RFID based Secured access system using 8051 microcontroller (AT89C51)

This is a very useful application of RFID (Radio-frequency identification) and is very commonly used in institutes, offices, homes and so on. An RFID system consists of a reader device and a transponder. A transponder or tag has a unique serial number which is identified by the reader. Here RFID has been interfaced with AT89C51 to provide secured access. The relevant messages are also displayed on a 16x2 LCD. The free source code for the program is available in C.

DESCRIBTION(click here)

• Low frequency RFID works on the principle of radio waves and at the frequency of 125 KHz. There is a coil inside the RFID tag and when it is influenced by magnetic field, it sends an identity code to a device for further processing. (For more details, refer interfacing RFID with AT89C51).
  
  
  The RFID tag is used as an identity for a particular user. If the identity (serial number of the tag) of the user is matched with the one already stored in this system, he gets immediate access through it. This RFID based secured access system also has many additional features. For example, a new user can register himself with the system. A registered user can also withdraw his entry from the system. These features can be accessed by pressing a tactile switch connected to the microcontroller.
  
  
  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 checking. If the ID is matched by the microcontroller, the user gets the access. 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 after which his identity is verified twice with RFID tag. The new record is stored by the microcontroller to grant future access. The system also shows ‘Error’ if the tags do not match during verification. An existing user can delete his record by pressing the same switch. Again the verification is carried out and the user is deleted if the IDs match. If a different tag is scanned through the reader, 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 treated as an ID for the user and is stored as an array in the microcontroller. If the ID is matched with this code, the user is granted access though the system. For more details on working and connections of the circuit, refer RFID interfacing through serial interrupt.
  
  
  

CIRCUIT DIAGRAM(click here)

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VIDEO(click here)

CODE(click here)

• 
  //Program for RFID based Secured access system using 8051 microcontroller (AT89C51)
  
  #include<reg51.h>
  
  sfr lcd_data_pin=0xA0; //P2 port
  
  sbit rs=P1^0; 
  
  sbit rw=P1^1; 
  
  sbit en=P1^2; 
  
  sbit new_user=P1^3;
  
  unsigned char card_id[12],index=0,key1=0,flag0=0,flag1=0,flag2=0,flag3=0;
  
  unsigned char card_mem[6][12];   //={/*'2','6','0','0','9','3','6','C','B','2','6','B',*/'2','6','0','0','9','1','1','D','D','B','7','1','2','6','0','0','9','3','6','F','7','2','A','8','0','F','0','0','2','D','D','7','D','0','2','5'};
  
  unsigned char current_byte = 0;
  
  void display();
  
  void memory();
  
  
  
  void delay(unsigned int count) //Function to provide time delay
  
  {
  
    int i,j;
  
    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 
  
  {
  
    int 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_command(0x80);
  
   delay(5);
  
  }
  
    
  
  void display()  // Function to display the unique ID
  
  {
  
   unsigned char count,i,key,flag=0,val;
  
   lcd_command(0x01);
  
   lcd_command(0x80);  //Place cursor to second position of second line
  
   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;
  
     lcd_command(0x80);
  
     lcd_string("Access granted");
  
     lcd_command(0xC4);
  
     lcd_string("USER ");
  
     lcd_command(0xC9);
  
     lcd_data(49+i);
  
     delay(100);
  
     break;
  
    }
  
   }
  
   if(flag==0)
  
   {
  
    lcd_command(0x84);
  
    lcd_string("Wrong ID");
  
    delay(200);
  
   }
  
   lcd_command(0x01);
  
   lcd_command(0x80);
  
   lcd_string("Pls scan your ID");
  
   current_byte=0;
  
  }
  
  
  
  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 memory()
  
  {
  
   unsigned char i,key=0,count,try=0,head=0,select=0,mod=0,size;
  
   unsigned int in,j;
  
   lcd_command(0x01);
  
   lcd_string("scan your ID");
  
   current_byte=0;
  
   while(current_byte!=12);
  
   current_byte=0;
  
   for(i=0;i<6;i++)
  
   { 
  
    key=0;
  
    for(count=0;count<12;count++)
  
    { 
  
       if(card_id[count]==card_mem[i][count])
  
     {
  
      key++;
  
     }
  
    }
  
    if(key==12)
  
    {
  
     size=i;
  
     lcd_command(0x01);
  
     lcd_string("Like to delete");
  
     lcd_command(0xC0);
  
     lcd_string("If yes scan ID");
  
     for(in=0;in<500;in++)
  
