How to interface Servo Motor with 8051 Microcontroller (AT89C51)

This project demonstrates the operation of a servo motor. The control signals for the rotation of the motor are provided by 8051 microcontroller (AT89C51). Here, the servo arm is rotated by 5° from the previous position, starting from 0 °as initial position. As the servo reaches a limit, the arm comes back to the initial position (0°). For basic concepts and know-how of a servo motor, refer to the article Servo Motor.

DESCRIBTION(click here)

• The servo motor is controlled by feeding pulse width modulated (PWM) signal at the control wire of the servo motor. In addition a 4.8V (ideally 5V) DC supply is provided to the red lead of the servo. The black lead of the servo is connected to Ground.
  
  The first pin of port P1 (P1^0) of AT89C51 microcontroller is set as the output pin to provide control signal to the servo motor. Before connecting to the control wire of servo, the output from the microcontroller is fed through a comparator IC (LM324) so that the signal is protected from any loss due to overloading.
  
  In the program, one of the 8051 timers is configured to generate flag after every 50 µs. Usually the pulse durations corresponding to 0° and 180° angular positions are 1ms and 2ms, but these durations may vary for different servos. Here, a pulse with ON time of 700 µs sets the motor closer to 0° and a pulse of 5500 µs sets the motor to 180°. A variable is taken which is initialized to a value 14. A function using timer is written that has the variable mentioned above as an argument. This function generates time delay in the multiples of 50 µs. Initially when the microcontroller executes program, a pulse with ON time of 700 µs (14 x 50 µs) followed by OFF time of 18 ms is generated. This shifts the servo horn to 0° angle.
  
  Every time the value of variable is increased by 5. This increases the ON time of pulse by 250 µs (5 x 50 µs). So every new pulse has an ON time 250 µs greater than the previous one. This is followed by an OFF time of 18 ms. In this way, at every loop the servo is rotated by 5° ahead.
  As the value of variable reaches above 100 it is again set to 14. This moves the servo back to the initial position of 0° after a full rotation.
  
  

CIRCUIT DIAGRAM(click here)

• 

VIDEO(click here)

CODE(click here)

• 
  
  // Program to rotate servo by 5 degree from previous position starting from 0 degree
  
  
  
  // 0 degree = 700us 
  
  // 180 degree = 5500us
  
  // Timer1 pulse after 50us -23
  
  
  
  #include<reg51.h>
  
  sbit output=P1^0;    //Output to motor
  
  int count;
  
  
  
  void delay(unsigned int msec)   // Function for delay
  
  {
  
   int i,j;
  
   for(i=0;i<msec;i++)
  
    for(j=0;j<1275;j++);
  
  } 
  
  
  
  void timer(int msec)  // Function for timer
  
  {
  
   int i;
  
   TR1=1;
  
   for(i=0;i<msec;i++)
  
   {
  
    while(TF1==0);
  
    TF1=0;
  
   }
  
   TR1=0;
  
  }
  
  void main()
  
  {
  
   int i;
  
   TMOD=0x20;   // Mode2
  
   TH1= -23;  // 50usec timer
  
   output=0;
  
   count=14;
  
   while(1)
  
   {
  
    if(count>=100)
  
     count=14;
  
    else
  
     count=count+5;
  
    for(i=0;i<200;i++)
  
    {
  
     output=1;
  
     timer(count);   
  
     output=0;
  
     timer(360);
  
    }
  
    delay(100);
  
   }
  
  }
  
  
  
  

COMPONENTS(click here)

• AT89C51 Microcontroller
  IC LM324

How to interface GPS with 8051 Microcontroller (AT89C51)

GPS has become an efficient tool in the field of scientific use, commerce, surveillance and tracking. This project presents a small application based on Global Positioning System. It depicts the use of GPS module/receiver to find latitude and longitude of its location. The data obtained from GPS receiver (GPGGA sentence) is processed by the microcontroller to extract its latitude and longitude values.

