KiCad PCB Layout for Automotive OBD2 Bluetooth Sensor (Phase 1)

Project Overview We are looking for an experienced embedded systems and hardware engineer to design a custom schematic, PCB layout, and core firmware for an automotive-grade, headless cabin air quality monitor named StanSense. The device plugs directly into a standard vehicle OBD2 port (SAE J1962) and acts as a passive safety monitor. It features no screen and no internal battery (for cabin thermal safety). It alerts the driver via an onboard buzzer/LED and communicates data to a smartphone via Bluetooth Low Energy (BLE). The design must be completely optimized for JLCPCB SMT automated assembly using their Basic/Extended parts library to achieve a low Bill of Materials (BOM) cost. Technical Specifications & Requirements 1. Hardware & Component Selection EDA Tool: Must be designed entirely in KiCad (v7 or v8). Microcontroller: Espressif ESP32-S3-MINI-1 (or ESP32-C3-MINI-1) utilizing its pre-certified modular FCC footprint to leverage modular approval rules. Sensor: Sensirion SCD40 Photoacoustic NDIR CO2 sensor configured over I2C. Power Supply Network (Critical): Input pulls from OBD2 Pin 16 (variable 12V to 14.4V DC). The design must feature robust transient voltage protection (unidirectional TVS diode + Pi filter) to survive automotive load dumps up to 40V. Voltage regulation must use a high-efficiency synchronous DC-DC Buck Regulator stepping down to 3.3V (Linear LDOs are prohibited due to thermal layout limits). Power Gating: Include a P-channel MOSFET switch controlled via an MCU GPIO line to completely cut the ground/power path to the SCD40 sensor during long-term sleep modes. Peripherals: 1x Passive Piezo Buzzer (PWM driven), 1x Dual-color status LED (Common Cathode), and 1x basic CAN Transceiver passively connected to OBD2 pins 6 and 14 for sniffed vehicle status. 2. Firmware & Security State Machine Architecture The core C/C++ firmware must implement a robust low-power state machine and modern BLE security protocol: State 1 (Deep Sleep): MCU in deep sleep, CO2 sensor completely isolated via the MOSFET switch. Wakes up on vehicle CAN activity or a voltage jump above 13.5V. State 2 (Ignition): Power gated to the sensor; executes a 3-minute warm-up sequence. State 3 (Active Monitor): Read data over I2C, evaluate thresholds, and advertise data via BLE. State 4 (24-Hour Calibration Buffer): When the engine turns off, enter a low-power duty cycle for 24 hours. Sleep for 29 minutes, wake for 1 minute to sample air and log baseline calibration values directly to the ESP32 internal non-volatile flash memory. After 24 hours, enter permanent deep sleep until the next engine start. BLE Security & Encryption: Data transmission and pairing must be secured using LE Secure Connections with Passkey Authentication (MITM protection). The firmware must validate connection requests against a unique, static 6-digit PIN code stored in the ESP32 Non-Volatile Storage (NVS). Deliverables Required Complete, uncorrupted KiCad project files (schematic and layout). Production-ready Gerber files, Drill files, BOM, and CPL files mapped directly to active JLCPCB components. A 3D STEP export of the completed PCB layout (to pass to our enclosure designer). Fully commented, production-ready C/C++ firmware source code implementing the power state machine and sensor communication. Local Production Provisioning Script: A simple desktop automation script (Python/esptool-based) that generates a unique random 6-digit pairing PIN, flashes it into the target ESP32 module's NVS partition over USB, logs the device serial number/PIN assignment to a local CSV file, and formats the pairing key into a printable label format for serial labeling. Project Schedule & Fixed-Price Milestones We are managing this project through three strict, fixed-price milestones totaling $350 USD: Milestone 1 ($100.00): Schematic Approval Delivery of the full schematic PDF showing the automotive power protection circuitry, MCU hooks, and power-gating layout. Milestone 2 ($150.00): PCB Layout & Production Files Delivery of the final routed 2-layer PCB layout, 3D STEP file, and verification that all selected parts are active and ready in the JLCPCB assembly library. Milestone 3 ($100.00): Firmware Implementation & Provisioning Hand-off Delivery and review of the functional firmware source code demonstrating the 24-hour low-power logging cycle, BLE secure pairing, and the desktop script for local production flashing. Experience Level Required: Intermediate or Expert. Please do not apply if you do not have direct, proven experience with automotive power design, low-power ESP32 state machines, and BLE security profiles. Please include the word "StanSense" at the top of your proposal so I know you have read this complete brief.