Published May 11, 2025 © GPL3+

Keypad

A simple Arduino-based authentication system that sends keypad input to a Windows Forms app via serial and verifies the password.

BeginnerFull instructions provided2 hours91

Things used in this project

Hardware components

Arduino Nano R3

Seeed Studio Grove - 12-Channel Capacitive Touch Keypad (ATtiny1616)

Software apps and online services

Arduino IDE

Story

The user can press buttons on either the IR remote or the keypad to control the stair lights
The IR receiver decodes signals from the remote, while the keypad sends key values directly to the Arduino.
Each key (from the remote or keypad) is programmed to perform a specific function, such as turning the light ON, OFF, or activating AUTO mode.
When in AUTO mode, a sensor like KY-033 (IR obstacle sensor) or a PIR motion sensor detects motion and turns the lights on automatically.
The TM1637 7-segment display shows real-time system status (e.g., “ON”, “OFF”, “AUTO”, or key number pressed).
Lights turn off automatically after a delay or when no movement is detected, saving energy.

Keypad

#include <Keypad.h>

const byte ROWS = 4;
const byte COLS = 4;
char keys[ROWS][COLS] = {
  {'1','2','3','A'},
  {'4','5','6','B'},
  {'7','8','9','C'},
  {'*','0','#','D'}
};
byte rowPins[ROWS] = {9, 8, 7, 6};
byte colPins[COLS] = {5, 4, 3, 2};

Keypad keypad = Keypad(makeKeymap(keys), rowPins, colPins, ROWS, COLS);

String password = "1234";  
String input = "";

int redLed = 13;
int greenLed = 11;
int buzzer = 12;

void setup() {
  pinMode(redLed, OUTPUT);
  pinMode(greenLed, OUTPUT);
  pinMode(buzzer, OUTPUT);
  Serial.begin(9600);
}

void loop() {
  char key = keypad.getKey();
  if (key) {
    if (key == '#') {
      Serial.println(input);

      if (input == password) {
        digitalWrite(redLed, HIGH);
        digitalWrite(greenLed, LOW);
        digitalWrite(buzzer, LOW);
      } else {
        digitalWrite(redLed, LOW);
        digitalWrite(greenLed, HIGH);
        digitalWrite(buzzer, HIGH);
      }
      
      delay(2000);
      digitalWrite(redLed, LOW);
      digitalWrite(greenLed, LOW);
      digitalWrite(buzzer, LOW);
      input = "";
      
    } else if (key == '*') {
      input = "";
    } else {
      input += key;
      
    }
//    Serial.println(input);
  
  }
}