The GPS Module has been interfaced with AT89C51 and the location values are displayed on a 16x2 LCD interface.

DESCRIBTION(click here)

• The GPS module continuously transmits serial data (RS232 protocol) in the form of sentences according to NMEA standards. The latitude and longitude values of the location are contained in the GPGGA sentence (refer NMEA format). In this program, these values are extracted from the GPGGA sentence and are displayed on LCD.
  
  The serial data is taken from the GPS module through MAX232 into the SBUF register of 8051 controller (refer serial interfacing with 8051). The serial data from the GPS receiver is taken by using the Serial Interrupt of the controller. This data consists of a sequence of NMEA sentences from which GPGGA sentence is identified and processed.
  
  The extraction of location values is done as follows. The first six bytes of the data received are compared with the pre-stored ($GPGGA) string and if matched then only data is further accounted for; otherwise the process is repeated again. From the comma delimited GPGGA sentence, latitude and longitude positions are extracted by finding the respective comma positions and extracting the data. The latitude and longitude positions extracted are displayed on the LCD interfaced with AT89C51.
  
  To obtain more details (other than latitude and longitude) from the GPS receiver, GPRMS sentence can be used. Refer next article.
  
  The circuit connections are as follows:
  Receiver1 (R₁) of MAX232 has been used for the serial communication. The receiver pin of GPS module is connected to R₁IN (pin13) of MAX232. R₁OUT (pin 12) of MAX232 is connected to RxD (P3.0) of AT89C51.
  
  Pins 1-3 of port P1 (P1.0, P1.1 & P1.2 respectively) of AT89C51 are connected to the control pins (RS, R/W& EN) of LCD. The data pins of LCD are connected to Port P2 of the controller. The latitude and longitude positions are displayed on the LCD. 
  
  

CIRCUIT DIAGRAM(click here)

• 

VIDEO(click here)

CODE(click here)

• 
  
  /* Basic program to show latitude and longitude on LCD extracted from GPGGA statement */
  
   
  
  #include<reg51.h>
  
  #define port2 P2
  
  sbit rs = P1^0;
  
  sbit rw = P1^1;
  
  sbit e = P1^2;
  
  char info[70];
  
  char test[6]={"$GPGGA"};
  
  char comma_position[15];
  
  unsigned int check=0,i;
  
  unsigned char a;
  
  void receive_data();
  
  void lcd_latitude();
  
  void lcd_longitude();
  
   
  
  //DELAY FUNCTION
  
  void delay(unsigned int msec)
  
  {
  
  int i,j ;
  
  for(i=0;i<msec;i++)
  
  for(j=0;j<1275;j++); 
  
  }
  
   
  
  // LCD COMMAND SENDING FUNCTION
  
  void lcd_cmd(unsigned char item)
  
  {
  
  port2 = item;
  
  rs= 0;
  
  rw=0;
  
  e=1;
  
  delay(1);
  
  e=0;
  
  return;
  
  } 
  
   
  
  // LCD DATA SENDING FUNCTION
  
  void lcd_data(unsigned char item)
  
  {
  
  port2 = item;
  
  rs= 1;
  
  rw=0;
  
  e=1;
  
  delay(1);
  
  e=0;    
  
  return;
  
  }
  
   
  
   // LCD STRING SENDING FUNCTION 
  
  void lcd_string(unsigned char *str)
  
  {
  
  int i=0;
  
  while(str[i]!='\0')
  
  {
  
          lcd_data(str[i]);
  
          i++;
  
          delay(10);
  
     }
  
          return;
  
  }
  
   
  
  // SERIAL PORT SETTING
  
  void serial()
  
  {
  
  TMOD=0x20;      //MODE=2
  
  TH1=0xfa;     // 4800 BAUD
  
  SCON=0x50  ;    // SERIAL MODE 1 ,8- BIT DATA ,1 STOP BIT ,1 START BIT , RECEIVING ON
  
  TR1=1;         //TIMER START
  
  }
  
   
  
  void find_comma()
  
