ESP32 GPS Monitoring Bracelet — 2 Complete Prototypes incl. Enclosure (1000 USD, 45 days)

PROJECT OVERVIEW We are building EMS Mauritania — an electronic monitoring platform for judicial supervision. Our backend API, web dashboard, mobile app, and geofencing are already built and working. We need an embedded hardware engineer to deliver TWO complete GPS bracelet prototypes with 4G LTE and SIM card integration, sending data to our REST API without WiFi. BUDGET: 1000 USD fixed price — all-inclusive TIMELINE: 45 days maximum WHAT IS ALREADY DONE (by us) - REST API: POST /api/v1/locations/ingest with header x-bracelet-api-key - Web + mobile apps with live map, alerts, geofencing - PlatformIO firmware scaffold (ESP32) - Software simulator tested end-to-end DELIVERABLES — 2 UNITS WITH SIM / 4G HARDWARE PER UNIT (x2) - ESP32-WROOM-32 - u-blox NEO-8M GPS + antenna (UART GPIO RX=16, TX=17) - 4G LTE modem with SIM slot — SIM7600CE or equivalent (UART GPIO RX=25, TX=26) - Nano-SIM or micro-SIM holder inside enclosure (technician access only) - 4G antenna + GPS antenna - Reed switch strap tamper (GPIO34, HIGH = alert) - Micro-switch enclosure open (GPIO35, LOW = alert) - Li-Po 2000 mAh + charging circuit - Battery ADC monitoring (GPIO36) - Wearable wrist or ankle strap - Prototype enclosure IP54 minimum - All wiring and assembly — not breadboard for final delivery SIM CARD INTEGRATION — REQUIRED - SIM slot on modem, SIM inserted inside case - Firmware connects to 4G on boot (TinyGSM or AT commands) - HTTP or HTTPS POST to our ingest endpoint every 60 seconds - Header: X-Bracelet-Api-Key (unique per device) - Report signal strength 0-100 in JSON - Document APN settings for Mauritania (Mauritel / Chinguitel) - Buyer can insert local SIM — guide required FIRMWARE - Real GPS NMEA — no fake coordinates - Unique braceletId per unit (e.g. EM-0003, EM-0004) - JSON fields: braceletId, timestamp ISO UTC, latitude, longitude, battery, signal, tamper - PlatformIO code via GitHub or ZIP - Extend our existing scaffold (shared after hire) API Endpoint: POST /api/v1/locations/ingest Header: x-bracelet-api-key: [unique key per device] DOCUMENTATION - BOM with costs and supplier links - Wiring schematic - SIM installation + APN guide for Mauritania - Configuration guide per device - Test report: 4G registration, GPS outdoors, API success, tamper tests MILESTONES — TOTAL 1000 USD M1 — Day 15: 400 USD — BOM + schematic + 1 unit with 4G + GPS + API working M2 — Day 45: 600 USD — 2 complete wearable prototypes with SIM modem inside + docs + test report BUDGET NOTE 1000 USD is fixed. Proposals must explain how you deliver 2 SIM-enabled units at this price (BOM breakdown required). We prefer efficient design over premium materials at this stage. WE PROVIDE AFTER HIRE - GitHub firmware scaffold - Test API URL + 2 API keys (private) - Software simulator reference PLEASE ANSWER IN YOUR PROPOSAL 1. SIM7600 or 4G + ESP32 projects — links or photos 2. BOM cost for 2 units (parts only) 3. APN / LTE bands for Mauritania 4. How SIM slot fits inside wearable enclosure 5. Can you deliver 2 SIM units for 1000 USD in 45 days — explain how NOT INCLUDED - Mass production - Official judicial certification - Backend or mobile app (done by us) COMMUNICATION: weekly video call, English or French OK