Schematic is Auto-placed

The schematic has been arranged automatically. Flux can redraw it to be more readable, with components placed in related groups and wires drawn more legibly. This takes about 10-60 mins.

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Project Specification
Status
Draft
Purpose
Redesign the project into a handheld, serviceable computing platform centered around a socketed salvaged CPU/module. The design must support portable battery-powered operation, dedicated charging input, battery balancing/protection, and compact handheld mechanical constraints.
Scope
  • Replace the fixed compute architecture with a removable socket or board-to-board module interface for a salvaged CPU/module.
  • Rework the power architecture for portable operation with charging, battery management, and regulated system rails.
  • Reorganize schematic and PCB placement for handheld dimensions and serviceability.
  • Preserve key external I/O for display, communication, audio, and debug where practical within the handheld envelope.
Architecture
Diagram



  
    
  
  
    
  

















USB C charge input
Battery charger and power path
Two cell battery pack
Battery balancing and protection
System rail to module socket
Board to board CPU module socket
Display USB storage debug network interfaces
Battery monitor and charger management
Mechanical Envelope
  • Target handheld layout size: 150 mm x 85 mm maximum.
  • Prefer board thickness compatible with standard handheld enclosures and standoffs.
  • CPU/module socket must remain accessible for replacement without full board disassembly.
  • Battery connector and charging input must sit near board edges for serviceability.
Electrical Requirements
  • Dedicated battery charging input.
  • Two-cell battery support with balancing/protection.
  • Regulated system rail routed to the CPU module socket.
  • Decoupling and bulk capacitance on each major power domain.
  • Battery-management telemetry exposed to the CPU module.
  • External I/O retained through the module interface plan: storage, display, USB, networking, and debug.
Board-to-board socket strategy
  • Use the Hirose DF40HC(3.0)-100DS-0.4V(51) mezzanine connector as the removable CPU module socket.
  • Reserve connector pin groups for:
    • power and ground
    • control and boot management
    • clocks
    • storage
    • display
    • USB
    • networking
    • debug
    • battery-management telemetry
  • Keep high-speed interfaces adjacent to solid return references on the 4-layer handheld stackup.
Fixed compute cleanup
The following fixed-compute / redundant peripheral blocks were removed from the baseboard concept:
  • ATmega328P helper MCU
  • ESP32 module
  • SX1276 radio
  • audio codec and audio jack
  • OLED module
The charger, balancing, and socket subsystems remain as the new baseboard foundation.
Implementation Notes
  • Default compute strategy is a socketed module or board-to-board connector instead of direct CPU rework onto the PCB.
  • Power section should prioritize safe charging, battery protection, and clear debug/test access.
  • Layout should group power, socket, and external I/O into clearly separated functional zones for easier routing and repair.

  • Status

  • Purpose

  • Scope

  • Architecture

  • Mechanical Envelope

  • Electrical Requirements

  • Board-to-board socket strategy

  • Fixed compute cleanup

  • Implementation Notes