Build a Calculator Using the ESP32 Board

ESP32 13-02-26

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Tutorial plan

1- Objective of the project

2- Required Components

3- Circuit Connections of system

4- Micropython program of ESP32 calculator

Objective of the project

The objective of this project is to design and implement a functional digital calculator using the ESP32 microcontroller. The system allows the user to enter numbers and select arithmetic operations through a 4x4 matrix keypad, while the results are displayed clearly on an LCD I2C display.

This project aims to:

1- Understand how to interface a 4x4 matrix keypad with the ESP32 to detect user input.

2- Learn how to control an LCD I2C display to show numbers and calculation results.

3- Program the ESP32 using MicroPython to perform basic arithmetic operations such as addition, subtraction, multiplication, and division.

4- Practice embedded systems programming and hardware–software integration.

5- Develop problem-solving skills through real-time input processing and output display.

By completing this project, learners will gain practical experience in microcontroller programming, electronic circuit connections, and interactive embedded system design.

Required Components

1. BBC Micro:bit (Microcontroller)

The ESP32 board is a small programmable microcontroller board designed for education. It acts as the main controller (brain) of the calculator.

2. 4x4 Matrix Keypad

The 4x4 matrix keypad is used to input numbers and operations.

4. LCD Display with I2C Module

The LCD I2C display is used to show: entered numbers, mathematical operations and calculation results.

5. Breadboard

Breadboard

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

6. Jumper Wires

Jumper wires

Jumper wires (male-to-male or male-to-female) are used to connect components to the ESP32 board.

Circuit Connections of system

1- Connection of keypad to ESP32 board

4x4 Keypad	ESP32 board
R1	GPIO23
R2	GPIO19
R3	GPIO18
R4	GPIO5
C1	GPIO17
C2	GPIO16
C3	GPIO4
C4	GPIO2

2- Connection of LCD I2C display to ESP32

LCD I2C display	ESP32
VCC	5V
GND	GND
SDA	P20
SCL	P19

Micropython program of ESP32 calculator

This program transforms the ESP32 into a functional calculator using a 4x4 matrix keypad for input and an I2C LCD display for output.

You need to install this libraries : i2c_lcd et lcd_api for I2C LCD screen.

# Import required libraries
from machine import Pin, I2C      # Used to control GPIO pins and I2C communication
from i2c_lcd import I2cLcd        # Library to control the I2C LCD display
import time                       # Used for delays

# ================= LCD I2C =================

# I2C address of the LCD module (commonly 0x27 or 0x3F)
I2C_ADDR = 0x27

# Initialize the I2C bus:
# I2C(0) -> I2C bus number 0
# scl=Pin(22) -> SCL connected to GPIO 22
# sda=Pin(21) -> SDA connected to GPIO 21
# 4, 20 -> LCD with 4 rows and 20 columns
lcd = I2cLcd(I2C(0, scl=Pin(22), sda=Pin(21)), I2C_ADDR, 4, 20)

# Clear the LCD screen
lcd.clear()

# Display startup message
lcd.putstr("ESP32 Calculator")


# ================= 4x4 KEYPAD =================

# Define the 4 keypad rows as outputs
rows = [
    Pin(23, Pin.OUT),
    Pin(19, Pin.OUT),
    Pin(18, Pin.OUT),
    Pin(5, Pin.OUT)
]

# Define the 4 keypad columns as inputs
# Pin.PULL_DOWN activates internal pull-down resistors
# to prevent false signals
columns = [
    Pin(17, Pin.IN, Pin.PULL_DOWN),
    Pin(16, Pin.IN, Pin.PULL_DOWN),
    Pin(4, Pin.IN, Pin.PULL_DOWN),
    Pin(2, Pin.IN, Pin.PULL_DOWN)
]

# Keypad layout (button mapping)
keys = [
    ['1', '2', '3', '+'],
    ['4', '5', '6', '-'],
    ['7', '8', '9', '*'],
    ['C', '0', '=', '/']
]

# Function to detect which key is pressed
def read_key():
    # Loop through each row
    for i in range(4):
        rows[i].on()  # Activate one row at a time

