Help undersstanding WHY this works...

Projects Programming
1

I have been trying to get an LED string that is Red Blue Purple to cycle through the colors and I FINALLY found some code that does what I want. Now I could really use some help as to why it works instead of an if or if/else statements...

Here's the working code:

 /*
 Fading
 
 This example shows how to fade an LED using the analogWrite() function.
 
 The circuit:
 * LED attached from digital pin 9 to ground.
 
 Created 1 Nov 2008
 By David A. Mellis
 modified 30 Aug 2011
 By Tom Igoe
 
 http://arduino.cc/en/Tutorial/Fading
 
 This example code is in the public domain.
 
 */


int ledPin = 9;    // LED connected to digital pin 9
int ledPin2 = 11;  // LED connected to digital pin 11

void setup()  {
} 

void loop()  { 
  // fade in from min to max in increments of 5 points:
  for(int fadeValue = 0 ; fadeValue <= 255; fadeValue +=5) { 
    // sets the value (range from 0 to 255):
    analogWrite(ledPin, fadeValue);         
    // wait for 30 milliseconds to see the dimming effect    
    delay(30);                            
  }
    
  // fade in from min to max in increments of 5 points:
  for(int fadeValue = 0 ; fadeValue <= 255; fadeValue +=5) { 
    // sets the value (range from 0 to 255):
    analogWrite(ledPin2, fadeValue);         
    // wait for 30 milliseconds to see the dimming effect    
    delay(30);                            
  }

  // fade out from max to min in increments of 5 points:
  for(int fadeValue = 255 ; fadeValue >= 0; fadeValue -=5) { 
    // sets the value (range from 0 to 255):
    analogWrite(ledPin, fadeValue);         
    // wait for 30 milliseconds to see the dimming effect    
    delay(30);                            
  } 
  // fade out from max to min in increments of 5 points:
  for(int fadeValue = 255 ; fadeValue >= 0; fadeValue -=5) { 
    // sets the value (range from 0 to 255):
    analogWrite(ledPin2, fadeValue);         
    // wait for 30 milliseconds to see the dimming effect    
    delay(30);                            
  }
}

One thing is I don't understand why the pins don't have to be specified as an OUTPUT and also IS there a way to do this inside a loop with using if statements. I haven't made it as far in the tutorials as for statements but I get the general idea. What I did by myself was this:

 int bluePin = 9; //PWM pin for Blue light
int redPin = 11; //PWM pin for Red light
int redLevel = 0;
int blueLevel = 0;

void setup() {
  // set pins for PWM output to control brightness & fading
pinMode(bluePin, OUTPUT);
pinMode(redPin, OUTPUT);
}

void loop() //Designed to fade from Red to Purple to Blue
{
  analogWrite(redPin, redLevel);
  redLevel = redLevel + 51;
  delay(500);
  
  if (redLevel == 255)
  {
  analogWrite(bluePin, blueLevel);
  blueLevel = blueLevel + 51;
  delay(500);
  }
}

However it never gets to the blue lights, just cycles through the red> I was even trying to mess around with else statements and switch/case statements but alas... I'm a newb and it didn't make sense. Could someone please explain to me why the first code works and the if statements I tried failed miserably... every time...

2

the code you posted is using PWM pins

look at analogWrite in the reference,in a nutshell if you dug into the raw code behind that function you would find that the PWM functions has to be an output .. if you were reading it you wouldnt need the function anyway

as far as if statements go, yea, for the short answer use

 if (redLevel >= 255)
3

Thanks a bunch for that, I also have another 2 questions:
The first is what is "+=" mean?? I know that a ++ & -- are increment and decrement but IDK what "+=5" means.

Also is there even a way to get the results I want with an if statement?

I have been reading a lot of tutorials (I like the ones from Jeremy Blum on Youtube) but I still can't quite figure out the if & else if statements. I want a PWM pin to go from 0-255 in increments of 5 until ledPin1 hits 255, have ledPin1 STAY at 255 while ledPin2 goes 0 - 255 and STAYS while ledPin1 goes from 255 - 0 before ledPin2 does as well. When I experimented with the loop command I could only get one LED to light up & dim. If someone can paste some code in here or link me to something I'd appreciate it. I like having something to compare to my code so I can see exactly what I did wrong...

4

P.S TY to the Arduino Forums community!!!

5

The first is what is "+=" mean??

It is C shorthand for "x = x + 5;".
Most binary operators can be combined in this way:
x += 5; is the same x = x + 5;
x -= 5; is the same x = x - 5;
x *= 5; is the same x = x * 5;
x /= 5; is the same x = x / 5;
x &= 5; is the same x = x & 5;
x |= 5; is the same x = x | 5;
X ^= 5; is the same x = x ^ 5;