Joystick-controlled color wheel powered by Arduino
This is a simple project for the Arduino Uno R3 but can probably be ported to other microcontrollers with ease. Using a joystick, three 330-ohm resisters, and a common cathode RGB LED, the LED can change its color with respects to the position of the joystick (similar to a color wheel).
It works by first taking the position of the joystick in cartesian coordiantes (x and y axis). The x and y axis are in range [0,1024], however, so to center the coordinates to some origin, each value is the absolute value of 512 less than itself. E.g. (x'-512, y'-512) = (x,y), where x' and y' are the raw values from the joystick and x and y are the final values to be used.
From the coordinates, simple trigonometry is used to find the angle of some line from the coordinate to the origin from the positive y-axis (positive clockwise). Using Arduino's atan2() function from math.h, one can find this in [-pi,pi]. This is then converted to [0,2pi], then conveted to degrees (original output in radians). This final value will be the hue angle.
Using HSV coordinates, the saturation and value are fixed to 1 (for now). Thus, by following the formulas found here, the needed RGB values ca be calculated.
Afterwards, it's as simple as updating the colors via analogWrite();
I plan to use the joystick to change the V value in HSV. The saturation can possibly changed as well but with another module in addition to the joystick (e.g. a button).
Arduino.cc - RGB LED hookup
Arduino.cc - Joystick hookup
AVR-libc - Arduino documentation for math.h
RapidTables.com - HSV to RGB conversion