PCB Board Design for BLE Device & Load Cell Sensor

# Design two PCB Boards in EasyEDA for later JLCPCB manufacturing, including assembly.

I am open to professional recommendations regarding peripheral components (sensors, power converters, connectors) and layout optimizations. However, the MCU selection for both boards is fixed as specified below. For Board 2, I prefer the CH32V003 but am open to other CH32 variants if there is a strong technical reason.

## Board 1: ESP32-H2 based BLE monitoring device prototype.

- MCU: ESP32-H2-MINI-1-N4 (Internal 4MB Flash).
- Sensors: LIS3DHTR (Accelerometer), GXHTC3 (Temp/Hum), MSM261DHT006 (I2S Mic Top Port).
- Constraints:
- Height: Max 5.0 mm (including components and PCB - Battery holder should be as low as reasonable like Keystone 3003).
- Width: Max 25 mm.
- Length: Any.
- PCB Thickness: 0.8 mm.
- Components should be placed only on one side (TOP) to minimize total height.
- Power:
- 4x CR2032 cells in parallel.
- Large buffer capacitor required (e.g., KEMET T520D687M004ATE025 or similar Polymer Tantalum).
- Features:
- Low-quiescent current voltage divider (1M/1M) for battery monitoring.
- Power Optimization: Use a P-Channel MOSFET (Load Switch) to disconnect the battery voltage divider when not in use to eliminate leakage current.
- Programming: 2.54mm pitch 2x3 POGO pin pads (GND, 3.3V, TX, RX, EN, GPIO9) with through-holes for clip-on jigs.
- One User/Boot button (GPIO9) and one Reset button (EN) - use ultra-low profile SMD tactile switches.
- One very dim RED LED (high value resistor).
- Solder pads for an external DS18B20 sensor.
- Bonus: If space allows, add an I2C expansion header (solder pads).

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## Board 2: 8-Channel Load Cell Node (CH32V003 / RS-485)

Design a high-precision sensor node for a distributed weighing system. The board reads 8 independent load cells via HX711 ADCs and communicates via RS-485 (Modbus RTU).

- MCU: CH32V006F8P6 (TSSOP-20) - (CH32 family mandatory)
- ADC: 8x HX711 (SOP-16).
- Wiring: All 8 HX711 chips must share a single SCK (clock) line from the MCU. Each HX711 has a dedicated DOUT line.
- Channel Usage: Use Channel A for load cells. Channel B of the 1st HX711 should be broken out to pads for an optional NTC thermistor.
- EEPROM: AT24C32 (SOP-8) for storing Modbus ID and calibration constants.
- RS-485: MAX485 or 5V equivalent (SOP-8). DE/RE pin must have a pull-down resistor.
- Power: 12V–24V Bus Input -> 5V Buck Converter (min. 500mA). System runs on 5V logic.
- Connectivity (Screw Terminals):
- 8x 4-pin 5mm Metric Screw Terminals (E+, E-, A+, A-).
- 2x 4-pin 5mm Metric Screw Terminal in parallel for Bus (VCC, GND, A, B) for daisy-chaining.
- Protection:
- TVS diodes on RS-485 lines (A, B) and on the Power Input.
- PTC Resettable Fuse on the main power input to protect against short circuits.
- Reverse Polarity Protection (diode or MOSFET based) on the power input.
- Termination: 120Ω resistor selectable via a jumper or solder bridge.
- Layout: Standard 1.6mm PCB. Linear layout. Prioritize noise isolation: keep the Buck converter distant from the analog section. Use a solid ground plane.
- Status Indication:
- 1x Power LED, 1x User LED (GPIO controlled).
- RX and TX activity LEDs (driven by hardware UART lines).
- Addressing: Software-based using MCU's Unique ID.
- Programming Interface: 2x3 Pogo Pin Pads (2.54 mm pitch) as through-holes (VCC 5V, GND, SWIO, NRST, TX, RX).
- Reset: Use two solder pads (to be shorted) instead of a mechanical button.