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00-99 Minutes Timer

This project describes how to program PIC16F628A to function as a 00-99 min programmable timer. User can set any time between 00-99 minutes and can turn ON a device for that period. The device will be automatically turned OFF after the time expires. For demonstration, the ON/OFF condition of device is simulated by switching LED ON and OFF. With the use of three input switches (unit, ten, start/stop) the user can set ON time of the timer and can also control Start/Stop operation. The two time set switches are for selecting unit and tens digit of minute time interval (00-99). Once you set the value of minute interval, pressing the Start/Stop will turn the timer ON (LED will glow), and pressing the same button again at any point of time during timer operation will interrupt the process (LED will turn OFF) and the timer will be reset. LCD display will provide timer status and user interface for setting time.

Connect SW1, SW2, and SW3 to RB0, RB1, and RB2 respectively. SW1 will serve Start/Stop, SW2 as unit minute, and SW3 as tens minute. Connect a LED to RA3 port.


  Project: 00-99 Minutes Timer
  Designed By: Rajendra Bhatt
  Date: Sep 03, 2010

  LCD Data D4-D7 connected to RB4-RB7
  LCD RS -> RA0
  LCD E -> RA1
  Start/Stop Time Select -> RB3
  Unit Min Switch -> RB0
  Tens Min Switch -> RB1
  Cancel Switch -> RB2
  Relay -> RA3

// LCD module connections
sbit LCD_RS at RA0_bit;
sbit LCD_EN at RA1_bit;
sbit LCD_D4 at RB4_bit;
sbit LCD_D5 at RB5_bit;
sbit LCD_D6 at RB6_bit;
sbit LCD_D7 at RB7_bit;
sbit LCD_RS_Direction at TRISA0_bit;
sbit LCD_EN_Direction at TRISA1_bit;
sbit LCD_D4_Direction at TRISB4_bit;
sbit LCD_D5_Direction at TRISB5_bit;
sbit LCD_D6_Direction at TRISB6_bit;
sbit LCD_D7_Direction at TRISB7_bit;
// End LCD module connections

// Tact switches and Relay ports
sbit Relay at RA3_bit;
sbit SS_Select at RB0_bit;  // Start Stop Time Select
sbit Unit_Button at RB1_bit;
sbit Ten_Button at RB2_bit;

// Messages
char Message1[]="00-99 min Timer";
char Message2[]="Device ON";
char Message3[]="Device OFF";
char Message4[]="Set Time:    min";
char Message5[]="Time Left:   min";
unsigned short i, j, unit=0, ten=0, ON_OFF=0, index=0, clear, time;
char *digit = "00";
// 300ms Delay
void Delay_300(){

void Display_Digits(){

void start_timer(unsigned short tmin){
 unsigned short temp1, temp2;
 Relay = 1;
 ON_OFF = 1;
 OPTION_REG = 0x80 ;
 INTCON = 0x90;
 for (i=0; i< tmin; i++){
  temp1 = (tmin-i)%10 ;
  temp2 = (tmin-i)/10 ;
  Lcd_Chr(2, 12, temp2+48);
  Lcd_Chr(2, 13, temp1+48);
  do {
  } while(((j<=60) && (Clear ==0)));
  if (Clear) {
   Relay = 0;
   INTCON = 0x00;
   goto stop;
stop: Relay = 0;
ON_OFF = 0;
unit = 0;
ten = 0;
clear = 1;

void interrupt(void){

    if (INTCON.INTF == 1)          // Check if INTF flag is set
     Clear = 1;
     INTCON.INTF = 0;       // Clear interrupt flag before exiting ISR

void main() {
  CMCON  |= 7;                       // Disable Comparators
  TRISB = 0b00001111;
  TRISA = 0b11110000;
  Relay = 0;

  Lcd_Init();                        // Initialize LCD
  clear = 0;
  Lcd_Cmd(_LCD_CLEAR);               // Clear display
  Lcd_Cmd(_LCD_CURSOR_OFF);          // Cursor off
  Display_Digits()  ;
 do {

     unit ++;
     if(unit==10) unit=0;
    } // If !Unit_Button

     ten ++;
     if(ten==10) ten=0;
    } // If !Ten_Button

     time = ten*10+unit ;
     if(time > 0) start_timer(time);
    } // If !SS_Select


    goto start;

    } while(1);


When the power is first turned on, you will see this on LCD screen.

Use SW2 and SW3 to chose time between 00-99 min.

When you press SW1 (Start/Stop), the LED connected at RA3 will be turned ON and you will see the time left message on the screen too.

When the time is UP, or you press SW1 again, the timer will be interrupted, LED will turn OFF, and the timer is reset to original condition.


  1. hi,
    can you upload .HEX file ?

  2. I can't upload files on I can send u in email if you want?

    1. hello
      please send me hexacode file

  3. Hello
    Please send me hexcode by email

  4. Thank you for your great example,

    I have modified the code and added extra function

    please see

  5. Please send me hexcode by email

  6. Great work
    all components available here in India at

  7. Hello
    Please send me hexcode by email

  8. I would appreciate a copy of your hex code.

    Please e-mail to


  9. Hi,
    Please send me hexcode by email

  10. It worked well. I just copy and paste it. I had same setup on portb same as urs, but used 20Mhz osc.

  11. Those 3 btns connected to portb with 10k resistors. The OPTION_REG = $80 meant it is disable. But 3 btns connected to portb w/out resistors. Meant it is enable. Am I right?

  12. It was my mistake, it is not required here as I already have external pull-up resistors. You can find my more advanced Timer project here:

  13. Hi
    Please send me hexcode by email

  14. hi,
    can you send me the .HEX file ?

  15. Hello,
    can you send me hex file?

    Thanks in advanced,

  16. Hi Raj-
    Thanks for a great intro for embedded ckts. Could you please send the hex file :

    Thanks and regards


    Could you please send the hex file

  18. hi, I would appreciate if you send me the hex file

  19. great project. can i add buzzer in this project.

    please reply with solution


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