The USB interface is all done by the PCM2705 IC. When the DAC is connected to a computer it recognizes it as a USB sound card and no manual installation of drivers is need. The DAC can control playback on the computer with the following HID-states:
- Volume up
- Volume down
The DAC used is the one integrated into the PCM2705, it is a 16-Bit Delta-Sigma Stereo DAC with a SNR at 98 dB. Many similar boards use an external DAC for better performance but since small size and cost is more importent in this project i choose the integrated DAC.
The amplifier used for this project is TPA2008D2 from TI. It is a 3-W Stereo Class-D amp.
PCM2705 has a SPI interface that can be used to set the HID-states. I wrote a small Arduino library so playback can easily be controlled from an Arduino.