• Collar-mounted prototype with production-intent component choices.
• Single-cell protected LiPo battery operation and USB-C charging.
• Periodic cellular/GNSS sessions; BLE and sensors operate at much lower duty-cycle power.
• Not a diagnostic medical device; measurements require validation against veterinary reference equipment.

• Acquire single-lead ECG through external collar electrodes.
• Measure optical pulse waveform at the skin-contact face.
• Record 6-axis motion for activity and artifact detection.
• Provide BLE configuration/data sync.
• Provide LTE-M/NB-IoT telemetry and GNSS location.
• Charge safely from USB-C and support deep-sleep/ship behavior.

• Nordic nRF52832 BLE controller.
• MAX30003 ECG AFE over SPI.
• MAXM86161 optical PPG over I2C.
• LSM6DSV16X IMU over I2C.
• Quectel BG95 controlled by UART plus PWRKEY/status signals.
• SWD programming/debug access, reset access, battery monitoring, and key rail test points.

Text
USB-C 5 V -> input protection -> LiPo charger/power management -> protected cell VBAT
                                                                      |-> BG95 + LTE/GNSS antennas
                                                                      |-> PPG LED supply
                                                                      |-> low-noise 1.8 V rail
                                                                            |-> nRF52832
                                                                            |-> MAX30003
                                                                            |-> MAXM86161 logic
                                                                            |-> LSM6DSV16X

nRF52832 --SPI--> MAX30003 --protected analog inputs--> ECG electrodes
nRF52832 --I2C--> MAXM86161 + LSM6DSV16X
nRF52832 --1.8 V UART/control--> BG95

• USB-C sink with independent 5.1 kΩ CC1/CC2 pull-downs and VBUS ESD/overcurrent protection.
• Charger must support a protected single-cell LiPo, battery thermistor input, safe charge-current programming, and operation during charging.
• Protected battery rail directly supports BG95 transmit bursts; a load switch or module shutdown path minimizes off-state current.
• Low-noise 1.8 V rail powers nRF52832 and sensor logic, avoiding UART level translation to the BG95 1.8 V interface.
• Large low-ESR local bulk capacitance and a short, wide power path are required at BG95 VBAT.

• nRF52832 QFN implementation with 32 MHz radio crystal, optional 32.768 kHz low-frequency crystal, complete decoupling, SWD, reset, and matched BLE antenna network.

• MAX30003 reference input network, electrode protection, lead-off support, and dedicated analog filtering per datasheet.
• ECG connector/electrode interface located at the opposite end of the PCB from BG95 and cellular antenna circuitry.

• MAXM86161 located on the skin-facing PCB edge/window.
• Optical barriers and enclosure sealing are required to suppress ambient light and LED-to-photodiode crosstalk.

• LSM6DSV16X on the shared I2C bus with interrupt lines to the MCU.

• BG95 with UART, PWRKEY, RESET_N, STATUS/netlight as available, SIM interface with ESD protection, and separate LTE/GNSS antenna connections.
• Cellular/GNSS antenna keepouts and module ground/pad requirements must follow the exact BG95 hardware design guide.

• SPI: nRF52832 to MAX30003, with dedicated chip select and interrupt.
• I2C: nRF52832 to MAXM86161 and LSM6DSV16X, one pull-up pair on the 1.8 V rail.
• UART: nRF52832 to BG95 at 1.8 V logic.
• SWD: SWDIO, SWCLK, RESET, 1.8 V reference, and GND.
• External: USB-C power, LiPo connector or welded leads, ECG electrodes, nano-SIM/eSIM option, LTE antenna, GNSS antenna.

• Ultra-low-power sensor/BLE operation between cellular sessions.
• BG95 must be fully shut down or hard power-gated when not required.
• Runtime is dominated by cellular registration, GNSS acquisition, PPG LED current, and reporting interval.
• Initial battery assumption: protected 800–1200 mAh LiPo; final cell and connector are enclosure-dependent.

• Battery path, protection, connector, switch, and copper: at least 2.5 A burst capability with low voltage drop.
• 1.8 V regulator: at least 100 mA continuous capability, low noise, low quiescent current, and adequate transient response.
• USB input current must remain conservative until Type-C source-current capability is known; no USB-PD assumption.

• Four-layer PCB preferred: signal / solid GND / power+signal / signal.
• Fine-pitch QFN/LGA assembly; 0201/0402 passives where justified, with 0402 preferred for first prototype reworkability.
• Controlled RF layout, filled ground-via fences, exposed-pad thermal vias, and impedance-controlled antenna feeds.

• Independent enables/shutdown controls for BG95 and optical sensing.
• Wake sources from MAX30003, IMU, BG95, and charger/power-good as available.
• Battery voltage measurement through a high-value switched divider or PMIC ADC.
• Watchdog-safe BG95 PWRKEY/RESET sequencing.

• Target initial PCB envelope: approximately 58 mm × 32 mm, driven primarily by BG95 size, SIM, antennas, and battery-current bulk capacitance.
• Rounded corners and no tall connectors on the skin-facing side.
• PPG optical window on the skin-facing edge/face.
• ECG analog section and electrode connector at one end; BG95, SIM, and LTE/GNSS antenna section at the opposite end.
• Solid ground plane retained under digital circuitry; no noisy switching or RF return currents routed through the ECG analog region.

• Operate MCU and sensor logic at 1.8 V to interface directly with BG95 UART and reduce active energy.
• Power BG95 from protected VBAT rather than the low-power logic rail.
• Use a low-noise regulator for the ECG/logic domain and avoid switching nodes near MAX30003.
• Use a four-layer partitioned layout rather than split ground planes; control return-current paths through placement and routing.

• External LTE and GNSS antennas are acceptable for the first prototype.
• A protected LiPo pack with 10 kΩ NTC is available.
• Cellular and GNSS are duty-cycled, not continuously active.
• Exact enclosure, electrode geometry, PPG optical stack, battery dimensions, and preferred SIM format remain open mechanical inputs.

• Initial architecture captured from the user requirements.