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### Topic: measuring time (Read 47551 times)previous topic - next topic

#### faruk_ultras

##### Mar 28, 2012, 10:25 am
i have to measure time in arduino.I think i should use stopwatch library but i didn't include this library in my computer.Maybe you can help me.thanks

#### johnwasser

#1
##### Mar 28, 2012, 05:58 pm
Code: [Select]
`unsigned long StartTime = millis();later...unsigned long CurrentTime = millis();unsigned long ElapsedTime = CurrentTime - StartTime;`

That will give you the elapsed time in milliseconds, up to about 40 days.  If you need more precise measurement you can use 'micros()' instead of ''millis()' to get microseconds, up to a couple of hours, I think.

The Arduino clock isn't very accurate so your timing may be off by minutes a day.
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#### robtillaart

#2
##### Mar 28, 2012, 07:04 pm
Quote
get microseconds, up to a couple of hours, I think.

micros() last for 2^32 micros = 4295 seconds = ~71.5 minutes  so just more than one hour
Rob Tillaart

Nederlandse sectie - http://arduino.cc/forum/index.php/board,77.0.html -
(Please do not PM for private consultancy)

#### faruk_ultras

#3
##### Mar 28, 2012, 11:04 pm
thanks all your replies i have another problem.I will make speedometer of te hydro car.Therefore i have to get time and measure the speed.i will use magnetic reed sensor.i use milis();

hiz =2*pi*r*3600/(elapsed time  );

my measuring time code is this. eplased time is ElapsedTime = CurrentTime - StartTime;
is it true approach?

#### robtillaart

#4
##### Mar 29, 2012, 12:01 am

you missed the factor 1000 as you measure in millis(). Just do the math for some known values and you see if a formula works.

e.g 1 second, 10 seconds 3600 seconds.

Partial code not tested
Code: [Select]
`unsigned long prev = 0;void loop(){   unsigned long now = millis();  float speed = 2.0*pi*r * 3600 * 1000 / (now- prev);  speed in meters/hour  prev = now;  Serial.println(speed);}`
Rob Tillaart

Nederlandse sectie - http://arduino.cc/forum/index.php/board,77.0.html -
(Please do not PM for private consultancy)

#### Constantin

#5
##### Mar 30, 2012, 04:10 pm
FWIW, once you get ready to finalize the code, try to compress all the math calcs in this example into a constant float or long up front. The reason being, there is no benefit to recalculating "2.0*pi* 3600 * 1000" over and over, it's 22619467.11... Ideally, Define R in that function as well and you may not even need to use a float.

Less calculations for Arduino to do = better responsiveness by Arduino.

If you want higher sampling speeds, look into the ways that are required to bypass Analog.read and have the ADC go directly to the pins in question. For example, you could set this up as a sub-routine with 100 samples taken, then return the speed based on the micro-seconds that have elapsed. One benefit of not using the analog.Read routines is that the ADC runs independently of the main CPU, you you can likely get some math done between each read (it's what I did with my energy logger - start sampling the voltage channel but work on the current data, then switch to measuring current while processing the just-sampled voltage data).

#6
##### Mar 30, 2012, 06:39 pm
"The Arduino clock isn't very accurate so your timing may be off by minutes a day. "

I think that partly depends on whether the arduino uses a Crsytal vs a Resonator, and also how the seconds are tracked.

I have done tests with my duemilanove, it has tracked the official US time with no losses over a day.
http://www.time.gov/timezone.cgi?Eastern/d/-5/java

Code: [Select]
`unsigned long previousTime = 0;byte seconds ;byte minutes ;bytes hours ;void setup(){Serial.begin {9600);}// I  think using microseconds is even more accurateif (millis() >= (previousTime)  ) {previousTime = previousTime + 1000;  // use 100000 for uSseconds = seconds +1;if (seconds == 60){seconds = 0;minutes = minutes +1;}if (minutes == 60){minutes = 0;hours = hours +1;}if (hours == 13){hours = 1;}Serial.print (hours, DEC);Serial.print (":");Serial.print (minutes,DEC);Serial.print (":");Serial.println(seconds,DEC);} // end 1 second} // end loop`
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

#### odometer

#7
##### Apr 16, 2012, 12:18 am

FWIW, once you get ready to finalize the code, try to compress all the math calcs in this example into a constant float or long up front. The reason being, there is no benefit to recalculating "2.0*pi* 3600 * 1000" over and over, it's 22619467.11... Ideally, Define R in that function as well and you may not even need to use a float.

