my friends and I want to play music from an SD card.
For this we bought an DFPlayer Mini Mp3 Player modul and used it with an Arduino Mega, see attached sketch to this post.
When we power the Arduino Mega via USB from my computer, it works fine. There was a bit of a crackling sound sometimes, but after adding a resistor this also worked fine, here you can see a working test video.
But whenever we attach an external power supply (9V) to the Arduino, as we want to do later, the mp3 shield makes strange cracking noises, here is a test video of this behavior.
We have read several forum posts that say add a resistor, also lead the second gnd pin to ground, but nothing changed the sound. We have absolutely no idea why it is not working with the external power, any advice is appreciated.