Posture tracker v2

Posture Tracker V2 — Product Grade Wearable

Branch: release/v2-product
Status: In development
V1 (MVP breadboard): See main branch

A product-grade evolution of the ESP32 posture tracker. V2 moves from a breadboard prototype to a wearable device — custom PCB, LiPo battery, haptic motor, and a compact shoulder-clip form factor small enough to wear all day.

Hardware: ESP32-S3-MINI-1 · MPU-6050 · DRV2605L + LRA · MAX98357A · 20mm speaker · 350mAh LiPo
Stack: ESP-IDF 5.5.0 · PlatformIO · C only (no Arduino, no C++)
Target size: 45×35×16mm (PCB + battery + clip)

What's New in V2

Alert UX — Layered Haptic + Audio

The key design principle: haptics for early alerts, audio only for escalation.

SW2 (snooze button) mutes all audio for 10 minutes while haptics continue — for meetings, calls, or quiet environments.

Hardware

Component List

Pin Assignment

Architecture

Three FreeRTOS tasks (V1) + Two new tasks (V2)

New modules vs V1

NEW:      haptic.c    — DRV2605L I2C driver, waveform playback (non-blocking)
NEW:      power.c     — battery ADC, low-battery warning, deep sleep entry
NEW:      buttons.c   — debounced GPIO, short/long press detection

UNCHANGED: mpu6050.c  — I2C driver, atan2 angle math, EMA filter
UNCHANGED: posture_fsm.c — state machine logic (only alert commands change)
MODIFIED:  audio.c    — adds haptic command dispatch alongside audio
MODIFIED:  main.c     — init order adds haptic, power, buttons

Power System

USB-C (5V) → Polyfuse → MCP73831 LiPo charger → 350mAh LiPo
                                                        ↓
                                                  AP2112K LDO
                                                        ↓
                                                    3.3V rail → all ICs

Battery life estimate:

• Active draw (IMU reading, no alerts): ~6mA average with light sleep
• 350mAh ÷ 6mA = ~58 hours theoretical
• Real world (audio bursts, haptic, occasional BLE): 12–15 hours

Low battery handling:

• < 3.5V → warning beep + haptic
• < 3.3V → shutdown tone + deep sleep

Form Factor

Assembled dimensions:
  PCB alone:        45 × 35 × 1.6mm
  PCB + battery:    45 × 35 × 8mm
  With clip:        45 × 38 × 16mm   ← final wearable size

Comparable to a car key fob.
Clips onto shirt collar, bra strap, or epaulette.
LRA motor faces the body for best haptic transmission.
Speaker grille faces outward.
USB-C and buttons accessible on edges.

Development Phases

Branch Structure

main                        ← V1 MVP (public, breadboard, complete)
  └── release/v2-product    ← this branch — all V2 work
        └── feature/haptics
        └── feature/speaker-swap
        └── feature/power-system
        └── feature/pcb-v2
        └── feature/enclosure

PCB Layout — Complete

Design decisions locked

• 2-layer board — F.Cu for all signal and power traces, B.Cu solid GND copper pour
• Trace widths (IPC-2221 verified, 1oz copper, 10°C rise) — VBUS/VBUS_FUSED: 0.4mm, +3V3/VBAT/audio/motor: 0.3mm, all signals: 0.2mm
• Net classes — HighCurrent (0.4mm), Power (0.3mm), Audio (0.3mm), Motor (0.3mm), USB_Diff (0.2mm impedance-controlled), Default (0.2mm)
• Via spec — 0.8mm outer / 0.4mm drill (JLCPCB standard rule compliant)
• Board size — ~47.6 × 28.3mm (fits 45×35×16mm wearable form factor with battery)
• Connectors — J1: USB-C (HRO TYPE-C-31-M-12), J2: JST PH 2mm (battery), J3: Molex PicoBlade 53261-0271 (LRA haptic), LS1: Molex PicoBlade 53261-0271 (speaker)

Routing status

Final DRC (2026-06-09): 0 errors, 0 unconnected, 2 cosmetic silk warnings (U1 silkscreen clips board edge — JLCPCB trims automatically).

File locations

hardware/
├── kicad/posture_tracker_v2/
│   └── posture_tracker_v2/    ← KiCad source (schematic + PCB + project files)
│       └── reports/           ← DRC.rpt, ERC.rpt
├── schematics/                ← Exported schematic PDF (posture_tracker_v2_v2.pdf)
├── pcb/
│   └── v2/
│       ├── gerbers/           ← 12 Gerber + drill files (canonical fab outputs)
│       └── posture_tracker_v2_gerbers.zip  ← upload this to JLCPCB
├── bom/                       ← Bill of materials
└── datasheets/                ← Component datasheets

Hardware Visuals

PCB — 3D View

PCB — Top Layer

PCB — Bottom Layer

PCB — Combined

Schematic

Full schematic PDF: hardware/schematics/posture_tracker_v2_v2.pdf

PCB layer PDFs (vector): Top · Bottom · Combined

Reference Docs

• CLAUDE.md — full V2 architecture, component decisions, hard rules, PCB design reference
• PHASES.md — V2 phase build guide (phases 7–11)
• hardware/schematics/SCHEMATIC_GUIDE.md — full reasoning for every schematic block