Ultra-Compact nRF52840 BLE Beacon Base (38x28mm)

A simple, ultra-compact 4-layer BLE beacon based on the Minew MS88SF2 (Nordic nRF52840) module.
Built for long-term autonomous deployment (up to 7+ years on a coin cell) and intended to be sealed in protective resin (potting). This board serves as the foundational base for multi-sensor extensions.

---

Hardware Overview

• Dimensions: 38 mm x 28 mm
• PCB Stackup: 4-layer PCB (L1: Top Signals/RF, L2: Solid GND Plane, L3: Power VDD, L4: Bottom Signals)
• Power Source: CR2477 3V Lithium Coin Cell (Keystone 3009 holder)
• Antenna: External Molex 2140610150 flexible FPC connected via U.FL (pre-matched 50 Ω output on Minew module)
• Power Optimization & Protection:
  • P-MOSFET (Q1 - AO3401A / DMG2305UX-7, SOT-23): Reverse-polarity protection with near-zero voltage drop (~0.6 mV).
  • N-MOSFET (Q2 - DMG2302UK-7, SOT-23): Gated switch to completely disconnect the 2x 1 MΩ battery voltage divider during sleep, eliminating leakage current (0 µA at rest).
  • Bulk Energy Storage: 100 µF 10V MLCC Ceramic Capacitor (1210 package, Murata GRM32ER61A107ME20L) with zero DC leakage (< 10 nA) to sustain RF peak currents without depleting the coin cell.

---

Visuals

---

Pin Mapping (nRF52840 GPIOs)

Peripherals

Component	Description	nRF52840 GPIO	MS88SF2 Pin	Config / Logic
D1	Diagnostic LED	P0.04	Pin 7	Active LOW
Q2	ADC Bridge Switch (DMG2302UK-7)	P0.29	Pin 5	Active HIGH
ADC	Battery Voltage Read	P0.02 / AIN0	Pin 4	Analog Input ($0.5 \times V_{BAT}$)

SWD Programming Header (J1)

Standard SWD pads to program/flash the board prior to potting and sealing.

J1 Pin	Function	MS88SF2 Connection
1	VDD	Protected VDD Line
2	SWDIO	Pin 25 (SWDIO)
3	GND	Ground Plane
4	SWDCLK	Pin 26 (SWDCLK)
5	NC	Not Connected

---

Potting & Assembly Notes

• Sealing / Encapsulation: Use an RF-transparent polyurethane or silicone elastomer (e.g., Electrolube UR5604 or RTV-2 silicone) to protect components from high humidity and harsh environments.
• Flashing Firmware: Always flash and validate your firmware via the SWD header before pouring the potting resin.
• Firmware Power Optimizations:
  • Configure the diagnostic LED (P0.04) as Input / Disconnected (floating) in production code to prevent battery drain.
  • Enable the internal DC-DC converter in code (CONFIG_BOARD_ENABLE_DCDC=y in Zephyr or Embassy equivalent) to reduce radio power consumption by ~40%.