Alarm Clock using 7-Segment Display and 8051 microcontroller (AT89C51)

An alarm clock is a clock that indicates a pre-set time by producing sound at that time. This functionality of digital clock is used to awaken people or remind them of something. This circuit is an extension to the digital clock with time setting option. Here an extra switch is provided to set the alarm. While the alarm is set, the clock time does not stop and runs in the background. The project is build around the 8051 microcontroller (AT89C51)

To provide various options in the digital clock, following switches are used:

Switch 1 (S₁) : Reset (to initiate the time set option)

Switch 2 (S₂) : Select (to select the segment where value is to be changed)

Switch 3 (S₃) : Increment (to increase the value at selected segment)

Switch 4 (S₄) : Start (to start the clock with the set time options)

Switch 5 (S₅) : Alarm (to initiate the alarm set option)

The option to set alarm is provided by providing an extra switch S₅, with the microcontoller At89C51, which is made active low. Whenever S₅ is pressed, the time display goes off and only 1^st segment is activated. But the clock time still runs in the background. In this mode, a segment can be selected in cyclic order by pressing S₂. After selecting the desired segment, its value can be changed by using S₃. Once the digits and hence the alarm is set, S₄ is pressed to start the clock again. As soon as the set alarm time is reached, a buzzer gets signal from the microcontroller thus producing sound.

The seven segments are interfaced to port P₂ of the microcontroller AT89C51 through its data pins (a – h). The enable pins are connected to pins 1-4 of port P₁ (P₁^0 – P₁^3). The switches S₁-S₅ and buzzer are connected as following:

S₁ : P₁^4 S₄ : P₃^3

S₂ : P₁^6 S₅ : P₁^5

S₃ : P₁^7 Buzzer : P₃^7

The buzzer is connected to the output pin of microcontroller at the negative end and to V_cc at the positive end.

Project Source Code

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// Program to make a digital clock with time and alarm setting features

#include<reg51.h>
sbit dig_ctrl_4=P1^0;  //Declare the control pins for the seven segments
sbit dig_ctrl_3=P1^1;
sbit dig_ctrl_2=P1^2;
sbit dig_ctrl_1=P1^3;
sbit buzzer=P3^7;
sbit resetalarm=P1^5;  //Reset alarm pin to reset the alarm.
sbit resetclock=P1^4;  //Reset clock pin to reset the clock.
sbit start=P3^3;  // Start pin for starting the clock after time setting
sbit incr=P1^7;  // Increment pin to increase the digits during time setting.
sbit set=P1^6;  // Set pin to set the time.
int sel_seg_to_incr=0;
int ret_seg_to_incre=0;
int recnt_incr_seg;
int begin;
unsigned char dig_disp=0;
int min2=0;
int min1=0;
int sec2=0;
int sec1=0;
int minalarm2=0;
int minalarm1=0;
int secalarm2=0;
int secalarm1=0;
int alarmmin2=0;
int alarmmin1=0;
int alarmsec2=0;
int alarmsec1=0;
int keepmin2=0;
int keepmin1=0;
int keepsec2=0;
int keepsec1=0;
int loop=0;
int mode;
char dig_val[10]={0x40,0xF9,0x24,0x30,0x19,0x12,0x02,0xF8,0x00,0x10};  // Hex values corresponding to digits 0 to 9

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

int setfn()  // Function to select miniute and seconds digit set time.
{      
while(set==0)
{
  switch(recnt_incr_seg)
  {
 
   case 1:
   if(set==0)  //Select the min2 digit
   {
    dig_ctrl_4=1;
    dig_ctrl_3=0;
    dig_ctrl_2=0;
    dig_ctrl_1=0;
    recnt_incr_seg=1;
    ret_seg_to_incre=1;
    P2=dig_val[minalarm2];  
    delay(100);
   }
 
   case 2:
   if(set==0)  //Select the min1 digit
   {
    dig_ctrl_4=0;
    dig_ctrl_3=1;
    dig_ctrl_2=0;
    dig_ctrl_1=0;
    recnt_incr_seg=2;
    ret_seg_to_incre=2;
    P2=dig_val[minalarm1];  
    delay(100);
   }
 
   case 3:
   if(set==0)  //Select the sec 2 digit
   {
    dig_ctrl_4=0;
    dig_ctrl_3=0;
    dig_ctrl_2=1;
    dig_ctrl_1=0;
    recnt_incr_seg=3;
    ret_seg_to_incre=3;
    P2=dig_val[secalarm2];  
    delay(100);
   }
 
   case 4:
   if(set==0)  //Select the sec1 digit
   {
    recnt_incr_seg=1;
    dig_ctrl_4=0;
    dig_ctrl_3=0;
    dig_ctrl_2=0;
    dig_ctrl_1=1;
    ret_seg_to_incre=4;
    P2=dig_val[secalarm1];
    delay(100);
    recnt_incr_seg=1;
   }
  }
}
return(ret_seg_to_incre);
}

void increase(int a)  //Function to set the minutes or seconds digit
{
while(incr==0)
{
  switch(a)
  {
  
   case 1:  // Set the min2 digit.
   P2=dig_val[minalarm2];
   delay(100);
   minalarm2++;
   if(minalarm2==6)
   minalarm2=0;
   P2=dig_val[minalarm2];
   delay(20);
   break;
 
