Aurora Hearing Device Design

flux

Blocked: your account is currently out of ACUs, so I can’t mutate the board/layout further in this run.
Accomplished this session:
  • Started the 12 mm product-like redesign workflow.
  • Loaded the required layout/component procedures for the crescent board, compact part replacement, and placement constraints.
  • Confirmed the next execution plan: 12 mm max-width smooth crescent, 4-layer stackup, compact USB-C replacement, high-SPL mic replacement, removal/shrinking of bulky hook-side parts, and dense two-sided placement.
Remaining:
  • Apply the new 12 mm crescent board outline and 4-layer stackup.
  • Replace/flag oversized parts: current USB-C, ICS-40730 mics, large flash, tactile switch, and bulky connectors.
  • Re-place the hook PCB components into the slim crescent form factor.
  • Run layout fit/congestion checks and update the project documentation.
V

vcabieles

Estimate the ACUs needed to finish the 12 mm redesign.

flux

Estimate: ~25–45 ACUs to finish a credible 12 mm hook redesign pass.
Breakdown:
  • Apply 12 mm crescent outline + 4-layer stackup: 2–5 ACUs
  • Research/replace compact USB-C + high-SPL mics + smaller flash/switch/connectors: 6–12 ACUs
  • Re-place dense two-sided hook layout: 8–15 ACUs
  • Fit/congestion/layout verification: 4–8 ACUs
  • Update project docs and next-step notes: 2–5 ACUs
If we also route the board afterward, budget another 40–90 ACUs, because fine-pitch nRF5340/CS47L63, RF, USB, and dense wearable placement will likely need multiple iterations.
Proceed after ACUs
Prioritize fit check
Research compact parts
Update migration plan
Review power impact
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Project Specification — Project Aura Hearing Device
Project Overview
  • Status: Draft / corrected architecture selected; schematic capture may proceed after final part/pinout sourcing.
  • Device: Left-ear prototype of a custom BLE hearing-device/IEM system with an over-ear electronics hook and an in-ear multi-driver body.
  • Goal: Personal hearing correction, BLE audio/control, onboard recording, per-ear DSP, and prototype validation.
Intended Use
  • R&D prototype for bench and acoustic-coupler validation before any in-ear use.
  • Not production-intent and not medically certified.
  • Must include hearing-safety limits before wearable testing.
What the Device Should Do
  • Capture ambient audio through two hook microphones.
  • Run BLE audio/control and high-level audio handling on the nRF5340.
  • Use a Cirrus Logic CS47L63 audio DSP/front-end to bridge the nRF5340 stereo I2S stream into a multichannel downstream audio stream.
  • Use the CS47L63 onboard DSP to share hearing-correction / filtering load where practical.
  • Store profiles and recordings in external QSPI flash.
  • Communicate with a phone over BLE / BLE Audio.
  • Recharge from USB-C and support firmware update/debug access.
  • Drive a multi-BA in-ear acoustic assembly through one downstream digital Class-D amp per BA branch.
Main Features
  • nRF5340-CLAA-R BLE SoC, WLCSP95.
  • Cirrus Logic CS47L63-CWZR audio DSP/front-end, WLCSP61.
  • Three Analog Devices / Maxim MAX98360AEFB+ mono digital-input Class-D amplifiers, one per BA branch.
  • nPM1100 PMIC/charger concept.
  • W25Q01JV 1 Gbit QSPI NOR flash concept.
  • 32 MHz crystal and 2.4 GHz chip antenna concept.
  • Hook microphones: 2× TDK InvenSense ICS-40730 analog differential MEMS microphones, 74 dB SNR target.
  • USB-C charging and firmware access.
  • SWD test pads for recovery/debug.
  • Removable 3.7 V 150 mAh LiPo prototype battery via JST-PH.
  • Triple balanced-armature IEM concept: WBFK woofer, CI mid, TWFK dual tweeter.
Corrected System Architecture
Diagram



  
    
  
  
    
  



































