Arduino Stopwatch

by Rezz on October 7, 2011

Arduino projects, running stopwatch on arduino.

Parts List;
1) 1x 16×2 parallel LCD display (compatible with Hitachi HD44780 driver)
2) 1x Arduino
3) 1x 10kΩ potentiometer
4) 1x 10kΩ resistor
5) 1x switch
6) Jumper wire

Instruction;
1) Connect all jumper wire as shown in diagram.

2) Connect digital input from switch to digital pin 2.

Upload this code to your arduino

/*
  Stopwatch
  Run stopwatch with arduino.
  
  Code based on: http://danthompsonsblog.blogspot.com/2008/11/timecode-based-stopwatch.html
  Coded by: arduinoprojects101.com
*/

// include the library code:
#include <LiquidCrystal.h>

// initialize the library with the numbers of the interface pins
LiquidCrystal lcd(7, 8, 9, 10, 11, 12);

int ledPin = 13;                    // LED connected to digital pin 13
int buttonPin = 2;                  // button on pin 2

int value = LOW;                    // previous value of the LED
int buttonState;                    // variable to store button state
int lastButtonState;                // variable to store last button state
int blinking;                       // condition for blinking - timer is timing
int frameRate = 100;                // the frame rate (frames per second) at which the stopwatch runs - Change to suit
long interval = (1000/frameRate);   // blink interval
long previousMillis = 0;            // variable to store last time LED was updated
long startTime ;                    // start time for stop watch
long elapsedTime ;                  // elapsed time for stop watch
int fractional;                     // variable used to store fractional part of Frames
int fractionalSecs;                 // variable used to store fractional part of Seconds
int fractionalMins;                 // variable used to store fractional part of Minutes
int elapsedFrames;                  // elapsed frames for stop watch
int elapsedSeconds;                 // elapsed seconds for stop watch
int elapsedMinutes;                 // elapsed Minutes for stop watch
char buf[10];                       // string buffer for itoa function

void setup()
{
  lcd.begin(16, 2);                // intialise the LCD.
  pinMode(ledPin, OUTPUT);         // sets the digital pin as output
  pinMode(buttonPin, INPUT);       // not really necessary, pins default to INPUT anyway
  digitalWrite(buttonPin, HIGH);   // turn on pullup resistors. Wire button so that press shorts pin to ground.
}

void loop(){
  digitalWrite(ledPin, LOW);            // Initiate LED and Step Pin States

  buttonState = digitalRead(buttonPin); // Check for button press, read the button state and store

// check for a high to low transition if true then found a new button press while clock is not running - start the clock    
   if (buttonState == LOW && lastButtonState == HIGH  &&  blinking == false){
    startTime = millis();                               // store the start time
      blinking = true;                                  // turn on blinking while timing
      delay(10);                                         // short delay to debounce switch
      lastButtonState = buttonState;                    // store buttonState in lastButtonState, to compare next time 
   }

// check for a high to low transition if true then found a new button press while clock is running - stop the clock and report
   else if (buttonState == LOW && lastButtonState == HIGH && blinking == true){
   blinking = false;                                    // turn off blinking, all done timing
   lastButtonState = buttonState;                       // store buttonState in lastButtonState, to compare next time

// Routine to report elapsed time            
   elapsedTime =   millis() - startTime;                // store elapsed time
   elapsedMinutes = (elapsedTime / 60000L);
   elapsedSeconds = (elapsedTime / 1000L);              // divide by 1000 to convert to seconds - then cast to an int to print
   elapsedFrames = (elapsedTime / interval);            // divide by 100 to convert to 1/100 of a second - then cast to an int to print
   fractional = (int)(elapsedFrames % frameRate);       // use modulo operator to get fractional part of 100 Seconds
   fractionalSecs = (int)(elapsedSeconds % 60L);        // use modulo operator to get fractional part of 60 Seconds
   fractionalMins = (int)(elapsedMinutes % 60L);        // use modulo operator to get fractional part of 60 Minutes
   lcd.clear();                                         // clear the LDC

 if (fractionalMins < 10){                            // pad in leading zeros
      lcd.print("0");                                 // add a zero
      }

    lcd.print(itoa(fractionalMins, buf, 10));       // convert the int to a string and print a fractional part of 60 Minutes to the LCD
      lcd.print(":");                                 //print a colan. 

