Circuit Documentation

Summary

This circuit is designed to interface an Arduino UNO with an RFID-RC522 module, an I2C LCD 16x2 screen, and multiple pushbuttons. The purpose of the circuit is to create a smart trolley billing system. The RFID-RC522 module reads RFID tags of items, the LCD screen displays item names and prices, and the pushbuttons are used to add or remove items from the bill or to reset the system. The circuit also includes resistors for debouncing the pushbuttons.

Component List

Arduino UNO

• Microcontroller board based on the ATmega328P
• It has 14 digital input/output pins, 6 analog inputs, a 16 MHz quartz crystal, a USB connection, a power jack, an ICSP header, and a reset button.

RFID-RC522

• An RFID reader/writer module
• Operates at 13.56 MHz and supports the MIFARE protocol.

I2C LCD 16x2 Screen

• A 16x2 character LCD display with an I2C interface module.
• It can display 16 characters per line and there are 2 lines.

Pushbutton

• A simple switch mechanism for controlling some aspect of a machine or a process.
• Typically used to provide input to a system.

Resistor (200 Ohms)

• A passive two-terminal electrical component that implements electrical resistance as a circuit element.
• Used for limiting current and providing voltage drops.

Wiring Details

Arduino UNO

• 5V connected to the 5V power rail supplying power to the pushbuttons and the I2C LCD screen.
• GND connected to the ground rail, which is common for the I2C LCD screen and the RFID-RC522 module.
• 3.3V supplies power to the RFID-RC522 module.
• SCL and SDA are connected to the corresponding pins on the I2C LCD screen for communication.
• Digital pins D2, D3, and D4 are connected to pushbuttons through 200 Ohm resistors.
• Digital pins D9, D10, D11, D12, and D13 are connected to the RFID-RC522 module for SPI communication and control.

RFID-RC522

• VCC (3.3V) connected to the 3.3V output from the Arduino UNO.
• RST connected to digital pin D9 on the Arduino UNO.
• GND connected to the ground rail.
• IRQ is not connected.
• MISO, MOSI, SCK, SDA connected to D12, D11, D13, D10 on the Arduino UNO respectively.

I2C LCD 16x2 Screen

• SCL and SDA connected to the corresponding pins on the Arduino UNO for I2C communication.
• VCC (5V) connected to the 5V power rail.
• GND connected to the ground rail.

Pushbuttons

• One side of each pushbutton connected to the 5V power rail.
• The other side of each pushbutton connected to digital pins D2, D3, and D4 on the Arduino UNO through 200 Ohm resistors.

Resistor (200 Ohms)

• Each resistor is connected in series with a pushbutton and an Arduino UNO digital pin to debounce the pushbutton signal.

Documented Code

#include <SPI.h>
#include <MFRC522.h>
#include <LiquidCrystal_I2C.h>

LiquidCrystal_I2C lcd(0x27, 16, 2); 
const int remove_button = 2;    
const int add_button = 3; 
const int reset_button = 4;
const int buzzer_Pin = 5; 
#define SS_PIN 10
#define RST_PIN 9
MFRC522 mfrc522(SS_PIN, RST_PIN);   // Create MFRC522 instance.

struct item
{
  String item_name;
  String item_number;
  int item_price;
};

const int number_of_item = 4;
const item item_list[number_of_item]= 
  {
  //Item Name       Item RFID Number   Item Price
  {"Tata salt",     "B3 23 E4 11",        100},
  {"Milk Powder",   "A3 51 A0 0D",        50},
  {"Bournvita",     "13 1F A3 0D",        20},
  {"Ball_Pen",      "E3 68 DC 12",        10},
  };

