Minty Tunes: Bluetooth Audio Player (w/ Rechargeable Battery)

So... I lost my iPhone headphone adapter a couple days ago... and the first thought that came to my mind was, "This is the perfect excuse to convert my headphones into wireless ones!" After a handful of wacky days and nights... Minty Tunes was born (homage to ye olde Minty Boost!). 👾

Please check out the video above☝️to see it working!

All the components managed to fit into a tiny Altoids Smalls tin, making a small but mighty bluetooth device! In fact, this little gadget is great not only for any headphones, but also speakers, car stereo (with AUX jack), and even for a PA system at say, an event/party when you don't feel like running all the way to the mixer to change your music playlist.

One last piece of back story... I've been trying to build some other bluetooth devices using Arduinos, but when it got to figuring out all the details required to incorporate rechargeable batteries, I felt a bit overwhelmed with all the options, lingo about boosters, LDOs, safety requirements to prevent explosion, etc. So this was a nice way to simplify a slice of what I've learned into a real application. If you find yourself in a similar position, I hope this tutorial can provide as a small stepping stone.

This project is great for anyone who…

• … wants to convert their audio devices to bluetooth, but is on a budget
• … wants to learn more about electronics
• … wants to learn the basics of wiring rechargeable batteries
• … wants to learn from my mistakes first!
• … is into Altoids tin projects
• … just think this idea is cool, and wants to try it out!

Let's get started!

To build this little guy, I've structured this Instructable into 2 main categories:

1. The Wiring
2. The Enclosure

Heads up -- I am going to write each section as thoroughly as possible, as if for an audience of n00bs (like me!)... but definitely feel free to skip around based on your experience / goals!

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Also, I always encourage prototyping first, especially before jumping right into soldering and drilling holes!

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Lastly, if you are an audiophile like me, you are probably wondering about the audio quality of this thing. Well, for just a couple bucks, it's surprisingly decent! I mean, if you are using super high def mixing headphones (which I tried out), I heard a slight difference in quality... for me, I'd say about the same difference as listening to a WAV vs mp3 file. For the average listener and for average use, this device totally works.

I will include more details regarding the audio decoder specs, as well as battery, and charger tech details in the Appendix at the bottom.

All the materials/tools you really need for this project are thankfully not terribly hard to find, and low-cost! I also included optional (but recommended) items that will make your life easier, and probably good to have around anyways if you are doing more of these types of projects.

I actually had all the components lying around already (mostly from other broken electronics), but I tried my best to find equivalent links for y'all. Gold Star if you can repurpose your materials as well! ⭐⭐⭐

Supplies

• Required
• Bluetooth Lossless Audio Decoder
• Found another vendor, even cheaper, Wish, but couldn't tell shipping costs...
• 3.7v LiPo Battery - 200-400mAh capacity (mine was 400mAh... ripped out of a broken electronic device)
• No bigger than 3 x 4 x 0.5cm, for those using the Altoids Smalls tin as an enclosure
• Battery Charger Module TP4056 (with overcharging protection)
• On/Off SPDT Switch with mounting holes (mine was also repurposed)
• Electrical Wire 20-30 AWG, Solid Core
• Altoids Smalls Tin / Enclosure (CVS or Walgreens usually has them)
• Note: During the process of making this, I realized the Altoids tin is not not the easiest material to work with, and is limited to where you can place holes due to the hinged lid covering up half of the wall... but I just liked the novelty and challenge of it ;) A plastic or wooden enclosure is probably easier...
• Double-Sided Mounting Tape
• Electrical Tape
• Optional
• Small Screws and Nuts for mounting (I used size M2, aka 2mm)
• Soldering Flux Paste
• Heat Shrink Tubing (1-3mm is ok depending on your wire size)
• Super Glue
• Hot Glue
• Foam Insulation
• 'Nother Note: I only used a seriously tiny amount. Like, a sneeze worth. I actually use it a lot for other projects, but if you are looking to buy materials solely for this one, I'm sure you can find an alternative

TOOLS

• Required
• Soldering Iron + Solder
• Drill and Small Drill Bits (2-5mm in my case)
• Ruler
• Basic Filing Kit
• Small Screw Driver
• Optional
• Needle Nose Pliers
• Wire Strippers
• Helping Hands (they really help!)
• Step Drill Bit
• Tweezers
• Basic Multimeter
• Tiny hands

I'm starting off with the Wiring first because this will be pretty standard, whereas there may be some variations to the enclosure method depending on if you choose to use the Altoids Smalls tin or not.

