A simple standalone calculator can be built with Arduino, a numeric keypad, and a display screen, performing the four basic arithmetic operations with no computer connection needed.
Components needed
An Arduino Uno R3 board, a 4x4 membrane keypad (with digits, letters A, B, C, D, and the * and # symbols), a 16x2 LCD screen fitted with an I2C module, and connecting wires.
Wiring it up
The keypad's eight rows and columns connect to eight digital pins as usual with the Keypad library, while the LCD connects via its I2C module through just two data pins (SDA and SCL), in addition to power and ground.
How it works
The keypad's letter keys are assigned to arithmetic operations: A for addition, B for subtraction, * for multiplication, and D for division, while C clears the current operation to start over, and # acts as the equals key to execute the operation and show the result. The code relies on state tracking: the user starts by entering the first number digit by digit, then presses the desired operation key, then enters the second number, and finally presses # to execute the matching operation and display the result on the LCD alongside the original expression. This basic project is limited to whole numbers and the four basic operations, but it can later be extended with more advanced math functions using Arduino's built-in math functions.
You can find membrane keypads and LCD screens with I2C modules at Juthour Tech.
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