  {
  
  unsigned int i,count=0;
  
  for(i=0;i<70;i++)
  
  {
  
  if(info[i]==',')
  
  {
  
  comma_position[count++]=i;
  
  }
  
      }
  
  }
  
  void compare()
  
  {  
  
  IE=0x00;       //Interrupt disable 
  
  find_comma();   //Function to detect position of comma in the string
  
  lcd_latitude();   //Function to show Latitude
  
  lcd_longitude(); //Function to show Longitude
  
  check=0;
  
  IE=0x90;   //Interrupt enable
  
  }
  
  void receive_data()   interrupt 4  
  
  {
  
  info[check++]=SBUF;  //Read SBUF
  
  if(check<7)         //Condition to check the required data
  
      {
  
  if(info[check-1]!=test[check-1])
  
  check=0;
  
      }
  
  RI=0;
  
  }
  
  void lcd_shape()      //Function to create shape of degree
  
  {
  
  lcd_cmd(64);
  
  lcd_data(10);
  
  lcd_data(17);
  
  lcd_data(17);
  
  lcd_data(10);
  
  lcd_data(0);
  
  lcd_data(0);
  
  lcd_data(0);
  
  lcd_data(0);
  
  }
  
   
  
  void lcd_latitude() //Function to display Latitude
  
  {
  
  unsigned int c2=comma_position[1]; //Position of second comma
  
  lcd_shape();
  
  lcd_cmd(0x01);         // Clear LCD display
  
  lcd_cmd(0x84);         //Move cursor to position 6 of line 1
  
  lcd_string("LATITUDE"); //Showing Latitude
  
  lcd_cmd(0xC0); //Beginning of second line  
  
  lcd_data(info[c2+1]);
  
  lcd_data(info[c2+2]);
  
  lcd_data(0); //Degree symbol
  
  lcd_data(info[c2+3]);
  
  lcd_data(info[c2+4]);
  
  lcd_data(info[c2+5]);
  
  lcd_data(info[c2+6]);
  
  lcd_data(info[c2+7]);
  
  lcd_data(info[c2+8]);
  
  lcd_data(info[c2+9]);
  
  lcd_data(0x27);          //ASCII of minute sign(')
  
  lcd_data(info[c2+10]);
  
  lcd_data(info[c2+11]);
  
  delay(250);
  
  } 
  
   
  
  void lcd_longitude()
  
  {
  
  unsigned int c4=comma_position[3];
  
  lcd_cmd(0x01);            //Clear LCD display
  
  lcd_cmd(0x84);            //Move cursor to position 4 of line 1
  
  lcd_string("LONGITUDE"); //Showing Longitude
  
  lcd_cmd(0xC0);    //Begining of second line  
  
  lcd_data(info[c4+1]);
  
  lcd_data(info[c4+2]);
  
  lcd_data(info[c4+3]);
  
  lcd_data(0);
  
  lcd_data(info[c4+4]);
  
  lcd_data(info[c4+5]);
  
  lcd_data(info[c4+6]);
  
  lcd_data(info[c4+7]);
  
  lcd_data(info[c4+8]);
  
  lcd_data(info[c4+9]);
  
  lcd_data(info[c4+10]);
  
  lcd_data(0x27);               //ASCII of minute sign(')
  
  lcd_data(info[c4+11]);
  
  lcd_data(info[c4+12]);
  
  delay(250);
  
  }
  
  void main()
  
  {
  
  serial();
  
  lcd_cmd(0x38);        //2 LINE, 5X7 MATRIX
  
  lcd_cmd(0x0e);         //DISPLAY ON, CURSOR BLINKING
  
  IE=0x90;
  
  while(1)
  
  {
  
  if(check==69)
  
  compare();
  
  }
  
  }
  
  
  
  

COMPONENTS(click here)

• AT89C51 Microcontroller
  MAX232
  LCD