USB-C 5 V
nPM1100 PMIC / charger
3.7 V LiPo
Battery reverse / current protection
3.0 V system rail
nRF5340 BLE SoC
CS47L63 audio DSP / codec
MAX98360A woofer amp
MAX98360A mid amp
MAX98360A tweeter amp
QSPI NOR flash
2x ICS-40730 hook analog differential mics
RF match + 2.4 GHz antenna
WBFK woofer BA
CI mid BA
TWFK tweeter BA
SWD pads
Hardware Subsystems
Power
  • USB-C provides 5 V input.
  • LiPo battery is removable for v0.1 prototyping.
  • Reverse-polarity protection is mandatory before the PMIC battery input.
  • PMIC rail current capability must be validated against SoC, flash, mics, CS47L63, and three MAX98360A audio amps.
  • Add USB-C CC pull-downs, ESD, VBUS protection, and no-backfeed safeguards.
Compute / Wireless
  • nRF5340 handles BLE, storage control, USB DFU strategy, system control, and host-side audio streaming.
  • CS47L63 handles audio front-end / DSP duties and expands the nRF5340 stereo I2S interface into the downstream multichannel audio path.
  • WLCSP + chip antenna is high RF/assembly risk for first revision; reference layout or module should be considered.
Microphones
  • Hook microphones are specified as 2× TDK InvenSense ICS-40730 analog differential MEMS microphones.
  • The ICS-40730 is not currently available in the Flux library and will require part creation/import or substitution before exact schematic capture.
  • Earlier PDM hook-mic assumptions are superseded by the ICS-40730 analog-differential mic decision.
  • Whether the IEM body still needs a local reference/feedback microphone remains an open system requirement unless explicitly removed.
Audio Output
  • Previous MAX98306 architecture is rejected.
  • Corrected path: nRF5340 stereo I2S into CS47L63; CS47L63 routes/processes audio and emits a multichannel digital ASP/TDM stream to three MAX98360A mono amplifiers.
  • The MAX98360A is a digital PCM/I2S/TDM input amplifier. It must not be driven from the CS47L63 analog OUTP/OUTN headphone output.
  • The CS47L63 analog output is mono differential OUTP/OUTN and is not the three-channel BA drive path.
  • MAX98360A TDM mode requires an 8-channel frame with 16-bit or 32-bit slots. Three amps can select different slots using DAI configuration plus GAIN_SLOT strapping.
Flex Interconnect
  • User decision: 7 conductors.
  • If CS47L63 and the three MAX98360A amps are in the IEM body, a 7-conductor flex can carry the hook-to-IEM digital/control link as: 3V0, GND, I2S_BCLK, I2S_FSYNC/LRCLK, I2S_DOUT, I2C_SCL, I2C_SDA.
  • This leaves no spare conductor for reset, interrupt, MCLK, shield, or extra ground; schematic capture must verify CS47L63 clocking/reset strategy before finalizing the connector pinout.
  • If the CS47L63 remains in the hook instead of the IEM body, the 7-conductor flex must be revisited because the downstream multichannel TDM or amplifier signals would cross the flex.
Interfaces and Connections
  • USB-C: VBUS, GND, D+, D-, CC1, CC2, shield strategy.
  • Battery: BAT+, BAT-, protected LiPo requirement, polarity marking.
  • SWD: SWDIO, SWDCLK, GND, optional VREF/VCC, 100 ohm series resistors.
  • Flash: QSPI SCK, CS, IO0-IO3, power, ground, hold/write-protect biasing as required.
  • CS47L63 control: I2C preferred for 7-conductor flex economy; SPI would require more conductors unless colocated with nRF5340.
  • nRF5340 to CS47L63 audio: stereo I2S / ASP link.
  • CS47L63 to MAX98360A amps: local 8-slot TDM digital audio bus with one slot selected per amp.
Power and Runtime Expectations
  • Battery: 3.7 V nominal, 150 mAh pouch cell prototype.
  • Runtime target is not yet validated; full power budget is required before PMIC/regulator commitment.
  • Charge current must be conservative for 150 mAh cell and thermal limits.
  • Audio output must be disabled or limited during USB attach/DFU unless validated.
