Create ledcWrite_RGB.ino (#688)

* Create ledcWrite_demo_ESP32_RGB.ino

adding the public domain example ledcWrite_demo_ESP32.ino to this repo.  Added RGB to the name for people searching, added some comments, and renames things to make a bit more sense.

* Update ledcWrite_demo_ESP32_RGB.ino

renamed to ledcWrite_RGB.ino and added a couple more comments based on https://github.com/espressif/arduino-esp32/issues/689

* Rename libraries/ESP32/examples/AnalogOut/ledcWrite_demo_ESP32_RGB/ledcWrite_demo_ESP32_RGB.ino to libraries/ESP32/examples/AnalogOut/ledcWrite_RGB/ledcWrite_RGB.ino

Renamed.

libraries/ESP32/examples/AnalogOut/ledcWrite_RGB/ledcWrite_RGB.ino

+/*
+  ledcWrite_RGB.ino
+  Runs through the full 255 color spectrum for an rgb led 
+  Demonstrate ledcWrite functionality for driving leds with PWM on ESP32
+ 
+  This example code is in the public domain.
+  
+  Some basic modifications were made by vseven, mostly commenting.
+ */
+ 
+// Set up the rgb led names
+uint8_t ledR = A4;
+uint8_t ledG = A5;
+uint8_t ledB = A18; 
+
+uint8_t ledArray[3] = {1, 2, 3}; // three led channels
+
+const boolean invert = true; // set true if common anode, false if common cathode
+
+uint8_t color = 0;          // a value from 0 to 255 representing the hue
+uint32_t R, G, B;           // the Red Green and Blue color components
+uint8_t brightness = 255;  // 255 is maximum brightness, but can be changed.  Might need 256 for common anode to fully turn off.
+
+// the setup routine runs once when you press reset:
+void setup() 
+{            
+  Serial.begin(115200);
+  delay(10); 
+  
+  ledcAttachPin(ledR, 1); // assign RGB led pins to channels
+  ledcAttachPin(ledG, 2);
+  ledcAttachPin(ledB, 3);
+  
+  // Initialize channels 
+  // channels 0-15, resolution 1-16 bits, freq limits depend on resolution
+  // ledcSetup(uint8_t channel, uint32_t freq, uint8_t resolution_bits);
+  ledcSetup(1, 12000, 8); // 12 kHz PWM, 8-bit resolution
+  ledcSetup(2, 12000, 8);
+  ledcSetup(3, 12000, 8);
+}
+
+// void loop runs over and over again
+void loop() 
+{
+  Serial.println("Send all LEDs a 255 and wait 2 seconds.");
+  // If your RGB LED turns off instead of on here you should check if the LED is common anode or cathode.
+  // If it doesn't fully turn off and is common anode try using 256.
+  ledcWrite(1, 255);
+  ledcWrite(2, 255);
+  ledcWrite(3, 255);
+  delay(2000);
+  Serial.println("Send all LEDs a 0 and wait 2 seconds.");
+  ledcWrite(1, 0);
+  ledcWrite(2, 0);
+  ledcWrite(3, 0);
+  delay(2000);
+ 
+  Serial.println("Starting color fade loop.");
+  
+ for (color = 0; color < 255; color++) { // Slew through the color spectrum
+
+  hueToRGB(color, brightness);  // call function to convert hue to RGB
+
+  // write the RGB values to the pins
+  ledcWrite(1, R); // write red component to channel 1, etc.
+  ledcWrite(2, G);   
+  ledcWrite(3, B); 
+ 
+  delay(100); // full cycle of rgb over 256 colors takes 26 seconds
+ }
+ 
+}
+
+// Courtesy http://www.instructables.com/id/How-to-Use-an-RGB-LED/?ALLSTEPS
+// function to convert a color to its Red, Green, and Blue components.
+
+void hueToRGB(uint8_t hue, uint8_t brightness)
+{
+    uint16_t scaledHue = (hue * 6);
+    uint8_t segment = scaledHue / 256; // segment 0 to 5 around the
+                                            // color wheel
+    uint16_t segmentOffset =
+      scaledHue - (segment * 256); // position within the segment
+
+    uint8_t complement = 0;
+    uint16_t prev = (brightness * ( 255 -  segmentOffset)) / 256;
+    uint16_t next = (brightness *  segmentOffset) / 256;
+
+    if(invert)
+    {
+      brightness = 255 - brightness;
+      complement = 255;
+      prev = 255 - prev;
+      next = 255 - next;
+    }
+
+    switch(segment ) {
+    case 0:      // red
+        R = brightness;
+        G = next;
+        B = complement;
+    break;
+    case 1:     // yellow
+        R = prev;
+        G = brightness;
+        B = complement;
+    break;
+    case 2:     // green
+        R = complement;
+        G = brightness;
+        B = next;
+    break;
+    case 3:    // cyan
+        R = complement;
+        G = prev;
+        B = brightness;
+    break;
+    case 4:    // blue
+        R = next;
+        G = complement;
+        B = brightness;
+    break;
+   case 5:      // magenta
+    default:
+        R = brightness;
+        G = complement;
+        B = prev;
+    break;
+    }
+}