• Status: Concept approved on 2026-10-23; first-pass enclosure CAD, verified component selection, and electrical capture authorized. PCB routing remains behind review checkpoints.
• A standalone smart espresso scale with phone connectivity, local shot records, a display on an off-board FPC, RGB shot-status lighting, USB-C power, and a rechargeable single-cell LiPo.
• This revision defines targets, not tested performance. Circuit capture and first-pass mechanical CAD exist, and all 77 captured components have a first-pass Top-only placement on a configured 90 × 55 mm four-layer board. Placement release fails USB/hardware, footprint, power-stage and escape checks; routing and firmware remain unfinished. Read the Placement Checkpoint project file for item-level evidence and dispositions.

• Home espresso machine drip tray or kitchen bench; prototype first, production qualification later.
• User places cup, tares, starts a shot, watches weight/time/flow, and optionally retrieves shot data from a phone.
• Splashes and warm cups expected; not immersion, dishwasher cleaning, commercial legal-for-trade weighing, or machine flow control.

• Work without a phone. Show mass, shot time, estimated flow, Bluetooth state, and battery state.
• Manual tare and timer start/stop; optional cup-detection auto-tare and flow-triggered auto-start with configurable thresholds.
• Record each shot locally; reconnect and export records after a phone disconnect.
• Signal ready, running, target reached, charging, low battery, and faults using a short RGB strip. Use text or patterns as well as color.
• Operate while USB-C charges the battery using a proper power path.

• 2 kg total supported load target; 0.1 g displayed increment. Accuracy, repeatability, drift, and settling time require calibration and prototype testing; display resolution is not accuracy.
• Target 40-80 raw samples/s with filtered UI/BLE updates at 10-20 Hz, subject to ADC selection.
• Bluetooth Low Energy phone interface; no Wi-Fi or cloud dependency in the initial firmware.
• Off-board approximately 1.3-1.7 inch high-contrast display on an FPC; exact module, pitch, contact orientation, backlight supply, and pinout must be sourced before connector selection.
• Two sealed tactile controls: power/timer and tare. Long press powers down; protect accidental shutdown during a shot.
• Short low-power RGB strip behind a front diffuser, provisional six addressable pixels.
• Nonvolatile shot logging; target at least 1,000 typical two-minute shots, with timestamp, calibration/settings, sample stream, and checksums. Separate serial NOR flash preferred over microSD to avoid an exposed slot and removable-media complexity.

• Floating cup platform transfers force only through a single-point load cell into a rigid base; avoid enclosure, gasket, cable, or button forces bypassing the sensor.
• Removable silicone cup mat, overload stops, nonslip feet, isolated battery bay, protected electronics cavity, and service access.
• Fixed display/control area beside the floating platform; FPC must not bridge the moving weighing mechanism.
• Matte dark enclosure, dark removable mat, high-contrast display, and diffused RGB light. Prototype print process: PETG; do not claim an IP rating without testing.
• Splash barriers around controls and connector; USB-C at rear or side, accessible without loading the platform. Charge only when port is dry.

Diagram

• BLE-capable module with onboard antenna, USB programming/debug if supported, and sufficient processing for sampling, filtering, display, and logging. ESP32-class direction, final device unselected.
• Four-wire bridge load cell and low-noise 24-bit bridge ADC with ratiometric excitation; final ADC selected for update rate and noise.
• Protected single-cell LiPo, charger with system power path and battery-temperature supervision, regulated digital/analog supplies, and a switched LED supply if required.
• Separate serial NOR storage, off-board FPC display, low-power addressable RGB strip with level translation as necessary.

Diagram

• External USB-C power/charging, and wired programming where feasible.
• Internal battery, bridge load cell, display FPC, RGB strip, and debug connections.
• BLE GATT interface: live mass/time/flow, device and battery status, tare/timer commands, settings, record listing, record transfer, calibration restricted to a deliberate user workflow.
• BLE disconnection does not interrupt weighing or recording. A custom mobile app is a separate deliverable; initial verification can use a generic BLE client.

• Default battery target: protected 1S LiPo, approximately 1,000 mAh, with pack NTC preferred; final size and safe charge rate pending sourced pack data.
• Active runtime target: at least 8 hours with dim display and brightness-capped lighting; an engineering target, not a calculated guarantee.
• Dim LEDs and display when idle, shut off high-current loads when asleep, and preserve battery protection independently of firmware.
• Battery state measurement and explicit low-battery shutdown before logging becomes unreliable.
• Charging current selected only after battery rating, USB source policy, charger dissipation, and enclosure thermal conditions are verified.

