0hmX/bluetooth-pedometer-pcb

prompt.md

# Bluetooth Pedometer PCB — Project Brief

## Current state

This repository is scaffolded only. No electrical design, component selection,
schematic, footprint work, placement, or routing has been completed. Do not
mistake the empty board entrypoint for a finished design.

## Goal

Design a compact, polished Bluetooth-connected pedometer in tscircuit. The
device must count steps with an accelerometer, show useful information on a
small display, and run for weeks from a tiny rechargeable battery.

The board is intended for JLCPCB fabrication and assembly. The schedule is
urgent: the design needs to become order-ready tomorrow so it can arrive at HQ
before the project owner travels to Texas. First-spin reliability and easy
firmware bring-up matter because there will be little time for rework.

## Proposed starting architecture

Treat these as preferred starting points, not pre-approved selections:

- BLE MCU: Texas Instruments CC2340R5 (Bluetooth Low Energy 5.3)
- Charger / power-management IC: Texas Instruments BQ25150
- Fuel gauge: Texas Instruments BQ27427
- Low-power accelerometer: to be selected
- Small OLED display: to be selected

For the accelerometer and OLED, compare practical I2C and SPI options. Record
the interface, pin requirements, power draw, package, supplier part number,
stock status, price, footprint availability, and firmware implications.

## Product requirements

- Reliable Bluetooth Low Energy connectivity.
- Step counting from a low-power accelerometer, preferably using motion or FIFO
  interrupts so the MCU can sleep aggressively.
- A small, legible display with a power strategy compatible with multi-week
  battery life.
- Rechargeable battery operation, charging, protection as needed, and useful
  state-of-charge reporting.
- Multi-week runtime on a tiny battery, supported by a documented power budget
  across sleep, sensing, display, radio, and charging states.
- Accessible programming, debugging, recovery, and production-test points so
  firmware can be loaded and diagnosed quickly.
- A compact and visually polished PCB suitable for a wearable prototype.
- Fabrication and assembly outputs suitable for JLCPCB, including verified
  Gerbers, BOM, pick-and-place data, footprints, pin-1 orientation, and sourcing.

## Sourcing requirements

- Check current JLCPCB/LCSC availability before committing to every assembled
  part, especially the MCU, charger, fuel gauge, accelerometer, display
  connector/module, crystal, antenna parts, battery connector, and switches.
- Record exact manufacturer part numbers and LCSC numbers; do not rely on a
  family name alone.
- Prefer stocked parts with appropriate lifecycle status and sensible assembly
  cost. Clearly identify basic versus extended parts and any minimum-order or
  inventory risk.
- If a preferred IC is unavailable, compare pin-compatible alternatives first,
  then other Texas Instruments options, and finally suitable parts from other
  vendors. Do not silently substitute a component.
- Verify package drawings, exposed-pad requirements, land patterns, assembly
  orientation, and any JLCPCB process limits against primary documentation.

## Decisions that must be resolved before layout

- Maximum board dimensions, shape, mounting method, and enclosure constraints.
- Battery chemistry, capacity, dimensions, connector, protection, and charge
  current.
- Charging connector or charging-contact strategy.
- Exact OLED size, resolution, interface, supply voltage, and mounting method.
- Exact accelerometer and whether the final bus should be I2C or SPI.
- User controls, indicators, vibration/buzzer needs, and any external connector.
- Antenna approach, keepout, ground strategy, matching network, and enclosure
  materials around the RF area.
- Programming/debug connector or pogo-pad arrangement.
- Step-counting ownership: accelerometer hardware feature versus MCU firmware.
- Expected display duty cycle, advertising/connection intervals, sensor sample
  rate, and other inputs needed for the battery-life estimate.
- Target quantity, cost ceiling, and JLCPCB assembly constraints.

## Expected implementation workflow

1. Resolve the open mechanical, power, interface, and user-experience decisions.
2. Verify the preferred parts against datasheets, reference designs, errata,
   current supplier inventory, and tscircuit footprint/package support.
3. Produce a short architecture and power budget before drawing the schematic.
4. Build the schematic in functional sections: power/charging, MCU/RF,
   accelerometer, display, programming/test, and user I/O.
5. Review electrical limits, decoupling, reset/boot behavior, I2C/SPI pull-ups,
   battery measurement, RF guidance, and test access.
6. Place the PCB around the mechanical and RF constraints, then route it with
   manufacturing and assembly rules in mind.
7. Run the tscircuit checks in this order: netlist, schematic placement, PCB
   placement, build/visual inspection, routing difficulty, trace length, and
   shorts. Resolve every unintended short before release.
8. Review the rendered board, schematic, BOM, pick-and-place output, and Gerbers
   before declaring the design order-ready.

## Deliverables for the design phase

- Complete tscircuit source with readable schematic sections and intentional PCB
  placement.
- Architecture notes and a battery-life estimate with explicit assumptions.
- Sourcing table with manufacturer and LCSC part numbers, stock checks, and
  approved alternatives.
- Firmware bring-up notes covering programming, debug access, peripherals, and
  the first hardware tests.
- JLCPCB-ready fabrication and assembly files plus a concise pre-order checklist.

## Guardrails

- Use primary datasheets and manufacturer reference designs for electrical and
  RF decisions; do not infer pinouts or requirements from memory.
- Flag any requirement that cannot be verified in time.
- Do not publish the tscircuit package or place an order without explicit user
  approval.
- Preserve a clear record of assumptions and part substitutions so the design
  can be reviewed quickly.