1. Buzzer Interface 
#include “at89c51xd2.h”
#define offTime 20
#define onTime 20
sbit buzz=P0^5;
idata unsigned int i;
void main()
{
TMOD=0X01;
TCON=0X00;
TL0=0;
TH0=0XF8;
TF0=0;
while(1)
{
buzz=1;
for(i=0;i<onTime TL0=0X00; TH0=0XF8; TR0=1; TF0=0; TR0=0; buzz=0; for(i=0;i TL0=0X00; TH0=0XF8; TR0=1; TF0=0; TR0=0; sw=1; led=0; led=1; led=0; SW=P3^0; xss=removed for(i=0;i xss=removed xss=removed buz=0x01; for(i=0;i buz=0x00; for(i=0;i port_val[10]={0x3F, arr_dec[6]={0,16,32,48,64,80}; for(i=0;i for(j=0;j input=987654; arr[6]={0}; i=5; while(input!=0) arr[i]=input; input=input/10; for(i=0;i p0=port_val(i); p1=arr_dec(arr[i]); Dir=0; Dir=~Dir;>0;x--);
}
void main()
{
   unsigned char val;
    int i;
   EA=0x01;
 EX1=0x01;
    while(1)
    {
        if(Dir)
        {
            val=0x08;
            for(i=0;i<4 P0=val; val=val>>1;
                delay(575);
            }
 }
else
   {
    val=0x01;
      for(i=0;i<4 P0=val; val=val>
#include <SD>
File myFile;
void setup()
{
  Serial.begin(9600); 
  Serial.print("Initializing SD card...");
   pinMode(10, OUTPUT); 
  if (!SD.begin(4)) 
  {
    Serial.println("initialization failed!");
    return;
  }
  Serial.println("initialization done."); 
}
void loop()
{
    char ch;
    ch=Serial.read();
    if(ch=='w' || ch=='W')
    { 
       myFile = SD.open("test.txt",FILE_WRITE);
       if (myFile) 
       {
             Serial.print("Writing to test.txt...");
             myFile.println("India is our Country");
             myFile.println("VIT is a Place to Learn");
             myFile.println("VIT is a Place to Grow");
             myFile.close();
             Serial.println("done.");
       }
       else {
       Serial.println("error opening test.txt");
            }
    }
  else if(ch=='r' || ch=='R')
  {
       myFile = SD.open("test.txt");
      if (myFile) 
       {
           Serial.println("test.txt:");
       while (myFile.available()) 
       {
        Serial.write(myFile.read());
        }
       myFile.close();
      } 
      else {
        Serial.println("error opening test.txt");
     }
  }
}

8. LM35 sensor interfacing
const int sensor=A1;
float tempc;
float tempf;
float vout;
void setup()
{
 pinMode(sensor,INPUT);
 Serial.begin(9600);
}
void loop()
{
 vout=analogRead(sensor);
 vout=(vout*1.8)/1023;
 tempc=vout;
 Serial.print("in DegreeC=");
 Serial.print("\t");
 Serial.print(tempc);
 Serial.println();
 delay(1000);
}

9. Data logging using flash memory system and LM35 sensor

#include <SPI>
#include <SD>

File myFile;
int i=1;
void setup()
{
Serial.begin(9600);
Serial.print("Initializing SD card...");
pinMode(10, OUTPUT);

if (!SD.begin(4)) 
  {
Serial.println("initialization failed!");
return;
   }
Serial.println("initialization done.");
}

void loop()
{
    
char ch='w';
ch=Serial.read();
int val;
    val=analogRead(0);
if((ch=='w' || ch=='W'))
    {
myFile = SD.open("test1.txt",FILE_WRITE);
val=analogRead(0);
if (myFile) 
       {
Serial.print("Writing to test.txt...");
myFile.print(i);
myFile.print("                      ");
myFile.println(val);
myFile.close();
i++;
Serial.println("done.");
       }
else {
Serial.println("error opening test.txt");
            }
    }
else if(ch=='r' || ch=='R')
  {
myFile = SD.open("test1.txt");
if (myFile) 
       {
Serial.println("test1.txt:");
while (myFile.available()) 
       {
Serial.write(myFile.read());
        }
myFile.close();
      } 
else {
Serial.println("error opening test.txt");
     }
  }
}