(keywords: bad sound, noisy sound, power supply, squawking)

I spend several hours trying to make the DFPlayer Mini MP3 player work in the simplest configuration on the a breadboard (no Arduino).

• How To Set Up And Use The DFPlayer Mini MP3 Player

I got erratic behaviour and sometimes the chip just looked dead.

Fix: Use a bench power supply

I was using an Elegoo Power conditioning circuit on my breadboard that was powered by a 9V battery. The MP3 player drew too much current, the voltage dropped and then it zombied.  The solution was to replace the 9V battery with a mains power supply. Everything worked well then.

I expect that this will also be necessary when using it with the Arduino.