MCP42100 Potmeter with SPI

Sat, Jun 5, 2010

The MCP42100 controls the resistance for the XR2206 function generator. Together with the MCP4921 the MCP42100 determines the output frequency. In such a configuration, it should be possible the generate exact musical frequencies. Testing will begin soon!

Pin 8 and 9 are connected to enable rheostat mode, the outputs function as a resistor. The output resistance of the MCP42100 can vary between 0 and 100 Kohms.

The MCP42100 connects to Arduino pins 10,11 and 13.

MCP pin 1 > Arduino 10

MCP pin 2 > Arduino 13

MCP pin 3 > Arduino 11

Inspired by Totus Terra’s work on the SX-150.

//--- SPI code

#define DATAOUT     11
#define DATAIN      12       //not used
#define SPICLOCK    13
#define SLAVESELECT 10
#define NOTEON      9

void SPIInitialize()
{
  byte clr;

  pinMode(DATAOUT, OUTPUT);
  pinMode(DATAIN, INPUT);
  pinMode(SPICLOCK,OUTPUT);
  pinMode(SLAVESELECT,OUTPUT);

  digitalWrite(SLAVESELECT,HIGH); //disable device

  SPCR = (1<<SPE)|(1<<MSTR);
  clr=SPSR;
  clr=SPDR;
  delay(10);
}

char SPITransfer(volatile char data)
{
  SPDR = data;                    // Start the transmission
  while (!(SPSR & (1<<SPIF)))     // Wait the end of the transmission
  {
  };
  return SPDR;                    // return the received byte
}

//--- MCP42100 code

byte SetPot(int address, int value)
{
  // Slave Select set low to allow commands
  digitalWrite(SLAVESELECT, LOW);

  // 2 byte command
  SPITransfer(0x10 + address);   // 0x10 = 'set pot' command
  SPITransfer(value);            // Value to set pot

  // Release chip, signal end transfer
  digitalWrite(SLAVESELECT, HIGH);
}

//--- Application code

void setup()
{
  SPIInitialize();          // Initialize the SPI interface
  SetPot(1,10);
}

void loop()
{
  // nothing
}