Project Idea Start

flux

Local spacing and neckdown attempts did not improve the 27 blocked 0.5 mm-pitch pins, so the limitation is now the standard-density routing rules rather than placement. The existing schematic, 50 mm outline, antenna keepout, and validated placement remain preserved.
A

aaronlovesflux

flux

I’ll switch the board to a high-density fabrication profile, keep the 50 mm outline and placement fixed, then re-run fine-pitch preflight. If the pins clear, I’ll route the board and complete the final DRC loop.

flux

The high-density profile cleared preflight, and the main routing pass completed with one remaining ground connection; that final connection is now routed. I’m running the full DRC and checking antenna, copper, power-stage, and manufacturing findings before closing.

flux

Routing is complete: 0 airwires, 0 redundant traces, and 0 blocking DRC/ERC errors. The BM83 antenna keepout is preserved, and the high-density four-layer profile supports the fine-pitch ICs.
Open items:
  • Advisory high board-density warning.
  • C7 decoupling-loop-area warning; electrically routed but worth tightening in a later optimization pass.
  • U2 uses a board-level workaround for an erroneous library footprint feature; the issue was reported internally.
Suggested next steps:
  1. Optimize C7 and re-route locally.
  2. Generate a board bring-up plan.
  3. Export Gerbers, BOM, and pick-and-place files.
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Files

Schematic

Layout

3D View

Project Specification
Project Overview
  • Status: Draft
  • 50 mm diameter circular PCB for receiving Bluetooth stereo audio and driving 32 ohm headphone transducers.
Intended Use
  • Prototype battery-powered Bluetooth headphone receiver board.
  • Mechanical enclosure and battery dimensions remain external to this board-only scope.
What the Device Should Do
  • Pair with a phone or computer using Bluetooth Classic audio (A2DP sink).
  • Produce stereo analog audio suitable for 32 ohm headphones.
  • Charge one protected 1-cell LiPo battery to 4.2 V from USB-C 5 V.
  • Operate from the battery when USB is disconnected.
Main Features
  • Module-based Bluetooth audio receiver with integrated antenna.
  • Stereo low-noise headphone amplifier.
  • USB-C power-only charging input.
  • Single-cell LiPo connector, charging indication, and power control.
  • 3.5 mm stereo headphone output.
System Architecture
Diagram



  
    
  
  
    
  















USB-C 5 V
LiPo charger and protection
1-cell protected LiPo
System supply
Bluetooth audio module
Stereo headphone amplifier
3.5 mm stereo output
Hardware Subsystems
  • Bluetooth: Certified/module implementation preferred to reduce RF and firmware risk; antenna faces the board edge with a copper/component keepout.
  • Charging: 4.2 V single-cell LiPo charger from USB-C 5 V, nominal charge current target 500 mA unless the selected cell requires less.
  • Audio: Stereo AC-coupled analog path and dedicated headphone driver rated for 32 ohm loads.
  • Protection: USB input protection and battery polarity/connector safeguards as supported by selected components.
Interfaces and Connections
  • USB-C receptacle: 5 V power only, dual 5.1 kOhm CC pull-downs.
  • 2-pin LiPo connector: BAT+ and GND.
  • 3.5 mm TRS jack: left, right, common ground.
  • User controls: power switch; Bluetooth module buttons/status signals may be exposed if footprint space allows.
Power and Runtime Expectations
  • Battery: protected 1-cell LiPo, 3.0-4.2 V operating range.
  • Runtime depends on external cell capacity and listening level.
Power Tree and Power Budget

Table

LoadTypicalPeak design allowance
Bluetooth audio module25-50 mA100 mA
Headphone amplifier, electronics5-15 mA25 mA
Stereo output into 32 ohmlevel dependent150 mA combined allowance
Indicators and losses5 mA25 mA
System estimate35-70 mA plus audio300 mA
  • Charger and battery path should tolerate at least 500 mA continuous system/charge operation.
  • Final values must be replaced with selected-part datasheet limits during schematic capture.
Manufacturing and Assembly Expectations
  • Standard FR-4 and standard copper.
  • Prototype-friendly SMT assembly; 0603 passives preferred where practical.
  • Four-layer stackup preferred for RF return continuity, audio grounding, and compact routing.
Firmware-Relevant Hardware Requirements
  • Prefer a Bluetooth audio module with production firmware already loaded; no custom Bluetooth stack required.
  • Expose module control/status pins only where documented and useful.
Physical Design Expectations
  • Circular board, 50.0 mm diameter.
  • USB-C and headphone jack accessible at the perimeter.
  • Bluetooth antenna at the perimeter with datasheet keepout extending through all copper layers.
  • Battery connector and power switch accessible from the perimeter.
  • Through-hole vias; no HDI requirement.
Important Design Decisions
  • Module-based Bluetooth receiver rather than a bare Bluetooth SoC.
  • Dedicated stereo headphone driver rather than loading module line outputs directly.
  • USB-C is power-only; no USB data or USB Power Delivery.
Assumptions
  • Stereo output is required.
  • External battery is protected and sized for a 500 mA charge rate; reduce charge current for smaller cells.
  • 3.5 mm TRS output is desired.
  • Buttons and microphone support are outside the required scope.
Change Notes
  • Initial specification created from the user request.

  • Project Overview

  • Intended Use

  • What the Device Should Do

  • Main Features

  • System Architecture

  • Hardware Subsystems

  • Interfaces and Connections

  • Power and Runtime Expectations

  • Power Tree and Power Budget

  • Manufacturing and Assembly Expectations

  • Firmware-Relevant Hardware Requirements

  • Physical Design Expectations

  • Important Design Decisions

  • Assumptions

  • Change Notes