Arduino starter kit example LEDS modification

Question

I just begun with the Arduino starter kit, and in the second example I would like to test some changes to learn more.

The point is to have a green LED shining, and when pressing the button the two red LEDs blink.

This is the code:

int switchState = 0;

void setup()
{
  pinMode(2, INPUT);
  pinMode(3, OUTPUT);
  pinMode(4, OUTPUT);
  pinMode(5, OUTPUT);

  // the button is pressed
  digitalWrite(3, LOW);

  digitalWrite(4, LOW);
  digitalWrite(5, HIGH);
  delay(250); // wait for a quarter second
  // toggle the LEDs
  digitalWrite(4, HIGH);
  digitalWrite(5, LOW);
  delay(250); // wait fo a quarter second
}

void loop()
{
  switchState = digitalRead(2);
  // this is a comment
  if(switchState == LOW)
  {
    // the button is not pressed
    digitalWrite(3, HIGH); // green LED
    digitalWrite(4, LOW); // red LED
    digitalWrite(5, LOW); // red LED
  }
  else
  {
    // the button is pressed
    digitalWrite(3, LOW);

    digitalWrite(4, LOW);
    digitalWrite(5, HIGH);
    delay(250); // wait for a quarter second
    // toggle the LEDs
    digitalWrite(4, HIGH);
    digitalWrite(5, LOW);
    delay(250); // wait fo a quarter second
  }
} // go back to the beginning of the loop

I added a modification into the schema (a fourth LED in parallel with the green), like this:

But the added LED is not shining. It's a long time ago I finish school and I forgot a lot of things. Am I wiring the fourth LED incorrectly?

Answer 1

Blue LEDs have a higher V_f than green LEDs, hence much less current will pass through it, not enough to make it visible. Give it its own resistor instead of sharing the resistor with the green.