pcb_scout/docs/design_decisions.md

Design Decisions

Components

npm1300

• Two bucks 1.8V and 3.3V
• Hopefully nice ONOFF logic possible https://chatgpt.com/share/693174fd-35cc-8007-8e88-06d77bcb8abc

stateDiagram-v2
    [*] --> OFF_HIBERNATE

    OFF_HIBERNATE --> ON_BATTERY : SHPHLD ≥ tshipToActive
    note right of ON_BATTERY
      Condition: VBUS not present
    end note

    OFF_HIBERNATE --> CHARGING_ONLY : USB plugged in
    note right of CHARGING_ONLY
      Condition: VBUS > VBUSPOR
    end note

    ON_BATTERY --> OFF_HIBERNATE : Short press SHPHLD
    note right of OFF_HIBERNATE
      FW calls TASKENTERHIBERNATE
      Condition: VBUS not present
    end note

    ON_BATTERY --> CHARGING_ON : USB plugged in while ON

    CHARGING_ON --> CHARGING_ONLY : Short press SHPHLD (SW-Off)

    CHARGING_ONLY --> CHARGING_ON : Short press SHPHLD (SW-On)

    CHARGING_ON --> ON_BATTERY : VBUS removed AND SW=ON

    CHARGING_ONLY --> OFF_HIBERNATE : VBUS removed AND SW=OFF
    note right of OFF_HIBERNATE
      FW calls TASKENTERHIBERNATE
    end note

Conclusion: Should work by attaching one button.

TRS Jack

• Detection
• Mono vs Stereo (Telecoil vs Headsets)
• Goal: Mono and Stereo 'just works'

https://chatgpt.com/share/69316f49-fc30-8007-8096-5d91e9cd69a5

TLV supports short circuit detection and powers down the output.

TLV supports headphone detection (no headphone, stereo, stereo with mic).

Conclusion: The TLV can handle everything we need to do to support both mono (telecoil) and stereo.

Schematic

Board

Impedance controlled