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The circuit described here is a SPDIF output with a USB interface. It allows connecting Personal Computers, Tablets or Smartphones to Audio equipment including AV receivers, high-end stereo amplifiers or stand-alone audio DACs. It has a infrared remote control receiver that allows controlling media playback and audio volume.
The SPDIF bitstream is generated in software on the same microcontroller that also provides USB connectivity. The SPDIF output is thus a single chip solution that can be implemented with very low hardware effort but is – compared to special USB audio ICs – still flexible and “hackable”. It is even possible to build it on a small breadboard (see below figure).
The PIC32MX270 microcontroller has been chosen for this project. It has the peripherals needed for USB audio applications enough RAM to store encoded SPDIF frames. In addition, there are low pin count variants of these chips that allow for simple PCBs.
The source code can be obtained from https://github.com/kiffie/usb-spdif and used under the terms of the GPL.
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