     {
  
      for(j=0;j<1275;j++)
  
      {
  
       if(current_byte==12)
  
       {
  
       break;
  
       }
  
      }
  
      if(current_byte==12)
  
      {
  
       break;
  
      }
  
     }
  
     if(current_byte==12)
  
     {
  
      for(in=0;in<12;in++)
  
      {
  
       if(card_id[in]==card_mem[size][in])
  
       {
  
        mod++;
  
       } 
  
      }
  
      if(mod==12)
  
      {
  
       for(in=0;in<12;in++)
  
       {
  
        card_mem[size][in]=5;
  
       }
  
       lcd_command(0x01);
  
       lcd_string("congratulation!");
  
       lcd_command(0xC0);
  
       lcd_string("You are deleted");
  
       delay(200);
  
       lcd_command(0x01);
  
       lcd_string("Pls scan your ID");
  
       key=0;
  
       try=1;
  
       break;
  
      }
  
      if(mod!=12)
  
      {
  
       lcd_command(0x01);
  
       lcd_string("You have shown");
  
       lcd_command(0xC0);
  
       lcd_string("different ID");
  
       delay(200);
  
       lcd_command(0x01);
  
       lcd_string("Pls scan your ID");
  
       key=0;
  
       try=1;
  
       break;
  
      }
  
     }
  
     if(current_byte!=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;
  
      break;
  
     }
  
    }
  
   }
  
   current_byte=0;
  
   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;
  
   if(key==12)
  
      {
  
    lcd_command(0x01);
  
    lcd_string("Pls varify again ");
  
    while(current_byte!=12);
  
    key=0;
  
    for(i=0;i<12;i++)
  
    { 
  
     if(card_mem[index][i]==card_id[i])
  
     {
  
      key++;
  
     }
  
    }
  
    current_byte=0;
  
   }
  
   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)
  
   {
  
    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 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++;
  
     }
  
   }
  
   
  
  void main()
  
  {
  
      new_user=1;
  
   TMOD=0x20;       //Enable Timer 1
  
   TH1=0XFD;
  
   SCON=0x50;
  
   TR1=1;
  
   IE=0x94;
  
   new_user=0;        // Trigger Timer 1
  
   lcd_ini();
  
   lcd_command(0x80);     //Place cursor to second position of first line 
  
   lcd_string("Pls scan your ID");
  
   delay(200);
  
   while(1)
  
   {
  
    if(new_user==1)
  
    {
  
     memory();
  
    }
  
    if(current_byte==12)
  
    { 
  
     display();
  
    }
  
   } 
  
  }
  
  
  
  

COMPONENTS(click here)

• AT89C51 Microcontroller
• MAX232 
• LCD

How to interface Stepper Motor with 8051 Microcontroller (AT89C51)

Stepper motor is one of the commonly used motors for precise angular movement. The advantage of using a stepper motor is that the angular position of the motor shaft can be controlled without any feedback mechanism. Stepper motors are widely used in industrial and commercial applications. They are also commonly used as in drive systems of autonomous robots.

This article explains the interfacing of a unipolar stepper motor with AT89C51 microcontroller. The microcontroller is programmed to rotate the stepper in wave drive and half drive stepping modes. For basic concepts and working of a stepper motor, refer the article on Stepper Motors.

DESCRIBTION(click here)

• A Unipolar Stepper Motor is rotated by energizing the stator coils in a sequence. In unipolar stepper, the direction of current in stator coils is not required to be controlled by the driving circuit. Just applying the voltage signals across the motor coils or motor leads in a sequence is sufficient to drive the motor.
  A two phase unipolar stepper motor has a total of six wires/leads of which four are end wires (connected to coils) and two are common wires. The color of common wires in the stepper motor used here is Green. Each common wire is connected to two end leads thus forming two phases. The end leads corresponding to each phase have to be identified
  In some cases, when the leads cannot be directly identified in the motor, the identification of endpoints and common points can be done by measuring the resistance between the leads. The leads of different phase will show open circuited condition with respect to each other. This way the leads corresponding to different phase can be separated. The resistance between any two end points of same phase will be twice the resistance between a common point and an end point. This way the common and end points of both the phases can be identified.
   
