EVT Testbed - Circuit design

PROPOSED TITLE USB-C Diving Camera EVT Testbed - Embedded Firmware + Electronics Engineer (milestone-based, visual proof required) PROJECT TYPE: Hourly or Fixed-price (milestone-based) CATEGORY: Electronics / Embedded Firmware / PCB Design EXPERIENCE LEVEL: Expert SUMMARY Build a bench-level EVT electronics testbed (not a production or waterproof device) for a USB-C diving-camera accessory, and validate every high-risk subsystem before any custom PCB is committed. 1) PROJECT OVERVIEW We are building Universal Pro Max, a smartphone-based diving camera accessory. Before committing to a custom PCB, we need a bench-level EVT (Engineering Validation Test) testbed assembled from dev boards and off-the-shelf modules to prove that the riskiest subsystems actually work on real phones. This contract is NOT a production PCB, NOT a diver-use device, NOT a waterproof or certified product, and NOT a high-pressure system. It is a controlled lab testbed used to retire technical risk. You will be paid and evaluated per milestone. Every milestone has a concrete, eye-verifiable deliverable (a video, photo, oscilloscope or logic-analyzer capture, log file, or screenshot) plus written pass/fail evidence. We do not accept "it works" without visual proof. 2) BACKGROUND AND HARD CONSTRAINTS (non-negotiable) - Communication is USB-C only. No BLE, no Wi-Fi, no wireless fallback. - Smartphone app data AND firmware update must run through the internal smartphone USB-C pigtail. - The same USB-C connection must validate app data PLUS 5 V smartphone charging from the testbed power system. - Primary power source is a commercial protected, replaceable 21700 Li-ion cell (nominal 3.6/3.7 V, typically 4,000 to 5,000 mAh). The cell must NOT be soldered or glued. - Power rails must be separated (system 3V3, backup 3V3, 5 V phone boost, auxiliary power for pump/valve/haptic). No single shared 5 V rail. - Depth sensing uses the MS5849-30BA pressure/temperature sensor. - Half-shutter uses Hall sensors; the rotary dial uses magnetic-field angle sensing (optical and mechanical encoders are not primary methods). - Haptic validation is mandatory (LRA plus driver preferred; ERM comparison optional). - Firmware update over USB-C must be fail-safe, resumable, chunk-verified, and rollback-capable with A/B slots. - Pump is testbed-only (low pressure), with hardware-level emergency stop that cuts pump power even if firmware is frozen. - Android is the first validation platform. iPhone 15+ is a separate feasibility gate and must not be assumed to work. 3) PROBLEM STATEMENT The team cannot safely commit to a custom PCB because the highest-risk behaviors - USB-C charge+data role on real phones, protected 21700 behavior under peak load, USB-C firmware update reliability, haptic interference with magnetic sensors, and pump safety - have not been proven on hardware. Committing a custom PCB before this validation risks an expensive, un-fixable board respin and schedule loss. We need a freelancer to build the testbed and produce visual, repeatable evidence that each subsystem works (or document exactly why a strategy fails) so we can make a go/no-go decision. 4) GOALS AND SUCCESS METRICS - Prove USB-C charge+data on real phones: Android phone charges at 5 W while the app streams telemetry for 30 min with zero USB disconnects. - Prove protected 21700 power path: no MCU reset, no USB disconnect, no nuisance cell trip under all defined load cases. - Prove USB-C firmware update: update survives disconnect at 10%, 50%, 99%; previous firmware stays bootable; resume and rollback verified. - Prove sensor and input subsystems: MS5849, Hall shutter, magnetic dial, and haptic all stream correct values over USB-C with documented tolerance. - Prove pump safety: overpressure, sensor fault, watchdog reset, and emergency stop all force pump off and vent open. - Enable go/no-go on custom PCB: all 5 validation gates pass with archived video/log evidence. 5) SCOPE OF WORK In scope: - Component selection and BOM for an off-the-shelf modular testbed (Version A). - Wiring/harness assembly, breakout integration, and bring-up. - Firmware for MCU (sensors, inputs, haptic, pump control, USB-C telemetry/commands, A/B firmware update). - Android-first USB-C app-side test harness sufficient to demonstrate charge+data, telemetry, command, and firmware update (a simple test/utility app or script is acceptable; full production app is out of scope). - iPhone 15+ feasibility assessment (documented findings plus any proof-of-concept). - Structured validation runs across all 5 gates with recorded evidence. - Documentation: schematics/wiring tables, test procedures, results, and a custom-PCB recommendation memo. Out of scope: - Production/custom PCB layout and manufacturing (a later, separate engagement; Version B). - Waterproof or pressure-certified enclosure or any diver-use safety certification. - High-pressure (60 m internal compensation) systems or any pressure above the defined testbed limits. - Full consumer app store release of the smartphone app. - Industrial design / cosmetic housing. 