ARDUINO & DAC for XY projector

// Send out the value in 2-byte integer x:
char I2COut[3];
I2COut[0] = 64; // The update command.  This only needs to be set once in the program if you reuse this array

unsigned short x = 1245; // Your unsigned X value

#define WRITE_I2C(ADDR, X) \
    I2COut[1] = (char) (0xFF & ((X) >> 4)); \
    I2COut[2] = (char) (0xFF & ((X) << 4)); \
    I2C.write((ADDR), 0, (void *) I2COut, 2);

WRITE_I2C(DACX, x);

#define SET_D(BIT)   (PORTD |= (1 << BIT))
#define CLEAR_D(BIT)   (PORTD &= ~(1 << BIT))


// Set green:

SET_D(GREEN_PORT_PIN)

/*
  MCP4922 test
  outputs steadily rising voltages through both DACs
  
  Steve Woodward, 2010
  most code borrowed from
  http://mrbook.org/blog/2008/11/22/controlling-a-gakken-sx-150-synth-with-arduino/
  
  connections
  ====================================================
  
  +5v           > 4922 pin 1
  Ard pin 10    > 4922 pin 3   (SS - slave select)
  Ard pin 13    > 4922 pin 4   (SCK - clock)
  Ard pin 11    > 4922 pin 5   (MOSI - data out)
  Ground        > 4922 pin 8   (LDAC)
  +5v           > 4922 pin 11  (voltage ref DAC B)
  Ground        > 4922 pin 12
  +5v           > 4922 pin 13  (voltage ref DAC A)
 
 
  4922 pin 14 DAC A > 1k resistor > synth CV in
  
 */
 
 
// MCP4922 DAC out
#define DATAOUT 11//MOSI
#define DATAIN 12//MISO - not used, but part of builtin SPI
#define SPICLOCK  13//sck
#define SLAVESELECT0 10//ss
 
int i = 0;
 
void setup() {
  SPI_setup();
  Serial.begin(9600);
}
 
void loop() {
 i++;
 Serial.println(i);
 write_note(i);
 if(i>=4096) {
  i=0; 
 }
}
 
void write_note(int i) {
  write_valueY(i);
  write_valueX(i);
}
 
 
 
 
// **************************************************
// SPI for DAC
 
void SPI_setup(){
 
  byte clr;
  pinMode(DATAOUT, OUTPUT);
  pinMode(SPICLOCK,OUTPUT);
  pinMode(SLAVESELECT0,OUTPUT);
  digitalWrite(SLAVESELECT0,HIGH); //disable device
 
  SPCR = (1<<SPE)|(1<<MSTR) | (0<<SPR1) | (0<<SPR0);
  clr=SPSR;
  clr=SPDR;
  delay(10);
}
 
// write out through DAC A
void write_valueX(int sample)
{
  // splits int sample in to two bytes
  byte dacSPI0 = 0;
  byte dacSPI1 = 0;
  dacSPI0 = (sample >> 8) & 0x00FF; //byte0 = takes bit 15 - 12
  dacSPI0 |= (1 << 7);    // A/B: DACa or DACb - Forces 7th bit  of    x to be 1. all other bits left alone.
  dacSPI0 |= 0x10;
  dacSPI1 = sample & 0x00FF; //byte1 = takes bit 11 - 0
  dacSPI0 |= (1<<5);  // set gain of 1
  digitalWrite(SLAVESELECT0,LOW);
  SPDR = dacSPI0;			  // Start the transmission
  while (!(SPSR & (1<<SPIF)))     // Wait the end of the transmission
  {
  };
 
  SPDR = dacSPI1;
  while (!(SPSR & (1<<SPIF)))     // Wait the end of the transmission
  {
  };
  digitalWrite(SLAVESELECT0,HIGH);
  //delay(2);
}
 
// write out through DAC B
void write_valueY(int sample)
{
  // splits int sample in to two bytes
  byte dacSPI0 = 0;
  byte dacSPI1 = 0;
  dacSPI0 = (sample >> 8) & 0x00FF; //byte0 = takes bit 15 - 12
  dacSPI0 |= 0x10;
  
  dacSPI1 = sample & 0x00FF; //byte1 = takes bit 11 - 0
  dacSPI0 |= (1<<5);  // set gain of 1
  
  digitalWrite(SLAVESELECT0,LOW);
  SPDR = dacSPI0;			  // Start the transmission
  while (!(SPSR & (1<<SPIF)))     // Wait the end of the transmission
  {
  };
 
 
  SPDR = dacSPI1;
  while (!(SPSR & (1<<SPIF)))     // Wait the end of the transmission
  {
  };
  digitalWrite(SLAVESELECT0,HIGH);
  //delay(2);
}