How to use millis () function?

Projects Programming
1

Hi all,

I am trying to blink an led without using delay function for 1 second on, 2 seconds off periodically. Instead, to use millis () function. However, I could not code using the millis () function successfully. Can someone kindly help me to code using the millis () function, please? Thanks for your time.

Here is the code with delay function:

int led = 13;

void setup()
{
  pinMode (led, OUTPUT);
}

void loop()
{
  digitalWrite (led, HIGH);
  delay (1000);
  digitalWrite (led, LOW);
  delay (2000);
}
2

You're using delay. Where is the millis()?

Look at the example file called 'blink without delay'.

4

You need to do something like this. (untested, typed on the fly)

You have two states. 

waitingOff  // ItsOff and I'm waiting 'till its time to turn it on.
waitingOn. // ItsOn and I'm waiting 'till its time to turn it off.

changeTime. // The value in miliseconds when I need to change the LED.

So, come into the loop function and..
Look at the clock.  millis();

if(millis()>changeTime) { //Then its time to change the LED ain't it. so..
  if(state==waitingOff) {.             // See above..
      turnOnLED();
      recalculate changetime
      state =  waitingOn;               // its on now, so were going to wait to turn it off.        
   } else {
      turnOffLED();
      recalculate changetime
      state =  waitingOff;
   }
}

// then do other things..

hope this helps

-jim lee

5

The demo Several Things at a Time is an extended example of BWoD and illustrates the use of millis() to manage timing. It may help with understanding the technique.

...R

6

Hi,

I tried using the Arduino example "BlinkWithoutDelay" to create pulses. I was able to produce correct pulses for millis () function but with the similar method, I was unable to create correct pulses for micros () function. Did I code correctly. Please help me. Thanks.

Below is the code for millis () function:

const int ledPin =  13;
int ledState = 1;
unsigned long previousMillis1 = 0;
unsigned long previousMillis2 = 0;

void setup()
{
  pinMode(ledPin, OUTPUT);
}

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

  if(currentMillis - previousMillis1 >= 1000)            //Pulse width
  {
    previousMillis1 = currentMillis;
    if (ledState == 0)
    {
      ledState = 1;
      digitalWrite(ledPin, HIGH);
    }
    else
    {
      ledState = 0;
    }
  }
  
  if(currentMillis - previousMillis2 >= 3000)              //Period
  {
    previousMillis2 = currentMillis;
    if (ledState == 0)
    {
      ledState = 1;
      digitalWrite(ledPin, LOW);
    }
    else
    {
      ledState = 0;
    }
  }
}
//led blinks on for 1 second, off for 2 second, continously

Below is the code for micros () function:

const int ledPin =  13;
int ledState = 1;
unsigned long previousMicros1 = 0;
unsigned long previousMicros2 = 0;

void setup()
{
  pinMode(ledPin, OUTPUT);
}

void loop()
{
  unsigned long currentMicros = micros();

  if(currentMicros - previousMicros1 >= 1400)            //Pulse width
  {
    previousMicros1 = currentMicros;
    if (ledState == 0)
    {
      ledState = 1;
      digitalWrite(ledPin, HIGH);
    }
    else
    {
      ledState = 0;
    }
  }
  
  if(currentMicros - previousMicros2 >= 13600)              //Period
  {
    previousMicros2 = currentMicros;
    if (ledState == 0)
    {
      ledState = 1;
      digitalWrite(ledPin, LOW);
    }
    else
    {
      ledState = 0;
    }
  }
}
7

I suspect your pulse width is too short to be visible in your micros() code.

...R

8

How, pray tell, do you expect to see an LED blinking almost 70 times per second?

9

Hi,

I monitored the pulses using an oscilloscope.

10

I'm no expert with pulses but you would need to use the timer pins to do this.

http://playground.arduino.cc/Code/Timer1

11

I think you need to check a flag in your elapsed time check to see which length is running, something ljke this.
You had a similar method, but not correct.

void loop()
{
  currentMicros = micros(); // declare as unsigned long before setup()

  if((currentMicros - previousMicros1 >= 1400) && (pulseLength == shorter))            //Pulse width
  {
    previousMicros2 = currentMicros; // capture start time of long pulse
pulseLength = longer; // change "mode"
digitalWrite (ledPin, LOW); // turn off
  }
  
  if((currentMicros - previousMicros2 >= 13600)) && (pulseLength == longer))              //Period
  {
    previousMicros1 = currentMicros; // capture start time of short pulse
pulseLength = shorter; // change "mode"
digitalWrite (ledPin, HIGH); // turn on

  }
}