   case 2:  //Set the min1 digit.
   P2=dig_val[minalarm1];
   delay(100);
   minalarm1++;
   if(minalarm1==10)
   minalarm1=0;
   P2=dig_val[minalarm1];
   delay(20);
   break;
 
   case 3:  // Set the sec2 digit.
   P2=dig_val[secalarm2];
   delay(100);
   secalarm2++;
   if(secalarm2==6)
   secalarm2=0;
   P2=dig_val[secalarm2];
   delay(20);
   break;
 
   case 4:  //Set the sec1 digit.
      //recnt_incr_seg=4;
   P2=dig_val[secalarm1];
   delay(100);
   secalarm1++;
   if(secalarm1==10)
   secalarm1=0;
   P2=dig_val[secalarm1];
   delay(20);
   break;
  }
}
}

void resetfn(mode)  // Function to bring the clock to reset or set mode.
{
  begin=1;
dig_ctrl_4=1;  //Enable the min2 digit and disable others
dig_ctrl_3=0;
dig_ctrl_2=0;
dig_ctrl_1=0;
if(mode==0)  //Check if clock is in set alarm mode
{
   IE=0x88;  //Disable Timer0 interrupt to stop the display of clock.
  sel_seg_to_incr=1;
  recnt_incr_seg=1;
  P2=dig_val[keepmin2];
  delay(100);
  minalarm2=keepmin2;
  minalarm1=keepmin1;
  secalarm2=keepsec2;
  secalarm1=keepsec1;
}
if(mode==1)  //Check if clock is in set clock mode
{
  IE=0x80;  //Disable Timer0 interrupt to stop the clock.
  minalarm2=min2;
  minalarm1=min1;
  secalarm2=sec2;
  secalarm1=sec1;
  sel_seg_to_incr=1;
  recnt_incr_seg=1;
  P2=dig_val[min2];
  delay(100);
}
while(1)
{   
  if(start==0)  //Check if start pin is pressed
  {
   if(mode==0)
   {
    keepmin2=minalarm2;
    keepmin1=minalarm1;
    keepsec2=secalarm2;
    keepsec1=secalarm1;
    alarmmin2=minalarm2;
    alarmmin1=minalarm1;
    alarmsec2=secalarm2;
    alarmsec1=secalarm1;
    }
   if(mode==1)
   {
    min2=minalarm2;
    min1=minalarm1;
    sec2=secalarm2;
    sec1=secalarm1;
    }
  TMOD=0x11;  //Reset the timer0
  TL0=0xf6;
  TH0=0xFf;
  IE=0x8A;  //Enabling Timer0 interrupt to start the display of clock
  TR0=1;
  break;
  }
  if(set==0)  //Check if set pin is pressed
  sel_seg_to_incr=setfn();
  if(incr==0)  //Check if incr pin is pressed
  increase(sel_seg_to_incr);
}
}

void display() interrupt 1  // Function to display the digits on seven segment using the concept of seven segment multiplexing.
{
TL0=0x36;  //Reload Timer0
    TH0=0xf6;
    P2=0xFF;
dig_ctrl_1 = dig_ctrl_3 = dig_ctrl_2 = dig_ctrl_4 = 0;
dig_disp++;
dig_disp=dig_disp%4;
switch(dig_disp)
{
  case 0:
  P2=dig_val[sec1];
  dig_ctrl_1 = 1;
  break;

  case 1:
  P2= dig_val[sec2];
  dig_ctrl_2 = 1;
  break;

  case 2:
  P2= dig_val[min1];
  dig_ctrl_3 = 1;
  break;

  case 3:
  P2= dig_val[min2];
  dig_ctrl_4 = 1;
  break;
}
}

void moveclock() interrupt 3  // Function to increment clock digits
{
loop++;
if(loop==20)
{
  sec1++;
  if(sec1==10)
  {
   sec1=0;
   sec2++;
   if(sec2==6)
   {
    sec1=0;
    sec2=0;
    min1++;
    if(min1==10)
    {
     sec1=0;
     sec2=0;
     min1=0;
     min2++;
     if(min2==6)
     {
      sec1=0;
      sec2=0;
      min1=0;
      min2=0; 
     }
    }
   }
  }
  loop=0;
}
}

void main()
{
mode=0;
set=1;  //Initialize set, reset, start and incr pins as input
resetalarm=1;
resetclock=1;
start=1;
incr=1;
begin=0;
TMOD=0x11;  //Intialize Timer 0
TL0=0xf6;  //Load timer0
TH0=0xFf;
IE=0x8A;  //Enable Timer0 interrupt
TR0=1;  //Start Timer0
TL1=0xFD;
TH1=0x4B;
TR1=1;  // Start Timer1
while(1)
{
  h
  if(resetalarm==0)  //Check if reset alarm pin is pressed
  {
   resetfn(0);
  }
  if(resetclock==0)//Check if reset clock pin is pressed
  {
   resetfn(1);
  }
  if(min2==alarmmin2&&min1==alarmmin1&&sec2==alarmsec2&&sec1==alarmsec1&&begin==1)// Check for Alarm condition
  {
  buzzer=0;
  delay(500);
  buzzer=1;
  }  
}
}


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