  To work with the unipolar stepper motor, the common points are connected to either Ground or Vcc and the end points of both the phases are usually connected through the port pins of a microcontroller. In present case the common (Green) wires are connected to Vcc. The end points receive the control signals as per the controller's output in a particular sequence to drive the motor.
   Since the coils related to each phase are arranged in alternate manner, the end points of two phases are energized in alternate fashion to rotate the motor. This means that the voltage signal should be applied to first end point of Phase1 and then to the first end point of the Phase2 and so on.
  1. Wave Drive Stepping Mode
  The above mentioned sequence is repeated to rotate the motor in Wave Drive Stepping Mode. (For more details on different Stepping Modes, refer to the article on Stepper Motors) The direction of rotation can be clockwise or anti clockwise depending upon the selection of end points.

  Signal sequence for Wave Drive Stepping Mode
  Step	Yellow lead (End point 1 of Phase1)	Blue lead (End point 2 of Phase1)	Red lead (End point 1 of Phase2)	White lead (End point 2 of Phase2)
  1	1	0	0	0
  2	0	0	1	0
  3	0	1	0	0
  4	0	0	0	1

  
  
  

  

  
  2. Full Drive Stepping Mode
  The Full Drive Stepping can be achieved by energizing two endpoints of different phases simultaneously. 

  Signal sequence for Full Drive Stepping Mode
  Step	Yellow lead (End point 1 of Phase1)	Blue lead (End point 2 of Phase1)	Red lead (End point 1 of Phase2)	White lead (End point 2 of Phase2)
  1	1	0	1	0
  2	0	1	1	0
  3	0	1	0	1
  4	1	0	0	1

  
  3. Half Drive Stepping Mode
  The Half Drive Stepping is achieved by combining the steps of Wave and Full Drive Stepping Modes. This divides the stepping angle by half.

  Signal sequence for Half Drive Stepping Mode
  Step	Yellow lead (End point 1 of Phase1)	Blue lead (End point 2 of Phase1)	Red lead (End point 1 of Phase2)	White lead (End point 2 of Phase2)
  1	1	0	0	0
  2	1	0	1	0
  3	0	0	1	0
  4	0	1	1	0
  5	0	1	0	0
  6	0	1	0	1
  7	0	0	0	1
  8	1	0	0	1

  
  Note:
  The stepping angle depends upon the resolution of the stepper motor. The direction of rotation and size of steps is directly related to the order and number of input sequence.  The shaft rotation speed depends on the frequency of the input sequence. The torque is proportional to the number of magnets magnetized at a time.
  Circuit Description:
  In the circuit, Port P2 is defined as output port to provide the input sequence for the stepper motor. Four transistors are used as switches to drive the motor. The motor leads are not directly interfaced with the microcontroller pins because stepper motor requires 60mA current while AT89C51 has the maximum current rating of 50mA. So the transistors switches are used to transfer signals from the microcontroller to the stepper wires.
  The sequence of signals mentioned in the tables above rotates the motor in clockwise direction. Reversing these input sequences would rotate the motor in counter clockwise direction.
  The four transistors used in this circuit could be replaced altogether by ULN2003 as has been explained in the next article.

CIRCUIT DIAGRAM(click here)

• 

VIDEO(click here)

CODE(click here)

• 
  // Program to interface Stepper Motor with 8051 Microcontroller (AT89C51)
  
  /**** Wave Drive Stepping ****/
  
  #include<reg51.h>
  
  sfr stepper=0xA0;
  
  
  
  void delay(unsigned int count)
  
  {
  
   int i;
  
   for(i=0;i<count;i++);
  
  }
  
  
  
  void main()
  
  {
  
   while(1)
  
   {
  
    stepper=0x01;
  
    delay(350);
  
    stepper=0x02;
  
    delay(350);
  
    stepper=0x04;
  
    delay(350);
  
    stepper=0x08;
  
    delay(350);
  
   }
  
  }
  
  /*****************************/
  
  
  
  /**** Half Drive Stepping ****/
  
  #include<reg51.h>
  
  sfr stepper=0xA0;
  
  
  
  void delay(unsigned int count)
  
  { 
  
   int i;
  
   for(i=0;i<count;i++);
  
  }
  
  
  
  void main()
  
  {
  
   while(1)
  
   {
  
    stepper=0x01;
  
    delay(300);
  
    stepper=0x03;
  
    delay(300);
  
    stepper=0x02;
  
    delay(300);
  
    stepper=0x06;
  
    delay(300);
  
    stepper=0x04;
  
    delay(300);
  
    stepper=0x0C;
  
    delay(300);
  
    stepper=0x08;
  
    delay(300);
  
    stepper=0x09;
  
    delay(300);
  
   }
  
  }
  
  /*****************************/
  
  

COMPONENTS(click here)

• AT89C51 Microcontroller
• Transistor BC547