Arduino LED fading

Hi Prof

I'm no expert on this stuff, so I'm sure that someone else will chime in with a more complete answer, but ......

You can fade LEDs in and out using pulse wave modulation though an analogwrite() which.is on a scale of 0 - 255, such that analogWrite(255) requests a 100% duty cycle (always on), and analogWrite(127) is a 50% duty cycle.

I have used it to do a slow fade of a red LED on a welding simulator sketch :

for (int i = 50; i> 0; i--)                             { //decrease i with 1
          analogWrite(ledPin_red_glow, i);
          delay(40);

Obviously you can speed up and alter this effect by changing the range and increment/decrement of "i" and also the delay factor.

Bit busy right now, but if I get a some time I'll have a go at a sketch for a fade/flicker (rather than just flickering) fire simulator because I do need one in the near future. However I am pretty sure someone will beat me to it .

Rob Clark

Try this

Hi Prof

Not knowing the "light quality" of what you are comparing the Arduino to' try this 3 led sketch (I used 1 * red and 2 * yellow).

int LED_Pin7 = 7;
int LED_Pin8 = 8;
int LED_Pin9 = 9;

int Intensity_7;   // Intensity of the LED: [0 = Off], [255 = Brightly Lit]
int Intensity_8;
int Intensity_9;

void setup()
{
 }
void loop()
{
  Intensity_7 = random(1, 255);    
  Intensity_8 = random(1, 240);
  Intensity_9 = random(1, 255);

  analogWrite(LED_Pin7, Intensity_7);
  delay(random(1, 36));          
  analogWrite(LED_Pin8, Intensity_8);
  delay(random(1, 36));          
  analogWrite(LED_Pin9, Intensity_9);
  delay(random(1, 25));         
}

Values will need some tweaking I'm sure.

Is this vaguely close to what you want?

Rob

Drunkard's walk

Prof--

Rob's code is a good framework for this, but you might get something closer to what you want with a drunkard's walk algorithm. 

int LED_Pin7 = 7;
int LED_Pin8 = 8;
int LED_Pin9 = 9;

long Intensity_7 = 100;   // Intensity of the LED: [0 = Off], [255 = Brightly Lit]
long Intensity_8 = 100;
long Intensity_9 = 100;
void setup() {
  // put your setup code here, to run once:
}

void loop() {
  Intensity_7 = drunk(Intensity_7, 32, 7);    
  Intensity_8 = drunk(Intensity_8, 64, 4);
  Intensity_9 = drunk(Intensity_9, 0, 4);

  analogWrite(LED_Pin7, Intensity_7);
  analogWrite(LED_Pin8, Intensity_8);
  analogWrite(LED_Pin9, Intensity_9); 

}

long drunk(long seed,long bottom, long maxstep){
  long change = random(1, maxstep + 1) ;
  if (random (0,2)== 0){
    change *= -1;
  }
  long result = seed + change;
  // keep in range
  if(result> 255

Instead of the random calls, I substituted a function that adds or subtracts a random step from the existing value. This version of the drunk function takes three arguments- starting value, the lowest value to ever return, and the largest step to take. The function:

• uses random to get an amount to step
• uses random(0,2) to decide which direction to change
• checks the result-- if it is out of range (bottom to 255) reverses the step

Originally bottom and maxstep were globals, but I found that there's quite a bit of differenct in the way LEDs (and even Arduino outputs) react to this code, so I designed the function to take these as arguments. That way you can tweak each color. Note that the smaller the maxstep, the slower the changes.

pqe

Dear Rob, PQ, Thanks for the

Sink source...

You could connect the leads of a two wire bicolor LED to Arduino pins, and flip/fade the colors by raising one pin while lowering the other. (Don't forget a resistor.) For anything heavier, you need a driver, like an L293. 

pqe

Why are you using long instead of int?

Does the algorithm require the precision of a 32 bit variable? It seems like a 16 bit would be sufficient, as the max value is going to be 255, or even a byte as it is an unsigned number between 0 and 255, or am I mistaken?

Long vs int

I used longs just because the random() function returns a long. Ints will work fine, and save a few bytes of memory. (Don't try that with time functions though.) Signs are required, so you can't convert to bytes. I've recently been working in another language that is really fussy about type matching so my habits have changed.

pqe

Flicker

I just tried pqe's version of the flicker sketch - much better than mine

Rob

It works better if you use different pins

Unless you are using a Mega or a Due, it works better if you use pins 5, 6, and 9 for the pwm outputs.  The analogWrite command only functions on pins 3,5,6,9,10,&11 on the Uno, Micro, or  Nano.  This is a function of the AVR chip features.  If you use it as written, the LED's on pins 7 and 8 flicker on and off, without dimming.  If you change the pin assignments, all 3 LED's vary continuously.

Haste makes waste

A bit of a hurry + misreading the pin labels led to a big goof. Here is corrected code:

int LED_Pin5 = 5;
int LED_Pin6 = 6;
int LED_Pin9 = 9;

long Intensity_5 = 100;   // Intensity of the LED: [0 = Off], [255 = Brightly Lit]
long Intensity_6 = 100;
long Intensity_9 = 100;
void setup() {
  // put your setup code here, to run once:
}

void loop() {
  Intensity_5 = drunk(Intensity_5, 32, 25);    
  Intensity_6 = drunk(Intensity_6, 32, 12);
  Intensity_9 = drunk(Intensity_9, 32, 25);

  analogWrite(LED_Pin5, Intensity_5);
  analogWrite(LED_Pin6, Intensity_6);
  analogWrite(LED_Pin9, Intensity_9); 

}

long drunk(long seed,long bottom, long maxstep){
  long change = random(1, maxstep+1) ;
  if (random (0,2)== 0){
    change *= -1;
  }
  long result = seed + change;
  // keep in range
  if(result> 255

pqe