From where this idea came from? Most of us have at least a one piece of old non working electronics, laying somewhere in house or shed. Recently I found old non working CRT TV, the first decision is simply to throw away this piece of history, but wait… It is always fun for me disassemble electronics and this old CRT TV is not exception it has a lot of small unnecessary and unknown parts, but one part is well known for me and this is speaker. The first decision is save this very useful part. And now this speaker found new place for new life.
- Time spent on the actual build: about a week
- Time spent waiting for the parts: few weeks
- Cost: 40 USD
- Dimensions(H:W:D): 8.5cm x 14cm x 16cm
- Weight: 660g
- Power: 3W
- Charging Voltage: 8.4-15V
- Working distance: 8-10m (open space)
Please Note! English not my native language, if you find any mistakes or misleading phrases, you can always contact me using private messages or comment section down below.
Step 1: Design, Materials and Tools Choice
There are no limits, when you building something like a bluetooth speaker, but when you set requirements, you also meet a lot of limitations.
Here we have only few limitations, volume needed for main components and volume needed for proper sound displacement, weight also very important.
The main point of this build is portability and cost, hardwood, paper and fabric is affordable and light. Also you do not need special tools to work with them.
No doubt, that CNC and Laser cutter is awesome tools, but there is small problem, accessibility of this tools quite limited. This is why I decided to use mostly hand tools, because they widely available. Still if you have access to CNC or Laser cutter simply skip a lot of step and use them.
TPA3110D2 amplifier designed for use in TV’s, speaker also salvaged from TV, looks like a perfect couple :)
Step 2: Materials
Size: 40cm x 40cm
20 grams will be enough.
25 Sheets A4 or Letter Newspaper
Piece about 30cm x 30cm
PVA Glue (wood glue)
Double sided pressure-sensitive tapes
- Clear 15mm tape
- 20cm x 10mm double sided foam pressure-sensitive tape
- 2m x 24mm double sided foam pressure-sensitive tape
Paracord (550 cord)
- Black 4mm, 12m;
- Yellow 4mm, 3m;
- Red 4mm, 1m.
4 Sheets “A4” or “Letter” office paper with density 80gsm
5gr, 0.3 or 0.4mm solder wire, with flux core
Food plastic wrap
Step 3: Tools
This is a complete list of tools needed and used in this project. A lot of tools is interchangeable, for example, it is possible to use “Three square file” which contains single and cross cut patterns, plastic ruler as a bubble remover etc.
A lot of tools should be available in your local “Home Improvement” or “DIY” stores.
Coping Saw with at least 20 cm of working depth.
Because coping saw is delicate hand tool, which requires a lot of spare saw blades, 50 pcs., should be enough.
We need only few holes, any drill should do this job.
Snap-off blade (18mm) or Fixed blade knife
Hot Glue Gun
Set of Files
- 8 inch, Single Cut Flat File;
- 8 inch, Cross Cut Round File;
- 8 inch, Cross Cut Flat File;
- Small needle files set.
30 cm ruler
Any multimeter, that can show voltage.
This project requires a little bit of soldering, any soldering iron suitable for this project, only one recommendation, soldering tip should be about 1.6-2.4mm wide.
60mm vise will be enough
Flat for potentiometer and cross for M3 screws.
- 3.2mm wood drill bit
- 7mm wood drill bit
- 12mm spade drill bit
15mm synthetic painting brush
Step 4: Electronic Components
3 watt, 8 Ohms, 4 Inch speaker (90X50mm).
Bluetooth Audio Board
TPA3110D2 based, Bluetooth audio board.
2x 18650 Li-Pol batteries
2S Battery holder for 18650 Li-Pol’s.
Voltage Boost Board
DC-DC step-up 3.2-35 V, 2 Amps voltage boost board.
Because we use 2S configuration, TP5100 charger board serfs our needs, this not a perfect solution, more about this down below.
Battery Protection Board
2S Li-Ion BMS
Screws, Nuts and Washers
- 10x M3 or M2.5, 20mm screws;
- 10x M3 or M2.5 washers ;
- 10x M3 or M2.5 nuts.
4x (10 mm diameter, 3 mm height) Neodymium magnets.
5 pairs of wires with JST connectors
5.5x2.1mm DC Barrel socket.
Red and Green 5mm, 2V LED’s.
Holders For LED Indicators
2x, 5mm Threaded Metal LED holders.
