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My mum wanted to play some music from my desktop computer on her stereo(which doesnt have usb support but has stereo jack audio input) - and I was looking for reasons to hack stuff.
so i took old broken bluetooth headset (that my ex broke...bla bla ) and hacked it to include a stereo jack - and now she just plugs it in and plays the tunes(audio streaming) :)
Future improvements:
1. Write a computer program to include voice control so she can just change music or switch of the computer off from her room using a voice command.
2.Hack the stereo to charge the bluetooth headset without unpluging it. (she probably wont let me do that lol )
so i took old broken bluetooth headset (that my ex broke...bla bla ) and hacked it to include a stereo jack - and now she just plugs it in and plays the tunes(audio streaming) :)
Future improvements:
1. Write a computer program to include voice control so she can just change music or switch of the computer off from her room using a voice command.
2.Hack the stereo to charge the bluetooth headset without unpluging it. (she probably wont let me do that lol )
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thanks in advance
dex3844, I applaud the spirit!
(but there's a problem with implementation : ) )
The most obvious being that it's not longer a stereo, so we ought to call it "on her mono" as opposed to "on her stereo" :) Seriously though, you're not supposed to just bridge the left and right channels. It's a task that requires an op amp and some circuitry but at the very least there should be resistors from the common wire to both left and right. I think in 10K range but you may need to play with the values in attempt to mitigate the impedance mismatch between the stereo's output and the bluetooth's mic. Which mismatch might also explain the bad quality. Also, a phone headset (BT or otherwise) would only be designed to cover frequency range of 300 to 3,400Hz which is a FAR cry from what you need to actually enjoy the output of that stereo (I mean, mono :) )
Anyhow, keep up great job hacking things, I'm with you on that!
I re-read my comment and it made no sense to me either :) , so I had to draw it. All three resistors are 10K or can try a few values as low as 600Ohm if the volume is too low at 10K. This is what I meant:
and as for the impendance mismatch - the stereo has its own amp and eq - so wudnt that kind of match the mic? (hey am only 1st year electronics so go easy on me lol )
-i also think the frequecy range accounts for the bad quality
thanks for the insight :)
Actually, you are correct - you're taking the output after the stereo's amp, not the line level output. In that case the proper solution would be even more complicated :) - you'd need transformers to de-couple the channels from one another.
You're not supposed to just bridge the left and right channels because you're then connecting outputs of two different amplifiers. So a situation may arise where the left channel is trying to drive it's speaker (headphone's earplug) low while the other one would at the same time try to drive it's speaker (earplug) high. In the end you'll overload both amps and you'll get neither correct high nor low.
If you have those resistors in place, at the very least that would assure that the amplitudes of signals (low and high) are separated by whatever is the voltage drop on those resistors. In other words, the low would still inhibit the high but just not as much as when you just bridged them.
As far as trying to match impedances, the difference is so big that probably no passive circuitry would do it anyhow: the headphones are in 40Ohm range whereas the electret mic of that Bluetooth headset is in 10K+ range.
So, try to play with those resistors to see what's the best quality / channel separation you can get, keeping in mind that the limitation of the phone line bandwidth set forth some 100+ years ago (300 to 3400 Hz) still applies. In other words, best you can ever get is the quality of music on hold you sometimes hear when you call some busy establishment.
Cheers!
"You're not supposed to just bridge the left and right channels because you're then connecting outputs of two different amplifiers. So a situation may arise where the left channel is trying to drive it's speaker (headphone's earplug) low while the other one would at the same time try to drive it's speaker (earplug) high. In the end you'll overload both amps and you'll get neither correct high nor low."
Please excuse me if I'm wrong, but, logically, that doesn't apply here, because the source (Bluetooth device) is mono, so there's only one (mono) output. Isn't it, then, safe to connect the single op-amp output to two channels?
Nick
I also agree with the horrible sound quality, kind of disappointing