Door opening control using Micro:bit and 4×3 matrix keypad

Tutorial plan

1- Secure Access System Using Digital Keypad

2- How open a door using Micro:bit and 4x3 matrix keypad ?

3- Required Components

4- Circuit Connections of system

5- Makecode program of system

Secure Access System Using Digital Keypad

A Secure Access System Using Digital Keypad is an electronic locking mechanism that controls entry to a restricted area—such as a room, building, or safe—by requiring the user to input a specific numeric code or password on a keypad. This type of system enhances security by eliminating the need for traditional physical keys, which can be lost, stolen, or duplicated.

Key Features (General Definition):

Digital Keypad: The main interface where users enter a personal identification number (PIN) to gain access.

Control Unit: Processes the input and compares it to a stored password.

Actuator/Lock Mechanism: Activates (unlocks) when the correct code is entered.

Security Measures: May include alarms, time delays, limited attempts, or automatic locking after failed entries.

Power Source: Usually powered by batteries or a direct electrical connection.

Applications:

Home and office door locks

Safes and lockers

Industrial and laboratory access

Smart home automation systems

How open a door using Micro:bit and 4x3 matrix keypad ?

This project demonstrates a digital door lock system that allows secure access through a numeric password entered on a 4x3 matrix keypad. The system is controlled by a BBC Micro:bit microcontroller, which processes the input and operates a servo motor to simulate the opening or closing of a door. An LCD I2C screen provides real-time feedback and instructions to the user.

How It Works

1. User Input via Keypad

The user enters a predefined 4-digit PIN code using the 4x3 matrix keypad. Each key press is detected and displayed briefly on the LCD screen.

2. Micro:bit Processing

The Micro:bit receives the input and checks whether the entered code matches the stored password.

3. Servo Motor Control

If the code is correct, the Micro:bit sends a signal to the servo motor to rotate (e.g., 20°) to unlock the door.

If the code is incorrect, the servo remains in the locked position.

4. LCD Display Feedback

The LCD shows messages like:

"Enter code"

"Invalid code"

"Door closed"

Required Components

1. BBC Micro:bit (Microcontroller)

The Micro:bit is a compact, beginner-friendly microcontroller developed by the BBC. It serves as the brain of the system, responsible for:

Reading user input from the 4x3 keypad

Verifying the password

Controlling the servo motor to open/close the door

Displaying feedback on the LCD screen

GPIO Extension Card for Micro:bit

GPIO extension card Expands the number of usable input/output pins on the Micro:bit, making it easier to connect multiple components like the RFID reader, LCD, and servomotor.

2. 4x3 Matrix Keypad

The 4x3 matrix keypad is used as a numeric input device, allowing users to enter a password (e.g., a 4-digit PIN code).

It consists of:

4 rows and 3 columns of buttons

Keys labeled from 0–9, along with “*” and “#” (optional use)

Working Principle:

When a key is pressed, a connection is made between one row and one column.

The Micro:bit scans the rows and columns to detect which key was pressed.

3. Servo Motor (e.g., SG90)

The servo motor acts as the door locking/unlocking mechanism.

It receives a control signal (PWM) from the Micro:bit and rotates its shaft to:

90°: Locked position

20°: Unlocked position

4. LCD Display with I2C Module

The LCD (Liquid Crystal Display) shows system messages to the user, such as:

"Enter code"

"Invalid code"

"Door closed"

Using an I2C interface, it requires only 2 pins from the Micro:bit (SDA and SCL), which simplifies wiring.

5. Breadboard 

Breadboard is used for building a non-permanent circuit without soldering.

6. Jumper Wires

Jumper wires (male-to-male or male-to-female) are used to connect components to the Micro:bit.

Wooden house prototype

A miniature wooden house represents a real-world structure.

The door mechanism is attached to a servo motor, which rotates to open or close it.

The wooden prototype provides a stable frame for installing components like the IR sensor and LCD screen.

Circuit Connections of system

Connection of LCD I2C display to Micro:bit

Connection of servo motor to Micro:bit

Connection of keypad to Micro:bit

Makecode program of system

1- Open MakeCode (makecode.microbit.org).

2- Click on Extensions.

3- In the search bar, type "I2C LCD," and you should find an extension for the I2C LCD display. Add it to your project.

4- In the search bar, type "https://github.com/lioujj/pxt-keypad" and you should find an extension for 4x3 matrix keypad. Add it to your project.

5- Go to advanced :

6- Go to Pin and choose 'servo write pinP0 to 180' instruction :

Here is a complete Makecode program with detailed comments for your Smart Door Access Control System