10-Day nRF51822 PCB/Firmware Update: Add AHT20 Sensor

We have an existing battery-powered BLE dive watch PCB and working firmware. We need an experienced embedded hardware/firmware engineer to add one AHT20 humidity sensor and prepare a small JLCPCB prototype run. The purpose of the sensor is internal water-leak detection. Humidity must NOT be measured continuously. One measurement should be triggered only when requested through the existing BLE communication, so the impact on CR2 battery life must remain negligible. Existing design files will be provided privately after selection/NDA. They include schematic/PCB manufacturing data and legacy Nordic nRF51822 firmware. Schedule - All engineering work, firmware/PCB files, and JLCPCB order submission must be completed within 10 calendar days from contract start and receipt of the required source files. - JLCPCB manufacturing and shipping lead time is excluded from the 10-day engineering deadline. Sample bring-up and test results must be completed within 2 business days after the freelancer receives the assembled boards. - Please apply only if you can start immediately and commit to this schedule. Scope 1. Review the existing circuit, PCB files, firmware build, actual pin mapping, power rail, and shared I2C bus. 2. First prove the function on an existing assembled board using our DHT20/AHT20 sensor and hand wiring if practical. 3. Modify the schematic and PCB artwork to add an SMD AHT20, including local decoupling, correct I2C connections, switched 3 V power, and checks for I2C back-powering. 4. Modify the nRF51822 firmware so a BLE request triggers one non-blocking AHT20 measurement and returns humidity/temperature data. 5. Preserve all existing BLE, pressure-sensor (MS5837), battery, and DFU/programming functions. 6. Prepare an order-ready JLCPCB package and support the prototype PCBA order. 7. Bring up and test the samples, then hand over all editable source files and documentation. Required deliverables - Editable native schematic and PCB source files, libraries, and footprints - Schematic PDF, Gerber/drill, BOM with exact MPN and JLC/LCSC C-codes, CPL/pick-and-place, assembly drawing, and STEP file - Complete firmware source/project, build and programming instructions, and final HEX - Short test report with photos/video showing BLE-requested humidity readings - Before/after current measurements and confirmation that no continuous humidity polling occurs - Pressure sensor, BLE, and firmware-update regression-test results - Final JLCPCB order files and order/DFM support Acceptance - A BLE command triggers a single humidity measurement and returns valid data - Existing MS5837 pressure readings and BLE functions still work - No meaningful increase in sleep/off current - Native CAD files reopen correctly and firmware builds from a clean checkout - Prototype samples operate successfully Budget and manufacturing - Fixed engineering budget: USD 500 - PCB/PCBA, components, shipping, duties, and other approved prototype expenses are paid separately by the client at actual cost - No part substitution or manufacturing order without client approval - Mobile-app development, certifications, enclosure redesign, and BLE module replacement are outside this scope Required experience - Nordic nRF51822/nRF51 and legacy SoftDevice S110 - Embedded C and Keil/J-Link/SWD - PCB schematic/layout work, preferably PADS/OrCAD - I2C sensors, low-power battery products, and current measurement - Actual JLCPCB PCBA ordering with BOM/CPL component matching When applying, please answer: 1. What exact nRF51/nRF51822 and S110 projects have you completed? 2. Can you open/edit PADS/OrCAD files and build legacy Keil firmware? 3. Have you personally ordered and brought up JLCPCB assembled prototypes? 4. What bench equipment do you have for SWD, oscilloscope, and low-current measurement? 5. Can you complete this defined scope for the USD 500 fixed engineering budget within 10 calendar days? Please propose milestones and a day-by-day schedule.