RGB LED Fader

Abstract

This is a neat little thing that will generate a very smooth fading RGB LED. I used these little ShiftBright modules which have the A6281 already mounted along with an RGB LED. I don't have the ability to solder a 3mm x 3mm QFN myself.

Parts

• ATtiny44
• A6281 3-Channel Constant Current LED Driver with Programmable PWM Control

Code

main.c

#include <avr/io.h>
#include <util/delay.h>

#define bit_get(p,m) ((p) & (m))
#define bit_set(p,m) ((p) |= (m))
#define bit_clear(p,m) ((p) &= ~(m))
#define bit_flip(p,m) ((p) ^= (m))
#define bit_write(c,p,m) (c ? bit_set(p,m) : bit_clear(p,m))
#define BIT(x) (0x01 << (x))
#define LONGBIT(x) ((unsigned long)0x00000001 << (x))
#define NOP asm("nop")

#define E_S bit_set(PORTA,BIT(0));
#define E_C bit_clear(PORTA,BIT(0)); //OE is active low, this turns lights on

#define L_S bit_set(PORTA,BIT(1));
#define L_C bit_clear(PORTA,BIT(1));

#define LED_OFF bit_clear(PORTA,BIT(7));
#define LED_ON bit_set(PORTA,BIT(7));

#define shift USICR|=(1<<USICLK);	//generates a shift in the SPI register
#define clock USICR|=(1<<USITC);	//generates a clock on the SPI bus 


//PA1 is Latch inout
//PA0 is Enable output

volatile uint8_t x=0;

void Port_setup(void){
	DDRA|=(1<<PA7)|(0<<PA6)|(1<<PA5)|(1<<PA4)|(1<<PA1)|(1<<PA0); //seting up the apropriate SPI i/o's
	USICR|=(0<<USIWM1)|(1<<USIWM0)|(0<<USICS1)|(0<<USICS0); //SPI mode
	DDRB|=(0<<PB1);
	PORTB|=(1<<PORTB0);
	LED_OFF;
	
	E_C;
	L_C;
}

void shft8bit(unsigned char val)
{
   USIDR = val;
   USISR = (1<<USIOIF);
   do {
      USICR = (1<<USIWM0)|(1<<USICS1)|(1<<USICLK)|(1<<USITC);
	  _delay_us(40);
   } while ((USISR & (1<<USIOIF)) == 0);
} 


void colors(uint16_t red, uint16_t green, uint16_t blue)
{
	volatile uint32_t packet=1;

	packet = (packet << 2)| (blue & 1023);
	packet = (packet << 10)| (red & 1023);
	packet = (packet << 10)| (green & 1023);

	shft8bit((packet>>24) & 0xff);
	shft8bit((packet>>16) & 0xff);
	shft8bit((packet>>8) & 0xff);
	shft8bit((packet>>0) & 0xff);
	L_S;
	_delay_us(40);
	L_C;
}

void LED_setup(void)
{
	shft8bit(0b11111111);
	shft8bit(0b11111111);
	shft8bit(0b11111111);
	shft8bit(0b00111111);
	L_S;
	_delay_us(40);
	L_C;
}

void Blue(void)
{
	// blue
	shft8bit(0b10111111);
	shft8bit(0b11110000);
	shft8bit(0b00000000);
	shft8bit(0b00000000);
	L_S;
	_delay_us(40);
	L_C;
}

void Red(void)
{
	// red		
	shft8bit(0b10000000);
	shft8bit(0b00001111);
	shft8bit(0b11111100);
	shft8bit(0b00000000);
	L_S;
	_delay_us(40);
	L_C;
}

void Green(void)
{
	// green
	shft8bit(0b10000000);
	shft8bit(0b00000000);
	shft8bit(0b00000011);
	shft8bit(0b11111111);
	L_S;
	_delay_us(40);
	L_C;
}

void Clear(void)
{
	// green
	shft8bit(0b10000000);
	shft8bit(0b00000000);
	shft8bit(0b00000000);
	shft8bit(0b00000000);
	L_S;
	_delay_us(40);
	L_C;
}

void Delay(void)
{
	_delay_ms(40);
}

int main (void)
{
	E_S;
	Delay();
	Port_setup();
	LED_setup();
	Clear();
	Clear();
	E_C;
	LED_ON;
	for(;;)
	{	
		int y=0;
		for(int i=1023;i>0;i--)
		{
			y++;
			colors(i,y,0);
			Delay();
		}
		y=0;
		for(int i=1023;i>0;i--)
		{
			y++;
			colors(0,i,y);
			Delay();
		}
		y=0;
		for(int i=1023;i>0;i--)
		{
			y++;
			colors(y,0,i);
			Delay();
		}
	}
}