Full-Stack Embedded Hardware Engineer: High-Efficiency ESP32 Power System & Display

# Full-Stack Embedded Hardware Engineer: High-Efficiency ESP32 Power System & Display ## Project Overview I am seeking an experienced **Full-Stack Embedded Hardware Engineer** for immediate development of a high-performance, ultra-compact rechargeable power system. The device combines: * High-efficiency DC-DC power conversion * Replaceable Li-ion battery * USB-C charging and external-power operation * ESP32 control * BLE * Color digital display * Real-time voltage/current/battery telemetry * Extremely low standby consumption * High-density custom PCB design The complete device must fit within a **highly constrained existing mechanical design**. Detailed dimensions, STEP CAD files, mechanical interfaces, target application, and proprietary product information will be provided to the selected engineer **after NDA**. This project is intended to become a commercially manufactured product. I need an engineer who can determine what is physically and electrically achievable, build a working prototype, test it, and prepare the design for subsequent production development. ## IMPORTANT — PLEASE READ BEFORE APPLYING I am **not** looking for someone who will simply agree that every target is possible. Several requirements compete directly with each other: **physical size, battery capacity, runtime, output power, charging speed, converter efficiency, thermal performance, display size and RF performance.** Your first responsibility will be to determine the best engineering solution within those constraints. If a requirement cannot realistically be achieved, I expect you to identify the limitation quantitatively and recommend the best alternative. **The priority is a product that actually works.** --- # 1. POWER SYSTEM Design a high-efficiency regulated power architecture for a dynamic electromechanical load. ### Target operating requirements * Adjustable output approximately **2.0–12.0 V DC** * 0.1 V user adjustment * Approximately **2 A continuous capability** * Approximately **3 A peak/transient capability** * Stable operation during motor startup and rapidly changing loads * Low output ripple * Fast transient response * High conversion efficiency * Minimal thermal loss A synchronous buck-boost architecture is currently preferred, but **topology and component selection are the engineer's responsibility**. The system must include appropriate: * Over-current protection * Short-circuit protection * Over-voltage protection * Battery under-voltage protection * Thermal protection * Safe shutdown/fault handling Safety-critical regulation should be implemented in hardware and should not depend entirely on the ESP32. --- # 2. BATTERY / ENERGY SYSTEM The current mechanical concept uses a **replaceable high-drain cylindrical Li-ion cell**, with 18350 currently under consideration. However, the engineer must validate the cell and energy architecture before PCB design. Required analysis includes: * Available battery energy (Wh) * Realistic usable capacity * Continuous discharge capability * Peak discharge capability * Internal resistance * Safe charging current * Expected runtime * Thermal performance * Battery protection * Cycle life **Long runtime is a major product objective**, but I do not want an unrealistic runtime number specified before the engineer completes the energy budget. The engineer should determine the maximum practical runtime that can be achieved within the supplied mechanical envelope and recommend changes if a substantially better result can be achieved with a reasonable dimensional adjustment. The battery must ultimately be replaceable/serviceable. --- # 3. USB-C CHARGING + CONTINUOUS EXTERNAL POWER USB-C is a core requirement. The system should support three operating states: **Battery operation:** Battery → regulator → load **Charging:** USB-C → charger/power management → battery **External/pass-through operation:** USB-C → power system → load The important requirement is that **when the internal battery is depleted, connecting an appropriate USB-C power source should allow continued device operation.** Where power and thermal conditions permit, the system should simultaneously operate the load and charge the battery. The engineer should select the appropriate USB-C / USB-C PD, charger and power-path architecture. Battery charging current must remain within the selected cell manufacturer's safe specifications. --- # 4. HARDWARE SHIP MODE / ULTRA-LOW STANDBY The product must minimize battery drain during long-term storage. The design should use **hardware-level power isolation** rather than relying solely on ESP32 deep sleep. Target battery-side Ship Mode consumption: **≤1 µA where technically achievable.** The engineer must measure and document the actual achieved value. The design should allow the device to remain stored for extended periods without significant electronic standby drain. --- # 5. ESP32 / EMBEDDED FIRMWARE Use an appropriate **ESP32-family MCU with BLE**. Firmware must be developed natively using: **ESP-IDF + FreeRTOS** **No Arduino framework.