ADR-0004 — ESP32 (WEMOS Lite) + NEO-M8N wearable baseline

Status: Accepted · Date: 2026-06-14

Context

The wearable must stream 10 Hz GPS (and later IMU) over WiFi, run a ~90-min session on battery, and be cheap enough to build ×10. Boards and GPS modules vary in capability and cost.

Decision

Prototype baseline per unit: - WEMOS Lite ESP32 (LOLIN32 Lite) — plain ESP32 is enough to stream at 10 Hz, and it has on-board LiPo charging (no separate TP4056). - GY-GPSV3 NEO-M8N — 10 Hz, multi-constellation, TTL/UART. - LP-503759CL 1S LiPo 1350 mAh — covers a session with margin. - IMU is optional for v1 (GPS gives ~80% of physical metrics); add MPU-6050 later for PlayerLoad / cleaner accel-decel.

Consequences

• + Cheapest, cleanest wearable for physical metrics; fewer parts (no TP4056).
• + 10 Hz cleanly captures sprints and accelerations.
• − Plain ESP32 isn't ideal for 500 Hz IMU shot-detection — that's the S3's job (Variant C).

Alternatives considered

• ESP32-S3 DevKitC — more capable (PSRAM, faster core) and future-proof for fast IMU / ML / camera, but overkill for Variant B and has no on-board LiPo charging. Choose it only as a single board for all variants.
• NEO-6M GPS — rejected: ~1 Hz, smears sprints/accelerations.
• NEO-M9N GPS — marginally better under cover; not worth the cost for youth; an option for a guaranteed-original batch via TME.