Interfacing a 4×4 Keypad with Arduino UNO: Step-by-Step Guide

In this guide, we will walk you through the process of interfacing a 4×4 keypad with an Arduino UNO. This step-by-step tutorial will provide you with detailed instructions on connecting and programming the keypad, making it easy for you to incorporate this versatile input device into your Arduino projects. Whether you’re a beginner or an experienced Arduino enthusiast, this guide will help you efficiently set up and use a 4×4 keypad with your Arduino UNO.

Overview of 4×4 Matrix Keypad

A keypad serves as an input device that detects and processes user key presses.

A 4×4 keypad arduino is structured with 4 rows and 4 columns, with switches positioned at the intersections.

When a key is pressed, it connects the corresponding row and column where the switch is located.

For additional details on the keypad and its usage, see the 4×4 Keypad topic in the sensors and modules section.

Connection Diagram of 4×4 Keypad with Arduino UNO

Reading a 4×4 Keypad with Arduino Uno

Learn how to read key presses from a 4×4 keypad and display them on the Arduino serial terminal.

We’ll use the Keypad library by Mark Stanley and Alexander Brevig for this task.

• Download the Library: Obtain the library from here.

• Install the Library: Extract the library and add it to the libraries folder in your Arduino IDE. For detailed instructions on adding a custom library to the Arduino IDE and using examples, refer to “Adding Library to Arduino IDE” in the Basics section.

• Import the Library: Find more information on the Keypad library and how to import it directly into the Arduino IDE here.

• Load the Example Sketch: Once the library is added, open the Arduino IDE and load the “CustomKeypad” example sketch from the newly added library.

Solution:
To avoid this, use pins other than 0 and 1. Refer to the sketch below for guidance:

byte rowPins[ROWS] = {R1, R2, R3, R4}; // Connect to the row pinouts of the keypad
byte colPins[COLS] = {C1, C2, C3, C4}; // Connect to the column pinouts of the keypad

4×4 Keypad Code for Arduino Uno

#include <Keypad.h>

const byte ROWS = 4; /* four rows */
const byte COLS = 4; /* four columns */
/* define the symbols on the buttons of the keypads */
char hexaKeys[ROWS][COLS] = {
  {'0','1','2','3'},
  {'4','5','6','7'},
  {'8','9','A','B'},
  {'C','D','E','F'}
};
byte rowPins[ROWS] = {10, 11, 12, 13}; /* connect to the row pinouts of the keypad */
byte colPins[COLS] = {6, 7, 8, 9}; /* connect to the column pinouts of the keypad */

/* initialize an instance of class NewKeypad */
Keypad customKeypad = Keypad( makeKeymap(hexaKeys), rowPins, colPins, ROWS, COLS); 

void setup(){
Serial.begin(9600);
}

void loop(){
  char customKey = customKeypad.getKey();

  if (customKey){
Serial.println(customKey);
  }
}

Functions Used

1.  makeKeymap(keys)

• Initializes the internal keymap to match the user-defined keymap.

2.  Keypad customKeypad = Keypad( makeKeymap(keys), rowPins, colPins, rows, cols)

• Creates an object customKeypad of the Keypad class and initializes it.
• rowPins and colPins are the Arduino pins connected to the keypad’s rows and columns.
• rows and cols specify the number of rows and columns on the keypad.

3.  customKeypad.getKey()

• Identifies which key is pressed on the keypad.

1-Wire interfacing of Keypad With Arduino

The previously described interfacing method uses 8 GPIO pins of the Arduino board. However, by utilizing the 1-wire interfacing method, we can achieve the same functionality using only 1 GPIO pin.

This technique employs a simple voltage divider to create distinct voltages for each key press.

Here’s how to connect a keypad to an Arduino using a single GPIO pin.

Connection Diagram of 1-Wire Keypad Interface With Arduino

Parts Required

One Wire Keypad Code for Arduino Uno

void setup() {
  Serial.begin(9600);	/* Define baud rate for serial communication */
}

void loop() {
  int adc_val;
  adc_val = analogRead(A1);	/* Read input from keypad */
  if (adc_val>850)
  {
    Serial.print("Key Pressed : ");
    Serial.println("0");
    delay(100);
  }
  else if ( adc_val>450  && adc_val<510)
  {
    Serial.print("Key Pressed : ");
    Serial.println("1");
    delay(100);
  }
  else if ( adc_val>300  && adc_val<350)
  {
    Serial.print("Key Pressed : ");
    Serial.println("2");
    delay(100);
  }
  else if ( adc_val>230  && adc_val<270)
  {
    Serial.print("Key Pressed : ");
    Serial.println("3");
    delay(100);
  }
  else if ( adc_val>160  && adc_val<180)
  {
    Serial.print("Key Pressed : ");
    Serial.println("4");
    delay(100);
  }
  else if ( adc_val>145  && adc_val<155)
  {
    Serial.print("Key Pressed : ");
    Serial.println("5");
    delay(100);
  }
  else if ( adc_val>125  && adc_val<135)
  {
    Serial.print("Key Pressed : ");
    Serial.println("6");
    delay(100);
  }
  else if ( adc_val>105  && adc_val<120)
  {
    Serial.print("Key Pressed : ");
    Serial.println("7");
    delay(100);
  }
  else if ( adc_val>92  && adc_val<99)
  {
    Serial.print("Key Pressed : ");
    Serial.println("8");
    delay(100);
  }
  else if ( adc_val>82  && adc_val<90)
  {
    Serial.print("Key Pressed : ");
    Serial.println("9");
    delay(100);
  }
  else if ( adc_val>77  && adc_val<81)
  {
    Serial.print("Key Pressed : ");
    Serial.println("A");
    delay(100);
  }
  else if ( adc_val>72  && adc_val<76)
  {
    Serial.print("Key Pressed : ");
    Serial.println("B");
    delay(100);
  }
  else if ( adc_val>63  && adc_val<68)
  {
    Serial.print("Key Pressed : ");
    Serial.println("C");
    delay(100);
  }
  else if ( adc_val>60  && adc_val<62)
  {
    Serial.print("Key Pressed : ");
    Serial.println("D");
    delay(100);
  }
  else if ( adc_val>57  && adc_val<59)
  {
    Serial.print("Key Pressed : ");
    Serial.println("E");
    delay(100);
  }
  else if( adc_val>52  && adc_val<56)
  {
    Serial.print("Key Pressed : ");
    Serial.println("F");
    delay(100);
  }
  else
  {
	  
  }
  delay(100);
}

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