Explanation:
This program demonstrates how to drive an RGB LED to create 4096 different colors. Each of the three elements (red, green and blue) responds to 16 different levels. A value of 0 means the element never turns on, while a value of 15 means the element never shuts off. Values in between these two extremes vary the pulse width.
This program is an interrupt driven three channel PWM implementation.
The basic carrier frequency depends upon the microcontroller clock speed. For example, with an 8 MHz clock, the LED elements are modulated at about 260 Hz. The interrupts are generated by Timer 0. With an 8 MHz clock they occur about every 256 uS. The interrupt routine consumes about 20 uS.
Do not forget the current limiting resistors to the LED elements. A value of around 470 ohms is typical, but you may want to adjust the individual values, to balance the color response.
In this demonstration, three potentiometers are used to set the color levels using the slalom technique.
Demonstration program:
;----- Configuration
#chip 16F88, 8 ;PIC16F88 running at 8 MHz
#config mclr=off ;reset handled internally
;----- Constants
#define LED_R PortB.0 ;pin to red element
#define LED_G PortB.1 ;pin to green element
#define LED_B PortB.2 ;pin to blue element
;----- Variables
dim redValue, greenValue, blueValue, ticks as byte
;----- Program
dir PortA in ;three pots for inputs
dir PortB out ;the LED outputs
on interrupt Timer0Overflow call update
initTimer0 Osc, PS0_1/2
do
redValue = readAD(AN0)/16 ;red -- 0 to 15
greenValue = readAD(AN1)/16 ;green -- 0 to 15
blueValue = readAD(AN2)/16 ;blue -- 0 to 15
loop
Sub update ;interrupt routine
ticks++ ;increment master timekeeper
if ticks = 15 then ;start of the count
ticks = 0
if redValue <> 0 then ;only turn on if nonzero
set LED_R on
end if
if greenValue <> 0 then
set LED_G on
end if
if blueValue <> 0 then
set LED_B on
end if
end if
if ticks = redValue then ;time to turn off red?
set LED_R off
end if
if ticks = greenValue then ;time to turn off green?
set LED_G off
end if
if ticks = blueValue then ;time to turn off blue?
set LED_B off
end if
end sub