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Activist Engineering, E-cig Salvage, a Distraction Free MP3 player

Salvaged E-cig LiPo to create an MP3 player

I wrote a while ago about the blight of “single-use” e-cigs which are discarded as litter and the fact that they contain rechargeable LiPo cells. In the previous article, we looked at their disassembly, with some nods to hygiene considerations and safety, and then looked at evaluating the cells and recharging methods. Rounding that article out I strapped a recovered e-cig LiPo cell to an air:bit quadcopter kit (222-9372) and went flying, all great fun, but what else can we use for these cells and can we upcycle any other parts of this annoying litter.

From the LiPo point of view, most of the cell varieties I find are 550mA cells in a cylindrical form factor. 550mA is a pretty good capacity that, if it can give a reasonable run time in a quadcopter, can certainly power a small electronics project with no moving parts for a long time. A great target project I decided on for one of these cells would be a “distraction free” MP3 player. I long ago gave up on having a dedicated portable music device as the tantalising excitement of having music on demand as well as video on my smartphone took over that functionality. It’s obviously a great solution but I find that it’s annoying at times. When I’m deep in a project in the shed and listening to some music via my phone it can be incredibly distracting to receive notifications, often nothing important, yet I feel some urgency to pick up the device and check what it is and respond. So an “old school” MP3 player where you load MP3’s into memory and they simply play is the order of the day.

With no formal brief for building a one-off device for myself, I set myself a couple of aims. One was to reuse as many salvaged e-cig components from the pile as possible, another was, as this is a recycling project, was to try and use as much stuff already in my possession from my spares bin. In fact, I didn’t end up buying anything for this project.

I had in my stock already some interesting MP3 modules. The “MP3-TF-16p” module is an incredibly cheap mass-produced module that has heaps of functionality, most of which we didn’t use in this project, and is widely available for very little money. It can receive up to a 32GB micro SD card loaded with MP3’s either in a big messy single directory or as separate folders of albums. Documentation is a little lacking for the device but plenty of people have built and documented all kinds of projects with it. You can address the module from a microcontroller, so it’s crept into usage in projects that need to automate audio, but you can also hook up a really simple MP3 player with limited, but useful functionality, just using 2 momentary press buttons.

schematic diagram

Looking at the schematic diagram you can see you can simply wire the IO-1 and IO-2 pins to ground through a press to make button. The IO-1 button, when short pressed, skips to the previous track to the currently played. The IO-2 button when short pressed skips to the next track in the folder or directory. If you long press, which is pressing and holding, IO-1 this turns the volume at the outputs down and if you long press the IO-2 button it increases the volume. Speaking of outputs you’ll notice that the module has both DAC/L and DAC/R as an output as well as SPK1 and SPK2. Counter-intuitively the SPK labelled pins seem to work better as a headphone output with the DAC outputs being more of a conventional “Line out”.

breadboard construction

With the simple schematic confirmed as operational on a breadboard, I then moved it all over to a small single pad per hole perfboard I had in the spares drawer. I could certainly have made the perf board smaller, but as it was neatly rectangular with mount holes in the corners, and I wasn’t too concerned about the overall size of the device, I used the whole board. I hadn’t used perfboard in years, it’s quite liberating to use it again with plenty of room to kludge around sculpting connections! There’s nothing too complex about the build, I was reasonably careful to make sure that the buttons had some clearance around them and were symmetrical on the board, with hindsight I could have moved the on/off switch back onto the board a little more so it was flush with the board edge, but again, it’s a functional and rugged layout.

perfboard with components mounted

In the previous e-cig article we talked about recharging the LiPo cells and I decided not to include any charging circuitry on this board, I’ve collected a lot of these cells now and therefore decided to leave the cell for the MP3 player accessible so I can swap cells for a charged one with ease. I’ve also saved a stack of the metal tubes from the salvaged e-cigs. Having hand-made a few metal tubes using pinch rollers I appreciate how difficult these would be to make and I’m determined to try and find uses for them! As such, I decided to mount an e-cig tube to the side of the mp3 player as a rugged container for the LiPo cell. With this in mind, I quickly drew a top and bottom plate to act as a simple enclosure for the device. These were drawn with mount holes that matched the perf board with the base piece being slightly larger than the circuit board to leave a section to glue the e-cig metal tube onto. The top half of the enclosure was drawn with the outer dimensions matching the perf board and with two 8mm holes directly above the momentary press buttons.

Board battery and enclosure

At a local makerspace I do some work for, I laser-cut an upper and lower panel. Keeping true to the "keep it simple and cheap" ethos of this project, I found pieces of material in the scraps bin to cut these parts. The base is cut from some 3.125mm birch plywood and the upper section was cut from some orange perspex. I then made a very quick CAD model for the buttons which are simply a stepped cylinder with the upper diameter being slightly under 8mm to allow them to slip into the upper plate holes and the lower diameter being 10mm so that they are retained in position. I then quickly printed a pair of these in some white PLA filament (832-0223) that was already loaded in the printer.

CAD design for button

To assemble the stack was straightforward, I knew I would need to tune the height of the top plate of the enclosure to get the movement of the 3D printed buttons correct so I used a sequence of nuts on a bolt in each corner to achieve this. I could, having worked out all the correct distances now make some custom stand off’s but it works fine with the collection of nuts and bolts. The final part of the puzzle was adding the battery holder. I ground a slot into the side of a (closest matching colour) e-cig tube that I could thread the battery connector cable through into the tube. I was aware that the thin metal tube could dig into these wires potentially causing a short, so I carefully added some hot glue to the slot once the wire was in position to act as a permanent kind of cable grommet to keep the wires protected. One note with that is to take care not to make a big blob of hot glue inside the tube or else your battery won’t fit!

Completed MP3 Player

As the recovered LiPo are designed for these tubes with a slight clearance I can insert a cell with the cell connector wiring flush to the side of the cell and they fit the tube perfectly with little play. Rummaging in the box of salvage e-cig parts I also found 2 of the e-cig base components which I then used to plug the battery tube at each end. These are quite a tight fit and make battery removal a little tricky so I could be tempted to design and 3D print a couple of similar items using a flexible TPU filament.

So overall, I’m quite pleased with it, the MP3-TF-16p modules are definitely not an audiophile product and they are prone to a little hiss and interference but it’s certainly good enough for some music in the shed or at the gym. It’s lovely to not get distracted by notifications and there’s a certain pride I find in using the things you’ve built, especially when some of the components were destined for landfill!

General tinkerer! Freelancing writing about making things, rocketry, boats, electronics and a mahoosive pile of unfinished and unstarted! Author of "FreeCAD for Makers" book on Raspberry Pi Press and writes for Hackspace Magazine, Tindie, Kids Code Computer Science, Toms Hardware and more!