** Required firmware functions include: * Voltage/setpoint control * Battery monitoring * State-of-charge reporting * Current monitoring * Temperature monitoring * Power-state management * Session/runtime tracking * Physical button/input handling * Display rendering * Charging status * Fault monitoring * BLE foundation for future peripherals * Firmware update capability where practical Firmware architecture should separate time-sensitive sensing/control functions from UI and non-critical processing. --- # 6. REAL-TIME LOAD SENSING & TELEMETRY The system should provide accurate real-time electrical telemetry. Required measurements include: * Output voltage * Current draw * Battery state of charge * Battery/system temperature * Session runtime * Charging/external-power status * Relative load indication I am also interested in deriving **operating frequency / Hz or other useful load diagnostics** from the electrical behavior of the connected load. Possible methods may include: * Current waveform analysis * Back-EMF sensing * ADC/DSP analysis * Another method recommended by the engineer This feature must be **validated experimentally**. I do not want an inaccurate frequency/RPM number displayed simply to satisfy a specification. --- # 7. COLOR DISPLAY The product requires a **compact color digital display**. The display must fit within the supplied mechanical envelope and should provide a clean professional interface for: * Output voltage * Battery percentage * Current * Session timer * Load indication * Charging status * System status **240×240 ST7789 is NOT a mandatory requirement.** The engineer should recommend the best commercially available display based on: * Physical dimensions * Resolution * Power consumption * Interface * Visibility * Availability * Cost * Manufacturability SPI/DMA or another appropriate high-performance interface may be used. The priority is obtaining the best display that realistically fits the complete product. --- # 8. PCB / MECHANICAL INTEGRATION A mechanical design already exists and will be supplied as STEP CAD after NDA. The engineer must perform a **complete packaging review before PCB layout begins.** The mechanical analysis must account for the complete assembly, including: * Battery * PCB(s) * Display * USB-C connector * Buttons * Power components * Inductor * Antenna/RF clearance * Electrical contacts/connectors * Thermal clearances * Assembly requirements I do not want only the PCB dimensions validated. **The complete electronic assembly must fit the mechanical envelope.** A multi-board, stacked-board, rigid-flex, or other architecture may be recommended if it produces a superior result. PCB design must account for: * High-current paths * Switching-loop area * Grounding * Analog measurement accuracy * EMI/EMC * RF antenna clearance * Thermal dissipation * Component availability * Assembly * Manufacturability Preferred design environment: **Altium Designer or KiCad** --- # 9. MILESTONES — $3,500 TOTAL ## Milestone 1 — Feasibility & System Architecture — $500 Before committing to PCB layout: * Review mechanical CAD * Confirm complete electronic packaging feasibility * Calculate power budget * Calculate battery/energy budget * Estimate achievable runtime * Perform preliminary thermal analysis * Select/recommend battery * Select power-conversion architecture * Select charging/power-path architecture * Recommend display * Create system block diagram * Provide preliminary BOM * Identify major engineering risks **PCB layout should not begin until this milestone is accepted.** If a target is not achievable, explain why and provide the closest practical solution. ## Milestone 2 — Schematic + PCB Design — $1,250 Deliver: * Complete schematic * Multi-layer PCB layout * Design source files * Gerbers * BOM with exact manufacturer part numbers * CPL/pick-and-place files * Assembly documentation * Manufacturing package Design should be suitable for prototype manufacturing through JLCPCB, PCBWay, or equivalent. ## Milestone 3 — Firmware + Prototype Bring-Up — $1,000 Deliver: * Native ESP-IDF project * FreeRTOS implementation * Display/UI * Battery monitoring * Current/voltage sensing * Power management * User controls * Telemetry * Fault handling * BLE foundation * Programming/build instructions Bring up and demonstrate the assembled prototype. ## Milestone 4 — Validation & Engineering Handoff — $750 Test and document: * Voltage accuracy * Load regulation * Output ripple * Continuous current * Peak/transient response * Converter efficiency * Thermal performance * Battery behavior * Charging * USB-C external/pass-through operation * Standby/Ship Mode current * Runtime * Load telemetry * General reliability Deliver final source files and a written engineering/test report. **TOTAL FIXED BUDGET: $3,500** Successful completion may lead immediately to additional paid milestones for PCB revision, optimization, DFM and production engineering. --- # 10. REQUIRED EXPERIENCE Please apply only if you have professional experience with: * High-efficiency DC-DC power electronics * Buck/boost/buck-boost converter design * Li-ion battery systems * Battery charging * USB-C / USB-C PD * Power-path management * High-current compact PCB design * ESP32 * ESP-IDF * FreeRTOS * Embedded C/C++ * ADC/current sensing * Displays/UI * BLE * Prototype bring-up * Hardware debugging Experience taking a commercial product through: **Schematic → PCB → Prototype → Testing → Manufacturing** is strongly preferred. --- # APPLICATION QUESTIONS Please answer these questions rather than sending a generic proposal: 1. Describe the most similar compact battery-powered product you have personally engineered. 2. What buck-boost converters and Li-ion charger/power-path systems have you previously designed with? 3. What is your experience with ESP-IDF and FreeRTOS? 4. Have you designed USB-C/PD products capable of operating a load while charging a battery? 5. What is the smallest/highest-density PCB you have successfully brought to production? 6. What PCB software do you use? 7. Have you personally performed prototype bring-up and power/thermal measurements? 8. **Which requirements in this posting do you expect to conflict with each other the most, and why?** 9. If the desired runtime cannot fit the mechanical envelope, how would you approach the tradeoff? 10. Can you begin **immediately**? ## Confidentiality A Mutual NDA is required before proprietary CAD, exact mechanical dimensions, target application details, mechanical interfaces and other confidential product information are released. The public listing intentionally omits the product name and final application. I am ready to begin immediately with the right engineer.