        # Check each column
        for j in range(4):
            if columns[j].value():   # If a column detects a signal
                rows[i].off()        # Deactivate the row
                return keys[i][j]    # Return the corresponding key

        rows[i].off()  # Deactivate the row before moving to the next one

    return None  # No key pressed


# ================= CALCULATOR =================

# Variable to store the typed mathematical expression
expression = ""

# Main loop (runs continuously)
while True:

    # Read pressed key
    key = read_key()

    # If a key is detected
    if key:

        # Small delay to avoid double reading (debouncing)
        time.sleep(0.3)

        # If key is "C" → clear everything
        if key == 'C':
            expression = ""     # Reset the expression
            lcd.clear()         # Clear the display

        # If key is "=" → calculate the result
        elif key == '=':
            try:
                # Evaluate the mathematical expression
                result = str(eval(expression))

                # Display the result
                lcd.clear()
                lcd.putstr("Result:")
                lcd.move_to(0, 1)  # Move to second line
                lcd.putstr(result)

                # Allow continued calculation using the result
                expression = result

            except:
                # If error occurs (e.g., division by zero)
                lcd.clear()
                lcd.putstr("Error")
                expression = ""

        # Otherwise → add the pressed key to the expression
        else:
            expression += key  # Append character
            lcd.clear()
            lcd.putstr(expression)

    # Small delay for stable reading
    time.sleep(0.1)

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# Import required libraries

from machine import Pin, I2C # Used to control GPIO pins and I2C communication

from i2c_lcd import I2cLcd # Library to control the I2C LCD display

import time # Used for delays

# ================= LCD I2C =================

# I2C address of the LCD module (commonly 0x27 or 0x3F)

I2C_ADDR = 0x27

# Initialize the I2C bus:

# I2C(0) -> I2C bus number 0

# scl=Pin(22) -> SCL connected to GPIO 22

# sda=Pin(21) -> SDA connected to GPIO 21

# 4, 20 -> LCD with 4 rows and 20 columns

lcd = I2cLcd(I2C(0, scl=Pin(22), sda=Pin(21)), I2C_ADDR, 4, 20)

# Clear the LCD screen

lcd.clear()

# Display startup message

lcd.putstr("ESP32 Calculator")

# ================= 4x4 KEYPAD =================

# Define the 4 keypad rows as outputs

rows = [

Pin(23, Pin.OUT),

Pin(19, Pin.OUT),

Pin(18, Pin.OUT),

Pin(5, Pin.OUT)

]

# Define the 4 keypad columns as inputs

# Pin.PULL_DOWN activates internal pull-down resistors

# to prevent false signals

columns = [

Pin(17, Pin.IN, Pin.PULL_DOWN),

Pin(16, Pin.IN, Pin.PULL_DOWN),

Pin(4, Pin.IN, Pin.PULL_DOWN),

Pin(2, Pin.IN, Pin.PULL_DOWN)

]

# Keypad layout (button mapping)

keys = [

['1', '2', '3', '+'],

['4', '5', '6', '-'],

['7', '8', '9', '*'],

['C', '0', '=', '/']

]

# Function to detect which key is pressed

def read_key():

# Loop through each row

for i in range(4):

rows[i].on() # Activate one row at a time

# Check each column

for j in range(4):

if columns[j].value(): # If a column detects a signal

rows[i].off() # Deactivate the row

return keys[i][j] # Return the corresponding key

rows[i].off() # Deactivate the row before moving to the next one

return None # No key pressed

# ================= CALCULATOR =================

# Variable to store the typed mathematical expression

expression = ""

# Main loop (runs continuously)

while True:

# Read pressed key

key = read_key()

# If a key is detected

if key:

# Small delay to avoid double reading (debouncing)

time.sleep(0.3)

# If key is "C" → clear everything

if key == 'C':

expression = "" # Reset the expression

lcd.clear() # Clear the display

# If key is "=" → calculate the result

elif key == '=':

try:

# Evaluate the mathematical expression

result = str(eval(expression))

# Display the result

lcd.clear()

lcd.putstr("Result:")

lcd.move_to(0, 1) # Move to second line

lcd.putstr(result)

# Allow continued calculation using the result

expression = result

except:

# If error occurs (e.g., division by zero)

lcd.clear()

lcd.putstr("Error")

expression = ""

# Otherwise → add the pressed key to the expression

else:

expression += key # Append character

lcd.clear()

lcd.putstr(expression)

# Small delay for stable reading

time.sleep(0.1)

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Build a Calculator Using the ESP32 Board

Tutorial plan

1- Objective of the project

2- Required Components

3- Circuit Connections of system

4- Micropython program of ESP32 calculator

Objective of the project

Required Components

Circuit Connections of system

Micropython program of ESP32 calculator

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