6) REQUIRED SKILLS AND EXPERIENCE - Embedded firmware in C/C++ on a native-USB MCU (e.g. STM32, RP2040, or ESP32-S3 with wireless disabled). - USB-C / USB 2.0 and Type-C CC/PD fundamentals (power role, data role, DRP/DRD, PD negotiation). - Bootloader / A/B firmware update / DFU design with external SPI/QSPI NOR flash. - Sensor integration over I2C/SPI/ADC (pressure, Hall, magnetic angle, humidity, temperature). - Motor/pump driver and valve control with current sensing and flyback protection. - Haptic driver experience (LRA/ERM, DRV2605L-class). - Lab instrumentation: oscilloscope, logic analyzer, multimeter, current measurement. - Clear English documentation and willingness to record video/screen-capture evidence. - Nice to have: Android USB host/CDC/accessory development; iOS ExternalAccessory/MFi knowledge. 7) WHAT WE PROVIDE - This brief and the full internal V1.2 EVT architecture document (telemetry schema, wiring table, BOM candidates, state machine, validation gates). - Target sensor part (MS5849-30BA) and required sensing approach. - Test phones (Android first; iPhone 15+ for the feasibility gate) or a budget to acquire them. - Component/module budget (reimbursed against the approved BOM). - Timely review and milestone sign-off. 8) MILESTONES AND DELIVERABLES Acceptance rule for every milestone: the deliverable is accepted only when (1) the visual proof is provided (video / photo / scope or logic-analyzer capture / log file / screenshot) AND (2) the acceptance criteria are met with written pass/fail notes. Each milestone is small enough to verify in one review session. M0 - Kickoff, Plan and BOM - Tasks: review architecture, confirm MCU and module choices, produce the testbed BOM and a block/wiring plan. - Visual deliverable: a shared BOM sheet plus a one-page block diagram image, and a short screen-recorded walkthrough of the plan. - Acceptance: BOM lists every module with part number, qty, and purpose; block diagram matches the required separated-rail architecture; reviewer approves before purchasing. M1 - Power Subsystem: Protected 21700 plus Separated Rails - Tasks: assemble protected 21700 holder, fuse/polyfuse, reverse protection, 3V3 system rail, 5 V boost, and rail separation. - Visual deliverable: photo of the wired power bench plus multimeter/scope captures of each rail at idle and under a test load. - Acceptance: all rails within spec; reverse-polarity protection demonstrated; battery telemetry (voltage/current/SOC) readable; no rail collapse under a defined step load. M2 - MCU Bring-up and Service Interface - Tasks: flash MCU, bring up debug (SWD/UART), confirm external SPI/QSPI flash. - Visual deliverable: screen recording of the MCU booting, printing version/heartbeat, and reading/writing external flash. - Acceptance: stable boot, heartbeat at 1 Hz, external flash read/write verified. M3 - USB-C Charge-Only (Android) - Tasks: implement Type-C source/CC logic plus VBUS load switch/eFuse; validate 5 W / 7.5 W / 10 W charge modes. - Visual deliverable: video of an Android phone charging from the testbed plus current/VBUS scope or meter captures at each mode. - Acceptance: correct current limiting, stable VBUS, no reverse current, acceptable thermal rise; charge state logged. M4 - USB-C Data-Only Telemetry (Android) - Tasks: implement USB-C telemetry link (CDC JSON Lines preferred; HID/vendor fallback). - Visual deliverable: screen recording of the Android test app/script receiving live telemetry for 30 min, including an unplug/replug recovery. - Acceptance: 30-min stable stream; at least 10 unplug/replug recoveries; no MCU reset. M5 - USB-C Charge plus Data Simultaneously (Strategy A) - Tasks: validate the target role (testbed = source plus USB device; phone = sink plus host) with charge and data together. - Visual deliverable: video showing the phone charging while the app streams telemetry, with on-screen current and telemetry, for 30 min. - Acceptance: no data drops, correct phone current/charge telemetry, zero USB disconnects. M6 - USB-C Role Feasibility Matrix plus iPhone 15+ Gate - Tasks: document Strategy A/B/C outcomes; test power/data role swap, DRP/DRD/PD needs, unplug/replug; run the iPhone 15+ feasibility assessment (accessory enumeration, app-level USB data, coexistence with charging, MFi/ExternalAccessory needs). - Visual deliverable: a results table plus supporting clips/captures, and a written iPhone feasibility memo with evidence. - Acceptance: each strategy marked pass/fail with proof; clear recommendation on whether Strategy A holds on target phones and what iOS requires. M7 - MS5849-30BA Depth Sensor Bring-up - Tasks: PROM/CRC read, compensated pressure/temp, surface baseline, depth-from-delta; distinguish sensor temp vs validated water temp. - Visual deliverable: screen recording of live pressure/temp/depth telemetry at 1 to 2 Hz plus a chart of a controlled pressure change. - Acceptance: PROM CRC valid; values plausible and stable; fault flags (e.g. port blockage, stuck value) trigger correctly in a forced-fault demo. M8 - Hall Shutter (Half/Full) - Tasks: implement released/half/full detection with thresholds, hysteresis, debounce; expose raw values and thresholds over USB-C. - Visual