What was once an expensive luxury is now widely accessible thanks to a prolific landscape of manufacturers mass producing speakers to fit every taste and budget. Some speakers are amenable to custom firmware, but only a small minority have attracted a software development community. It doesn’t help that most Bluetooth audio modules are opaque, their development toolchains difficult to obtain. So what if we just take advantage of the best parts of these speakers: great audio fidelity, portability, and the polished look of a consumer good, to serves as the host for our own audio-based hacks.
I’ll show you how to drop an Arduino into a cheap speaker as the blueprint for your own audio adventures. But by changing our Bluetooth speaker mindset from “it’s a reprogrammable computer” to “it’s an integrated collection of useful electronic components”, we turn market diversity into our ally. Surprising the customer with big sound from a little box is key for success, so each product can offer a unique combination for driving the audio, all housed inside an eye-catching enclosure that lets consumers tell one portable Bluetooth speaker from another. For best sound, they will need matching audio amplifier modules, which will have their own power requirements, which dictates battery performance, and so on.
But before we begin, an obligatory note in case it is not obvious to any beginners reading this: This activity very definitely voids the warranty (do it, it’s worth it! Once the circuit board has been extracted, the Bluetooth interface module should immediately stand out as the most sophisticated component sitting close to an antenna. We want the system to believe we are connected via an audio cable plugged into the line-in jack, but for compactness we’d prefer to do this without using an actual cord. Soldering a wire to always ground that detection pin will keep this speaker constantly in “playing external audio” mode.
An alternative approach is to bypass existing input and volume control, sending audio directly to the amplifier chip. This particular Bluetooth device uses a Mixinno MIX2052 chip sitting adjacent to the voice coil wire connector, with a peak power of 6 watts. Similar to how we look for our amplifier near our voice coil wires, we can look for our regulator sitting near inductors, capacitors, and diodes. So as long as the audio source stays quiet during this time, we would have a little extra power to support boot. I cut the trace leading to the Bluetooth interface module and soldered a wire so the switch now pulls an Arduino pin to ground when pressed. A few pieces of internal plastic reinforcements for ruggedness were cut away to create enough volume for an Arduino Nano inside this enclosure.
To conclude this proof of concept, the Arduino Nano is using the Mozzi audio library to play the classic Wilhelm scream whenever our repurposed button is pressed.
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