I have a project where I need a sound file to be played continuously whilst at the same time being able cycle through two other sound files by using a momentary switch.
My basic plan is to use two DFPlayers, one to play the continuous file and one to swap between the two other files. My problem comes when I want to combine the two DFPlayer outputs. I was considering using a PAM8302 amp but how to combine the two DFPlayer outputs into one speaker? I was considering a 1K resistor in each line before the amp, but will this drop the output too much?
The alternative was a PAM8403 and have each DFPlayer connected to each input channel - but how to combine the outputs into the single speaker?
You are correct that you should not directly connect two outputs together. (It's OK to connect 2 or more inputs together).
I was considering a 1K resistor in each line before the amp, but will this drop the output too much?
Line-level signals (the "DAC" outputs) are usually designed to drive 10K or more so 10K would be "safer".
I believe the speaker outputs are bridged so they might not work properly, but they might and you won't damage anything with the 1K (or more) resistors in series.
With two equal-value resistors the signal will be cut in half (-6dB) when only one signal is present. You have a voltage divider, and a passive mixer is essentially an averaging circuit.
I'm not sure what the input impedance of the PAM amplifier is, but if it's input impedance is too low (relative to the "mixer resistors") the signal will drop even more.
You are correct that you should not directly connect two outputs together. (It's OK to connect 2 or more inputs together).
Does this mean I could simply connect both DFPlayer outputs together, prior to the PAM8302 input? If so, can I assume I could connect the SPKR+ of each DFPlayer together and both SPKR- together and then connect them to A+ and A- on the PAM8302 board, and this would not damage either DFPlayer?
I think, due to my inexperience with things audio, I'm going to simply go down the route of having a PAM8302 assigned to each DFPlayer (they're cheap enough) and to use two speakers, one for each amp. That way I have two separate systems that won't affect each other. The only thing they'll have in common will be the 5v power supply.
On a connected note, I want one of the DFPlayers (which will not be connected to an Arduino) to permanently loop the same single file whenever and while it is powered up. Can I safely achieve this by permanently grounding pin ADKEY1 on the DFPlayer, or would that be a bad idea? If it is not the most elegant way of looping a file, what would be the alternative, again bearing in mind it won't be connected to the Arduino?
