My first idea was to use the DFRobotDFPlayerMini Arduino library. But I quite soon discovered that my DFPlayer was not a genuine one ...

I got the bad error message at startup :

Unable to begin:
1.Please recheck the connection!
2.Please insert the SD card!

Looking at the Audio chip on the back of the DFplayer I found a reference which was not the genuine one 

I ordered this one

I got that one:

Well... After searching on internet I found the datasheet of this TD5580A chip... but in chineese !

So I translated this document with the help of Google Translate. And I got a readable document : TD5580A datasheet

I carefully read this document and found that it was the same as the original one excepted the end byte of the frame which was said to be 0xEE instead of 0xEF.

Original:

TD5580A:

Unfortunately it was a mistake into the Chineese datasheet... End byte is actually 0xEF as with the original chip.

So after digging into the DFPlayer serial output I finally discovered that this clone was sending an error message after receiving a chip reset command :

Of course this 0x7E error code was not documented into the datasheet nor implemented into the library!

So I finally decided to skip this error and to write my own code as the protocol was quite simple and as I didn't need all the commands offered by the DFrobotDFplayerMini libray...