After the success of retrofitting a Raspberry Pi into my old guitar amplifier, I started the design of my next project. This time I didn’t want to reuse old parts. I had the following objectives.
- Cabinet that could be mounted in the kitchen.
- Small speaker size.
- Powered from one replaceable power supply.
My long-term goal is to create a Sonos-like system for my entire house. My girlfriend and I want to have zone-based audio (think: stream to each room at the same time) for parties and our own enjoyment. My first step was to build a system for the kitchen and experiment with some off-the-shelf parts.
I also wanted to learn how to build a wood cabinet from scratch. I’ve got some experience in wood-working from my days of building Dance Dance Revolution dance pads from scratch. This would be different – it needed to be light but durable.
My original speaker, PurpleBlu, was a bit disappointing in audio quality. Despite the size of the speaker, it sounds pretty poor. I learned this is probably because it’s not a full-range driver. It’s just… a speaker. What I needed for this project was a full-range driver.
Most speakers cover only a small range of frequencies. If you pull the cover off your home Hi-Fi speakers you’ll probably see 3 speakers in one – one for the high-end (treble), one for the mid-end (vocals) and one for the low-end (bass). What I needed was a full-range, or essentially three speakers in one.
The Parts – Hardware
I ended up finding these little guys – Gikfun 2″ full range speakers on Amazon. In theory, they would be perfect. I just needed something to power them, and thanks to the power of predictive analytics on Amazon, they suggested a low-power amplifier. I went with a Drok 5 watt class D amplifier.
Why did I use that amplifier instead of something more powerful? Simple – I could get a power supply that was powerful enough to power both the Raspberry Pi and that at the same time with minimal modifications. Speaking of the Pi, I went with a Model 3 B+.
I made a critical decision which affected the project as well. I’ll cover it in more detail in a later post. My decision was to directly connect the headphone output jack of the Pi to the amplifier.
Finally, I bought a few small accessories since I was building my own case. I got a set of standoffs so I could mount the Pi to my case (and the amp).
Mistake #1: I used the wrong size screws to mount the Pi.
What I failed to look up before I ordered this set was the size of screw the Pi and amplifier used. It turns out they use M2.5. The kit I ordered was M3. When I assembled the whole thing, the screws did work, but it was an extremely tight fit.
The last piece I ordered was purely for quality of life. I hate devices that have hard-wired power cords you can’t replace. They always end up being too short, too long, or attached to some awful brick that takes up too many outlets. For this project, I added a Micro USB panel mount extension. This meant I could use any power supply I wanted.
Case Design
After I ordered the parts, I set about my case design. Initially I thought about using 1/4″ sheets of wood to make a box. After some thought, I decided to use 1/2″ sheets as a safety measure. If I was off with my screws, it wouldn’t matter as much. It would also give it lots of durability.
I first determined how much space the speakers would need on the front. I used my scale ruler (the first time I used it for more than just a straight line!) to sketch out a small design. To keep it simple, my design eventually hinged on one decision.
- Have the front and back screw onto the box.
- Have the front and back inset into the box and screwed on from the side.
I settled on the former. It would be an easier first design, since there were already lots of unknowns. It also made the cuts a bit more forgiving. If they were off slightly, I could still make it work.
The case has the following parts.
- Top & Bottom: 8″ x 12″ x 1/2″
- Left & Right Side: 3″ x 8″ x 1/2″
- Front & Back: 4″ x 12″ x 1/2″
For extra stability I added two inside panels, same size as the left and right side panels. Later I would learn these weren’t necessary at all.
With the design in hand, I went to the hardware store, bought a 2’x2′ 1/2″ sheet of wood, marked out the cuts I wanted them to make, and they cut it down to size. I bought some 1″ deep screws as well to secure everything together.
Mistake #2: I didn’t account for the saw blade width when I measured my cuts.
An obvious mistake in retrospect, but it bit me. When I marked out the cuts, I failed to account for the width of the saw blade. This meant with each cut, I lost about 1/8″ off the wood panel. As it turns out, this only affected the two inside panels which weren’t integral to the design.
With the supplies in hand, I was ready to start construction. Next time I will cover the dry fit and how I started to put the project together.
Elias Puurunen - My Thoughts on the World 