This devices is zx-spectrum tape emulator. This device reads the tap-file from SD-card (FAT16 not directory) and provides a sound tape zx-spectrum.
Basic details: atmega-16 and DRAM MB81C4256.
Board in SPrint layout 4: ZXTapeEmulator-board.rar
Firmware v1.0: ZXTapeEmulator-Firmware.rar
Movie: http://www.youtube.com/watch?v=EgXSIcPxkco&feature=youtu.be