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Portable stereo mod: D cell -> 18650, Tape -> Bluetooth, CD -> Pi Zero music player (brainstorming)


I have an old Philips Portable Stereo at home and it gets no use with all the modern replacements and alternatives for hearing radio and music, the CD player in it also stopped working years ago.
I work in a metal fabricating workshop and music is nice to have, we are however a little short of the blue 220v sockets otherwise I would just rewire the plug, but this presents an opportunity as it has a battery compartment.

I could change the current 6x D cell battery option to a lithium battery option like 18650s. That way I could charge the cells at home and use the stereo in work with no plug.

As mentioned the CD player is also dead in it, and I would like Bluetooth ability for it (I also have some old phones that can act as music players just for this). There is also a tape player but I am not sure which is easier to mod in a Bluetooth module.

And ideas or comments on what or how to do this would be appreciated. I know there is a post from a user that did a nice one and @DeusQain demoed which I will also have a look at.

As you can see it is no super cool retro boombox, the workshop gets dusty so I don’t want anything super nice anyway.

The option is also available to maybe paint the shell of it just for shits and giggles while I am at it.

I am also interested in which of the battery techs would be best.

  • Flat square lithium like from a battery bank,
  • Lifepo? The iron ones just for safety but no idea what battery life is like.
  • NiMh? But not sure if C or D cells are available or if it is a good idea, longest battery life is the goal.
  • RC Car battery block.

Current ideas:

  • Simple Bluetooth drop in to make it a wireless speaker.
  • RasPi headless to be an offline jukebox, attachments could be added for other functionality like Bluetooth.
    -BOTH!? CD as the Pi Player and Tape as the Bluetooth?


There are also 7.4V lithium pack for models available, they come in huge (kinda) capacities.
Charging is done via off the shelf unity and you only need to get 7.4V to what you need instead of having to deal with charge circuitry.

Audio/Feature wise:
Pi-Zero W + Pimoroni pHAT Dac give your bluetooth and audio, leaving you to figure out how to get it to the amplifier.



Nice one, I would have forgotten all about the RC Car packs, they might work perfectly. I had never intended to integrate the charge circuits into the stereo, just a holder for some sort of battery and charge them at home.

I will look at the Pi stuff in a bit, that gives me other options for music storage too with an SD card or USB stick.

Further thinking, I should load it up with the batteries it takes and see what voltage and so on it takes out and see if there is a near drop in replacement.

If I do the onboard music it would be helpful to see what I am looking at… But then again maybe a dumb jukebox would be simpler and easy, just load up files on the USB and SD card and let it rip, no configuring or searching just whatever is there gets played.
This is mostly from the adafruit website showing me a piHat that is an led matrix and stupid ideas coming to mind. Haha the tapedeck has a window, I could put the lights in there and have it do RGB things but that would be a waste of battery just for the sake of silliness.

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I back up what MazeFrame suggested and I add that you could buy a small OLED screen and use it to replace the current 7 segment one, just to make it cool.
If you wanted something really really easy you could buy a bluetooth transmitter, solder inside the 3.5mm wires to the 3.5mm jack in that thing has somewhere (I’m pretty sure it has one) and call it a day.

P.S. if you want to just play files from an SD card I think your best bet is a Pi connected to the headphone jack inside the thing.

P.P.S. what about going all out and connecting a display to the CD lid and keep the mechanism so that you could click the open cd compartment and having a screen pop up? Haha



How about epaper display?
Only takes power when putting something on, keeping it is “free”.
They are on the expensive side though.



Exactly. Small OLEDs are cheaper and more broadly available. But that’s just something I thought about just for funsies. I don’t think he wants to go all out just for a portable player



I don’t think it has 3.5mm in actually, it has out all right.

I could do the screen, thinking about it but also it is not something to look at, it will be in a corner or a box or something just making noise, won’t be seen most of the time. And I want to maximise the the battery life.

I also want to keep the radio part functional. The stereo has a slider switch to pick radio, cd or tape so I will just hook into one of those last two. It need not, and probably better if it didn’t, play any tapes or CDs, it is pretty dusty like I said so they would not last long anyway and the CD is all ready not working.

I had an idea to get the Pi all configured so that when it gets power it auto boots and all it does is open a music player and start playing on shuffle. Nothing else, rock dumb so it does not go wrong. Once it is hooked up I only ever want to touch the batteries, no messing around with playlists and so on. I will need to keep the SD card slot or USB sockets open to me though.

Maybe I will just leave the board in the CD tray, one of those flip up lids, just having the wires go down into the stereo so it is loose in there and I can get at it with out it being permenantly inside the stereo where I would need screwdrivers to get at it.



Might be easier to just buy one of those all in one Bluetooth amps and replace the internals


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Was also thinking that depends on which route I want to go with it. But i am liking the internal Pi idea instead of having Bluetooth on all day and charging two things. I do have a large library of my own music to pull from at home. Streaming is definitely a no go, the data is just too slow here and again batteries.

This is just ideas for now though so nothing is set in stone, which ever works better or is more practical when it comes time to cut wires will be the winner.



why would you be charging 2 things?



The boom box my buddy built, he used a Bluetooth module, and wired into the tape deck.
Getting on a plane. Will discuss later today if I have time.



The thing to send the music and the thing to play it.

Much edit:

The more I think about it the more I want this to just be a mega long life thing. So in my mind that would be against the Bluetooth idea because not using wireless at all will be better right? Unless the dedicated Bluetooth all in one boards are ultra efficient to make up the difference between it and the no wireless and playing locally on a Pi Zero.

But wait…

What if I do BOTH!?

The CD does not work all ready and I am never going to play tapes on this, radio is all ready its own thing on the switches. So do the Pi Zero random music player in the CD player for access and the Bluetooth module in the Tape deck.

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The majority of your power consumption is going to be the stereo itself and I think you’ll run into issues there in terms of run time. I doubt a pi or bluetooth would even make a noticeable difference in run time.



I have pictures!

R20 is D cells, something learned.

And yes I have the battery door.

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Looks like its putting those batteries in series. 9v is a tough one. I wonder if you could get away with a 3s li setup and not have it burn up…

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Either would be interesting.

The Tape Deck is interesting, depending on how it’s wired into the AMP.

The 80s FunkBox was all sorts of convoluted, so @speedfox wired the BT module to the TAPE-B power switch, and the audio output to the play head.

Depending on how this one is wired. Would really determine how you connect it all.
Also, He had an issue with how it was modulating the audio frequencies into the amp. Like it either had TOO much BASS, and had to reduce signal, or he had to boost it.

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Either take 7.4V and boost it or take 12V and regulate it down.

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yeah, I was thinking of avoiding buck/boost for efficiency.

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You can leave the existing board in and find the contact points for the buttons and solder them to GPIO pins and you can still use the buttons

You’d need to configure them as a media inputs

I think traditional NiMh are usually 1.2v so 7.2(ish) no idea if that’ll work for 7.4 stuff or if they have VDroop like nicad

Looks like they come in up to 10,000mah, since it’ll be in series 10,000 is total capacity. Seems NiMh don’t have the memory effect so you can charge it at any point regardless of how much charge is remaining or used.



At that point you can build your own pack to get to 9v.

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