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Hardware design · case study 00 · Sep 2014 – Apr 2015 · 5-minute read

Where it started: a portable amplifier speaker

Before university, a college brief asked me to find a problem and solve it with an electronic circuit on a £20 budget. I picked my own problem: music on my phone was too quiet when I was out. Seven months later I had a working, battery-powered amplifier speaker.

My roleSolo: problem finding, research, circuit and PCB design, sourcing, build and test
WhenSep 2014 – Apr 2015, BTEC National Diploma in engineering (college)
StageThe whole loop: discover, define, develop, deliver
MethodsProblem list, competitor teardown, simulation, PCB layout, Gantt plan, weekly design diary, presentations
The headline

A working speaker for under £20 of parts

£16.79 first order

Built around an LM386 audio amplifier chip, with volume and gain controls, a 9 V battery and a 3.5 mm input, so any phone, iPod or laptop could plug in.

Discover

Start with problems I actually had

In week one I listed four everyday problems and a possible fix for each: dishes left unwashed, a fridge door left open, a phone speaker too quiet, and a phone battery dying away from a plug. I looked at how others had solved each one in maker communities online.

Mind map of four project ideas: fridge door alarm, portable USB charger, portable amplifier speaker, solar mosquito scare
My four candidate ideas.

I chose the speaker. It met the brief with the most components, and it was the problem I hit most often.

Research

Take the competition apart

To see how a commercial product did it, I opened up a Numark NPM5 studio speaker and studied its amplifier boards. I also read up on how sound works: frequency, pitch, and the 20 Hz to 20 kHz range people can hear.

Back panel of a Numark NPM5 speaker during a teardown
The Numark NPM5 teardown.
A turning point. In my University of Bristol interview that November, I walked a professor through this circuit. He asked about bandwidth, filters and the range of human hearing, and I didn't know all the answers yet. So I went and learned them, and that's how I've treated every gap since.
Develop and deliver

Simulate, lay out, solder, adapt

  1. Simulate first

    I built the circuit in Circuit Wizard and designed the PCB from it, so mistakes showed up on screen, not on the board.

  2. Source the parts

    I priced a full parts list for £16.79. When part of the order didn't arrive, I bought the missing parts locally instead of waiting.

  3. Build and test

    Hand-soldered through-hole parts on the PCB, then drilled the case for the knobs, switch and speaker.

  4. Adapt the design

    Two speakers wouldn't fit the case, so I went back to one. I also wanted to put it inside a torch body; the board was too big, and I wrote down what I'd shrink for production.

The soldered amplifier PCB with battery
The soldered board.
Close-up of the amplifier circuit board
Testing the circuit.
Gantt chart project planner with weekly tasks from September 2014 to April 2015
My plan against what actually happened, week by week.
Thinking past the prototype

How I'd make it for real

For one prototype, hand-soldered through-hole parts were cheapest. For mass production I planned surface-mount parts, a smaller multi-layer board and machine assembly, to make it more portable and competitive. I also pitched it honestly: not the best speaker on the market, but a "good enough" one for people saving money, like me.

What I took from it

The same loop I run today

Then → Now

Then: A weekly diary of every decision. Now: written handovers after every build session.

Then → Now

Then: Took apart a rival speaker. Now: competitor teardowns of platforms, from Spotify to creator marketplaces.

Then → Now

Then: A device to make music louder. Now: products that help music be heard.