Circuit Documentation

Summary

This circuit is designed around an Arduino UNO microcontroller and includes various peripherals such as an RFID-RC522 module for RFID reading, a 16x2 I2C LCD for display purposes, and two LEDs (red and green) for status indication. The circuit is powered by the Arduino's 3.3V output, which is also used to power the RFID module and the LCD. The LEDs are connected to digital pins on the Arduino through 220-ohm resistors to limit the current. The RFID module communicates with the Arduino via the SPI interface, while the LCD uses the I2C protocol.

Component List

Arduino UNO

• Microcontroller board based on the ATmega328P
• Provides digital I/O pins, analog inputs, a USB connection for programming, and power supply pins

LED: Two Pin (red)

• A red LED used for status indication

LED: Two Pin (green)

• A green LED used for status indication

16x2 I2C LCD

• A 16-character by 2-line display that communicates over the I2C bus

Resistor (220 Ohms)

• Two resistors used to limit the current through the LEDs

RFID-RC522

• An RFID reader/writer module that operates at 13.56 MHz

Wiring Details

Arduino UNO

• 3.3V connected to RFID-RC522 VCC and 16x2 I2C LCD VCC
• GND connected to RFID-RC522 GND, 16x2 I2C LCD GND, and common cathode of both LEDs
• A4 (SDA) connected to 16x2 I2C LCD SDA
• A5 (SCL) connected to 16x2 I2C LCD SCL
• D13 (SCK) connected to RFID-RC522 SCK
• D12 (MISO) connected to RFID-RC522 MISO
• D11 (MOSI) connected to RFID-RC522 MOSI
• D10 (SS) connected to RFID-RC522 SDA
• D9 connected to RFID-RC522 RST
• D7 connected to one end of a 220-ohm resistor (other end connected to red LED anode)
• D6 connected to one end of a 220-ohm resistor (other end connected to green LED anode)

LED: Two Pin (red)

• cathode connected to common ground
• anode connected to a 220-ohm resistor, which is connected to Arduino UNO D7

LED: Two Pin (green)

• cathode connected to common ground
• anode connected to a 220-ohm resistor, which is connected to Arduino UNO D6

16x2 I2C LCD

• GND connected to Arduino UNO GND
• VCC connected to Arduino UNO 3.3V
• SDA connected to Arduino UNO A4
• SCL connected to Arduino UNO A5

Resistor (220 Ohms)

• One resistor connected between Arduino UNO D7 and red LED anode
• One resistor connected between Arduino UNO D6 and green LED anode

RFID-RC522

• VCC (3.3V) connected to Arduino UNO 3.3V
• RST connected to Arduino UNO D9
• GND connected to common ground
• IRQ not connected
• MISO connected to Arduino UNO D12
• MOSI connected to Arduino UNO D11
• SCK connected to Arduino UNO D13
• SDA connected to Arduino UNO D10

Documented Code

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

#define SS_PIN 10
#define RST_PIN 9

#define LED_DENIED_PIN 7
#define LED_ACCESS_PIN 6

LiquidCrystal_I2C lcd(0x3F,16,2);
MFRC522 mfrc522(SS_PIN, RST_PIN); // Instance of the class

int code[] = {32,154,149,117}; //This is the stored UID (Unlock Card)
int codeRead = 0;
String uidString;

void setup() {
   Serial.begin(9600);
   SPI.begin();       // Init SPI bus
   mfrc522.PCD_Init(); // Init MFRC522
   Serial.println("Arduino RFID reading UID");

   pinMode(LED_DENIED_PIN, OUTPUT);
   pinMode(LED_ACCESS_PIN, OUTPUT);

   lcd.init();
   lcd.backlight();
   lcd.setCursor(0,0);
   lcd.print("Show your card:)");
}

void loop() {
   if (mfrc522.PICC_IsNewCardPresent()) {
       if (mfrc522.PICC_ReadCardSerial()) {
           lcd.clear();
           Serial.print("Tag UID:");
           lcd.setCursor(0,0);
           lcd.print("Tag UID:");
           lcd.setCursor(0,1);
           for (byte i = 0; i < mfrc522.uid.size; i++) {
                  Serial.print(mfrc522.uid.uidByte[i] < 0x10 ? " 0" : " ");
                  Serial.print(mfrc522.uid.uidByte[i], HEX);
                  
                  lcd.print(mfrc522.uid.uidByte[i] < 0x10 ? " 0" : " ");
                  lcd.print(mfrc522.uid.uidByte[i], HEX);
            }
            
            Serial.println();

            int i = 0;
            boolean match = true;
            while(i<mfrc522.uid.size) {
               if(!(int(mfrc522.uid.uidByte[i]) == int(code[i]))) {
                  match = false;
               }
              i++;
            }

            delay(3000);
           lcd.clear();
           lcd.setCursor(0,0);
           
           if(match) {
              digitalWrite(LED_ACCESS_PIN, HIGH);
              lcd.print("Authorized access");
           } else {
              digitalWrite(LED_DENIED_PIN, HIGH);
              lcd.print(" Access denied  ");
              Serial.println("\nUnknown Card");
           }
             
             Serial.println("============================");
             
             mfrc522.PICC_HaltA();

             delay(3000);
             reset_state();
        }
   }
}

void reset_state() {
    lcd.clear();
    lcd.setCursor(0,0);
    lcd.print("Show your card:)");
    
    digitalWrite(LED_ACCESS_PIN, LOW);
    digitalWrite(LED_DENIED_PIN, LOW);
}

This code is responsible for initializing the RFID reader and the LCD display, reading RFID tags, comparing the read UID with a stored UID, and then turning on the appropriate LED based on whether the UID matches. The LCD displays messages to guide the user and to show the UID of the scanned tag.