Self locking Push button
2 pin, 16mm.
Heat shrink tubes
- 5 mm at least 20 cm tube for paracord
- Set of differently sized tubes
Step 5: Print Stencils
It is already complete design, but you can always correct size by your preferences.
Drawings for printing attached for two paper sizes “Letter” and “A4”, reason for that stencil size is in 1:1 aspect ratio. You can simply print whole document, without any modification. It is possible to print directly from the phone, using compatible printer.
Some printers don't support printing without borders and can scale images, this happens to me, not a big deal, but in some cases differences can be noticeable.
Step 6: Apply Stencils to Hardboard
The are a lot of different methods to transfer printed image on the wood, for this project we can simply glue stencils to the wood, because all frame parts will be hidden.
For this you'll need PVA glue. Put thin line of glue on the area in stencil size, smooth glue using plastic ruler. You should apply thin layer of glue, it can be uneven, main point is get area that fully covered with glue. Because PVA glue dries very slow, we can move stencil in proper place quit easy, but don't try to move stencils after 15-20 minutes. When all stencils is ready, let them dry for at least 10 hour (this is for ideal drying conditions), recommended drying time 24 hours.
PVA Glue is water based, this is mean that inkjet printed lines, can be dissolved while gluing. It is better to use laser printer, or in case if this not possible, try to apply very thin layer of glue.
Step 7: Precut
There are a reason for this step. Because coping saw has limited working depth it's quite uncomfortable use even half of it potential.
To do this we can use Jig Saw, this save a lot of time, if you don't have one, you can use “Hack Saw” still it saves a lot of time.
Step 8: Coping Saw Preparation
While working on this project I found, that coping saw is quite easy to use, but only after a lot of hours working with it.
There few tips that makes process much easier:
- Insert saw blade on push;
- Maximum tension on saw blade makes cutting process much more easier and cuts smoother;
- Don’t hurry;
- Make a rest after 15 minutes of work especially for eyes.
Step 9: Outer Cut
Now when we have our RAW pieces, we can begin making main cuts, by following the stencil.
This step requires a lot of time, don't rush and try to make cuts as smooth as possible. Don't afraid if something goes wrong, small mistakes can be easily polished later.
Step 10: Joints Cut
There are no reason to make tight joins, it is better to polish joins after coping saw, using needle files.
In total, there are more than 80 joining points, it takes about 4 hours just to finish all of them.
First we should cut vertical lines, this the easiest part, you can do first this procedure for all parts, this will be more efficient.
When all parts is done, take utility knife and slightly precut horizontal lines from both sides, after this we can easily break and pull small pieces. Don't worry about chipping surface, that is fine.
Because this method far from perfect, joints should be polished. For this we will need small flat file, and one square needle file. Using flat file we can smooth vertical sides, bottom can be polished by using square needle file.
To prevent HDF from chipping we can simply smooth all sharp angles.
This step should be done before inner cuts will be made, reason for that is structural rigidity, after inner part is removed, it is hard properly fix part in the vise and structurally part becomes more weak.
Step 11: Inner Cut
This step should go much easier, because we already have a skills after outer cutting, the main point is placing part comfortable each time when you reach difficult points.
For this we can use spade drill bit and make at least two big holes from both side, but I prefer making small holes, there are no need for 4 holes, but sometimes you need make a break between cuts or change hand, additional holes makes process much easier, you don't need move coping saw at the start point or remove blade completely, simply reach next point and you can leave your work ;)
Coping Saw blade placement
This is quite easy procedure, simply unscrew one side of the blade, feed saw blade into the hole, than tension saw again, after this, fix part in the vise and that's all, you ready to make a cut.
After inner part is cut out, take "half round file" and smooth rough surface.
Try to cut inner part as a one piece, this allows fix whole frame in the vise, also this reduces wobbles and makes cutting process much easier.
Step 12: Temporary Assembly and Measurements
At this stage, we can carefully assemble ours skeleton, as shown on the pictures, also we can made necessary measurement for our internal parts.
This Bluetooth speaker is serviceable, at least some parts, this is mean we should leave enough wire to ensure that:
- Back panel can be easily pulled, while (charging port, LED and on/off switch) are attached;
- Battery module and Bluetooth audio board should come out from the shell, without disconnecting them from the speaker.
Bluetooth audio board, Step Up converter and batteries in this build holder is mounted on the mounting plate, charging board on the back plate, it will be attached to the support, all marking points and measurements for this parts should be done on this stage.
