so as you suggested…
I have the following connections made.
I have a breadboard with both the dfplayer mini and the nano connected, with jumpers connecting the 2 rails on either side of the breadboard.
I have the following DFplayer connections.
PIN 1 VCC ------> Breadboard rails RED
PIN 2 (RX) -------->Arduino PIN11 (TX) with a 1k resistor on the Arduino side at that pin.
PIN 3 (TX) --------->Arduino PIN10 (RX)
GND -----> Breadboard rails BLUE
ARDUINO is being powered via USB, and the GND pin is connected to the same set of rails on the BLUE side.
DFplayer is being powered by a talent cell usb battery, stopped down to 4.2v with a buck converter that is connected via the same rails RED/BLUE
When I do this, everything seems to have power, but the DFplayer does nothing unless I put another GND wire on the other GND pin, and touch the other end to the surrounding pins that are intended for “NEXT TRACK” and “PREVIOUS TRACK” functions if the player was being used as a standalone unit. The CODE I am using is just the test code provided by DFrobot, and I have all of the required libraries installed… SoftwareSerial, etc.
This is completely baffling to me.