🔢 4x4 Matrix Keypad Interface with Arduino

This project demonstrates how to interface a 4x4 matrix keypad with an Arduino UNO to read and display key presses on the Serial Monitor.

🧠 Working Principle

A 4x4 keypad consists of 4 rows and 4 columns (total 16 keys). When a key is pressed, it connects a specific row to a column. The Arduino scans each row sequentially and checks which column input goes LOW — this identifies the pressed key.

🧩 Components Required Component Quantity Arduino UNO 1 4x4 Matrix Keypad 1 Jumper Wires 8 Breadboard 1 USB Cable 1 ⚡ Circuit Connections Keypad Pin Arduino Pin R1 13 R2 12 R3 11 R4 10 C1 9 C2 8 C3 7 C4 6

Columns are set as INPUT_PULLUP and rows as OUTPUT to scan key presses.

💻 Arduino Code

const int C1 = 9;
const int C2 = 8;
const int C3 = 7;
const int C4 = 6;

const int R1 = 13;
const int R2 = 12;
const int R3 = 11;
const int R4 = 10;

void Keypad()
{
  digitalWrite(R1,LOW);
  digitalWrite(R2,HIGH);
  digitalWrite(R3,HIGH);
  digitalWrite(R4,HIGH);
  if(digitalRead(C1) == LOW) { Serial.print('1'); delay(400); }
  if(digitalRead(C2) == LOW) { Serial.print('2'); delay(400); }
  if(digitalRead(C3) == LOW) { Serial.print('3'); delay(400); }
  if(digitalRead(C4) == LOW) { Serial.print('A'); delay(400); }

  digitalWrite(R1,HIGH);
  digitalWrite(R2,LOW);
  digitalWrite(R3,HIGH);
  digitalWrite(R4,HIGH);
  if(digitalRead(C1) == LOW) { Serial.print('4'); delay(400); }
  if(digitalRead(C2) == LOW) { Serial.print('5'); delay(400); }
  if(digitalRead(C3) == LOW) { Serial.print('6'); delay(400); }
  if(digitalRead(C4) == LOW) { Serial.print('B'); delay(400); }

  digitalWrite(R1,HIGH);
  digitalWrite(R2,HIGH);
  digitalWrite(R3,LOW);
  digitalWrite(R4,HIGH);
  if(digitalRead(C1) == LOW) { Serial.print('7'); delay(400); }
  if(digitalRead(C2) == LOW) { Serial.print('8'); delay(400); }
  if(digitalRead(C3) == LOW) { Serial.print('9'); delay(400); }
  if(digitalRead(C4) == LOW) { Serial.print('C'); delay(400); }

  digitalWrite(R1,HIGH);
  digitalWrite(R2,HIGH);
  digitalWrite(R3,HIGH);
  digitalWrite(R4,LOW);
  if(digitalRead(C1) == LOW) { Serial.print('*'); delay(400); }
  if(digitalRead(C2) == LOW) { Serial.print('0'); delay(400); }
  if(digitalRead(C3) == LOW) { Serial.print('#'); delay(400); }
  if(digitalRead(C4) == LOW) { Serial.print('D'); delay(400); }
}

void setup()
{
  pinMode(C1,INPUT_PULLUP);
  pinMode(C2,INPUT_PULLUP);
  pinMode(C3,INPUT_PULLUP);
  pinMode(C4,INPUT_PULLUP);

  pinMode(R1,OUTPUT);
  pinMode(R2,OUTPUT);
  pinMode(R3,OUTPUT);
  pinMode(R4,OUTPUT);

  Serial.begin(9600);
}

void loop()
{
  Keypad(); 
}

🧩 Output

When a key is pressed, the corresponding value (0–9, A–D, *, #) appears in the Serial Monitor at 9600 baud rate.

Example Output:

1 2 3 A 4 5 6 B ...

🚀 How It Works

Arduino sets one row LOW at a time.

It reads the column inputs — if any column reads LOW, that key is pressed.

The program prints the key value to the Serial Monitor.

The scanning repeats continuously to detect any new key press.

🛠️ Applications

Password entry systems

Menu navigation in embedded projects

Home automation input interface

Access control systems