ATmega328p driving RGB LED WS2801

Question

I am using an ATmega328p to control this RGB LED module. The ATmega is on an Arduino Uno, but I am programming it in C, without using the Arduino libraries.

To power the RGB module I am also using a 12V power supply. To power the Arudino Uno I am using the USB power. I connected it the following way:

• RGB LED Module 12V -> 12V power supply 12V
• RGB LED Module GND -> 12V power supply GND
• RGB LED Module SDI -> ATmega PORTB0
• RGB LED Module SCK -> ATmega PORTB1
• RGB LED Module GND -> ATmega GND

Now if I send some data R=0xFF, G=0xFF, B=0xFF (Set SDI to 5V and make every second 24 SCK pulses) according to the datasheet nothing happens. The lights stay off. But randomly I found out, that if I disconnect the 12V power supply and connected it again randomly, sometimes the Lights turning on in a random color. So I don't have any clue whats going on.

What can cause this behavior, what can I do to find the error?

    #include <avr/io.h>


// 16ms delay.
static void delShort()
{
    TCCR0B = 0;
    TCCR0A = 0;
    TIMSK0 = 0;
    TCNT0 = 0;
    GTCCR = 0;

    TIFR0 = TIFR0 | (1 << TOV0);
    TCCR0B = (1 << CS02) | (1 << CS00);

    while(!(TIFR0 & (1 << TOV0)))
    {

    }

    TCCR0B = 0;
}

// 1000ms delay.
static void delLong()
{
    for(unsigned char lI = 0; lI < 61; ++lI)
    {
        delShort();
    }
}

static void ledSetup()
{
    PORTB &= ~(1 << PORTB0);
    DDRB |= (1 << DDB0);

    PORTB &= ~(1 << PORTB1);
    DDRB |= (1 << DDB1);
}

static void ledWrite(uint32_t pData)
{
    uint32_t lValue = pData;

    for(uint8_t lIndex = 0; lIndex < 24; ++lIndex)
    {
        if(lValue & 0x1)
        {
            PORTB |= (1 << PORTB0);
        }
        else
        {
            PORTB &= ~(1 << PORTB0);
        }

        delShort();

        PORTB |= (1 << PORTB1);

        delShort();

        PORTB &= ~(1 << PORTB1);

        delShort();

        lValue = lValue >> 1;
    }
}


void main(void)
{
    ledSetup();

    delLong();

    while (1) 
    {
        delLong();
        ledWrite(0xFFFFFFFF);
    }
}

Answer 1

The chip timings are in nanoseconds, not milliseconds, so you only have a few cycles between bits, definitely not enough that you need a timer. The long delay between bits resets the devices after each bit, so the next bit is again interpreted as the first bit of a block.

I'd use a few consecutive

asm volatile ("nop");

as delays, seven should be a good start.

Answer 2

Have you tried an example first? Just to eliminate the possibility of a wiring problem.

I suggest trying this library: Adafruit-WS2801-Library

WS2801 Library