Project Getting Started

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flux

I preserved your manually adjusted J4 and LED placement and stopped the earlier correction passes that could overwrite them. A replacement pass was dispatched to handle only the remaining U1 support, C4/U5, USB support, buck-stage, pump-stage, and antenna-keepout work.
I could not inspect or reconcile that executor’s completed changes, so their exact state is unverified. Before routing, the live board still needs a read-only check confirming:
  • J4 and all LEDs remained unchanged.
  • U1, C1, and R2 clear the center-hole and antenna regions.
  • C4 is properly oriented beside U5.
  • U6/R9/R10/U7 are suitably arranged behind J4.
  • U3/L1/C18–C22/R11/R12 and Q1/D2/R7/R8 are compact and clear.
  • The antenna copper keepout exists across all copper layers.
  • No new overlaps, bounds errors, or center-hole violations were introduced.
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Project Specification
Project Overview
Single smart-bar bottle-position CAN node. Status: schematic draft. The board measures load-cell force, drives a 12 V brushed pump, and presents a controlled 24-pixel RGBWW light ring.
Intended Use
One node is connected as a short CAN stub to a regulated 12 V bar network. This is a production-intent SMD assembly; all functional components will be top-side during later layout.
What the Device Should Do
  • Measure a 4-wire bridge load cell through a NAU7802 I2C ADC.
  • Communicate on one 500 kbit/s classic-CAN stub; no pass-through and no local bus termination.
  • Provide native USB-C data/programming and optional USB 5 V service power.
  • Drive 24 SK6812RGBW-WS (2700–3000 K) LEDs with firmware-limited LED current.
  • Switch a 12 V, 0.5–0.7 A brushed pump (2 A inrush) with a protected low-side MOSFET.
System Architecture
Text
12V/CAN connector -> fuse + TVS -> 12-to-5 buck -> 5-to-3V3 buck -> ESP32-C3
                          |                 |                 |-> CAN + NAU7802
                          |                 |-> LED buffer -> 24 LEDs
                          |-> pump terminal + flyback + NMOS
USB-C -> ESD -> ESP32 native USB; USB 5V -> reverse-blocking ideal-diode option -> 5V rail
Load-cell connector -> NAU7802 -> I2C -> ESP32
Hardware Subsystems
  • Compute: Espressif ESP32-C3-MINI-1-H4X, 3.3 V.
  • CAN: TI TCAN334GDR, 3.3 V, normal mode tied active; CANH/CANL only to J1.
  • Load cell: specified Nuvoton NAU7802KGI with E+/E-/S+/S- connector. The library part is unavailable; its exact symbol/footprint remains a blocker.
  • LEDs: 24 SK6812RGBW-WS, 5 V, daisy chain; AHCT level buffer and 330 ohm first-pixel series resistor.
  • Pump: low-side N-MOSFET, 100 ohm gate resistor, 100 kΩ gate pull-down, SS56 flyback diode.
  • Power: protected 12 V input, TPS54302 5 V / 3 A buck, LMR33630 3.3 V synchronous buck.
Interfaces and Connections
  • J1: 12V, GND, CANH, CANL; 4-position 3.50 mm terminal block.
  • J2: E+, E-, S+, S- load-cell input.
  • J3: 12V_SW, GND pump output.
  • USB-C: USB 2.0 D+/D-, CC sink resistors, VBUS protection/OR option.
  • Factory pogo pads: 5V, GND, USB_D+, USB_D-, EN, GPIO9_BOOT.
Power Tree and Budget
See the separate Power Budget project file. LED firmware shall limit the 5 V LED load to <=0.5 A; hardware is nevertheless sized for the stated 1.9 A full-white LED worst case plus margin.
Physical Design Expectations
  • Later PCB layout: circular, 80 mm target OD and <=90 mm maximum.
  • Single-sided assembly, functional parts top-side, LEDs upward.
  • Provisionally reserve a rounded-rectangle 44 x 20 mm central opening and adjacent low-profile/component-free corridor for an 80 x 12.7 x 12.7 mm TAL220-class load-cell bar. Keep all connectors out of that corridor.
  • Future layout must report tallest component under the bar path so enclosure CAD can set boss height; no height limit is assumed now.
  • Later place 24 LEDs on 60 mm diameter centerline.
  • Later edge-mount ESP antenna with no copper/plane beneath antenna.
  • Reserve 3–4 enclosure standoff mounting holes for later placement.
Important Design Decisions
  • GPIO19/GPIO18 are fixed native USB D+/D−.
  • GPIO9 is reserved for BOOT with pull-up and button to GND. GPIO2 is pulled up only; GPIO8 is left unburdened. No peripheral uses GPIO9.
  • Proposed GPIO allocation: GPIO4 CAN_TX, GPIO5 CAN_RX, GPIO6 I2C_SDA, GPIO7 I2C_SCL, GPIO10 LED_DATA, GPIO3 PUMP_GATE, GPIO1 BUTTON_IN. ESP32 GPIO matrix permits TWAI and I2C assignment, subject to firmware configuration.
  • USB 5 V is limited by its source advertisement; it must not be relied on for the 1.9 A LED full-white condition.
Assumptions and Open Risks
  • 12 V input is regulated and remains below 14 V in normal operation; SMBJ14A is selected provisionally with a ~23.2 V clamp. All 12 V power-path parts require voltage rating above this clamp.
  • The selected 2 A-hold PTC must be thermally derated during final BOM review; it does not protect the pump branch selectively.
  • NAU7802KGI is missing from Flux library; no unverified substitute is allowed. This blocks a complete manufacturable load-cell schematic.
  • USB VBUS ideal-diode option is 1.5 A rated and therefore is service/low-load only; it is not a 2 A LED supply path.
Change Notes
  • Initial requirements captured; project renamed Smart Coaster CAN Node.

  • Project Overview

  • Intended Use

  • What the Device Should Do

  • System Architecture

  • Hardware Subsystems

  • Interfaces and Connections

  • Power Tree and Budget

  • Physical Design Expectations

  • Important Design Decisions

  • Assumptions and Open Risks

  • Change Notes