Hello
I would like to play DFmini using external power, and Arduino only as a trigger. I am not sure, which pins to use.
When I put 3.7v 18650 to DFMini VCC and GND, and connect Ground from DFMini to ground on Nano, I see that Nano is getting some power. So I am assuming this is wrong.
If nanos 5v and GND are connected to VCC and GND pins of DF Mini, it works. But I am not interested , I want to use external power fro DFMini.
Any help for Karma 
Did you make sure the GND pins of the power supply, Arduino, and DFPlayer are all connected to each other?
Power_Broker:
Did you make sure the GND pins of the power supply, Arduino, and DFPlayer are all connected to each other?
Power supply to arduino is now via USB. I need to be sure that DFPlayer is detected.
Arduino power supply is different from DFMIni power supply [in my scenario]. Lets me know, which grounds to be connected.
Scenario: power supplied to DFMini VCC and GND. good
Now took ground pin from DFmini to 1 of Nano's GND, I seea small led powering up. I dont know if that is ok or not, as at this time Arduino is not powered at all.
Grounds must be connected. All of them. That includes BOTH ground pins of the DF Player Mini.
Note that there is a risk of phantom powering the Arduino through the Tx/Rx pins when it receives no power, but the DF Player does, and the other way around.
wvmarle:
Grounds must be connected. All of them. That includes BOTH ground pins of the DF Player Mini.Note that there is a risk of phantom powering the Arduino through the Tx/Rx pins when it receives no power, but the DF Player does, and the other way around.
ok. thanks
How big is that Phantom powering risk? I dont want to brick my parts. If connecting GNDs is not a good idea, then any alternate please.
Also the reason for supplying different battery power inputs is because Nano is serving a different purpose, and may not be turned on always. [DF is always powered on]
please advice
Connecting grounds is not just a good idea, it's mandatory for things to work.
Phantom powering can always happen when two devices are connected through I/O pins, while one is powered and the other not. Simple solution: power them both from the same supply. Resistors in the I/O lines can help prevent any damage.
wvmarle:
Connecting grounds is not just a good idea, it's mandatory for things to work.Phantom powering can always happen when two devices are connected through I/O pins, while one is powered and the other not. Simple solution: power them both from the same supply. Resistors in the I/O lines can help prevent any damage.
This is my setup limitation. I cant power up both. Nano is driving some motor, and want DF player to run standalone . Arduino is only required to trigger automatic start, without the need to press button. If Arduno is powered, the motor will also run [ not needed]
About resistors solution can you draw something or paste a link.
You don't need resistors, just connect the grounds and you'll be good to go!
If both the Nano and the MP3 player are always powered on together (even with separate supplies), why care about phantom power? Also, why not power the Arduino, the motors, and MP3 player off the same external power supply? Would work perfectly that way.
1k resistors on the Tx/Rx lines between Arduino and DF Player (both of them, OP's schematic only shows one) help a lot keeping the sound from distorting. No idea why, but from experience I know it's a good idea to place those resistors there.
Power_Broker:
You don't need resistors, just connect the grounds and you'll be good to go!If both the Nano and the MP3 player are always powered on together (even with separate supplies), why care about phantom power? Also, why not power the Arduino, the motors, and MP3 player off the same external power supply? Would work perfectly that way.
As mentioned, I want to keep them as 2 different features. So powering both is not what I want.
Resistors thing , yes, I see suggestions to use 1K resistor , for connection from Arduino to DF, and I am using 1.
My problem still remains open.
I was suggested the link. TTL input on powered off arduino? - #7 by JohnLincoln - Project Guidance - Arduino Forum
need to look at it this weekend
krisferrari:
As mentioned, I want to keep them as 2 different features. So powering both is not what I want.
Why? What functionality does that give you? I'm not saying it's a bad decision, but without knowing what your project is and what you want it to do, there's no way of knowing why you're making this odd decision.
Even still, if you want to independently select which electronics are turned on at specific times, you can just use switches in conjunction with a single power supply. Same functionality with less mess.
