PROBLEM USING millis() INSTED OF delay()

Using Arduino Programming Questions
1

hello world, I'm new to this world. I want to make an LED light up when the number in the counter is even but with the condition that I can't use the delay() function.
I'm just lost and I can't see what's wrong with my code.
I would be so thankful to receive some help.

Thank you.

This is my code:

//Arduino code for lighting up an LED using millis() as timer and dealy.

int ledPin = 6;
int contador = 1;

int ledState = LOW;
unsigned long previousMillis = 0;
const long interval = 2000; 

void setup()
{
  Serial.begin(9600);
  pinMode( ledPin, OUTPUT);
  Serial.print("Arduino, READY");
  
}
void loop()
{
  unsigned long currentMillis = millis();

  for (contador=1; contador<=12; contador++)
  {
    if (currentMillis - previousMillis >= interval)
  {
    previousMillis = currentMillis;
    if (ledState == LOW)
    {
      ledState = HIGH;
      
    }

    else
    {
      ledState = LOW;
      
    }

    digitalWrite (ledPin, ledState);
    
  }

  Serial.print (contador);

 switch(contador) {
    case 1:
    Serial.println(" - one");
    break;
    case 2:
    Serial.println(" - two");
    
    break; 
    case 3:
    Serial.println(" - three");
   
    break;
    case 4:
    Serial.println(" - four");
   
    break;
    case 5:
    Serial.println(" - five");

    break;
    case 6:
    Serial.println(" - six");
  
    break;
    case 7:
    Serial.println(" - seven");
   
    break;
    case 8:
    Serial.println(" - eight");
    
    break;
    case 9:
    Serial.println(" - nine");
    
    break;
    case 10:
    Serial.println(" - ten");
   
    break;
    case 11:
    Serial.println(" - eleven");
   
    break;
    case 12:
    Serial.println(" - twelve");
    break;

  }

  if(contador%2==0)
  {
    digitalWrite(ledPin, HIGH);
    
  }
 

  else
  {
    digitalWrite(ledPin, LOW);
    
  }

 if (currentMillis - previousMillis >= interval)
  {
    previousMillis = currentMillis;
    if (ledState == LOW)
    {
      ledState = HIGH;
      
    }

    else
    {
      ledState = LOW;
      
    }

    digitalWrite (ledPin, ledState);
    
  }
}
    
  }
2

Marta-Dius:
I'm just lost and I can't see what's wrong with my code.

You have not told us what it actually does and what you want it to do that is different.

...R

3

A for loop looks to me to be inappropriate in such a case (sorry, no pun intended)
You should be doing what the 'for' does explicitly, each timeout period.

4

I'm just lost

You don't need a for loop, the loop() function will do what you want

Initialise the counter to zero and turn on the LED in setup()
Each time through loop() check whether the period has elapsed
If not then keep going round loop() until it has
When it has elapsed, invert the state of the LED and add one to the counter and print it if you want to, save the start time and off you go again.

5

You've got two of these in your sketch:

  if (currentMillis - previousMillis >= interval)
    {
      previousMillis = currentMillis;
      if (ledState == LOW)
      {
        ledState = HIGH;
      }
      else
      {
        ledState = LOW;
      }
      digitalWrite (ledPin, ledState);
    }

It flashes the LED every interval milliseconds. If I understand your question, I think you should make it increment contador instead.