As mentioned, I designed the enclosure for this project to be CNC machined out of plywood – I won’t show the process of that here, since it’s essentially the same as I showed for the BlockBox v2. After some basic post-processing, I was left with six beautiful enclosure walls – only blemished by some delamination of the plywood near the top and bottom side countersinks, but that’s easy to fix with some small wooden chips (or just ignore where it’s not visible).
Five of the walls (all except the back) were glued together using wood glue, forming a strong box, which fit the electronics assembly very nicely. Some matching screw holes in the side walls hold the PCB in place using its soldered screw terminals. For an easy USB connection, a USB Micro-B jack was glued into the the side and wired to the board, and the SCD30 module was installed on a long pin header.
The back side of the enclosure received four small wooden blocks with threaded inserts, allowing it to be screwed in securely, while still being easily removable.
And with that, the CO2 Station was fully assembled, and looking great, in my opinion!
Just like before, the build process started with the electronics. So it was time to order new circuit boards and components.
Building the electronics for this second speaker followed the exact same procedure as I described for the BlockBox v1, so I won’t repeat it here. In the end, I had another nice circuit board that looks just slightly different from the first version (shown without the amplifier heat sink here).
Then, it was time for firmware development. This would be a much bigger task than it was for the BlockBox v1, again, because I had to implement a central system controller, as well as touch display communication. I was able to find a community-made library/driver for the FT81X graphics processor in the display module, which certainly made the job easier, though I had to make quite a few modifications to make it work on the PIC32MZ microcontroller. Aside from that, I implemented my own serial communication drivers for controlling the digital audio processor, Bluetooth module, LEDs, and other peripherals, as well as some central system management logic connecting them together, and of course a user interface for the touchscreen. The firmware source code is available in the same GitHub repository as the electronics design files, though I cannot guarantee anything about its correctness, completeness, and especially code quality (I was quite careless sometimes back then).
Clearly, still some bugs to iron out…
When it came to building the enclosure, however, I knew that my methods from the BlockBox v1 would not be viable any more. Making smaller and simpler shapes using my hand saws may have been possible (even if tedious), but the more complex and much bigger pieces needed for this project would just be too much to ask for. Especially considering the idea I had for LED-lit logos on the sides, which require quite significant precision. The translucent parts for the LEDs, as well as some black decoration and cover plates, were laser cut out of acrylic plastic, which I was able to order relatively inexpensively.
As for the main enclosure walls, I decided to use CNC milling – thankfully, though a personal connection to a machine shop at my university, I was able to do so for free, as long as I brought the materials and my own CNC programs. Materials were easy, I just ordered some plain 12mm plywood panels, already cut to the sizes I needed, and got a small piece of aluminium plate stock for the connector panel. The CNC programs were more complicated – Fusion 360 has some great tools for CNC programming based on my CAD design, but as I’d never done anything like that before, it took me a while to research, understand, and learn the basics of machining and CNC programming. In the end, it was time for some machining.
This could be milled much faster with a higher tool RPM, but this machine can’t do more, as it was mostly designed for hard materials. Anyway, I was not in a rush.
With that, I had some rough-looking side panels, which would need quite a bit of post-processing to remove extra tabs and pieces, sand down sharp/rough edges, file away unwanted internal corner radii, and so on.
After post-processing, they looked much better, and also fit the acrylic pieces nicely.
Now it was time to assemble the speaker. I built the main wooden box by screwing the walls together using metal corner pieces, then hand-cut some extra plates with LED strips to go behind the acrylic inserts, installed the drivers, port resonator, display, circuit board, connector plate, battery, and some plastic wool for acoustic damping inside the enclosure.
With everything connected and closed up, the BlockBox v2 was complete.
The first part of the BlockBox build process was the circuit board. Once my custom boards arrived, along with the components for them, I decided it would be best to build and test the power supply circuits first. Because battery management is not trivial in itself, I would start with external adapter power – which I needed to get from somewhere. So, it was time to modify my laptop power supply, adding a compatible connector.
With that done, I could solder the necessary components for basic power path. This was followed by constructing the main switching power supplies (52V, 12V, and 5V), allowing me to test that they work and produce the desired voltages.
Next, I added the Bluetooth module and auxiliary controller, as well as the corresponding connectors and support components. I also soldered the power amplifier chip, since its small pin pitch would make it annoying to solder with more components in the way later.
To do any real testing, I would also need the user buttons mentioned in the previous post. They were soldered on a separate little board, to be inserted into the enclosure later. I chose some nice tactile buttons with LED backlights. They also support custom labels to be inserted into them, for which I took some printable transparent foil, resulting in presentable, self-explanatory buttons.
After adding the rest of the analog audio path and amplifier output stage, the circuit was ready for testing and firmware development. And yes, some of the power amplifier output components (especially the inductors) were severely undersized in hindsight, leading to more distortion at high power. As you can see, the amplifier also got a heat sink, along with a temperature sensor and a temperature-controlled fan, which worked quite well.
During firmware development, I also realised that my initial idea for LED music synchronisation didn’t work – so I had to work around it, and the results were quite mediocre, but still did work somewhat.
Finally, all that was left was the battery protection and charging circuit, as well as some transistor heat sinks, and we have a complete and working circuit board!
Speaking of the battery – that needed some assembly as well. I ordered 16 Li-ion cells (in the standard 18650 size) with pre-installed spot-welded nickel tabs. To keep them arranged nicely and safely, I also got some plastic cell spacers.
These cells were then arranged into four groups of four, creating the desired 4s4p (four series, four parallel) configuration. I soldered the four parallel groups together, before using some solder wick to connect them in series. Soldering isn’t ideal, as it could overheat the cells – spot welding is the way to go, but needs tools I don’t have, so I just had to carefully solder the nickel strips – it ended up working out quite well.
Now I could get to the last piece of the puzzle: The enclosure. I didn’t have access to the ideal tools for such a build (CNC mill, or at least woodworking power tools) – so I made everything by hand out of plywood stock, using a drill, various hand saws, files, and sandpaper. The resulting cuts were far from perfect, but good enough for this project.
For the RGB lighting, I glued RGB LED strips to some acrylic rods, before gluing everything (except for the back wall) together to create the enclosure (just missing the side compartment in this image).
The only thing left to do now was to install all of the components inside it, and I had a complete BlockBox!
This would be the time to say something along the lines of, “That concludes the BlockBox project, thank you for reading”. But… let’s not rush it.
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