In a way, it is good that he is using "float", because this way there is less chance of overflow.
Also, I highly recommend using "micros()" here instead of "millis()".
You will probably also want to check for switch bounce (that is, when the sensor registers twice when it should only register once). If the "elapsed time" for one revolution of the wheel is less than 5 milliseconds, then the measurement should be rejected.
You will also need to check for speeds close to zero (that is, a long time without the wheel moving).

#### runaway_pancake

#8
##### May 13, 2012, 08:16 am
There were a couple of typos, oversights in your code; it didn't compile.
I took the liberty of fixing that.
It works good!

Code: [Select]
`/*  CrossRoads Time-clock  */unsigned long previousTime = 0;byte seconds ;byte minutes ;byte hours ;void setup(){Serial.begin (9600);}void loop (){// I  think using microseconds is even more accurate  if (millis() >= (previousTime))   {     previousTime = previousTime + 1000;  // use 100000 for uS     seconds = seconds +1;     if (seconds == 60)     {        seconds = 0;        minutes = minutes +1;     }     if (minutes == 60)     {        minutes = 0;        hours = hours +1;     }     if (hours == 13)     {        hours = 1;     }  Serial.print (hours, DEC);  Serial.print (":");  Serial.print (minutes,DEC);  Serial.print (":");  Serial.println(seconds,DEC);  } // end 1 second} // end loop`
"Who is like unto the beast? who is able to make war with him?"
When all else fails, check your wiring!

#9
##### May 13, 2012, 09:25 am
Well, making it from scratch at work while on a short break without a chance to compile will do that.
Can't believe I left out void loop(){ !
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

#### robtillaart

#10
##### May 13, 2012, 12:00 pm
Quote
// use 100000 for uS

100000 ?  ==> 1000000
Rob Tillaart

Nederlandse sectie - http://arduino.cc/forum/index.php/board,77.0.html -
(Please do not PM for private consultancy)

#11
##### May 13, 2012, 06:05 pm
Yeah 5 zeroes, 6 zereos, whatever it takes
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

#### 2014sideline

#12
##### Feb 18, 2016, 09:41 am
Hello,

Though this comment is too late but it might be helpful as knowledge base for newbies.

The above code is only correct if the loop is ticked every 1 second. Hence, you have to add delay(1000); as last row at the end of the loop() function.

Så the final version of lovely CrossRoad's code looks like below:

unsigned long previousTime = 0;
byte seconds ;
byte minutes ;
byte hours ;
void setup()
{
Serial.begin (9600);
}

void loop ()
{
// I  think using microseconds is even more accurate
if (millis() >= (previousTime))
{
previousTime = previousTime + 1000;  // use 1000000 for uS
seconds = seconds +1;
if (seconds == 60)
{
seconds = 0;
minutes = minutes +1;
}
if (minutes == 60)
{
minutes = 0;
hours = hours +1;
}
if (hours == 13)
{
hours = 1;
}
Serial.print (hours, DEC);
Serial.print (":");
Serial.print (minutes,DEC);
Serial.print (":");
Serial.println(seconds,DEC);
} // end 1 second

delay(1000); //This will ensure one loop per second

} // end loop

#### JohnLincoln

#13
##### Feb 19, 2016, 08:54 pmLast Edit: Feb 19, 2016, 08:56 pm by JohnLincoln
The above code is only correct if the loop is ticked every 1 second. Hence, you have to add delay(1000); as last row at the end of the loop() function.
I have to disagree with you, 2014sideline.

If you use the function delay(1000), then the sketch will wait for 1 second (=1000 ms), during which time it can't do anything else, and then after that time has elapsed it has to update the hours, minutes and seconds, and then send the results to the serial monitor.

This will take a finite time, so I think that means that your solution will always run slow (maybe not a lot).

#### avalon90

#14
##### Aug 19, 2016, 09:10 am
Hi there, I'm new to arduino, I need some help trying to measure time between actuating to different switches.
ie. press  sw1 once and the press sw2 later. The time in between can be milliseconds.

Thanks.

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