For the circuitry, thankfully it's fairly simplistic. Still, I made my own basic visual diagram to make it easier to read than a hardcore schematic. Please take a look at it, as it provides a clearer map to the wiring strategy - better than I could do in writing. For seasoned solderers, maybe that is all you need and can skip to the next section!

Some Notes:

1. The Actual Process will probably require some back and forth between soldering a bit at a time, and then fitting everything into the enclosure. This section is meant to serve more as an overview of the wiring, and you can use it for prototyping as well. In general:
2. Solder the wires after determining where all the components are placed and prepped, and before you mount.
3. [Sort of] Optional Wiring - The blue and black - - - - - dotted lines are so that you can use a single Micro USB port (the one on the audio decoder) for both powering the decoder during use, AND charging the battery simultaneously. It does require super careful soldering of the blue wire to the decoder's USB terminal that carries the 5V power... because that terminal is pretty much the size of a baby eyelash. However, I will add some tips below for that.
4. Otherwise, if your soldering confidence is really not with you today, you do have the option of drilling two separate USB holes, or perhaps only using the one for charging (but will have to figure out placement for that). Either way, there didn't seem to be space for these options in the Altoids Smalls tin, so you would likely need a larger enclosure in this case.

Helpful Wiring Tips for Beginners:

1. Positive & Ground Wires - always double check you've got the right wires running before you solder, and especially before you connecting the battery... there is no reverse polarity protection, which mean it could fry up your boards
2. Add heat shrink when possible to cover exposed wire to prevent shortages. You can also add a dab of hot glue to cover the soldered terminals on the board
3. If you're not that great at soldering, I would highly recommend using soldering flux, and generously. I just use a toothpick, wipe it along the wires/terminals, and the solder will flow towards it upon contact.
4. On/Off Switch Orientation - by itself, there is no "correct" orientation for the switch. Meaning, after you wire the center leg, you can just pick a side leg to wire (doesn't matter Left or Right). When the latch is flipped to that side, that means it's On.
5. Wire Length - To determine your ideal wire length, you will need to first define the placement of each component.
6. If you're not sure, then err on the longer side, then cut the wire down as needed.
7. I generally measured what is my minimum length (a straight line from one point to the other), then wrap the wire around my finger 2-3 times for extra length.
8. The order in which I soldered was: audio decoder -> the on/off switch -> charger -> battery.
9. Soldering to the Baby Eyelash-Sized USB Terminal (the blue dotted line in the diagram) - everyone's got a different method for soldering to really small contacts. Here's how I did it:
10. Plug a USB cable into the audio decoder to power it up. Use a multimeter to double check you are soldering to the correct USB terminal (positive to the terminal, negative to any GND) - you should get 5V
11. Unplug the USB cable
12. Definitely use 30 AWG wire and soldering flux
13. Wipe some flux with a toothpick on the terminal
14. Strip a tiny bit (like 2-3mm) of the wire.
15. Dip the bare end into the flux
16. Add just a tiny bit of solder to the wire so it's tinned
17. Place the tinned side of the wire to the terminal, careful that it's not touching other legs. Then apply your iron so the solder melts and connects the wire to the terminal. Use helping hands if necessary.
18. Attach a wire to GND (usually black)
19. Plug the USB back in, and check with your multimeter again for the voltage reading between the two wires.
20. If you get 5V, then pat yourself on the back!

On to the enclosure!

Fitting everything into a tiny enclosure like the Altoids Smalls tin is a bit like Tetris. I will be describing specifically what I did for the tin, but feel free to adapt according to whatever case you use!

I decided I wanted the USB and Audio Jack to come out of the short side of the tin, kind of like an old school walkman or iPod Shuffle (remember those??). This added a few extra steps, but not bad. You could also use the longer side of the tin as well. Either way, once you decide where to place the audio encoder, everything else seems to fall into place.

