recently i bought cheap DFPlayers named MP3-TF-16P, they were very cheap.
i wanted to created a talking clock.

but there were problems-
1. No sound
2. Cannot play file by number.
3. volume control not working etc.

i searched on internet everywhere about these issues but it seems that no one on internet is finding solution,
instead everyone is depend on internet itself.

so i digged deep and finaly found solution.

CAUSE OF PROBLEMS-
problem was that if we send command, the command only works if there is no parameters or parameters are 0x00, 0x00
every command which needed parameters(such as play file by number, setting volume), did not worked.
i tried many things, but everything indicated that command was rejected by the module chip.

only reason a command is rejected, can be the checksum error.
either command is currupted during transmission, which couldnt be the case because jumper wires are too short.
or we are calculating checksum wrongly,

so i tried varius method to calculate checksum, but failed.
then bruit forced all possible checksums and aaaila...suceess!

i concluded that correct formula for calculating checksum is just-
checksum = 0xFFFF - (0xFF + 0x06 + CMD)

while in every library, para1 and para2 are also added in this formula which is not working for this particular chip.

so this is the solution for commands not working which needs parameters,

---------------
SOLUTION OF NO SOUND
--------------
no sound occures when module is not started.
module does not start without resetting.
so we need to send reset command first (0x0C) , which does not need parameters.
and then wait 4-5 senconds. because module need some time to init.

-------------------
SOLUTION OF VOLUME CONTROL NOT WORKING
------------------
every library states that you can set volume from 0x00 to 0x30, which is absolutly wrong!!!
you can only set volume from decimal 0 to decimal 30, not hex zero to hex 30.
which means that in hex, you can only set volume from 0x00 to 0x1E
if you provide higher value than this, the command will be rejected by this particular module.

thanx guys, circulate this post to all over the internet, because i know that no one will bother to find their own solution, everyone is dependent on internet as i was.
regards, 

ManojBhakarPCM ,(Grad II Teacher of Maths @ GSSS Choulukhan(Didwana->nagaur->rajasthan->India)