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### Topic: Millis(), an interesting problem (Read 2231 times)previous topic - next topic

#### positivelydoped23

##### Jan 10, 2013, 07:38 pm

Quote

long t1 = 0;
long t2 = 0;
void setup()
{
Serial.begin(9600);
}

void loop()
{
t1 = millis();
t2 = t1 - 1000;
while(t2<t1)
{
t2 = millis();
}

Serial.println("Hello");

}

Above is a simple code using millis function in arduino. According to me, it should print "Hello" on serial after a second passes.
However "Hello" keeps printing all the time, there is not a delay of 1 second between 2 prints.
Can anyone try this code and figure out why?

#### Jack Christensen

#1
##### Jan 10, 2013, 07:43 pm
The way it is written, the Serial.print statement will execute every time loop() runs, which is to say continuously. There is no conditional logic to prevent it, the rest of the code has no effect the way it is written.

millis() returns an unsigned long data type, so variables like t1 and t2 should be unsigned long as well. In this case it wouldn't make any difference until the sketch had run for some days, but it's just good form.

#### UKHeliBob

#2
##### Jan 10, 2013, 07:44 pm
How many times does the loop() function run ?
Please do not send me PMs asking for help.  Post in the forum then everyone will benefit from seeing the questions and answers.

#### Jimmy60

#3
##### Jan 10, 2013, 07:44 pm
It can only stay in that while loop for one iteration. You immediately assign t2 the current millis() which will obviously make it larger than t1. Looks to me like you should update t1 not t2 in that loop.

You've really just programmed your own delay() which isn't a good way to do this. Read through and understand the blink without delay for the better way to do this.

#### holmes4

#4
##### Jan 10, 2013, 07:47 pm
loop() runs for ever and ever and ........................

Mark

#### AWOL

#5
##### Jan 10, 2013, 07:49 pm
Quote
You immediately assign t2 the current millis() which will obviously make it larger than t1.
sp. "larger or (more likely) the same"
"Pete, it's a fool looks for logic in the chambers of the human heart." Ulysses Everett McGill.
Do not send technical questions via personal messaging - they will be ignored.
I speak for myself, not Arduino.

#### Arrch

#6
##### Jan 10, 2013, 07:50 pm
Jimmy nailed it.

Once you update t2 with millis() it will always be greater than or equal to t1, so the while loop will only ever run once. Hopefully this is just an academic exercise, because practically, that's an atrocious way of writing a 1 second delay.

#### retrolefty

#7
##### Jan 10, 2013, 08:07 pm

Jimmy nailed it.

Once you update t2 with millis() it will always be greater than or equal to t1, so the while loop will only ever run once. Hopefully this is just an academic exercise, because practically, that's an atrocious way of writing a 1 second delay.

I agree, and especially when there is an 'official arduino example sketch' that shows how to properly implement a 1 second interval.

Code: [Select]
`/* Blink without Delay Turns on and off a light emitting diode(LED) connected to a digital  pin, without using the delay() function.  This means that other code can run at the same time without being interrupted by the LED code. The circuit: * LED attached from pin 13 to ground. * Note: on most Arduinos, there is already an LED on the board that's attached to pin 13, so no hardware is needed for this example. created 2005 by David A. Mellis modified 8 Feb 2010 by Paul Stoffregen This example code is in the public domain. http://www.arduino.cc/en/Tutorial/BlinkWithoutDelay */// constants won't change. Used here to // set pin numbers:const int ledPin =  13;      // the number of the LED pin// Variables will change:int ledState = LOW;             // ledState used to set the LEDlong previousMillis = 0;        // will store last time LED was updated// the follow variables is a long because the time, measured in miliseconds,// will quickly become a bigger number than can be stored in an int.long interval = 1000;           // interval at which to blink (milliseconds)void setup() {  // set the digital pin as output:  pinMode(ledPin, OUTPUT);      }void loop(){  // here is where you'd put code that needs to be running all the time.  // check to see if it's time to blink the LED; that is, if the   // difference between the current time and last time you blinked   // the LED is bigger than the interval at which you want to   // blink the LED.  unsigned long currentMillis = millis();   if(currentMillis - previousMillis > interval) {    // save the last time you blinked the LED     previousMillis = currentMillis;       // if the LED is off turn it on and vice-versa:    if (ledState == LOW)      ledState = HIGH;    else      ledState = LOW;    // set the LED with the ledState of the variable:    digitalWrite(ledPin, ledState);  }}`

Lefty

#### positivelydoped23

#8
##### Jan 10, 2013, 08:30 pm
Well, that wasn't an interesting problem, it was an embarrassing one.

#### Jack Christensen

#9
##### Jan 10, 2013, 08:48 pm

Well, that wasn't an interesting problem, it was an embarrassing one.

I wouldn't worry too much, you're in very good company!

#### positivelydoped23

#10
##### Jan 10, 2013, 11:02 pm

[/quote]

I wouldn't worry too much, you're in very good company!
[/quote]

Thankyou! Really appreciate the kind of quick replies i get on this forum.

#### AWOL

#11
##### Jan 10, 2013, 11:06 pm
The one thing you've really got to bear in mind if the immense difference in timescales.
One 1/1000th of a second is a tiny amount of time to us, but your Arduino could execute 16000 instructions in that time.
"Pete, it's a fool looks for logic in the chambers of the human heart." Ulysses Everett McGill.
Do not send technical questions via personal messaging - they will be ignored.
I speak for myself, not Arduino.

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