Play a static sound over audio (in a cassette tape)


I'm looking to build a small arduino unit (with bluetooth) into a cassette tape, so that I can play music from the cassette tape when put into a tape player.

I'm aware that these already exist (in 3mm jack and bluetooth form), however I'd like to alter the functionality built into it - namely I wish to play audio from an SD card as opposed to a bluetooth connection, and control what audio plays using bluetooth.

I've seen that I could get a TinyPico and a DF player or similar, to then hook into the magnetic tape head of the cassette tape, and I'm happy to do some trial and error with that (although if anyone has any better suggestions, please please please feel free to share!!) - however from what I've researched it would appear I can't play two tracks simultaneously.

Namely as what I would like is to have one track playing, while using the bluetooth input to select what other track plays. Think of it as a choose-your-own-adventure tape, but with a background song that never stops; however in this instance, I just want a continuous tape/static sound, that makes it feel like it's not just individual files playing one after another, but rather a single audio stream.

I hope that makes sense - is anyone aware of a way to do this "layered" audio effect with arduino? Most things I've found would suggest I can only read one file from the SD card reader at-a-time, and while I could put two in, I don't know if it'd be able to handle the simultaneous read.

Also, size of components is a slight issue as I need them to fit inside of the cassette tape - so the smaller the better. My ideal is that I'd be able to have the magnetic tape inside move as well, but I think I'll have to sacrifice that space accordingly.

Thank you so much for reading this, and I'm hoping you can steer me in a direction! :slight_smile:

How are you going to power this?

I'm planning on using a small lipo battery to power it (3.7v) which I believe should be sufficient to read from a SD card breakout board (from what I researched online).

Maybe with 2 DF mini Player and simple audio mixer.

So all in all you would like to have:

  • the original magnetic tape inside a standard-casette rotating unwinding on one side winding on the other side
  • a bluetooth-receiver
  • a microcontroller
  • a SD-card socket

microcontroller beeing able to replay two different files from the SD-card

hm maybe Mr. Q from James Bond can create something
or at least a secret high-tech company for electronic investigative equipment

Do you really thing this space will be enough?

If unwind / wind the space left is the very tiny space left in the left edges

Yeah having the magnetic tape in there is the main problem - without it, things should be able to fit in fine, the inside of one of the bluetooth cassettes looks like this:

Screenshot 2022-05-27 at 17.34.20

So while not a tonne of room, there should be enough to play with without the tape. Ideally I'd like the tape so it travels across when playing, but it's not a dealbreaker. I did consider 'halving' the tape lengthwise so it might be able to sit on top of the components - or just trimming the tape content down to allow for more room.

I'm also willing to 3D print the cassette to "fit" if needs be.

Would you be able to recommend me an audio mixer?

Why on earth does it have to be inside an old audio-casette?
maybe this guy can help as he seems to be a micronising specialist

Do you not realize you can inductively couple your audio to the tape read head. This has been done for years to access an automobile audio system back when cars only had cassette tape players.

Yes, but I presumed that I still need to read the audio from an SD card, and also pass it through the board to the tape read head - and because I want to be able to control the stop/start output of the audio using bluetooth (along with controlling which track plays), I need all the other component parts.

Or are you suggesting I can read from the two SD cards, directly to the tape head without using a mixer?

If I say its for a magic trick, does that help? :slight_smile:

Just suggesting you can put all this stuff inside a tape cassette case and inductively couple the audio to the tape player's amplifier.

If you magnetically send a signal into the tape head (like the Bluetooth gizmo) you're going to erase the tape. (And/or record on-top of the existing audio and end-up with a tape that has a permanent poor-quality audio-mix.)

And whenever I've tried to "make stuff small" it's been a nightmare! If you're an electronics manufacture and you've got the equipment to manufacture high-density surface mount boards, that one thing, but if you're a hobbyist it just makes the whole project more difficult.

You can build a passive line-level audio mixer with two resistors (4 resistors for stereo). There may be some signal loss with a passive mixer so audio mixers are normally built-around op-amp summing amplifiers. That's an easy thing to build (if you have the space :wink: ) and it's even easier (and smaller) if you don't need any mixing controls.

Not really. If it is a magic trick,
what has a real chance to shrink it to to that tiny space
is a two channel supertiny FM-receiver and having everything else implemented into your real or fake beer belly :wink:

though there has to be an additional part that connects / converts the line-in signal to a signal for the inductive head.
maybe these guys build you one in their freetime

Oh I've no issue with the tape being erased - the tape is merely for aesthetic, and to throw off the idea of electronics in a cassette player.

I mean technically speaking, i could just use the existing bluetooth cassette tape and play the audio from my phone - job done (bar the tape inside the cassette but of all), as i could build an app to manage/do that. However I would prefer to contain as much of it as i can within the tape for practical(ish) purposes.

How about implementing an inductive sender into your hand?
So laying your hand on top of the cassette-player near to the playback-head makes the music play? No experience at all if this can be practically done.

If you take a look at how small the free space in this already reduced tape-length cassette is

putting together off the shelf buyable components are too big.
Even if you use a nano-simcard sized SD-card.

The only chance I see is building a custom supertiny PCB that is winding around the spools
not using a micro-sd-card but an SMD-flash-chip, SMD-microcontroller, SMD-bluetooth-receiver.
How many thousand dollars is it worth to you to do this "magic" ?

Maybe if you search for a micronising-nerd that is eager to realise a new micronising challenge with SMD-parts

As i say though, seeing the tape inside move is optional. It would be great, but suave being a premium I'm happy to sacrifice it (or open to another way of making it "look" like its moving)

Maybe a small OLED display shows the rotation of the tape.