Arduino: Change the color & color intensity of a LED periodically

Question

Prerequisites:

A RGB-LED is attached and wired to the Arduino Uno-board.

Process description:

In the beginning the LED is turned off.

A loop starts and an output-signal is put on the red-part of the LED.

With every iteration the output-signal becomes increased in the following way: 0, 1, 2, 3, ...

The loop stops after 255 (maximal red) is reached. After a delay the output-signal becomes decreased (by using a loop again) in the way: 255, 254, 253 ... until 0 is reached.

Then the increasing and decreasing starts again but this time with the green-part of the LED.

After the blue-part of the LED has been increased and decreased the whole process starts again with the red-part.

GitHub-README with Image of the board-setup

Implementation:

 // -------- Declarations --------------
const int GREEN_LED_PIN = 9;
const int RED_LED_PIN = 11;
const int BLUE_LED_PIN = 10;
const int DELAY_WITHIN_LOOP = 10;
// ---------------------------------------
// ------- Own Functions -----------------
void setLed(int valRed, int valGreen, int valBlue) {
 analogWrite(RED_LED_PIN, valRed);
 analogWrite(GREEN_LED_PIN, valGreen);
 analogWrite(BLUE_LED_PIN, valBlue); 
}
void changeColorIntensity(int position, int step, int i, int stop) {
 while (i != stop) {
 switch (position) {
 case 0:
 setLed(i, 0, 0);
 break;
 case 1:
 setLed(0, i, 0);
 break;
 case 2:
 setLed(0, 0, i);
 break;
 }
 i += step;
 delay(DELAY_WITHIN_LOOP);
 } 
}
// -------------------------------------------
void setup() {
 pinMode(GREEN_LED_PIN, OUTPUT);
 pinMode(RED_LED_PIN, OUTPUT);
 pinMode(BLUE_LED_PIN, OUTPUT);
}
void loop() {
 for (int i = 0; i < 3; i++) {
 changeColorIntensity(i, 1, 0, 256);
 changeColorIntensity(i, -1, 255, -1);
 } 
}

The sketch works just fine and solves exactly the described task.

What annoys me is the part with the switch-statement and the multiple function-invocations.

If someone has an idea how to solve that part then his/her answer would be very appreciated.

Generally: What would you have done different and why?

Looking forward to reading your comments, recommendations and hints!

Answer 1

I agree that the switch statement smells. One way to avoid it is to abstract LED values into the array, and let change_color_intensity operate on it:

void change_color_intensity(int which, int start, int stop, int delta)
{
 int values[] = { 0, 0, 0 };
 for (values[which] = start; values[which] != stop; values[which] += delta) {
 set_leds(values[0], values[1], values[2]);
 delay(DELAY_WITHIN_LOOP);
 }
}

Note that I change a while loop into a IMHO more readable for. I also changed some names for the same reason.

---

Another approach is to abstract LED names, and get rid of setLed altogether:

void change_color_intensity(int which, int start, int stop, int delta)
{
 for (in value = start; value != stop; value += delta) {
 analogWrite(which, value);
 delay(DELAY_WITHIN_LOOP);
 }
}

with the caller defining a pin array:

 int LED = { RED_LED_PIN, GREEN_RED_PIN, BLUE_RED_PIN };
 for (pin = 0; pin < 3; pin++) {
 change_color_intensity(LED[pin], 0, 256, 1);
 ....
 }

---

I am not sure I understand what you mean by multiple function invocations. If you are concerned with invoking change_color_intensity twice in a loop, I see no problem with it.

• michael.zech: I meant the three times setLed() with different parameter within the switch. Anyway: Thanks a lot for your answer. It‘s just great.