The Smooth and Creamy Hot Chocolate Speaker

Ever wanted to play some smooth Jazz or creamy funk? Well I have the perfect device for you – the Hot Chocolate Speaker! It’s a fully-functioning speaker upcycled from a Cadburys hot chocolate tin, complete with volume control and a power switch.

I think this is a really exciting project because it uses rubbish we’d normally just throw away and turns it into a genuinely useful little speaker. For our mutual enjoyment, I documented the full design, build and testing in this video.

In the following article, I’ll go through everything you need to recreate this project, as well as some lessons I learned along the way which I didn’t manage to fit into the video.

BOM (Bill of Materials)

The bill of materials is as follows:

  • Cadburys hot chocolate tin
  • Sparkfun mono audio amplifier
  • 8 ohm speaker
  • 10k ohm potentiometer
  • DC barrel jack
  • Switch
  • 3D prints (as detailed below)
  • 10 (ish) M2 bolts with nuts
  • 10 (ish) M3 bolts with nuts

3D prints

The 3D prints for the hot chocolate speaker were one of the first things I designed in Fusion 360. I’m not especially good at CAD so it’s a tribute to how user-friendly Fusion 360 is that even I could put this together!

There are three main parts to the 3D prints:

1) Internal structure: this is the green bit which slides inside of the hot chocolate tin and which physically holds the speaker. It also has mounting holes, onto which the circuitry screws.

2) Control panels: the two panels (coloured red in the CAD picture) hold the controls which fit on the outside of the hot chocolate tin.

3) Lid cover: the orange bit on the top with holes pushes inside the lid and provides strength/protection, whilst still letting the sound out.

You can download all of the 3D print files here:

Wiring guide

The wiring is fairly straightforward and I just did exactly what the Sparkfun guidance says – you can find the official guidance here. However, for ease I created a diagram:

The speaker has a + and – connection which I made sure matched up to the Out + and Out – on the Sparkfun board. The hardest bit was wiring the audio jack – I found it surprisingly difficult to find useful wiring information, until I stumbled across this blog post: https://www.cigarboxguitar.com/knowledge-base/wiring-stereo-and-mono-jacks-for-cigar-box-guitars-amps-more/

As this is a mono amplifier board, I only needed to wire two connections, as shown in the picture below, taken from the above Cigar Box Guitar link

The potentiometer didn’t require any special wiring – you just solder it into the holes. However, there is a little solder jumper you have to remove to allow the volume control – it is not enabled by default.

Lessons Learned – Ground Loops

Okay, I have to admit that I lied a little… In the video, I showed the speaker working first time – of course this isn’t what happened, projects hardly ever work first time! When I turned it on, I got nothing but noise which I soon tracked down to a ground loop. Here is the minute or so of video I cut out with my finding and resolving the ground loop.

If you’ve not come across them before, ground loops are where a piece of circuitry is connected to ground (GND) in two different places. This causes a problem because ground is not a perfect zero volts, it wobbles and fluctuates and will have a slightly different voltage potential at different points.

Therefore, if you connect your electronics to ground in two places, the slight potential difference between the two grounds causes a current to flow through your electronics, introducing noise.

If the grounds are right next to each other on the same circuit, they will basically be exactly the same potential, so you will get very little noise. However, if the grounds are on different circuits you’ll encounter problems. Don’t say I didn’t warn you!

I think that’s everything

So there you have it – everything you need to recreate this project for yourself, as well as a little additional knowledge on ground loops chucked in. I hope you liked the Hot Chocolate Speaker and the video – I would love to hear your thoughts on my smooth and creamy creation.

Happy hacking,

Robin

Leave a Reply