Documentation

Overview

The 4×3 membrane matrix keypad is a low-profile flexible keypad with 12 buttons (digits 0-9 plus * and #) arranged in 4 rows and 3 columns — the same layout as a phone, calculator, or door access keypad. It connects to any microcontroller using just 7 GPIO pins (4 rows + 3 columns) and provides a clean way to take user input for menu navigation, PIN entry, calculator displays, security keypads, lock controls, or any application that needs numeric or numeric-plus-symbols input.

The keypad is constructed as a thin flexible PCB with conductive traces and silicone-rubber dome switches under each labeled key. Pressing a key shorts one row line to one column line; the microcontroller scans the matrix by driving rows LOW one at a time and reading the columns to detect which key is pressed. The popular Arduino Keypad library handles all of this with a single one-line read call.

Common uses: door entry / access control with PIN, simple calculators, digital safes, vending-machine simulators, garage-door openers, robot-arm command pads, IoT control panels, RFID-paired entry systems, and just about any project where 12 buttons in a phone-style layout is the right input.

At a Glance

Specifications

Pinout Diagram

Wiring Guide

The 7-pin ribbon header connects to the microcontroller. Each row pin (R1-R4) and column pin (C1-C3) goes to a digital GPIO pin. The Keypad Arduino library handles scanning, debouncing, and decoding.

Code Examples

Read Keys (Arduino, Keypad library)

#include <Keypad.h>

const byte ROWS = 4;
const byte COLS = 3;

char keys[ROWS][COLS] = {
  {'1','2','3'},
  {'4','5','6'},
  {'7','8','9'},
  {'*','0','#'}
};

byte rowPins[ROWS] = {9, 8, 7, 6};   // R1..R4
byte colPins[COLS] = {5, 4, 3};       // C1..C3

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

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

void loop() {
  char key = keypad.getKey();
  if (key) {
    Serial.print("Pressed: ");
    Serial.println(key);
  }
}

4-Digit PIN Entry with Lockout

#include <Keypad.h>

const byte ROWS = 4, COLS = 3;
char keys[ROWS][COLS] = {
  {'1','2','3'},{'4','5','6'},{'7','8','9'},{'*','0','#'}
};
byte rowPins[ROWS] = {9,8,7,6};
byte colPins[COLS] = {5,4,3};
Keypad keypad = Keypad(makeKeymap(keys), rowPins, colPins, ROWS, COLS);

const String correct = "1234";
String entered = "";

void setup() { Serial.begin(9600); Serial.println("Enter 4-digit PIN, end with #"); }

void loop() {
  char k = keypad.getKey();
  if (k) {
    if (k == '#') {
      Serial.println(entered == correct ? "ACCESS GRANTED" : "DENIED");
      entered = "";
    } else if (k == '*') {
      entered = "";
      Serial.println("Cleared");
    } else {
      entered += k;
      Serial.print('*');
    }
  }
}

Frequently Asked Questions