• Countertop espresso preparation in a splash-prone environment.
• Target capacity: 2 kg; target displayed resolution: 0.1 g.
• Prototype-to-production-intent, assembled SMT PCB in a sealed enclosure beneath a mechanically isolated weighing platform.

• Measure weight continuously and calculate flow rate.
• Auto-tare and detect shot start/stop.
• Display weight, elapsed time, flow rate, battery, and connection status.
• Connect to iOS/Android over Bluetooth Low Energy.
• Log timestamped shot samples locally and sync them to the phone.
• Operate while charging and protect the LiPo from unsafe charge/discharge conditions.

• 2 kg single-point load cell interface with 24-bit ADC.
• BLE 5 phone connectivity using an ESP32-S3 module.
• 1.3-inch high-contrast I2C OLED with segment-style UI graphics.
• External SPI NOR flash for durable onboard logging; internal MCU flash reserved primarily for firmware/configuration.
• USB-C 5 V sink, LiPo charger with power-path management, battery fuel/status measurement.
• Three sealed user buttons: power/tare, timer, and mode.
• USB firmware update/debug plus boot/reset controls.

Diagram

• Compute/wireless: ESP32-S3 module with integrated antenna, native USB, BLE, adequate RAM/flash, and low-power modes.
• Weight measurement: NAU7802-class 24-bit bridge ADC, ratiometric load-cell excitation, input filtering, and DRDY interrupt.
• Display/UI: 128x64 OLED over I2C; three buttons and optional vibration/buzzer footprint not populated by default.
• Storage: 8–16 MB SPI NOR flash with wear-leveled circular logging.
• Power: USB-C sink protection, single-cell charger with system power path and battery temperature input, efficient 3.3 V regulation, power switch/load gating where useful.
• Battery monitoring: charger status plus ADC/fuel-gauge measurement sufficient for battery percentage and low-battery shutdown.
• Debug: USB D+/D-, boot/reset buttons, UART/JTAG-accessible pads.

• USB-C: 5 V sink, USB 2.0 data, CC pull-downs, ESD protection.
• I2C: load-cell ADC, OLED, optional battery gauge.
• SPI: external log flash.
• GPIO: three buttons, ADC DRDY, charger status/interrupt, display reset if required.
• Load cell: 4-wire bridge connector (E+, E-, A+, A-), with optional shield connection.
• Battery: keyed 2-pin connector plus 10 kΩ NTC input where supported.

• Assumed battery: protected 1000 mAh single-cell LiPo, 3.0–4.2 V.
• Target active runtime: at least 12 hours of intermittent café use.
• Target deep-sleep current: below 300 µA at battery level.
• Device may operate during charging; charge current target 500 mA unless the selected cell requires less.

• Size the 3.3 V rail for at least 500 mA continuous/peak capability with transient margin.
• At 77 mA average active load, a 1000 mAh cell provides roughly 10–12 hours after regulator losses and reserve; duty-cycled use should exceed this.
• USB input limit and charging current must be set conservatively for default USB power; no USB-PD is required.

• 4-layer PCB preferred for RF, low-noise load-cell measurement, and compact routing.
• Mostly 0402/0603 passives; no BGA parts.
• Standard SMT assembly with hand-accessible battery/load-cell connectors.
• Add test pads for 5 V, battery, system rail, 3.3 V, GND, I2C, SPI, ADC DRDY, USB, boot, and reset.

• BLE GATT service for live weight/flow and shot-history sync.
• 80–100 Hz raw load-cell sampling, digitally filtered to stable 0.1 g output.
• Circular local log with timestamp, weight, flow, event flags, calibration version, and CRC.
• USB and BLE firmware-update path.
• Wake from buttons and optional weight-change interrupt strategy.

• PCB target envelope approximately 80 mm x 45 mm, subject to enclosure/mechanics.
• USB-C accessible on a side edge; display and buttons accessible from the top/front.
• Radio antenna at a board edge with strict copper/component keepout and away from the load cell metalwork.
• Analog load-cell section separated from USB, display switching currents, and antenna region.
• Conformal-coating-compatible layout; enclosure must provide splash protection.

• ESP32-S3 chosen for broad phone BLE support, native USB, development ecosystem, and sufficient processing for filtering/logging.
• NAU7802-class ADC chosen over HX711 for I2C control, higher integration, and flexible sampling.
• OLED chosen instead of a fixed numeric segment module so the UI can still look segment-based while showing menus, graphs, and icons.
• Dedicated SPI NOR chosen instead of removable microSD for compactness, lower idle power, and better splash resistance.
• Charger must include power-path operation; a charge-only topology is not acceptable because the scale should work predictably while plugged in.

• BLE, not Wi-Fi, is the primary phone connection.
• 2 kg capacity and 0.1 g user resolution are acceptable; final accuracy depends heavily on load-cell mechanics and calibration.
• The battery pack includes protection, but board-level charger safety and NTC monitoring remain required.
• The phone provides absolute time during sync; the first revision does not require a standalone RTC.

• Initial architecture and requirements derived from the user request; ready for review before schematic implementation.