Consumer Electronics / Audio / TWS Earbuds
TWS earbuds electronics: Bluetooth audio SoC platform schematic in KiCad and a reusable audio block library
For a consumer-audio brand we rebuilt a true-wireless earbud platform, built on a mainstream TWS Bluetooth audio SoC, as a verified KiCad schematic (87 parts, 55 nets, 0 ERC errors) and set up a reusable block library. Status: schematic delivered August 2026.
What we did: We reconstructed the SoC vendor's earbud reference material as a hierarchical KiCad schematic, proved its connectivity three independent ways and defined a reusable block library; PCB layout was not part of this stage.
Consumer-audio brandJuly–August 2026Rapid Circuitry hardware team
Published Last reviewed:
Illustrative imageThe challenge
The brand wanted to own well-documented electronics for its product range instead of treating every product as a one-off. For the earbuds, it needed a trustworthy schematic of the Bluetooth SoC platform: a sound basis for design changes and new models.
Reference material is hard to reuse
Vendor hardware kits ship reference schematics as drawings and layout files, not as an editable, checked schematic in the brand's own tools.
Every product treated as a one-off
Re-documenting each product from scratch repeats the same power, radio and audio circuits many times over.
Small errors are costly
A 0.35 mm-pitch QFN SoC package leaves no room for a wrong pin or net. A schematic read by eye is not good enough to lay out from.
Licensed technology boundaries
Some products use licensed audio decoding. The work had to stay within hardware and firmware and never touch licensed algorithms.
Impact figures describe the situation before the project, as the client reported it to us; we did not measure them.
Our solution
We reconstructed the SoC vendor's earbud reference material as a hierarchical KiCad schematic and proved its connectivity three independent ways. In parallel we defined a company-wide library of reusable schematic blocks so future products can be assembled from validated blocks, with new work scoped only to what changes.
System architecture
What the reconstructed earbud platform contains, organised as reusable blocks.
Power and charging
- Single-inductor, dual-output buck: core rail 0.6–0.9 V and I/O/audio rail 1.6–2.0 V
- Internally generated supplies decoupled at the SoC; no extra regulators
- Charger 5 V and one-wire UART share one pad behind TVS and Schottky clamps
- Download UART runs at 1.8 V logic
Audio and sensing
- Three analog MEMS microphone channels: feedback, feed-forward and talk
- Mic bias with RC filtering; AC-coupled inputs
- Capacitive touch channels with series resistors
- NTC temperature divider sharing a touch GPIO
Radio and package
- π-matched RF path to a printed meander antenna
- Crystal layout rules that protect ESD performance
- 0.35 mm-pitch QFN package; custom footprint drawn from the datasheet
Schematic facts
- Bluetooth audio SoC
- Mainstream TWS Bluetooth audio SoC (fine-pitch QFN)
- Components
- 87
- Nets
- 55
- Hierarchical sheets
- 7 block sheets
- ERC (KiCad 10)
- 0 errors, 2 intentional warnings
- Outputs
- KiCad project, PDF, netlist, BOM, design notes
What we delivered
- Hierarchical KiCad schematic of the earbud platform
- Rendered PDF, netlist and two BOM formats
- Design notes covering power, charging, audio, touch and RF
- Custom footprint for the 0.35 mm-pitch QFN
- List of open items to confirm against the production BOM
- Hardware and firmware re-engineering plans for the product range
- Modular block-library strategy covering the brand's product categories
- Engagement options, from schematic-and-BOM only to full replication
Key engineering decisions
What we chose, and why.
Prove connectivity mechanically
The reference schematics are vector drawings
Rebuilt every connection from wire segments, junction dots and off-page ports
Grouping of every SoC pin matched the KiCad netlist exactly
Cross-check against a machine-readable netlist
An independent source for the same connections
Supply and key signal nets matched
Also confirms parts were mapped to the right symbols
Report deltas, don't hide them
Where reference sources disagree
Differences are listed, not silently resolved
Flagged for a decision before layout
Build blocks, not products
Power, radio, audio output, input and control blocks
A block enters the library only with a sheet, interface spec, BOM with alternates and validation tag
Success measure: share of each new product built from existing blocks
Outcome and status
The earbud platform schematic was delivered in August 2026 with zero ERC errors and connectivity proven three independent ways. Some items still need confirming against the production BOM, such as a few bead-or-link positions and passive package sizes, and these are listed in the delivery.
How to read the labels: Client-reported baseline = the client's own figure for the situation before the project; we did not measure it. Figures without a label are specifications or project scope.
Connectivity
55 / 55 nets
Matched by manual trace, an independent re-derivation and a mechanical proof
Electrical rule check
0 errors
KiCad 10; the 2 warnings are intentionally unused touch channels
Netlist cross-check
Matched
Key supply and signal nets agree with a machine-readable netlist
Technologies used
- Bluetooth audio SoC
- KiCad 10
- Netlist cross-check
- Python
- PyMuPDF
- MEMS microphones
- Capacitive touch
- TWS earbuds
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