ESP8266 MCU PCB Design & Schematics

Project Title: Custom ESP8266 MCU PCB Design (LoRa, Current Monitor, RTC, Auto-Switching Battery, USB-C) Project Overview: I need an experienced PCB designer to design the schematic, route the board, and generate manufacturing files. Hardware & Schematic Requirements: • Microcontroller: ESP8266 (e.g., ESP-12F bare module footprint). • Programming & Debugging (USB-C): o Onboard USB-C port for programming only. Power comes from primary buck converter. o Integrated USB-to-UART bridge IC (e.g., CH340C, CP2102, or similar). o Standard NodeMCU-style auto-reset circuitry (two NPN transistors connected to DTR/RTS) to allow seamless, one-click flashing from the IDE without requiring physical boot/reset buttons. • Specific Pin Mapping (STRICT REQUIREMENT): o D0 (GPIO16): LoRa RST o D1 (GPIO5): Start Relay IN (Screw Terminal for External Control) o D2 (GPIO4): LoRa DIO0 o D3 (GPIO0): RTC SDA o D4 (GPIO2): Stop Relay IN (Screw Terminal for External Control) o D5 (GPIO14): LoRa SCK o D6 (GPIO12): LoRa MISO o D7 (GPIO13): LoRa MOSI o D8 (GPIO15): LoRa NSS (CS) o RX (GPIO3): RTC SCL o A0 (ADC0): SCT-013 Input o Critical Note for Designer on Boot Strapping:  D3 (GPIO0) is used for RTC SDA and the auto-program circuit. Ensure the I2C pull-ups and UART flashing circuit do not conflict.  D4 (GPIO2) must be HIGH at boot. Since it is connected to an external relay terminal, ensure the circuit design prevents external loads from pulling this pin LOW during startup.  D8 (GPIO15) must be LOW at boot. Since it is used for LoRa NSS (Chip Select), please design the external circuitry carefully to avoid boot failure while maintaining proper SPI communication.  RX (GPIO3) is used for RTC SCL. Ensure the I2C bus does not interfere with standard UART flashing over the USB-C port. • Power Supply (Main): Wide input range of 5V to 12V DC, utilizing a high-efficiency DC-DC Buck Converter to step down the voltage for the main logic system. • Battery Backup & Auto-Switching (MCU/RF Only): o Connector/terminals for a single-cell 3.7V Li-ion/LiPo battery. o Onboard battery charging circuit (e.g., TP4056 or similar). o Power Path Management / Load Sharing circuit to seamlessly switch to battery power when the main 5-12V DC (or USB power) drops out, preventing the ESP8266 from rebooting. • Relay Control (External Only): o No onboard relays. The board should only provide screw terminals to connect to an external off-the-shelf relay module. o Provide screw terminals for the logic signals: Start Relay (D1) and Stop Relay (D4). o Critical Power Note: Provide a dedicated 5Vpower and ground screw terminal output to power the external relay board. This power output MUST come directly from the primary buck output and bypass the battery backup system. This ensures the relays naturally drop out when main power is lost, while the ESP8266 and RF logic stay alive on battery. • Power Supply (RF Isolated): A dedicated, separate AMS1117-3.3V LDO (or equivalent low-dropout regulator suitable for battery operation) specifically for the LoRa Ra-02 module to ensure stable transmission and prevent brownouts. • RF Communication: Footprint and integration for an Ai-Thinker LoRa Ra-02 module (433MHz) directly on the board, with proper RF layout practices for the antenna connection. • Current Monitoring: o 1x screw terminal input for an SCT-013 current transformer. o Includes the necessary burden resistor and voltage divider bias circuitry to safely interface the AC current transformer with the ESP8266’s ADC pin (keeping in mind the ESP8266 1.0V internal ADC limit). • Timing: PCF8563 Real-Time Clock (RTC) with a coin-cell battery backup holder. Design Considerations: • Mixed-Signal Layout: Proper separation of the high-voltage/power traces from the sensitive analog ADC bias circuit and RF lines. • Form Factor: [60X100mm or "As compact as reasonably possible"]. Deliverables Required: 1. Complete Schematic files. 2. Complete PCB Layout files. 3. Standard Gerber files (ready for fabrication at standard houses like JLCPCB or PCBWay). 4. Bill of Materials (BOM) with common, easy-to-source generic parts (preferably LCSC part numbers). 5. Pick & Place (CPL) files for PCBA. Ideal Freelancer Qualifications: • Proven experience designing custom PCBs for the ESP8266/ESP32 ecosystem. • Deep understanding of ESP8266 boot-strapping pins, auto-reset circuitry, and GPIO states. • Experience with Battery Management Systems (BMS) and seamless power path switching architectures. • Experience with RF layout guidelines (LoRa). • Familiarity with analog signal scaling (ADC voltage dividers for AC transformers). • Proficiency in modern EDA software (KiCad preferred so I can easily review). To Apply: Please include examples of past IoT or power-switching boards you have designed. Let me know your preferred EDA software and your estimated timeline for completing the schematic and final layout. Budget: INR 5000/-

Project ID: 40618629