Step 13: Speaker
Now we can attach speaker to the front plate. There are no holes on the stencil, but on this step we will make them.
The easiest way to properly place the speaker is: plate height minus speaker height and divide by two, the we should make equal mark from top and bottom at the center of the plate, the same procedure for width. Now, using these marks as a guidelines, we can place speaker exactly in the center, and temporary fixing it using hot glue.
Hole drilling and Fastening
Speaker has M4 holes, but in my local shop they had only M2.5 because they more common in use, this is not a big deal. Because hardwood still easy to break and M2.5 bolts very small, we additionally need 4 washers.
Step 14: Bluetooth Audio Board
According to TPA3110D2 datasheet, this Class D Amplifier can provide up to 15W per channel, this a lot of power, especially for 3W speaker, no doubt that this speaker can hold much more, only the question, how long.
The main drawback of this board is no name Bluetooth chip. This Bluetooth module not bad, but steel, CSR based bard is much better.
My Bluetooth audio board arrived damaged, 2 capacitors is fol out, but for me this is not the issue, because this project requires only one channel.
There are not much preparations for the main board, simple soldering speaker wires and power wires. In my case, this is cables with JST connectors.
Another small detail, that can be added is tiny heat sinks, from the Raspberry Pi Kit.
Step 15: Power Circuit
As mentioned before, TPA3110D2 amplifier can provide up to 15 Watts per channel, this amount of power can easily damage our speaker in seconds.
This why 2S configuration looks reasonable. At the maximum charge Li-Ion batteries can provide output voltage up to 4.2 Volts 2S = 8.4, minimum required voltage for amplifiers is 8 Volt, sounds fine, at least for now. But, li-ion battery voltage can drops to 3 Volts, that much lower than required minimum.
I found, that even using 3 Watt speaker, Bluetooth board provide clear sound only at maximum voltage. To solve this problem we need step up voltage converter.
Seamly connect boost converter to the power source, (in our case fully charged 2S Li-Ion assembly, more details about that in the next step), and ther end to the multimeter. On the boost board, we can find small potentiometer, gradually turn it clockwise, until multimeter shows voltage about 12-16 Volts, and that is all.
At 16 Volts we can get about 0.55Amps, according to amplifier datasheet, we should get 8 Watts of power. I've tried a lot of different voltages presets and still, at low voltage sound is not very good, at high voltage sound is acceptable, but you can't listen at the maximum volume, there are no golden point. If you know reason for that, please leave a comment or send me direct message.
Step 16: Charging Circuit
Charging circuit is based on TP5100 chip, this chip new for me, but there a few reason, why this module used in this build:
- Wide range of input voltages support, from 5 to 15, this mean we can use even router power supply for charging or even car battery, but for 2S minimum input voltage 8.4V :);
- Dedicated soldering points for status LED;
- 1S/2S charging modes.
There are also a one drawback, this module can charge two li-ion batteries in sequence, but there are no monitoring for individual cells. This is not a big deal, if we will use protected batteries, or similar batteries, with same capacity and voltage, but still this not safe.
This charging board has 7 soldering points and one bridge point:
- Charging port, soldering points;
- Soldering points for status LED;
- Soldering points for battery, in our case 2S BMS (P+ and P-) points.
For this I use 2S BMS protection board based on AO4406 mosfet.
This board has 5 soldering points:
- (B+ and B-) soldering points for 2-x Li-Ion batteries in sequence;
- (BM) - connection between batteries;
- (P+ and P-) - soldering points for load and TP5100 charging board. Circuits and final assembly you can see on the pictures.
Charge two Li-ion/pol batteries with different capacities and voltages in sequence, can damage batteries.
Step 17: Testing
Before beginning final assembly, whole circuit should be tested.
- Status LED, should properly show charging stages;
- Overcharge - measure battery voltage one by one, after full charge;
- Overdischarge - this take some time.
- Play few song, on different volume levels and distances from the Bluetooth speaker;
- Check amplifier and Bluetooth chips temperature.
Step 18: Frame Assembling
After soldering, we can begin assembling the frame.
- Insert supporting rod on the side, insert it only half way, this allows to place other supporting rods much easier without damaging other parts.
- After side supports is half installed we can insert top and bottom supports. There are no specific installation order for bottom supports, but they also should be half installed on this stage.