Power Tree and Power Budget
  • Initial power tree is conceptual only.
  • Required next step: current budget for nRF5340 active/radio/DSP, CS47L63, three MAX98360A amps at expected SPL, flash read/write/erase, microphones, PMIC losses, USB charging, and sleep mode.
Library / Sourcing Status
  • Found in Flux library: CS47L63-CWZR, MAX98360AEFB+T / MAX98360AEFB+, NRF5340-CLAA-R7, NPM1100-QDAA-R7, W25Q01JVZEIQ, USB4125-GF-A, SPH0641LM4H-1, BAT54 variants.
  • Not found in Flux library: TDK InvenSense ICS-40730, Knowles WBFK-30095-000, Knowles CI-22955-000, Knowles TWFK-30017-000, exact 32 MHz 2.0×1.6 mm crystal, exact 7-pin 0.5 mm FFC/FPC connector.
  • A 7-pin exact flex connector may need a specific MPN; the library has similar 0.5 mm FFC/FPC connectors at higher pin counts.
Manufacturing and Assembly Expectations
  • Prototype v0.1 left ear only.
  • Rigid-flex PCB is expected eventually, but first electrical prototype may benefit from a larger rigid validation board.
  • WLCSP assembly and RF tuning are high risk.
  • Include test pads for power rails, SWD, USB, I2S/TDM/flex, I2C, mic outputs, and audio outputs.
Firmware-Relevant Hardware Requirements
  • Boot/DFU entry button on GPIO P0.11 concept.
  • USB DFU behavior must be validated for nRF5340 and PMIC port-detect timing.
  • SWD recovery pads are mandatory.
  • Zephyr / nRF Connect SDK support exists for CS47L63 in the nRF5340 Audio DK ecosystem, but custom routing to three MAX98360A amps may require devicetree/driver/audio-routing work.
  • Firmware must implement hard output gain limits, startup mute, watchdog/mute policy, and no full-scale audio test defaults.
Physical Design Expectations
  • Over-ear hook module contains battery, USB-C, SoC, PMIC, antenna, flash, hook microphones, and debug pads.
  • IEM body should contain CS47L63, three MAX98360A amps, acoustic drivers, and any local reference microphone if retained, so the 7-conductor flex carries only power, I2C, and nRF-to-CS47L63 audio.
  • Antenna keepout and battery/enclosure proximity must be defined before PCB layout.
Important Design Decisions
  • CS47L63 audio front-end selected to resolve nRF5340 native multichannel/TDM limitation.
  • Use CS47L63 digital ASP/TDM output, not its analog headphone output, to feed MAX98360A amps.
  • Keep flex cable at 7 conductors only if CS47L63 and amps are located in the IEM body and I2C control is acceptable.
  • Add battery reverse-polarity protection for prototype safety.
  • Add hearing-safety constraints before any in-ear test.
Assumptions
  • Current project is left-ear prototype only.
  • User-provided component list is a concept BOM, not yet fully validated.
  • The uploaded images are treated as v0.1 architecture sketches, not final schematics.
  • CS47L63 will be placed on the IEM-side electronics if the 7-conductor flex remains fixed.
Change Notes
  • 2026-07-15: Requirements extracted from uploaded concept text/images. Architecture review found blocking issues in audio amp compatibility and flex conductor count.
  • 2026-07-16: Updated architecture to nRF5340 → CS47L63 → 3× MAX98360A → three BA branches; retained 7-conductor flex and 2× ICS-40730 hook microphones; added sourcing status and digital-TDM-only constraint for MAX98360A.

  • Project Overview

  • Intended Use

  • What the Device Should Do

  • Main Features

  • Corrected System Architecture

  • Hardware Subsystems

  • Power

  • Compute / Wireless

  • Microphones

  • Audio Output

  • Flex Interconnect

  • Interfaces and Connections

  • Power and Runtime Expectations

  • Power Tree and Power Budget

  • Library / Sourcing Status

  • Manufacturing and Assembly Expectations

  • Firmware-Relevant Hardware Requirements

  • Physical Design Expectations

  • Important Design Decisions

  • Assumptions

  • Change Notes