tlc5940 multiplexing code assistance

Using Arduino Programming Questions
1

I have changed up Joe's LED table code for my simple 9 RGB LED common Cathode VU meter. It works... But I have no idea how the heck to update my ledArray[] of the RGB grey-scale values so that his code will change my colors.

Ultimately I will use the arduino analog input to control it, but I can't even figure out how to knight rider this code... WHAT THE HECK IS XLAT DOING?? (I added a bunch of info below code to answer questions about circuit)

const int ledCount= 9;     // number LED's - i have a column of 9 RGB LEDS

const byte RedPin = 5;     // digital pin to control red color
const byte GreenPin =6;    // digital pin to control green color
const byte BluePin = 7;    // digital pin to control blue color

const analogInputPin = 1; //analog input from low pass filter 0-5volts of music bass

byte Current_Color = 'R';
int power = 16;            // allow changing the greyscale power

struct led{	//this makes the ledArray pretty
  byte red;
  byte green;
  byte blue;
};

// structured array to hold the led colors
led ledArray[ledCount] = { {0,0,0}, {0,0,0}, {0,0,0}, {0,0,0}, {0,0,0}, {0,0,0}, {0,0,0}, {0,0,0}, {0,0,0} }


#include "Tlc5940.h"



void setup()
{
   // Setup pins
  pinMode(RedPin,OUTPUT);digitalWrite(RedPin,HIGH); //HIGH is off, using a PNP transistor
  pinMode(GreenPin,OUTPUT);digitalWrite(GreenPin,HIGH); //samesies
  pinMode(BluePin,OUTPUT);digitalWrite(BluePin,HIGH); //samesies 
  


   // setup tlc5940
   Tlc.init(0);
   startXLATCallback(); //WHAT IS THIS??? 
   Tlc.update();
        
}


void loop()
{

}



// do something every 2 periods, so ~2048us
// TLC5940 multiplexing code
#define XLAT_PERIODS  2

volatile uint8_t timesCalled;

volatile void myXLATCallback()
{

  if (timesCalled != 0) timesCalled--;
  else
  {
   timesCalled = XLAT_PERIODS;
   Send_data();
   Tlc.update();
  }
  set_XLAT_interrupt(); // so this will continue to be called
}

void startXLATCallback() {
   timesCalled = XLAT_PERIODS - 1;
   tlc_onUpdateFinished = myXLATCallback;
   myXLATCallback();
}


// update the tlc5940 chip

void Send_data()
{
	if(Current_Color == 'R')
	{
		for(int i=0; i < ledCount ; i++)
		{
			Tlc.set(i+1, ledArray[i].red*power); //my leds are attached to pin 1-9 on tlc
		}
		Turn_off();
		Tlc.update();
		while(tlc_needXLAT);     //WHAT THE HECK??? whyy
		Turn_on();
		Current_Color = 'G';
	}
	else if(Current_Color =='G')
	{
		for(int i=0; i <ledCount ; i++)
		{
			Tlc.set(i+1, ledArray[i].green*power);
		}
		Turn_off();
		Tlc.update();
                while(tlc_needXLAT);	//what is this?
		Turn_on();
		Current_Color = 'B';  
	}
	else
	{
		for(int i=0; i < ledCount ; i++)
		{
			Tlc.set(i+1, ledArray[i].blue*power);
		}
		Turn_off();
		Tlc.update();
                while(tlc_needXLAT);	//MEOWWW
		Turn_on();
		Current_Color = 'R';      
	}
}


// turn on or off the respective anode transistor

void Turn_off()
{
	digitalWrite(RedPin,HIGH);
	digitalWrite(GreenPin,HIGH);
	digitalWrite(BluePin,HIGH);  
        	delayMicroseconds(10);

}

void Turn_on()
{
  switch(Current_Color){  //switch the transistors sexy volt
    case 'R':
    delayMicroseconds(10);
    digitalWrite(RedPin, LOW);
    digitalWrite(GreenPin, HIGH);
    digitalWrite(BluePin, HIGH);
    break;
    
    case 'G':
    delayMicroseconds(10);  
    digitalWrite(RedPin, HIGH);
    digitalWrite(GreenPin, LOW);
    digitalWrite(BluePin, HIGH);
    break;
    
    case 'B':
    delayMicroseconds(10);
    digitalWrite(RedPin, HIGH);
    digitalWrite(GreenPin, HIGH);
    digitalWrite(BluePin, LOW);
    break;  
  }
}

EXTRA INFO
I use arduino outputs to switch PNP transistor base to ground and send my high current supply (800mA @ 5.5 V) to the 9 LED anodes. 3 transistors are used, one for each color (R G B). So at any time, only one transistor/color is engaged...
My LEDs are in a column of 9. pin 1 on tlc5490 relates to LED 1 at the bottom of my column...etc pin 9 is LED 9 at top of my column.
I limited current to 25mA per LED.

2 
   startXLATCallback(); //WHAT IS THIS???

This is a function call. That's kind of obvious, isn't it?

Is there something about the function call that you don't understand?

3

off course I do, but I don't understand the XLAT_PERIODS portion

??

#define XLAT_PERIODS  2

volatile uint8_t timesCalled;

or ??

set_XLAT_interrupt();

or??

tlc_onUpdateFinished = myXLATCallback;
4

The code is using interrupts to trigger actions. The interrupt handler sets a flag, indicating that it has been called. When that flag is true, some functions, called callbacks, are called.

Rather than the TLC library doing everything for you, it lets you create a function that it will call when there is something to be done. You need to tell it which function to call. That is what

tlc_onUpdateFinished = myXLATCallback;

is doing.

You should look through the library, to see what the number of periods is for.

5

thanks that helps with that, but I'm hoping someone can demystify the TLC library a little for me..

how to change ledArray while maintaining a proper transmission of grey scale?

6

bump

any help would be awesome

7

After a lot of research, It seems that XLAT is the pulse that is sent at the end of each grayscale update cycle. So, I guess Joe is using this "interrupt" to trigger his color update?

I could really use any help on understanding this so I can just manually put a blink or fade function in this code?