- Prepare epoxy glue. On this stage we need about 3-4 cm blob of glue. Mix two compounds together and stir them using disposable plastic or wooden stick.
- First of all, apply a little bit of epoxy glue inside the joining point, then gently hammer them, one by one, but first, try insert each part by hands, when this becomes difficult or require additional force, try to use screwdriver hand or small hammer.
- When glue dry up, carefully place, all electronics parts on the mounting plate, using M2.5 screws.
- Insert support plate and apply a little bit of hot glue, in places where it touches supports.
Step 19: Paper Mache Shell
This is where project got his name. There are a lot of different ways to do a shell, but paper mache shell, immediately has been chosen for this Bluetooth Speaker as most affordable and easy to make.
For paper mache we need not less than 250ml of PVA glue, there no exact measurement, because you can make walls as thick as you want, about two or three dozens of office paper or newspapers, newspapers much more preferable, you can read more about this here.
- Mix warm water with glue in the 1:1 proportion (1:2 also possible);
- Shred paper in pieces, about 2x2 centimeters;
- Place shredded paper pieces into this mix, for about 10 minutes;
- Wrap the frame in plastic wrap;
- Cover half of the Bluetooth speaker frame using cardboard sheet, fasten it using masking tape or scotch tape;
- Apply shredded paper pieces on the cardboard surface, layer by layer, about 12 layers should be enough;
- Leave paper mache shell to dry, about for a day, this process depend on conditions, you can check shell after 12 hours. If you use office paper, drying time significantly longer and structure significantly weaker, this is why I don't recommend using it;
- Repeat same steps for top of the speaker frame.
Now we have two pieces of paper mache shell, that should be attached to the frame, for this, we will use epoxy or hot glue again.
- Remove cardboard from the shell;
- Apply glue on the frame joints;
- Fasten paper mache shell to the frame, using masking tape;
- Difficult, but still possible, try to put glue, between shell and frame, inside the speaker;
- Apply glue on uncovered parts of the frame.
Step 20: Back Panel
To keep the same style I decided to use fabric with almost the same structure as for front grill.
- Cut a piece of the fabric, slightly bigger than our back plate;
- Apply thin layer of epoxy glue, on the back panel;
- Place fabric on the back plate and gently smooth it using ruler.
- When glue is dry, cut excessive material from the bottom side, using back plate as a stencil. There are no need to make cuts even, because they will be hidden;
- Add push button, charging port and LED indicator, also charging board, should be mounted to the back plate;
- Attach back plate to the main frame and fasten it using hot glue.
When back plate is installed, we can hide joins, continuing winding paracord, but now using a lot of hot glue or epoxy.
Step 21: Paracord Wrap
Our Bluetooth speaker is ready to wear some “suit” and become more appealing.
Paracord is very common and useful thing, but more important it has very wide choice of colors.
There are few steps to nicely wrap your Bluetooth Speaker:
- Wrap whole shell, using double sided tape, don't peel off protective layer at this stage;
- Attach one end on the bottom, using hot glue, leave about 3 cm of cord we will use it later;
- Peel off small amount of protective layer, from double sided tape, and begin winding speaker, try to make each wind as close as possible to the previous one;
- When a half of Bluetooth speaker is wrapped in paracord it's time to add another color:
- Cut excessive paracord;
- Apply small amount of epoxy glue on paracord end;
- Pull 3mm heat shrink tube on the paracord end;
- Repeat previous step for additional color;
- Continue winding, repeating steps above, when additional color is added.
If you decided to use only one color, simply attach end as described in the subparagraph two of this step.
Step 22: Front Grill
Wrapping process for front grill, will be a little bit different as for back panel, but not much difficult.
- Prepare fabric as in previous step but now, precisely leave excessive fabric: 15mm from top and bottom and 40mm from sides;
- Cut off piece from thick fabric in shape of your front grill and make holes for magnets;
- Glue magnets to the Bluetooth speaker body.
- Mark guiding points using correction liquid;
- Attach another two magnets to the bottom of the grill using epoxy.
That's all, now we can mount front grill using magnets.
Step 23: Conclusion
A lot of mistakes, changes and improvements was made while making this project.
Main mistake is scale, and this is my fault, because I forgot about printer scaling and don't check measurement, after prints was done. When I realized this, a lot of work is already done and there was no time to repeat whole process again, this is why final product has some changes.
Hope you enjoyed.