Simple toll plaza system using low frequency RFID interfaced with 8051 microcontroller (AT89C51)

Electronic/automated toll collection systems are very popular these days. They do not require manual collection and operation of toll barriers. The details about the vehicles and payment are stored in an RFID based system.

This article explains the working of a simple toll plaza system interfaced with RFID. Each user holds a unique ID for his vehicle. When the user scans his tag while passing through the plaza, a certain amount is deducted from his account. A user may also recharge his account in case of insufficient balance. The project has been developed by interfacing RFID with AT89C51. The relevant messages are also displayed on a 16x2 LCD. The free source code for the program is available in C.

Low frequency RFID work at 125 KHz frequency with radio waves. There is a coil inside the RFID tag and when it is influenced by a magnetic field, it sends a 12 byte identity code to RFID reader for further processing. (For more details, refer interfacing RFID with AT89C51).

The RFID tag is used as a unique identity for account of a particular user. When a vehicle drives through the toll plaza, its driver is prompted to scan his RFID tag. If the identity (serial number of the tag, i.e., 12 byte data) is matched with the one already stored in the system, the toll amount is deducted from his account. After this, the vehicle gets immediate access to drive through.

This RFID based toll system also has some additional features. A new user can register him with the system. Also an old user can recharge his account balance. The amount for recharge can be entered in the system through a numeric keypad interfaced with AT89C51.

In beginning, the user is prompted to scan his tag or ID. The serial code of the tag is identified by the reader module and is sent to AT89C51 for comparison with stored data. If the ID is matched by the microcontroller, the toll amount (in this case Rs.10) is deducted from user’s balance and user gets to drive through the plaza. On the contrary, if the tag is not identified, a message (‘Wrong ID’) is displayed on LCD screen.

A new user needs to press the ‘*’ switch to register himself after which his identity is verified with RFID tag. The new record is then stored by the microcontroller to grant future access. The system also shows ‘Error’ if the tags do not match during verification. If balance in user’s account becomes less than Rs.30, a warning message ‘Low balance’ is displayed on LCD. In this case the user still gets the access through the system. The system also prompts the driver to recharge the account. If balance reaches below Rs.10, ‘Insufficient balance’ is indicated on LCD screen. The user does not get access until he adds more balance to his account. The recharge amount is entered by using a keypad. Back space can be used while entering the amount by pressing ‘*’ button on keypad. It also has a safety feature that if different tags are scanned through the reader at the time of registration, LCD displays ‘you have shown different ID’.

When an RFID tag comes in this range, the reader detects it and sends a unique code of the tag serially. This serial code, consisting of 12 bytes, is received by the microcontroller. This code is the ID for the user and is stored as an array in the microcontroller. If the ID is matched with this code stored in array of microcontroller, the user is granted access though the toll plaza. For more details on working and connections of the RFID, refer RFID interfacing through serial interrupt.

Project Source Code

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//Program for a simple toll plaza system using low frequency RFID interfaced with 8051 microcontroller (AT89C51)
#include<reg51.h>
#define port P1
#define key P0		  // Port for keypad
 void memory();

 sfr lcd_data_pin=0xA0;
 sbit rs = P1^3;
 sbit rw = P1^4;
 sbit en = P1^5;

 sbit col1=key^4;
 sbit col2=key^5;
 sbit col3=key^6;
 sbit row1=key^0;
 sbit row2=key^1;
 sbit row3=key^2;
 sbit row4=key^3;
 unsigned int number=0,pointer=1;
 unsigned char card_mem[4][12];
 unsigned char card_id[12],index=0,key1=0,lcd,print=0,new_user=0,recharge=0,user_index,t,tool=0;
 unsigned int amount[4];
 unsigned char current_byte = 0,money[6];
 unsigned char pos=0,set=0;

void delay(unsigned char count)	//Function to provide time delay
{
 	unsigned int j;
	unsigned char i;
 	for(i=0;i<count;i++)
 	for(j=0;j<1275;j++);
}

void lcd_command(unsigned char comm)   //LCD command funtion 
{
 	lcd_data_pin=comm;
 	en=1;
 	rs=0;
 	rw=0;
 	delay(1);
 	en=0;
}

void lcd_data(unsigned char disp)  //LCD data function 
{
 	lcd_data_pin=disp;
 	en=1;
 	rs=1;
 	rw=0;
 	delay(1);
 	en=0;
}

lcd_string(unsigned char *disp)	 //LCD string function 
{
 	char x;
 	for(x=0;disp[x]!=0;x++)
	{
 		lcd_data(disp[x]);
	}
}

void lcd_ini()				  //Function to initialize the LCD
{
	lcd_command(0x38);		   
	delay(5);
	lcd_command(0x0F);        
	delay(5);
	
