Mono to stereo to Mono?

I’m doing a project that’s based on the use of the DF mini player. Originally I plugged the speaker directly in the +/- of the DF mini player

I want to add the radio unit. Someone already figured it out so I’m copying them.

However, my set up is only one speaker. I am so confused as to how I can get this break out to one speaker and not have horribly messed up music as many of my songs are in stereo.

Am I just in over my head?

I am reading that you want to combine the right and left channels into a mono channel. You can sum the right and left channels, that will give you a mono out. Your impedances have to be fairly high or you will back feed one channel into the other. Not knowing what your stuff is, I would suggest working with about 100K to start. I have never done this with this class of equipment but I have done it in a pinch with commercial equipment. There you can generally do the mixing etc with the board if it is available. I use attenuators etc to keep the impedances matched and the levels proper. The commercial stuff I use is normally about 600 Ohm, home use stuff is in the range of 10K or higher.

Basically you can’t do this in a simple way. You need to transmit a single signal on a radio that contains two channels. This sort of thing is done on commercial FM radio and it involves a complex encoder at one end and a complex decoder at the other. While in theory it could be done I doubt if any of the licence free transmitters you can buy would have the bandwidth to handle the resulting signal.

Am I just in over my head?

I would say so yes.

Gil again wrong end of the stick. He wants at the end to have a stereo signal.

Grumpy_Mike:
Basically you can’t do this in a simple way. You need to transmit a single signal on a radio that contains two channels. This sort of thing is done on commercial FM radio and it involves a complex encoder at one end and a complex decoder at the other. While in theory it could be done I doubt if any of the licence free transmitters you can buy would have the bandwidth to handle the resulting signal.
I would say so yes.

Gil again wrong end of the stick. He wants at the end to have a stereo signal.

I'm not trying to broadcast signal.
The image is a breakout for a the DF player mini that I am using to play MP3. This is a mod that someone hacked so the MP3 player includes a radio. However, their set up was 2 speakers and mine is just one (as the original build went)

I think you're saying that you have 2 stereo signals that you want to mix into one single mono output/speaker. Is that right?

And when you talk about "the speaker" do you mean an AMPLIFIER connected to a speaker? Because the combined DF Mini and radio signal will not directly drive a speaker on its own.

If that's what you mean then you just need another two resistors that go from the L and R outputs of your board to the single input to the amplifier. 10K would probably work.

Steve

As long as you're using an amplifier the little mixer board should work by connecting all 4 resistors at the "output" of the mixer (input to the amplifier). You'll simply be mixing 4 signals together (4 -> 1) instead of mixing two pairs of signals (4 -> 2).

You should NEVER directly-short two (or more) audio OUTPUTS together, but it's OK through the 2.2K resistors. (It is OK to short INPUTS together, so if you have a mono source you can directly connect it to both inputs on a stereo amplifier.)

The downside to a passive mixer is that you have a voltage divider and the signal gets cut in half (assuming two signals, equal resistors, and equal output impedance). Mixing left & right cuts the signals in half again but only the different left-only and right-only signals. The "center channel" information that's common in left & right is not reduced. Hopefully, your amplifier has enough gain to make-up for it.

Real mixers are built around a summing amplifier. That's pretty easy to build with an op-amp but it gets trickier if you don't have positive & negative supplies. If you have a single supply, the signal has to be biased (so you don't loose the negative half of the signal) and then the bias has to be filtered-out, so that's a few more components.

Of course, receivers and other regular home-audio equipment don't mix... There's a selector switch so only one source is connected at a time.

slipstick:
Because the combined DF Mini and radio signal will not directly drive a speaker on its own.

The DF mini can connect to a speaker on it's own. That's the way the build was originally.
Although I noticed in the code there was a stereo output so I am thinking of trying that or just saying PROFANITY REMOVED it, make a whole new box and get another speaker.

@iseoni

1st and last profanity warning…nobody gets a second chance on those.

Bob.

@ballscrewbob

Im sorry. I had a no filter today. Was awoken at 3am because a horrible excuse for a human being high on drugs smashed his car into the trees in front of my house. The girl who was his passenger had to be airlifted and later passed away. My entire front yard has been a crime scene all day. Cops here for 15 hours...they just left I was the first civilian on scene. It was bad. Car was in millions of pieces. Some flung over 50 feet. No longer safe to be outside until it's all cleaned and no one is open to help deal with the oil and gas spills. I'm toast. Not my usual behavior. Again, I'm sorry