int bill_amount = 0;
int remove_buttonState = 0;  
int add_buttonState = 0;  
int reset_buttonState = 0;
int add_item_flag = 1;
int remove_item_flag = 0;
void setup() 
{
  pinMode(remove_button, INPUT);
  pinMode(reset_button, INPUT);
  pinMode(add_button, INPUT);
  pinMode(buzzer_Pin, OUTPUT);
  Serial.begin(9600);   // Initiate a serial communication
  SPI.begin();      // Initiate  SPI bus
  mfrc522.PCD_Init();   // Initiate MFRC522
  Serial.println("Approximate your card to the reader...");
  Serial.println();
  digitalWrite(buzzer_Pin, LOW); 
    lcd.init();
  // Turn on the Backlight
  lcd.backlight();
  lcd.clear(); 
  // Set cursor (Column, Row)
  lcd.setCursor(0, 0);  
  lcd.print("Smart Trolley"); 
  lcd.setCursor(0,1);
  lcd.print("Billing System");
  delay(2000);
  lcd.clear(); 
  // Set cursor (Column, Row)
  lcd.setCursor(0, 0);  
  lcd.print("Start purchasing"); 
  lcd.setCursor(0,1);
  lcd.print("your item");
  delay(100);
}
void loop() 
{
  remove_buttonState = digitalRead(remove_button);
  add_buttonState = digitalRead(add_button);
  reset_buttonState = digitalRead(reset_button);
  if(remove_buttonState)
  {
    add_item_flag = 0;
    remove_item_flag = 1;
    lcd.clear(); 
    // Set cursor (Column, Row)
    lcd.setCursor(0, 0);  
    lcd.print("You Can now"); 
    lcd.setCursor(0,1);
    lcd.print("Remove your item");
    delay(2000);
  }
  else if(add_buttonState)
  {
    add_item_flag = 1;
    remove_item_flag = 0;
    lcd.clear(); 
    // Set cursor (Column, Row)
    lcd.setCursor(0, 0);  
    lcd.print("You Can now"); 
    lcd.setCursor(0,1);
    lcd.print("add your item");
    delay(2000);
  }
  else if(reset_buttonState)
  {
    lcd.clear(); 
    // Set cursor (Column, Row)
    lcd.setCursor(0, 0);  
    lcd.print("Resetting"); 
    lcd.setCursor(0,1);
    lcd.print("Trolley data");
    delay(2000);
    lcd.clear(); 
    // Set cursor (Column, Row)
    lcd.setCursor(0, 0);  
    lcd.print("Start Purchasing"); 
    lcd.setCursor(0,1);
    lcd.print("Your item");
    delay(2000);
    bill_amount = 0;
  }
  
  // Look for new cards
  if ( ! mfrc522.PICC_IsNewCardPresent()) 
  {
    return;
  }
  // Select one of the cards
  if ( ! mfrc522.PICC_ReadCardSerial()) 
  {
    return;
  }
  //Show UID on serial monitor
  Serial.print("UID tag :");
  String content= "";
  byte letter;
  for (byte i = 0; i < mfrc522.uid.size; i++) 
  {
     Serial.print(mfrc522.uid.uidByte[i] < 0x10 ? " 0" : " ");
     Serial.print(mfrc522.uid.uidByte[i], HEX);
     content.concat(String(mfrc522.uid.uidByte[i] < 0x10 ? " 0" : " "));
     content.concat(String(mfrc522.uid.uidByte[i], HEX));
  }
  Serial.println();
  Serial.print("Message : ");
  content.toUpperCase();
  for(int i = 0 ;i < sizeof(item_list) ; i++)
  {
    if (content.substring(1) == item_list[i].item_number) //change here the UID of the card/cards that you want to give access
    {
      if(add_item_flag == 1)
      {
          bill_amount = bill_amount + item_list[i].item_price;
  //      Serial.println("you have purchased = " + item_list[i].item_name);
  //      Serial.print("Purchased item price");
  //      Serial.println(item_list[i].item_price);
  //      Serial.print("Total billing amount");
  //      Serial.println(bill_amount);
  //      delay(1000);
          digitalWrite(buzzer_Pin, HIGH);
          delay(500);
          digitalWrite(buzzer_Pin, LOW); 
          lcd.clear(); 
          // Set cursor (Column, Row)