}

lcd_display(unsigned int val)
{
	unsigned char flg=0;
	lcd_command(0xCC);
	if(val==0)
	lcd_data('0');
	while(val>0)
	{ 
		lcd=val%10;
		val=val/10;
		lcd_command(0xCC-flg);
		lcd_data(lcd+'0');
		flg++;
	}
}


void recieve() interrupt 4	 //Function to recieve data serialy from RS232 
{
	card_id[current_byte]=SBUF;
	RI=0;				// Reset the serial interrupt after recieving the byte
	current_byte++;	
}

void display(unsigned char value)
{
	lcd_command(0x80+pos);
	if(value==10)
	{
		print=1; 
	}
	if(value==12)
	{
		set=1; 
	}
	if(value<=9)
	{
		lcd_data('0'+value);
		money[pos]=value;
		pos++;
	}
}

check_col1()
{
	row1=row2=row3=row4=1;
	row1=0;
	if(col1==0)
	display(1);
	row1=1;
	row2=0;
	if(col1==0)
	display(4);
	row2=1;
	row3=0;
	if(col1==0)
	display(7);
	row3=1;
	row4=0;
	if(col1==0)
	display(10);
	row4=1;
}

check_col2()
{
	row1=row2=row3=row4=1;
	row1=0;
	if(col2==0)
	display(2);
	row1=1;
	row2=0;
	if(col2==0)
	display(5);
	row2=1;
	row3=0;
	if(col2==0)
	display(8);
	row3=1;
	row4=0;
	if(col2==0)
	display(0);
	row4=1;
}

check_col3()
{
	row1=row2=row3=row4=1;
	row1=0;
	if(col3==0)
	display(3);
	row1=1;
	row2=0;
	if(col3==0)
	display(6);
	row2=1;
	row3=0;
	if(col3==0)
	display(9);
	row3=1;
	row4=0;
	if(col3==0)
	display(12);
	row4=1;
}

keypad()
{
	row1=row2=row3=row4=0;
	if(col1==0)
	check_col1();
	if(col2==0)
	check_col2();
	if(col3==0)
	check_col3();
}
  
void show()		
{
	unsigned char count,i,key,val,flag=0,in;
	unsigned int balance,j;
	TMOD=0x00;							//Enable Timer 1
	TH1=0x00;
	SCON=0x00;
	TR1=0;
	IE=0x00; 
	lcd_command(0x01);		
	 val=index;
	for(i=0;i<index;i++)
	{ 
		key=0;
		for(count=0;count<12;count++)
		{ 
			if(card_id[count]==card_mem[i][count])
			{
				key++;
			}
		}
		if(key==12)
		{
			flag=1;
			if(amount[i]<=10)
			{
				user_index=i;
				lcd_string("Insuff. balance");
				lcd_command(0xC0);
				lcd_string("Pls recharge");
				delay(250);
				lcd_command(0x01);
				lcd_string("To recharge");
				lcd_command(0xC0);
				lcd_string("press *");
				for(in=0;in<250;in++)
				{
					for(j=0;j<1275;j++)
					{
						row1=row2=row3=row4=0;
						if(col1==0)
						{
							tool=1;
							recharge=1;
							t=1;
							keypad();
							break;
						}
					}
					if(t==1)
					break;
				}
				lcd_command(0x01);
				lcd_string("Pls scan your ID");
				break;  
			}
			if(tool==0)
			{
				lcd_string("Thank you User ");
				lcd_command(0x8F);
				lcd_data(49+i);
				delay(250);
				lcd_command(0x01);
				lcd_string("Charges 10.00");
				amount[i]=amount[i]-10;
				lcd_command(0xC0);
				lcd_string("Amt left  ");
				balance=amount[i];
				lcd_display(balance);
				lcd_command(0xCD);
				lcd_string(".00");
				delay(250);
				lcd_command(0x01);
				if(amount[i]<=30)
				{
					user_index=i;
					lcd_string("Pls recharge");
					lcd_command(0xC0);
					lcd_string("your account");
					delay(250);
					lcd_command(0x01);
					lcd_string("To recharge");
					lcd_command(0xC0);
					lcd_string("press *");
					for(in=0;in<250;in++)
					{
						for(j=0;j<1275;j++)
						{
							row1=row2=row3=row4=0;
							if(col1==0)
							{
								recharge=1;
								t=1;
								keypad();
								break;
							}
						}
						if(t==1)
						break;
					} 
				}
			}
		t=0;
		lcd_command(0x01);
		lcd_string("Pls scan your ID"); 
		break;
		}
	}
	if(flag==0)
	{
		lcd_string("Wrong ID");
		delay(100);
	}
	if(flag==0)
	{
		lcd_command(0x01);
		lcd_string("New user press *");
		new_user=1;
	}
	current_byte=0;
	tool=0;
	TMOD=0x20;							//Enable Timer 1
	TH1=0xFD;
	SCON=0x50;
	TR1=1;
	IE=0x94;
}