 if (fractionalSecs < 10){                            // pad in leading zeros
      lcd.print("0");                                 // add a zero
      }

 lcd.print(itoa(fractionalSecs, buf, 10));          // convert the int to a string and print a fractional part of 60 Seconds to the LCD
   lcd.print(":");                                    //print a colan. 

 if (fractional < 10){                                // pad in leading zeros 
      lcd.print("0");                                 // add a zero
      }     

 lcd.print(itoa(fractional, buf, 10));              // convert the int to a string and print a fractional part of 25 Frames to the LCD
   }

 else{
      lastButtonState = buttonState;                  // store buttonState in lastButtonState, to compare next time
   }

// run commands at the specified time interval
// blink routine - blink the LED while timing
// check to see if it's time to blink the LED; that is, the difference
// between the current time and last time we blinked the LED is larger than
// the interval at which we want to blink the LED.

 if ( (millis() - previousMillis > interval) ) {

    if (blinking == true){
       previousMillis = millis();                    // remember the last time we blinked the LED

       digitalWrite(ledPin, HIGH);                   // Pulse the LED for Visual Feedback

       elapsedTime =   millis() - startTime;         // store elapsed time
         elapsedMinutes = (elapsedTime / 60000L);      // divide by 60000 to convert to minutes - then cast to an int to print
         elapsedSeconds = (elapsedTime / 1000L);       // divide by 1000 to convert to seconds - then cast to an int to print
         elapsedFrames = (elapsedTime / interval);     // divide by 40 to convert to 1/25 of a second - then cast to an int to print
         fractional = (int)(elapsedFrames % frameRate);// use modulo operator to get fractional part of 25 Frames
         fractionalSecs = (int)(elapsedSeconds % 60L); // use modulo operator to get fractional part of 60 Seconds
         fractionalMins = (int)(elapsedMinutes % 60L); // use modulo operator to get fractional part of 60 Minutes
         lcd.clear();                                  // clear the LDC

       if (fractionalMins < 10){                     // pad in leading zeros
         lcd.print("0");                             // add a zero
         }

       lcd.print(itoa(fractionalMins, buf, 10));   // convert the int to a string and print a fractional part of 60 Minutes to the LCD
         lcd.print(":");                             //print a colan. 

       if (fractionalSecs < 10){                     // pad in leading zeros 
         lcd.print("0");                             // add a zero
         }

       lcd.print(itoa(fractionalSecs, buf, 10));   // convert the int to a string and print a fractional part of 60 Seconds to the LCD
         lcd.print(":");                             //print a colan. 

       if (fractional < 10){                         // pad in leading zeros 
         lcd.print("0");                             // add a zero
         }
          lcd.print(itoa((fractional), buf, 10));  // convert the int to a string and print a fractional part of 25 Frames to the LCD
         }

    else{
          digitalWrite(ledPin, LOW);                 // turn off LED when not blinking 
          }
 }

}

It works..

{ 2 comments… read them below or add one }

Gary Psalmon October 10, 2011 at 3:13 pm

Hi,
first of all amazing website with clear schematics etc… =)
could you implement it with a “Start”, ‘Stop” and “Reset” buttons ?
With “Start” only works when the stopwatch is stoped.
That will really help me because I’m a total beginner into arduino =$
Cheers

Gary

Reply

Rezz October 11, 2011 at 5:43 am

Thank you Gary, this is the basic stopwatch. I’ve done some experimentation to the code to have start, stop and reset, I’ll post the new code later…

Reply

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