
while True:
    pressed_keys = read_keypad()
    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

Code Overview #

Initialization: The rows and columns are initialized as lists of DigitalOutputDevice and Button objects, respectively, outside any class.

Function read_keypad(): This function scans the keypad for pressed keys, similar to the previous class method, and returns a list of pressed keys.

Main Loop: The main loop continuously calls the read_keypad() function to check for pressed keys and prints them if they differ from the last recorded keys.

No Class Structure: The code is now simpler and does not use classes, making it straightforward for basic usage.

Code Explanation #

Imports and Setup #

from gpiozero import DigitalOutputDevice, Button
from time import sleep

# 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"]

# Initialize row pins as DigitalOutputDevice
rows = [DigitalOutputDevice(pin) for pin in rows_pins]
# Initialize column pins as Buttons
cols = [Button(pin, pull_up=False) for pin in cols_pins]

Imports: The necessary classes from the gpiozero library are imported.

Pin Configuration: GPIO pins for rows and columns are defined, along with the keypad layout.

Initialization: Row pins are set as DigitalOutputDevice, and column pins are set as Button instances.

Keypad Reading Function #

def read_keypad():
    pressed_keys = []
    for i, row in enumerate(rows):
        row.on()  # Enable the current row
        for j, col in enumerate(cols):
            if col.is_pressed:  # Check if the column button is pressed
                index = i * len(cols) + j  # Calculate the key index
                pressed_keys.append(keys[index])  # Append the pressed key
        row.off()  # Disable the current row
    return pressed_keys

Function Definition: read_keypad() scans the keypad to check which keys are pressed.

Row and Column Scanning: Each row is activated in turn, and the corresponding columns are checked for button presses.

Key Index Calculation: The index of the pressed key is calculated based on the active row and column, and the key is added to the pressed_keys list.

Main Loop #

last_key_pressed = []
print("Press keys on the keypad. Press Ctrl+C to exit.")
while True:
    pressed_keys = read_keypad()  # Read current pressed keys
    if pressed_keys and pressed_keys != last_key_pressed:
        print(pressed_keys)  # Print newly pressed keys
        last_key_pressed = pressed_keys  # Update last pressed keys
    sleep(0.1)  # Short delay to reduce CPU load

Last Key Tracking: A list last_key_pressed is initialized to keep track of the last detected keys.

Continuous Loop: The program enters an infinite loop to continuously read the keypad.

Key Printing: If new keys are detected, they are printed, and the last pressed keys list is updated.

CPU Load Management: A brief sleep of 0.1 seconds is included to reduce CPU usage.

Conclusion #

This code initializes a keypad using GPIO pins, continuously reads the pressed keys, and prints them to the console. The structure is straightforward, making it easy to understand and modify for basic keypad functionality.