I have a MP3 DFPlayer Mini connected to a Mega2560. I'm using serial to control it. The Mega is powering/grounding the DFPlayer, and USB is powering the Mega. If I plug a small speaker directly to the DFPlayer speaker pins, I hear the audio as expected. Tracks play correctly, at the proper volume, etc.

I also have a 20w audio amplifier (MAX9744, and 20w speaker ofc), powered separately by a 12v DC wall plug. If I plug an iPod into that via the stereo jack, I hear nice loud audio, as expected. Everything is fine.

For months, I have had the DFPlayer speaker pins supplying audio into the headphone jack on the amplifier. It has been working perfectly. Until recently...

Now, for some reason, the Mega2560 instantly resets, and will continue to reset every couple of seconds while the speakers are plugged in to the amplifier. As soon as the line in stereo jack is removed from the amplifier, the Mega works again.

This has me completely stumped. This setup has previously been working perfectly, for several months. The amplifier is clearly affecting the Mega somehow (via the DFPlayer!), even when no audio is actively playing. But I'm stuffed if I can figure out where the problem is!

I appreciate any ideas and suggestions you may have.

  • Sounds as the ampifier is drawing too much current from the DFPlayer. Maybe try to add a resisitor between amplifier and DFPlayer to check for this. The resistor will reduce the possible current. So if I'm right the mega will then work as intended. I don't know why this would have happend though. Maybe some current rating exceeding
    – chrisl
    May 14 '18 at 8:13
  • 1
    You should not connect the speaker outputs to an amplifier. There are separate outputs on the DFPlayer for doing that.
    – Majenko
    May 14 '18 at 11:14
  • chrisl: The amp is drawing power from a totally separate source. The DFPlayer and Amplifier are connected in only one way - via stereo headphone jack. May 15 '18 at 1:07
  • majenko: which pins should I be using? The dac ones? If so, any ideas why it's been working just fine for months using the speaker out pins? May 15 '18 at 1:08

For externally amplified speakers, you should be feeding the DAC and GND pins to the amp's inputs. Those DAC pins provide a signal that varies by a small number of volts and is shifted so that they're always positive. This is in the range expected by small headphones (ear buds) and line level inputs to audio components like an amplifier.

The speaker pins on the DF Player mini are pre-amplified (a little tiny bit) to directly drive a very small speaker (like 2 Watts at 8 Ohms). They are a differential signal that includes both positive and negative voltages (relative to GND). Note that the two speaker outputs (SPK+ and SPK-) are not left and right, but two sides of a differential signal. Based on the schematic on page 11 of the datasheet (Chinese), it's a mono output made from mixing the outputs of the left and right DACs.

I could see how you might have gotten away with sending those to the amp, since the pre-amped speaker outputs are low power, and a good amp probably has input protection.

I don't know enough about electronics to know why it's failing now when it seemed to be working before. It could be sensitive to the amplifier's gain or a ground loop between the power sources, but I'm just shooting in the dark. Somehow, I suspect the DF Player Mini struggled to provide enough current to your amp, and since the DF Player Mini was powered from your Arduino, the Arduino essentially browned out, triggering a reset.


As Adrian McCarthy pointed out, you don't want to be running the speaker outputs into an amp like that. Use a DAC pin and Ground. As to why its stopped working - I've had trouble powering an arduino plus dfplayer from USB. The combination can quite easily draw more current than USB is designed to give. It's a bit fuzzy because not all USB supplies work exactly to proper spec. and exactly how much current you need can depend on factors as unpredictable as how much bass there is in your piece of music. If definitely nothing at all has changed in your setup, I would check in case you've got a joint going bad and shorting in the connection from the dfplayer to the amp...

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