NXT and I2C

Lets face it I am a terrible blogger, but no one reads this anyway so who cares.

Anyway recently I had some serious grief getting a Devantech CMPS03 digital compass to work with a Lego NXT. The info doesn't appear to be anywhere else on line and I couldn't find a decent I2C example in nxc.

Here is some basic code showing how to get it working.

#define cmpAddr 0xC0 // Machine address of the compass
#define cmpPort S1 // Port that the compass is plugged in to

byte bufLSWrite[] = {cmpAddr, 0x01, 0xC1}; // Written to the compass... (Compass, give me data from register 1, now)

// Take a compass reading
int compassReading()
{
byte r;
byte outbuf[1];
byte byteNumber;
int result;
byteNumber = 1; // Read byte 1

while (I2CCheckStatus(cmpPort) == STAT_COMM_PENDING);

if (I2CBytes(cmpPort, bufLSWrite, byteNumber, outbuf))
{ r = outbuf[0];
}
else
{ r = -1;
}

result = r;

return result;
}

task main()
{
int reading;
int counter = 0;

SetSensorLowspeed(cmpPort);

while( true )
{ reading = compassReading();

NumOut( 1, LCD_LINE1, counter++, false );
NumOut( 1, LCD_LINE3, reading, false );

Wait(1000);
}
}

This is actually just a stepping stone to getting the sensor to work via NXT++ from my netbook but I'll post that code later.