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The device works pretty well ! I did the smoke-test with 4GB micro sd HC4 card and it works. Be aware that this is not a generic mp3 player and there is a special folder structure and file and folder name convention (RTFM). The speaker output is VERY powerful. If the attached speaker is with low-impedance the power source shall be able to provide enough power (current) otherwise you will get "bad" noise.
It works but 3 items to remember 1 Speaker Out may be burned out if You use 8 Ohm speaker - please be careful. 2 In datasheet is a very very ugly error, p.6 - error in control summe, insteade of 7E FF 06 03 00 00 01 FF E6 EF command must be 7E FF 06 03 00 00 01 FE F7 EF 3 Control summe bytes - you can calculate it using equation CS= -(256*256-Bytes), it must be hex 2-byte unsigned type, Bytes - summ of all bytes of comman with exeption of 7E, EF ans control summe bytes