The Minty Amp – My First Altoids Tin Project

My life is filled with embedded computers and tiny components, and I love it. I’ve always had an affinity for underpowered equipment. The limitations force you to become creative. I love working with multi-processor computers, don’t get me wrong. But there is something that fuels my creative drive something fierce when I work with embedded computers and electronics.

Recently, I built a RetroPie setup using a Raspberry Pi 3b+. I’ve used it as a DOSBox machine – it’s phenomenal. It emulates the sound of an OPL-3 synthesizer chip so well. I’ve spent quite a few evenings playing some old shareware and reliving childhood memories.

For this particular build, I decided to pair up the Pi with some old speakers I had lying around. Their sound is bang on for the era of games I’m trying to replicate. Just enough bass to get the punch of those OPL-3 sounds across, but not too hi-fi.

After I rebuilt PurpleBlu2 using a Raspberry Pi Zero and a HiFiBerry MiniAmp, I freed up my Pi 3 and the old Drok amplifier that was in it. At a recent LAN party (yes, these still exist!) I set up a Doom deathmatch using the Pi.

This test run confirmed this was a nearly perfect setup. The sound was perfect, and the whole setup was compact. The only issue was that the amp had no case. This meant a mess of wires everywhere along with exposed electronics. Not a great combination.

Fast forward to this past weekend (November 2, 2019 to be exact). I was searching for a case for my Drok amplifier, then it hit me. I’d never used an Altoids tin as a project box. This seems to be a rite of passage for all embedded computer people. With a free evening I decided to give it a try. After all, I hadn’t yet worked with anything metallic as a project box, just wood and plastic. How hard could it be?

My first two steps were simple: drill a pilot hole (to see how hard it would be to drill through metal) and confirm the amplifier would actually fit. Both turned out to be easy.

With the positioning confirmed, I marked out the mounting holes on the bottom of the tin. I used a very small drill bit first, then moved up to a size that would give me a pseudo-thread for a 2mm thread machine screw.

Electrical tape provided a nice insulating barrier between the board and the tin. I also coated the bottom of the amp with some electric tape too.

I measured out approximately where the volume knob would be, then used progressively larger drill bits to enlarge the hole. This turned out to be the most difficult bit, as the fit for the amplifier was quite tight.

For power, I sliced a USB extension cord apart and connected the female lead to the amplifier. At first, I wasn’t sure how I was going to mount the power connector and the speaker connectors. My first thought was to leave the various connectors with enough slack that I could simply connect them up once the tin was open.

I had another problem to solve first – plugging in the 3.5mm audio cable.

After measuring (approximately) where the audio lead would plug in, I started to drill out two holes. After some filing with sandpaper, I managed to get a large enough hole that I could insert the audio cable.

Finally, I dealt with the power issue. With scissors I managed to trim away more of the USB connector sheathing. This allowed the connector to fit snugly beside the amplifier. I drilled one more hole in the corner so I could permanently mount the connector on the outside of the case. A few globs of hot glue helped to secure the connector so it wouldn’t move when unplugged.

As for the speaker connectors, I decided to keep the short leads and only have them accessible when the case is opened. Mounting them so they’re externally facing might be possible, but it’s a very tight fit.

…and the test was a success! Since it can only output 5 watts of power, it can easily be powered off the USB port of the Raspberry Pi, or a smartphone. When I used a USB OTG hub on my phone, it provided enough power to the amp. This gave me plenty of ideas for future projects, but more on that another time.

A few hours later, and I got to settle in for some old-school Quake 3 gaming on my Raspberry Pi. The amp works well.

One last quality-of-life mod to this tin – some rubber feet to keep it from sliding around (and to keep the screws from scratching the surface the amp rests upon).

What kinds of projects have you put inside an Altoid tin?