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trying to get an LED to come on for 3 seconds and come off without delay

Former Member

hey guys i'm just trying to get an led to come on for 3 seconds and then comeoff, without using delay, i'm not understanding the millis function but i've tried a bit. kindly let me know what i'm doing wrong. thank you.

 

int count = 0;
long previousMillis = 0;        




long interval = 3000;           


void setup() {
  // set the digital pin as output:
  pinMode(ledPin, OUTPUT);    
  
}


void loop()
{
  
  unsigned long currentMillis = millis();

  if(currentMillis - previousMillis > interval) {
    
    previousMillis = currentMillis;   


     if (count <=1)
      digitalWrite(ledPin,HIGH);
    else
      digitalWrite(ledPin,LOW);
count ++;
    
    
  }
}

Parents

  • It looks like the led will only be on for 6 secs and then stays off.

    If you replace

      Count <= 1

    With

      count % 2 == 0

     

    Then it will be on for even counts and off for odd counts.

     

    (% is modulo, aka remainders of division)

     

    Hope that helps :)

     

    Ps maybe make previousMillis unsigned to match.

     

    Cheers,

    Nico

  • in reply to ntewinkel

    Hi Nico, how would you write the code if you want to have a red led on for the even counts and a green led for the odd counts? I'm very new to programming and tried to use blink twice and switch the number on the led, then I tried to use switch case, then I tried to set a parameter where it will read the ouput and try to switch the led (like how a pushbutton would change the led from off to on described in Getting Started with Arduino by Massimo Banzi pgs. 55-64) but I have not had any progress. Am I wrong for thinking that programming would replace a switch? Well I thank the both of you for discussing this since it is somewhat similar to my problem and Navin gave me an idea to search for the Millis function!

  • in reply to Former Member

    for the even it would be %2==0 and for off %2==1,, %2 will divide by 2 giving the remainder, therefore if its even you will get = 0 and odd will be =1. I am not an expert but i'd just use an if else statement, like mmm,

    if(count%2==0)

    {

    digitalWrite(led,HIGH);

    }

    else

    digitalWrite(led,LOW);

     

     

     

    and of course you'll have a counter.try your best not to use delay, if causes problems if you need to read inputs during the time it delays, since it literally pauses the entire program. Theres a timer library, search arduino timer library, it has oscillate and pulse and so on, not sure if thats what you're looking for.

     

    http://playground.arduino.cc/code/timer

  • in reply to Former Member

    To have red and green alternating on, you basically copy the lines of code that turn the ledpin high and low and set opposite values for the other LED.

    ie, when you turn the red led on, at that time you would turn the green led off. And when you turn the red led off, you turn the green led on.

     

    if(count%2==0)

    {

    digitalWrite(redLed,HIGH);

    digitalWrite(greenLed,LOW);

    }

    else {

    digitalWrite(redLed,LOW);

    digitalWrite(greenLed,HIGH);

    }

     

    You'd have to define and setup redLed and greenLed, of course, just like you did for ledpin.

     

    And you are correct - you can use programming instead of a physical switch, or instead of pretty much any input.

  • in reply to ntewinkel

    Nico teWinkel wrote:

    .

    ie, when you turn the red led on, at that time you would turn the green led off. And when you turn the red led off, you turn the green led on.

     

    Just remember what Steve Ciarcia always said about designing in hardware verses software.  It is always a choice.

     

    One digital pin and 2 leds with current limiting ( I <= 20 mA ) resistors.  Polarity inverted for one of the LED legs and connected to the opposite rail.

     

    http://playground.arduino.cc/Main/ArduinoPinCurrentLimitations

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