recharge_acc()
{
	unsigned char pin;
	lcd_command(0x01);
	lcd_string("Pls enter the");
	lcd_command(0xC0);
	lcd_string("Balance");
	delay(250);
	lcd_command(0x01);
	while(set!=1)
	{
		keypad();
		delay(40); 
	}
	set=0;
	lcd_command(0x01);
	lcd_string("Your balance is");
	for(pin=0;pin<=pos;pin++)
	{
		number=number+money[pos-pin-1]*pointer;
		pointer=pointer*10;
	}
	amount[user_index]=amount[user_index]+number;
	lcd_command(0xC0);
	lcd_display(amount[user_index]);
	lcd_command(0xCD);
	lcd_string(".00");
	delay(250);
	lcd_command(0x01);
	number=0;
	pointer=1;
	pos=0;
	lcd_string("Pls scan your ID");
}

void memory()
{
	unsigned char i,key=0,count,pin,try=0;
	lcd_command(0x01);
	lcd_string("New user scan ID");
	current_byte=0;
	while(current_byte!=12);
	for(i=0;i<4;i++)
	{ 
		key=0;
		for(count=0;count<12;count++)
		{ 
			if(card_id[count]==card_mem[i][count])
			{
				key++;
			}
		}
		if(key==12)
		{
			lcd_command(0x01);
			lcd_string("Sorry ! You are");
			lcd_command(0xC0);
			lcd_string("already an user"); 
			delay(200);
			lcd_command(0x01);
			lcd_string("Pls scan your ID");
			key=0;
			try=1;
			current_byte=0;
			break;
		}
	}
	if(key<12 && try==0)
	{
		key=0;	 
		for(i=0;i<12;i++)
		{
			card_mem[index][i]=card_id[i];
		}
		current_byte=0;
		lcd_command(0x01);
		lcd_string("Pls scan again");
		while(current_byte!=12);
		for(i=0;i<12;i++)
		{
			if(card_mem[index][i]==card_id[i])
			{
				key++;
			}
		}
		current_byte=0;
		TMOD=0x00;							
		TH1=0x00;
		SCON=0x00;
		TR1=0;
		IE=0x00; 
		if(key==12)
		{
			lcd_command(0x01);
			lcd_string("Congratulation !");
			lcd_command(0xC0);
			lcd_string("You are User");
			lcd_command(0xCC);
			lcd_data(index+49);
			delay(250);
			lcd_command(0x01);
			lcd_string("Pls enter the");
			lcd_command(0xC0);
			lcd_string("Balance");
			delay(150);
			lcd_command(0x01);
			while(set!=1)
			{
				keypad();
				delay(40); 
			}
			set=0;
			lcd_command(0x01);
			lcd_string("Your balance is");
			for(pin=0;pin<=pos;pin++)
			{
				number=number+money[pos-pin-1]*pointer;
				pointer=pointer*10;
			}
			lcd_command(0xC0);
			lcd_display(number);
			lcd_command(0xCD);
			lcd_string(".00");
			amount[index]=number;
			delay(250);
			lcd_command(0x01);
			number=0;
			pointer=1;
			pos=0;
			lcd_string("Pls scan your ID"); 
		}
		else	
		{
			lcd_command(0x01);
			lcd_string("ERROR");
			delay(200);
			for(i=0;i<12;i++)
			{
				card_mem[index][i]=0;
			}
			lcd_command(0x01);
			lcd_string("Pls scan your ID");
		}
		if(key==12)
		index++;
	}
	TMOD=0x20;							//Enable Timer 1
	TH1=0xFD;
	SCON=0x50;
	TR1=1;
	IE=0x94;
}

void main()
{
	col1=col2=col3=1;
	TMOD=0x20;							
	TH1=0xFD;
	SCON=0x50;
	TR1=1;
	IE=0x94;
	lcd_ini();					//Place cursor to second position of first line 
	lcd_string("Pls scan your ID");
	while(1)
	{
		row1=row2=row3=row4=0;
		if(col1==0)
		{
			keypad();
		}
		if(print==1 && new_user==1)
		{
			memory();
			print=0;
			new_user=0;
		}
		if(print==1 && recharge==1)
		{
			recharge_acc();
			print=0;
			recharge=0;
		}
		if(current_byte==12)
		{
			show();
		}
	}
}

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