1. Audio Encoder
2. Filing Away the Edges - As you can see in the first image, with placing the decoder along the short wall, you will need to file down the corners and front edge of the board for it to fit snugly.
3. Be extra careful not to overshoot and file off the connectors! I ended up having to get extremely close though.
4. When done, you can go ahead and solder the wires
5. I lined the bottom of the tin with electrical tape, as a precaution to insulate the tin from the circuit.
6. Place the decoder in position, and mark the locations of the audio jack and USB port with a thin permanent marker, inside the tin
7. Drilling the Holes
8. Audio Jack
9. I found it worked well to push the pointy end of my round file from inside the tin to mark the center point of the hole.
10. From the exterior, I was able to see the location, and push it back in from the outside to create a groove
11. Using a 2mm drill bit, I made a pilot hole first in the center, then worked my way up to 5mm.
12. It is important to drill from the outside in so that the fraying pushes inside
13. Be careful with the frays, as they are quite sharp. Use the round file and/or pliers to break them off and smooth it out.
14. If you have a small buffing tool, even better.
15. USB port
16. It's a good habit to check your markings each time after each previous hole is drilled, and adjust the markings if necessary. I learned the hard way, so I have a few extra mistake holes on the bottom of my tin. Whoops!
17. Using the same techniques as above, I marked 3 center points across the span of the required hole
18. From the outside, I drilled the 2mm pilots first, then expanded to a 3mm drill bit.
19. Then with the files, I smoothed out the edges until the slot was straight(ish).
20. Mounting
21. You may be able to use super glue and call it a day.
22. I decided I wanted to utilize the 2mm holes that are already on the board - one near the center, the other on the bottom corner.
23. Align the decoder, and drill 2 holes, mounting it with M2 screws/nuts.
24. On/Off Switch
25. I placed the switch centered on the opposite short wall.
26. Drill More Holes
27. Pretty much the same method. The hole for the latch was similar to the USB hole - also using a 3mm drill bit in the end.
28. Also be careful not to overshoot on the width so you can then also drill 2mm holes for mounting
29. Mounting
30. Use M2 screws/nuts for mounting
31. My latch happened to be extra long, so I also used M2*4mm standoffs to create some spacing. You probably won't have this issue, but if needed you can easily use extra nuts/washers instead.
32. Detailing (Optional)
33. It's always good practice to seal the soldered joints to prevent electrical shorts. Use heat shrink when possible, or a small dab of hot glue will do the trick (not to thick!)
34. To seal the gaps in my holes, I added itty bitty pieces of the foam insulation - so small I needed tweezers. You could probably fill them with other material like bits of rubber or electrical tape... or not.

Ok, we are almost there!

What's under the hood, you ask? The battery and charging module!

1. TP4056 Charging Module
2. You can go ahead and wire this puppy up to the decoder and switch (turned OFF) if you haven't already
3. I used helping hands to hold it while I soldered
4. Battery
5. Cut the wires to ~3-4cm long.
6. Solder the positive (red) and negative (black) wires to the corresponding terminals on the charger
7. Double check you solder to the correct terminals! Otherwise you risk frying the thing.
8. Mounting
9. Using double-sided mounting tape for:
10. Attaching the charger to the battery (centered)
11. Attaching the battery to the lid (centered)
12. Make sure there is enough of a margin around the battery for the lid to close
13. Detailing (Optional)
14. Again, probably a good idea to seal the soldered joints on the charging module with a small dab of hot glue.
15. I was lazy and just folded a piece of electrical tape upon itself (sticky side in), laid it over the charger like a mini blanket, and then used another piece of tape to strap it into the lid.
16. This method is not recommended as it also covers the LED indicator lights, and will certainly raise eyebrows with TSA if they were to ever come across it... (see image) 🧐
17. Turn it ON
18. If it lights up, you are GOLDEN.
19. Pair the Minty Tunes to your device
20. Get out of here and play some music!!

