Calculator using TM4C123GH6PM microcontroller

01 · Project Introduction

This project involved designing and implementing an embedded calculator using the TM4C123GH6PM microcontroller.

The system receives user input through a matrix keypad, processes numbers and arithmetic operators using the microcontroller, and displays the entered expression and calculated result through an LCD or character display module.

The project integrated GPIO configuration, matrix keypad scanning, display control, button debouncing, data processing, and embedded C programming.

02 · Project Objectives

The primary objectives were to:

• Enter numbers and operators using a matrix keypad

• Display user input in real time

• Perform basic arithmetic operations

• Present the calculated result

• Support clear and reset operations

• Detect and process invalid inputs

• Create a complete embedded human-machine interaction workflow

03 · Hardware Components

The system mainly consisted of:

• TM4C123GH6PM microcontroller

• Tiva C Series TM4C123G LaunchPad

• Matrix keypad

• LCD or character display module

• Breadboard

• Connecting wires

• Power and debugging interfaces

The matrix keypad was used to enter numbers, operators, and control commands. The display module presented the current input, operating status, and calculated result.

04 · Core Functions

Numerical Input

The user enters numbers through the matrix keypad. The microcontroller continuously scans the row and column states, identifies the pressed key, and combines individual digits into complete numerical values.

Operator Selection

The calculator supports the following arithmetic operations:

• Addition

• Subtraction

• Multiplication

• Division

After the user selects an operator, the system stores the first operand and waits for the second operand.

Result Calculation

When the equals key is pressed, the system performs the selected arithmetic operation and sends the result to the display module.

The software manages the operands, operator, and calculation state to prevent conflicts between inputs at different stages.

Clear Function

The clear key resets the current input, operands, operator, and result. The calculator then returns to its initial state and becomes ready for a new calculation.

Error Handling

The system detects invalid inputs and exceptional conditions, including:

• Incomplete expressions

• Multiple consecutive operators

• Division by zero

• Values exceeding the supported data range

• Additional input while the system is in an error state

When an error is detected, the calculator displays an error message or resets the current operation.

05 · Matrix Keypad Scanning

The matrix keypad is connected to the GPIO pins of the microcontroller through row and column lines.

The software activates each row sequentially and reads the voltage levels of the column pins to identify the pressed key. The corresponding row-column combination is then converted into a number, operator, or control command.

The keypad-scanning process includes:

1. Initializing the row and column GPIO pins

2. Activating each row sequentially

3. Reading the state of each column

4. Identifying the pressed key

5. Converting its position into the corresponding character

6. Processing the number or control command

7. Waiting for the key to be released before continuing

Button-debouncing logic was added to prevent a single press from being registered multiple times.

06 · Display Control

The display module provides real-time feedback to the user by presenting:

• Entered numbers

• Selected arithmetic operators

• Complete expressions

• Calculated results

• Clear or error states

The program sends characters to the display through the appropriate data and control interfaces, allowing the user to understand the current calculator state.

07 · Software Design

The system was developed using a modular software structure. Its primary modules included:

• GPIO initialization

• Matrix keypad scanning

• Button debouncing

• Numerical input processing

• Operator processing

• Arithmetic calculation

• Display control

• Error-state handling

• System reset

The main program continuously scans the keypad and determines how each key should be processed according to the current system state.

For example, a numerical key may be used to enter either the first or second operand, while the equals key triggers calculation and result display.

08 · System State Management

The calculation process was divided into several operating states:

1. Waiting for the first operand

2. Receiving the first operand

3. Waiting for an operator

4. Receiving the second operand

5. Performing the calculation

6. Displaying the result

7. Clearing the system or starting a new calculation

This state-based approach enables the system to process numbers, operators, and control keys in the correct sequence while reducing input conflicts.

09 · Development and Testing

The project was developed through modular implementation and incremental integration.

The development process included:

• Configuring the TM4C123GH6PM GPIO pins

• Testing individual keypad inputs

• Implementing the matrix keypad scanning algorithm

• Testing character output on the display

• Implementing multi-digit number entry

• Developing the arithmetic operations

• Adding clear and error-handling functions

• Integrating the keypad, calculation logic, and display

• Testing the complete user interaction process

Testing covered different numerical lengths, four arithmetic operations, repeated calculations, clear operations, division-by-zero errors, and invalid key combinations.

10 · Project Challenges

Keypad Input Recognition

The matrix keypad determines key positions through row and column scanning. Incorrect scan timing or GPIO configuration can cause missing, incorrect, or repeated inputs.

Button Debouncing

Mechanical keys may produce short voltage fluctuations when pressed or released. Without debouncing, the system may interpret one press as multiple inputs. Delay and key-release detection were used to reduce this problem.

Multi-Digit Number Processing

Because the keypad provides one digit at a time, the software must combine consecutive inputs into complete values while distinguishing between the first and second operands.

Calculation State Control

The system must determine whether it is receiving a number, waiting for an operator, or displaying a result. Clear state management is essential for maintaining the correct calculation sequence.

Invalid Input Handling

Conditions such as division by zero, incomplete expressions, and consecutive operators require separate handling to prevent incorrect results or unstable system behavior.

11 · Project Outcome

The final system implemented a complete calculation process from keypad input to result display. It supported numerical input, basic