This digital clock not only displays time (on four seven segment displays) but also provides the user an option to set the time. For this the user has to first press the reset switch after which he/she can select and set a particular digit by incrementing its value. To run the clock with the set time, the user needs to press the start button. The seven segment and switches are interfaced with microcontroller AT89C51.
This idea to provide option for setting time can be implemented in conjunction with the digital clock circuit. The control options for time setting are provided by means of tactile switches which are made active low. This circuit uses four such switches for following functions.
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)
As soon as S1 is pressed, the running clock stops and it goes into the reset mode where the first segment is activated. The segment to be set can be selected in cyclic order each time S2 is pressed. After selecting the desired segment, its value can be changed by using S3. Once the digits and hence the time is set, S4 is pressed to start the clock again.
The seven segments are interfaced to port P2 of the microcontroller 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-S4 are connected as following to provide ground to the corresponding pins of port P1:
S1 : P1^4
S2 : P1^5
S3 : P1^6
S4 : P1^7
Project Source Code
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// Program to make a clock with time setting functionality. #include<reg51.h> sbit dig_ctrl_4=P1^0; //Declare the control pins of the seven segment sbit dig_ctrl_3=P1^1; sbit dig_ctrl_2=P1^2; sbit dig_ctrl_1=P1^3; sbit reset=P1^4; // Reset pin to reset the clock. sbit start=P1^7; //Start pin to start the clock after the time is set. sbit incr=P1^6; //Increment pin to increase the digits during time setting. sbit set=P1^5; // Set pin to set the time. int sel_seg_to_incr=0; int ret_seg_to_incre=0; int recnt_incr_seg; unsigned char dig_disp=0; int min2=0; int min1=0; int sec2=0; int sec1=0; char dig_val[10]={0x40,0xF9,0x24,0x30,0x19,0x12,0x02,0xF8,0x00,0x10}; // to store values corresponding to digits 0 to 9 void delay(int a) // Function to provide a time delay of approx. 1 second using Timer1. { int i; for(i=0;i<a;i++) { TL1=0xFD; TH1=0x4B; TR1=1; while(TF1==0); TR1=0; TF1=0; } } int setfn() // Function to select minute and seconds digit to be set. { 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[min2]; delay(20); } 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[min1]; delay(20); } 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[sec2]; delay(20); } 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[sec1]; delay(20); recnt_incr_seg=1; } } } return(ret_seg_to_incre); } void increase(int a) //Function to set the minute or seconds digit { while(incr==0) { switch(a) { case 1: // To set the min2 digit. P2=dig_val[min2]; //Display the value of min2 delay(15); min2++; if(min2==6) min2=0; P2=dig_val[min2]; delay(5); break; case 2: //To set the min1 digit. P2=dig_val[min1]; delay(15); min1++; if(min1==10) min1=0; P2=dig_val[min1]; delay(5); break; case 3: // To set the sec2 digit. P2=dig_val[sec2]; delay(15); sec2++; if(sec2==6) sec2=0; P2=dig_val[sec2]; delay(5); break; case 4: //To set the sec1 digit. P2=dig_val[sec1]; delay(15); sec1++; if(sec1==10) sec1=0; P2=dig_val[sec1]; delay(5); break; } } } void resetfn() // This function brings the clock to reset or set mode. { IE=0x80; //Disable timer0 interrupt to stop the display of the clock sel_seg_to_incr=1; recnt_incr_seg=1; dig_ctrl_4=1; dig_ctrl_3=0; dig_ctrl_2=0; dig_ctrl_1=0; P2=dig_val[min2]; delay(5); while(1) { if(start==0) //check if start pin is pressed { TMOD=0x11; //reset the timer0 TL0=0xf6; TH0=0xFf; IE=0x82; //enabling again the timer0 interrupt to start displaying of the clock TR0=1; break; // break loop and return to main program } if(set==0) //if set pin is pressed call set function sel_seg_to_incr=setfn(); if(incr==0) // if incr pin is pressed call incr function increase(sel_seg_to_incr); } } void display() interrupt 1 // function to display the values on seven segmnet. For more details refer seven segment multiplexing. { TL0=0x36; //reloading 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 main() //main function the programs begins from here { set=1; //delaring set, reset, start and incr as input pins reset=1; start=1; incr=1; TMOD=0x11; //enabling timer0 TL0=0xf6; //loading timer0 TH0=0xFf; IE=0x82; //initialize timer0 interrupt TR0=1; //triggering timer0 while(1) //forward counting of clock { while(min2<6) { while(min1<10) { while(sec2<6) { while(sec1<10) { if(reset==0) resetfn(); delay(20); sec1++; } sec1=0; sec2++; } sec1=0; sec2=0; min1++; } sec1=0; sec2=0; min1=0; min2++; } min2=0; } }###
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Filed Under: 8051 Microcontroller
Filed Under: 8051 Microcontroller