If you made it all the way to this point... CONGRATULATIONS TO YOU!! 🎉🎊

You deserve to take your newly-made Minty Tunes out for a spin, like these rad ladies! ☝️☝️

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Wow - it took me longer to write this Instructable than it did to make the device! 🤓

So if you enjoyed this Instructable or learned from it, would love to have you follow me on the socials:

FB: @dolcewangmusic

IG: @dolcewang

My YouTube DIY stuff (mostly music-related)

Until next time!! ✌️

For extra resources and learning, here's some more nerd info on:

1. Audio Decoder
2. LiPo Batteries
3. TP4056 Charger Module

AUDIO DECODER

1. Observations:
2. For the record, I am not a spokesperson by any means for any of the materials in this project. Below I will share some of my observaysh over time.
3. Range Test:
4. So far I've placed my phone in a closet with the door half-open, rounded a corner and walked about 30 ft away - signal was still fine! When I rounded another corner to another room, I started to get drop-off.
5. I did the same with the door totally closed, and the signal started to get funky more like 15 ft away.
6. I also went up to the 2nd floor while my phone was still downstairs, I started losing signal when I was directly above my phone (still on the 1st floor). But this is to be expected from bluetooth devices.
7. Okay, then I went to a public venue (lots of cross-frequences) and hooked Minty Tunes to a PA - started off fine, and then walked ~50 ft away... which is just beyond the product spec range (15m). Started to experience some drop off there... so it seems the spec is verified! (You never know...)
8. Interference Test:
9. With using tin as the enclosure material, I wasn't sure what to expect. So far, I haven't run into any problems with power or signal, even with my sparse insulation using electrical tape and foam.
10. I've also used it while on the subway, paired to my phone (within a few feet), where there is plenty of cross-frequencies and weird signals... Minty Tunes continues to play on.
11. I even tried putting the entire tin inside another ABS enclosure like a babushka doll while playing music... signal was still good!
12. Battery Test:
13. It's not written on the specs, but by measuring, it seems that the device runs on ~35mA when playing music and ~15mA when not used but still connected via bluetooth. This helps you figure out how long your battery will last. i.e. A 400mAh battery will last ~11.4 hrs of continuous playback.
14. The decoder is spec'ed out to use Bluetooth 4.1, aka BLE, which means it should automatically go to sleep when not in use, which helps to save quite a bit on battery usage over time. I have not tested this out myself yet.
15. The decoder I got plays an old-school-AOL-you've-got-mail-sounding notification when turned on, and another when paired.
16. First off, the sound quality of this notification is terrible...but don't be alarmed, the music quality played sounds fine.
17. Secondly, I saw on YouTube that others have an accented voice saying "Bluetooth is Connected," which they found rather annoying. Just a fair warning - not sure which version you will get!
18. I didn't utilize the L/R/GND terminals on the board -- it seems that you could potentially add small stereo speakers as well, or a connection cable... just some ideas!
19. Specs (Copy/Pasted):
20. General
21. Power Supply 3.7-5V
22. SNR 90dB
23. THD+N -70dB
24. Crosstalk -86dB
25. DNR 91dB
26. Support Profile A2DP/AVCTP/AVDTP/AVRCP/HFP
27. LOS >15m
28. Interface details
29. USB powered Universal Micro USB 5V power supply
30. 3.7-5V Supply Pad External 3.7-5V lithium battery power conversion
31. LED indicator Bluetooth blue light
32. 3.5mm stereo audio interface Standard 3.5mm interface, output stereo sound source, plug in headphones, connect amplifiers and other devices

LiPo BATTERIES

1. Why did I choose a LiPo Battery for this project?
2. The 3.7v is a perfectly efficient battery to power the board
3. The size and form factor
4. LiPos are generally safer than Li-ion batteries
5. For further learning on the basics of batteries
6. I found this Sparkfun article extremely helpful for getting started
7. This dude made an educational video comparing different types of batteries

TP4056 CHARGER MODULE

1. I decided to use this particular module because of its size, it seems widely used/tested out, most (but not all, so check the specs!) modules include overcharge protection, and inexpensive.
2. I've included an image of the basic pinout diagram, taken from this site if you are curious.
3. There are some variations to TP4056 -- for this project, make sure yours also has OUT +/- terminals to also power your device (same as in Step 3: The Wiring)
4. BTW, I also saw different options for ports: Micro-USB, Mini USB, USB-C (although, it didn't matter in my case because I used the port from the Audio Decoder)

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Cheers!