Quickest, easiest way of controlling the DFPlayer Mini

[ScruffR]

You mean this one?

A great & very cheap MP3 sound module without need for a library!

I’ve whipped up a very rudimentary test sketch that allows you to test the MP3 commands via Particle.function(). You’d e.g. trigger the loop for folder 2 with this command string 0x17 2 0 (command, data low byte, data high byte) and this seems to start playing file 001.mp3 in that folder and then carries on to 002.mp3 - I’m not yet through the whole folder if it will loop back to 001.mp3 once it finishes, but it doesn’t look too bad uint32_t msCmdReceived; void sendCmd(int cmd, int lb,…

In that case it would be

uint16_t num = 1234;
uint8_t lo = num & 0xFF;
uint8_t hi = num >> 8;

sendCmd(0x12, hi, lo); 
// optionally you can request a reply from the MP3 module via
// sendCmd(0x12, hi, lo, true); 

But in order to have that work you need to have your mp3 files named as four digit numbers with leading zeros (e.g. 0123.mp3) and stored in a root folder mp3.

Your request reply in your example above means this

0x7e 0xff 0x06 0x41 0x00 0x00 0x00 0xfe 0xba 0xef // 0x41 Reply ? [DH]=0, [DL]= 0~? Return code when command feedback is high
0x7e 0xff 0x06 0x40 0x00 0x00 0x06 0xfe 0xb5 0xef // 0x40 Error ? [DH]=0, [DL]= 0~7 Error code(Returned codes not yet analyzed) 

0x41 indicated that you have requested a reply but the module doesn't request you to reply.
0x40 provides the error code 0x06 (what that means might be found in the datasheet of the MP3 chip)