Diagram

• Numerical per-rail budget is intentionally pending component selection. Verify simultaneous radio, display, LEDs, ADC, and charging peaks; evaluate sleep current and thermal dissipation before final runtime claims.

• LCSC-compatible components preferred where practical; no unsupported substitutes for sensor, display connector, charger, or RF module.
• Prototype PCB target: four layers with an uninterrupted reference plane; final stackup and outline follow the approved enclosure.
• Provide test access for power rails, battery, ground, ADC signals, reset/boot, and programming.
• Validate assembly, load-cell mounting and calibration before production. No orders or manufacturing-ready claim at this stage.

• Sample and filter mass without blocking on display, BLE, or flash writes; log monotonic timestamps and raw/calibrated data as appropriate.
• Store multi-point calibration, tare, configuration, firmware/data format versions, and records with wear management.
• Provide guided zero/span calibration with a known mass; investigate temperature compensation experimentally.
• Implement BLE protocol and a documented versioned data format, reconnect behavior, and record export.
• Firmware updates, sensor disconnect detection, saturation detection, watchdog, and brownout-safe recovery required.
• Actual firmware, mobile app, and testing are not complete in this concept phase.

• Mechanical Handoff records the current 36-model editable assembly, exact source selections, measured clearances, asset links and item-level blockers; Mechanical Interfaces contains source citations and full electrical pin mapping.
• Local datum: PCB centre (0,0), top z0, +Y rear; configured PCB outline 90×55 mm with a custom nominal 1.6 mm four-layer recipe and Ø2.4 holes (±41,±23.5). All 77 captured components are Top-only; no Bottom components are permitted. The nominal stackup/thickness convention needs vendor reconciliation. PCB placement is not fit-approved: J1 conflicts with the rear-right hardware reservation, and exact USB mating reach remains unverified.
• First-pass shell 138×138 mm, approximately 47 mm assembled height including mat/feet; fixed front 15°, rear platform132×85 mm. Selected TAL220B5kg cell, LP543450 protected PHR-3/10K-NTC pack, WEO012864ALAP3N00000 SSD1309 OLED.
• Release blocked: residual Timer boot/lid interference, unverified display FPC contact orientation and ZIF, battery physical pinout/NTC return, USB reach, control sealing, print tolerance and performance validation. See Mechanical Handoff before placement or manufacturing.

• PROVISIONAL PCB envelope: maximum 90 x 55 mm, chosen as a packaging budget rather than an existing board; exact outline and mounting points depend on the accepted concept and sourced parts.
• PROVISIONAL product footprint budget: no more than approximately 140 x 140 mm to fit many home-machine drip trays; actual fit must be checked against the intended espresso machine.
• Fixed front display/control zone, rear/side USB-C access, internal FPC routing, front diffuser, and mechanically isolated floating platform.
• Battery, load cell, display, strip, cable bend radii, keepouts, height limits, connector positions, mounting holes, and overload-stop dimensions must be resolved from sourced geometry before CAD is committed.
• No invented mounting-hole or connector pad geometry. Overall height, angles, seams, radii, and control spacing will be derived from the approved drawing.
• Splash resistance is a design goal only; no IP rating assigned.

• BLE for direct phone connectivity, avoiding dependence on local Wi-Fi or internet access.
• Local flash rather than microSD: fewer openings and more predictable power-fail behavior.
• Standalone display/buttons so a phone is optional.
• Proper charger power path rather than a charger-only circuit with uncontrolled load sharing.
• Single-point bridge load cell with mechanically isolated platform; nominal 2 kg range requires allowance for platform tare and overload.

• User authorized selection of unspecified details. All targets above are proposed defaults and can be steered.
• No machine model, exact drip-tray fit, display SKU, battery SKU, runtime measurement, or certified accuracy is supplied.
• Prototype consumer device, not legal-for-trade or a machine-control safety function.
• First-pass enclosure CAD, electrical capture and Top-only PCB placement are saved but incomplete and blocked as described above. Placement release and routing retain separate review checkpoints; this record does not authorize routing, fabrication or charging.

• 2026-10-23: User approved the proposed concept and authorized first-pass CAD and electrical capture; accepted form recorded in Enclosure Concept.
• 2026-10-23: Recorded user requirements, selected product-level defaults, and established concept approval checkpoint.