deliverable: video of 100 press cycles with on-screen event log plus a raw-value plot across magnet distance/offset. - Acceptance: no missed or chattering events over 100 cycles; raw values and thresholds logged; threshold tolerance map produced. M9 - Magnetic Rotary Dial - Tasks: magnetic angle sensor bring-up; map angle to 24 detents per revolution; CW/CCW, step count, velocity, wraparound, missed/extra-step handling. - Visual deliverable: video of 100 rotations with on-screen direction/step/velocity log plus raw-angle plot. - Acceptance: correct direction and step count over 100 rotations; no missed/extra steps beyond tolerance; raw angle telemetry available. M10 - Haptic Subsystem plus Interference Test - Tasks: LRA driver plus pattern library; measure interference with Hall/dial/MS5849/USB/charging using an accelerometer or vibration sensor. - Visual deliverable: video of each haptic pattern plus an interference test matrix with measured data (latency, current, recognition). - Acceptance: input-to-haptic latency under 50 ms; no false shutter/dial events; no USB disconnect or MCU reset during haptic; recognition targets documented. M11 - Pump Control plus Hardware Safety - Tasks: pump driver, vent valve, current sensing, flyback; pressure targets +5/+10/+20/+30 kPa; software limit +35 kPa; hardware emergency stop. - Visual deliverable: video of pressurize/hold/vent cycles with live pressure telemetry plus a recorded safety demo (overpressure, sensor disconnect, watchdog reset, e-stop). - Acceptance: targets reached with controlled overshoot; every fault condition forces pump off and vent open; e-stop cuts pump power in hardware even with firmware frozen. M12 - A/B Firmware Update Over USB-C - Tasks: bootloader with A/B slots, chunk CRC, resumable progress, full-image verification, pending-boot confirm, rollback, USB recovery mode, redundant metadata. - Visual deliverable: screen recording of a full update plus forced disconnects at 10%, 50%, 99% showing resume, plus a rollback and a recovery-mode demo. - Acceptance: previous firmware always bootable; resume from last verified chunk; corrupt chunk/image rejected; failed boot rolls back; both-invalid-slots enters USB recovery. M13 - Full Validation Gates plus Final Report - Tasks: run Gates 1 to 5 end-to-end; compile evidence; write the custom-PCB go/no-go recommendation. - Visual deliverable: a consolidated evidence pack (videos/logs/captures indexed by gate) plus final report and updated schematics/wiring tables. - Acceptance: all 5 gates pass with archived proof; report clearly states what is proven, what failed, and the recommendation for Version B (custom PCB). 9) VALIDATION GATE REFERENCE - Gate 1 - Minimum power and USB validation: M1 to M5. - Gate 2 - High load and transient validation: M5, M10, M11. - Gate 3 - Firmware update validation: M12. - Gate 4 - Pressure and pump safety validation: M11. - Gate 5 - Sensor and input validation: M7 to M10. 10) NON-FUNCTIONAL REQUIREMENTS - Reliability: no unexpected USB disconnects or MCU resets during any defined test run. - Safety: pump defaults to off on reset, fault, update mode, backup mode, and USB disconnect; vent fails open where hardware allows. - Traceability: every test produces a timestamped log and an indexed evidence file. - Maintainability: firmware is modular and documented; build/flash instructions provided. - Portability: telemetry/command protocol documented so the production app team can reuse it. - Reproducibility: each test includes a written procedure so we can re-run it independently. 11) RISKS AND MITIGATIONS - USB-C charge+data role fails on target phones (top risk): test Strategy A/B/C with jumpers/DNP/eval modules before any PCB commitment. - iPhone 15+ blocks app-level USB data: separate feasibility gate; document MFi/ExternalAccessory requirement early. - Protected 21700 nuisance trips or brownout under peak: measure peak current per load case; derate charging before unsafe conditions. - Haptic corrupts magnetic sensing or USB: quantitative interference matrix with accelerometer before sign-off. - Firmware update bricks device: A/B slots, chunk CRC, rollback, and independent USB recovery mode. 12) ENGAGEMENT, IP, AND HOW TO APPLY Terms: - Engagement: milestone-based fixed-price or hourly with milestone gates (your proposal). - Budget / rate: please propose per-milestone pricing and total. - Timeline: please propose duration per milestone group. - IP and confidentiality: all deliverables, firmware, schematics, and findings are work-for-hire and our exclusive property. NDA required before sharing the internal architecture document. Screening questions (please answer in your proposal): 1. Describe a USB-C charge+data (or USB host/device) project you delivered on real phones. What broke and how did you fix it? 2. Which MCU would you choose for this testbed and why (native USB, A/B update, external flash)? 3. How would you prove a firmware update is rollback-safe after a mid-transfer disconnect? 4. Have you done iOS ExternalAccessory/MFi USB work? Summarize the constraints. 5. Share links/photos/video of a comparable hardware bring-up you can show.