I'm building a drum machine, and I have stored a sample header file with a kick sound which takes values between 0 and 170. I want to send it over SPI to a 10-bit MCP4811 DAC which then outputs it to a 3.5mm audio jack.
I have my MISO,MOSI,SCK and RESET pins connected to my USB programmer as well as the DAC.
Here is a snippet of the audio file stored in "samples.h"
unsigned const char sample_1[2221] PROGMEM = {0, 0, 0, 1, 1, 1, 2, 2, 2, 3, 3, 4, 4, 4, 5, 5, 5, 6, 6, ...}
unsigned int sample_len[1] = {2221}
So it is a sample of 2221 bits. This I want to send to the DAC using SPI with freq = 22 kHz.
I'm using a 16 MHz Crystal, so I set the fuses accordingly to use it.
I am using a Timer which overflows 22 kHz.
volatile unsigned int sample_count[1] = {0};
volatile unsigned int audio_out = 0;
volatile unsigned char spi_junk;
int main (void)
sei();
DDRB = 0b10110000; //Set MOSI, SCK and SS as output.
PORTB = (1 << PINB4) //active low on SS.
TIMSK1 = (1<<OCIE1A); //Enable interrupt
TCCR1B = (1<<WGM12) | (1<<CS11); // set CTC mode and divide clk by 8
OCR1A = 91; //16 MHz/(8*91) ~ 22068 Hz
//SPI Init
SPCR = (1<<SPE) | (1<<MSTR); //master, 8 MHz
SPSR = (1<<SPI2X);
ISR (TIMER1_COMPA_vect) {
audio_out = 0;
//If play_track == 1, then the sound should be played back.
if (play_track && sample_count[0] < sample_len[0]){
audio_out += (pgm_read_byte(&(sample_1[sample_count[0]++)));
// send audio_out to 10-bit DAC on SPI
PORTB &= ~(1<<PINB4); // B.4 (DAC /CS)
SPDR = (char) ((audio_out >> 6) & 0x000f); //byte 1 0 0 0 0 b9 b8 b7 b6
while (!(SPSR & (1<<SPIF)));
spi_junk = SPDR;
SPDR = (char) ((audio_out & 0x003f) << 2); //byte 2 b5 b4 b3 b2 b1 b0 0 0
while (!(SPSR & (1<<SPIF)));
spi_junk = SPDR;
PORTB |= (1<<PINB4);
}
My PIN set up is.
Atmega644 -> DAC
MOSI -> SDI
SCK -> SCK
SS -> /CS
On MCP4811
Vdd -> 5V
Vss -> GND
V_out -> Audio jack.
The rest of the pins on the MCP4811 are not connected to anything.
I have seen that the audio_out is working as expected, by displaying the audio_out value on a LCD screen. But nothing is being output to the DAC. Anyone see what could be wrong?
EDIT: Added the SPI init which I had missed to add.
Your line here
SPDR = (char) ((audio_out >> 6) & 0x000f); //byte 1 0 0 0 0 b9 b8 b7 b6
Will set ¬SHDN to 0 which will shutdown the DAC
0 = Shutdown the device. Analog output is not available. VOUT pin is connected to 500 kohm typical)
Set bit 12 to 1 instead
SPDR = (char) ((audio_out >> 6) & 0x0f)|0x10; //byte 1 0 0 0 1 b9 b8 b7 b6
from datasheet
1 = Active mode operation. VOUT is available.