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//use SPI to control the AD5206 Digital Potentiometer
 //with LEDs connected to each potentiometer channel (6)

#define DATAOUT 11//MOSI
 #define DATAIN 12//MISO - not used, but part of builtin SPI
 #define SPICLOCK 13//sck
 #define SLAVESELECT 10//ss

byte pot=0;
 byte resistance=0;
 byte waitVariable = 0;

///////////////////////////////////////////////////////////////////
 //spi transfer function (from ATmega168 datasheet)
 char spi_transfer(volatile char data)
 {
 SPDR = data; // Start the transmission
 while (!(SPSR & (1<<SPIF))) // Wait the end of the transmission
 {
 };
 return SPDR; // return the received byte
 }

///////////////////////////////////////////////////////////////////
 ///////////////////////////////////////////////////////////////////
 void setup()
 {
 byte i;
 byte clr;
 pinMode(DATAOUT, OUTPUT);
 pinMode(DATAIN, INPUT);
 pinMode(SPICLOCK,OUTPUT);
 pinMode(SLAVESELECT,OUTPUT);
 digitalWrite(SLAVESELECT,HIGH); //disable device
 ///////////////////////////////////////////////////////////////////
 // SPCR = 01010000
 //interrupt disabled,spi enabled,msb 1st,master,clk low when idle,
 //sample on leading edge of clk,system clock/4 (fastest)
 SPCR = (1<<SPE)|(1<<MSTR);
 clr=SPSR;
 clr=SPDR;
 delay(10);
 ///////////////////////////////////////////////////////////////////
 for (i=0;i<6;i++) //set value of each pot to 0, turns off LEDS
 {
 write_pot(i,255);
 }
 }

///////////////////////////////////////////////////////////////////
 ///////////////////////////////////////////////////////////////////
 byte write_pot(int potAddress, int potValue) //dig pot data transfer function
 {
 digitalWrite(SLAVESELECT,LOW); //digital pot chip select is active low
 //2 byte data transfer to digital pot
 spi_transfer(potAddress);
 spi_transfer(potValue);
 digitalWrite(SLAVESELECT,HIGH); //release chip, signal end transfer
 }

///////////////////////////////////////////////////////////////////
 ///////////////////////////////////////////////////////////////////
 void loop()
 {
 waitVariable = 50; //delay variable begins at 50ms
 for (resistance = 0; resistance <50; resistance++) //0 to 50 is most effective range for LED brightness
 {
 write_pot(pot,resistance); //send SPI data to digital potentiometer
 delay(waitVariable); //wait, leave pot at current setting
 waitVariable--; //increase fade rate each time through for loop
 }
 write_pot(pot, 255); //set resistance to 0 to turn off LED completely
 pot++; //cycle through each of the 6 pots in the 5206 chip
 if (pot==6) 
 {
 pot=0;
 }
 }