/**
\example i2cDACFast.cpp 

This sketch talks to a MCP4725 digital-to-analog converter (as sold in
the Sparkfun breakout board at http://sparkfun.com/products/8736).  This
version uses the 'fast mode write' feature of the MCP4725, which
allows the DAC to be updated with only two bytes (and two ACK bits)
sent on the I2C bus.

Contrary to some claims around the web, with the fast mode write the
MCP4725 can produce credible, if low-fidelity, audio output.  For
example, see the demo at http://www.youtube.com/watch?v=lAZ0fpSPscw,
which uses fast mode writes -- although it also uses quite a bit more
and more complex code than is shown here.

Furthermore, the sample rate can be nearly doubled over the 11.025KHz
used in that demo, while staying within the 'official I2C' clocking
range, and it also appears to be possible to drive the MCP4725 with an
I2C clock significantly above 400KHz without obviously ill effects.

 */
