The TLC5940 is a LED driver IC, which we use today to drive 5 RGB LEDs with common anode. The advantage of this circuit is that it provides a constant adjustable output current for the LEDs and only requires minimal wiring.

A TLC5940, 5 RGB-LEDs and an Arduino

The IC has 16 PWM outputs (from which we use 15), one of them for each of the three colors of the 5 LEDs. We build the following circuit:

The common anodes of the RGB LEDs are connected to +5 V and the Arduino is also still connected to the power supply.

TLC5940NT – Pinout

RGB-LED, common anode – Pinout

Source code (sketch):

We install the following TLC5940 library and then upload the sketch on our Arduino …

#include "Tlc5940.h"

#define NUM_LEDS 5 

struct RGB { byte r; byte g; byte b; };

RGB rgb;
int global_dim=16;

void setup(){

	Tlc.init();  
}

void loop(){
  
	randomSeed(millis());
 
	int wait=random(1,30);
	int dim=random(4,6);
	int max_cycles=8;
	int cycles=random(1,max_cycles+1);
	
	rainbowCycle(wait,cycles,dim);
	
}

void setLed(byte num,int red,int green,int blue){

	if(global_dim){
		red=red/global_dim;
		green=green/global_dim;
		blue=blue/global_dim;
	}
	
	Tlc.set(num*3,red);
	Tlc.set(num*3+1,green);
	Tlc.set(num*3+2,blue);
	
} 

void rainbowCycle(uint8_t wait,byte cycle,byte dim) {
  
  int cycles, j, k;
  
  for(cycles=0;cycles<cycle;cycles++){
  
    byte dir=random(0,2);
    k=255;
    
    for (j=0; j < 256; j++,k--) {     // cycles of all colors in the wheel
      
      if(k<0)k=255;
 
   // Tlc.clear();
 
      for(int i=0; i<NUM_LEDS; i+=1) {
        
        Wheel(((i * 256 / NUM_LEDS) + (dir==0?j:k)) % 256,dim);        
        setLed(i,rgb.r*16,rgb.g*16,rgb.b*16);
	    

      }
	Tlc.update();
      delay(wait);
    }
  }
}


void Wheel(byte WheelPos,byte dim){
  
  if (WheelPos < 85) {
   rgb.r=0;
   rgb.g=WheelPos * 3/dim;
   rgb.b=(255 - WheelPos * 3)/dim;;
   return;
  } 
  else if (WheelPos < 170) {
   WheelPos -= 85;
   rgb.r=WheelPos * 3/dim;
   rgb.g=(255 - WheelPos * 3)/dim;
   rgb.b=0;
   return;
  }
  else {
   WheelPos -= 170; 
   rgb.r=(255 - WheelPos * 3)/dim;
   rgb.g=0;
   rgb.b=WheelPos * 3/dim;
   return;
  }
}

Download Source Code

… and soon will be running a rainbow color transition on our LEDs.

Components:

eBay:	Breadboard jumper wires Breadboard power module Resistor 10k Resistor 2k RGB LED common anode TLC5940
Amazon:	Breadboard jumper wires Breadboard power module Resistor 10k Resistor 2k RGB LED common anode TLC5940

Good?