Skip to main content

PIC Countdown Timer (0-99)

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.


Compiled using MikroC for PIC


  Project: PIC Countdown Timer (0-99)
  Vishal K M
  Jan 10, 2012


// 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 Timer Select
sbit Unit_Button at RB1_bit;  // Set unit min
sbit Ten_Button at RB2_bit;   // Set ten min

// Messages
char Message1[]="Timer by VISHAL";
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 MinVal){
 unsigned short temp1, temp2;
 Relay = 1;
 ON_OFF = 1;
 OPTION_REG = 0x80 ;
 INTCON = 0x90;
 for (i=0; i<MinVal; i++){
  temp1 = (MinVal-i)%10 ;
  temp2 = (MinVal-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;
 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);

Facebook page 


  1. Which cristal frequency are you using? 4MhZ, 8Mhz, 20Mhz...

  2. I used 4Mhz, compiler will take care of the Cristal frequency u can use any of them.

  3. hi, hw to modify this circuit & coding if I don't want to use lcd? I want a 10-30 mins countdown timer with alarm (piezo buzzer) as audio output.

  4. How do you set the timer? If you are using a fixed timer its ok.

  5. sir i want its 4 digit for micro second, so what the program please help me


Post a Comment

Popular posts from this blog

PIC 16F877A Microcontroller Based Electronic Lock 16x2LCD 4x3 Keypad

Circuit Diagram

Security is a prime concern in our day-today life. Everyone wants to be as much secure as possible. An access control for doors forms a vital link in a security chain. The microcontroller based digital lock for Doors is an access control system that allows only authorized persons to access a restricted area.
An electronic lock or digital lock is a device which has an electronic control assembly attached to it. They are provided with an access control system. This system allows the user to unlock the device with a password. The password is entered by making use of a keypad. The user can also set his password to ensure better protection. The major components include a Keypad, LCD and the controller PIC16F877A. This article describes the making of an electronic code lock using the 16F877A microcontroller.
The system is fully controlled by the 8 bit microcontroller 16F877A which has a 8Kbytes of ROM for the program memory. The password is stored in the EPROM so that we c…

PIC Serial Communication Tutorial (UART)

First, a quick history of RS232. What is RS232? It's just a name for a standard that has propagated from generation to generation of computers. The first computers had serial ports that used RS232, and even current computers have serial ports (or at least USB ports that act like RS232 ports). Back in the day, serial information needed to be passed from devices like printers, joysticks, scanners, etc to the computer. The simplest way to do this was to pass a series of 1s and 0s to the computer. Both the computer and the device agreed on a speed of information - 'bits per second'. A computer would pass image data to a printer at 9600 bits per second and the printer would listen for this stream of 1s and 0s expecting a new bit every 1/9600 = 104us (104 micro-seconds, 0.000104 seconds). As long as the computer output bits at the pre-determined speed, the printer could listen.
Zoom forward to today. Electronics have changed a bit. Before they were relatively high power, high …