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  • Author Author: andyforeverest
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[PROJECT] Color mixing with a RGB LED

andyforeverest
  1. Color mixing
  2. RGB LED - description and types
  3. Color mixing program

 

  1. Color mixing


One can display a certain color by mixing only three basic colors: Red, Green and Blue. Adding different levels of each color we get many colors.


If all colors are OFF, we get black, and if colors are fully ON, we get white. You can find many color mixing web sites to understand better and to play with different percentages of colors (for example: https://www.colortools.net/color_mixer.html).

 

 

image

2. RGB LED


An RGB LED is made of three LEDs: a red one, a blue one and a green one. Some RGB LEDs have the anode terminal (or "+" terminal) in common and some have the cathode terminal (or "-" terminal) in common.

 

The one we are going to use in our project is a Common Cathode RGB LED.

 

Connections:

 

Micro:bit pinsRGB LED pins
0Red (via resistor)
1Green (via resistor)
2Blue (via resistor)
GNDCommon Cathode


Like with all LEDs we are going to use a resistor (220 Ohms, in our case) in series in order to limit the current, thus protecting the LED and the micro:bit.

3. Program

 

  • pressing button B will switch between colors. Also the initial of the color will be displayed (“R” or “G” or “B”);
  • pressing button A will increase the quantity of the color selected at the previous step. The quantity will be visually displayed on the LED matrix (using the “plot bar graph” block). The values are between 0 and 100;
  • microbit can generate 1024 steps of color (from 0 to 1023). Our program will only generate 1000 steps of color, by multiplying each value selected by the A button with 10 and writing this value to the pins that are connected to the LED color pins. Of course we can choose different values if we want the colors to increase quicker or slower.

 

image

  • in reply to andyforeverest

    yes, I went with the AND because it was less costly than a shift, but your approach works also.  Now if the hardware would allow for saturation levels, you could use your website to make a lot of different colors image

  • in reply to james.flynn

    I like this! This is a clever way - combining the bits coresponding to the LEDs and ANDing with some masks. Then you can call SetLedColor(MAGENTA_LED) - for example. Right?

     

    Another way to write the SetLedColor function:

     

    void SetLedColor(unsigned char ucColor)

    {  

        //Note that when an LED is on, you write a 0 to it:

        led_red = !(ucColor & (0x1 << 0));     //bit 0

        led_green = !(ucColor & (0x1 << 1)); //bit 1

        led_blue = !(ucColor & (0x1 << 2));   //bit 2

    }

  • in reply to andyforeverest

    // LED Colors

    #define BLACK_LED        0

    #define RED_LED            0x01  //RED

    #define GREEN_LED       0x02  //GREEN

    #define YELLOW_LED     0x03  //RED + GREEN

    #define BLUE_LED           0x04  //BLUE

    #define MAGENTA_LED   0x05  //BLUE + RED

    #define CYAN_LED           0x06  //GREEN+ BLUE

    #define WHITE_LED         0x07  //GREEN+BLUE+RED

     

    // GPIOs for RGB LED

    DigitalOut led_green(LED_GREEN);

    DigitalOut led_red(LED_RED);

    DigitalOut led_blue(LED_BLUE);

     

    void SetLedColor(unsigned char ucColor)

    {   

        //Note that when an LED is on, you write a 0 to it:

        led_red = !(ucColor & 0x1);     //bit 0

        led_green = !(ucColor & 0x2); //bit 1

        led_blue = !(ucColor & 0x4);   //bit 2

    }

  • in reply to james.flynn

    How would you use these values in your program?

  • Nice site reference for the colors!  I always used:

     

    #define BLACK_LED     0

    #define RED_LED          1  //RED

    #define GREEN_LED     2  //GREEN

    #define YELLOW_LED   3  //RED + GREEN

    #define BLUE_LED         4  //

    #define MAGENTA_LED 5  //BLUE + RED

    #define CYAN_LED         6  //GREEN+ BLUE

    #define WHITE_LED       7  //GREEN+BLUE+RED

     

    But your referenced site allows for a lot of variation (in fairness, I always just used RGB leds that were either just on or off).