Hardware & Firmware Design for Wireless Heat Pump Sensor Gateway (Zigbee/WiFi) - 12 Outputs

Project Title: Hardware & Firmware Design for Wireless Heat Pump Sensor Gateway (Zigbee/WiFi) - 12 Outputs Project Overview: We are developing a premium, "plug-and-play" wireless ecosystem to replace wired NTC thermistors and dry-contact commands in HVAC / Heat Pump installations. The system eliminates complex wiring by reading physical sensor data wirelessly and emulating the exact corresponding resistance or relay state directly into the heat pump's mainboard. We are aiming for a high-end, minimalist product aesthetic (Tesla/Apple design language). System Architecture: 1. Wireless Sensor Nodes (Transmitters): * Function: Must read standard NTC thermistors (e.g., 10kΩ, 50kΩ) or dry contacts. * Protocol: Zigbee (Sleepy End Devices). * Power: Battery-powered (CR123A or AA), highly optimized for 2+ years of battery life. 2. Main Gateway (Receiver on the Heat Pump): * MCU: Must use pre-certified RF modules (CE/RoHS compliant, e.g., Espressif ESP32-C6 / ESP32-H2) supporting Zigbee (to communicate with sensors), WiFi (for OTA updates), and BLE (for initial installer setup via mobile app). * Outputs (12 Total): * 6x Variable Resistance Outputs (Analog Emulation): Must use high-quality Digital Potentiometers (DigiPots). * DigiPot Specs: 0 - 100kΩ range, 10-bit resolution (1024 taps) for smooth temperature curve emulation, and adequate voltage tolerance to handle the measurement voltage applied by heat pump mainboards (typically 3.3V to 5V, but please add protection circuitry if necessary). Important Safety Note on DigiPot Initialization & Startup Behavior:Most standard digital potentiometers reset to a mid-scale value (e.g., 50kΩ) upon power-up before the MCU can fully boot and send the correct data. This temporary invalid resistance could cause the Heat Pump to trigger an error or malfunction. To prevent this, the hardware design must satisfy one of the following: •Use DigiPots with Non-Volatile Memory (EEPROM/WiperLock) that retain their last set value or boot directly into a safe, predetermined resistance state. •Implement a hardware isolation/blanking circuit (e.g., using a transistor or multiplexer) or use the dry-contact relays to keep the Heat Pump sensor terminals disconnected/disabled during the boot sequence, until the MCU stabilizes and writes the correct initial values to the DigiPots. * 6x Dry Contact Relays (Digital Outputs): For On/Off commands. * Connections: Push-in, screwless terminal blocks (Wago style) for fast, tool-free installation. * Sourcing: All components (MCU, DigiPots, Relays, Passives) MUST be selected from the JLCPCB (LCSC) parts library (preferably Basic parts) to ensure automated and cost-effective PCBA. 3. Form Factor & UI Constraints (Crucial for our Industrial Design): * Antennas: No external antennas. You must use PCB trace antennas or internal FPC antennas. Keep-out zones must be clearly defined. * Connectors Placement: Wago connectors must be placed strategically (e.g., bottom edge or recessed) so our industrial designer can easily create a cable-hiding cover. * Minimalist UI: The gateway should only have 1x RGB LED (for status indication) and 1x tactile button (for pairing/reset) positioned logically. Key Software Features (Firmware): * Fail-safe Mode: If a sensor's signal is lost (timeout), the gateway must default to a predetermined "fault" resistance value (e.g., open circuit) to safely halt the heat pump. * NTC Look-up Tables: Firmware must store selectable profiles for different heat pump brands (translating received °C to specific resistance values). * OTA Updates: System must be capable of receiving over-the-air updates. Deliverables: * Complete Schematic & PCB Layout (KiCad preferred). * 3D Model: A .STEP file of the fully populated PCB for our industrial designer. * Manufacturing files (Gerber, BOM, and Pick & Place/CPL) fully verified for JLCPCB. * Well-commented Firmware source code for both Nodes and Gateway. To Apply: Please provide a brief overview of your experience with wireless protocols (Zigbee/ESP32), your approach to NTC emulation using DigiPots, and confirm your familiarity with JLCPCB's workflow.