Unoq power shield

UNO Q power & I/O demo shield

Status: UNBUILT. No physical board of this design has been fabricated or powered on yet. Until one has, treat this as a reference for exercising the pipeline, not a verified design.

The design has passed its pre-order gates (2026-08-30): routed with 0 unconnected and 0 clearance violations across 5 identical DRC runs, validate_gerbers 14/0, ERC clean, every BOM line in stock. The 17 residual DRC items are all form-factor or courtyard-graze artifacts, individually explained in the ledger in rev-1-plan.md. Passing gates is not the same as working hardware — the UNBUILT warning above stands until a board has been powered on.

The stacking headers ship DNP — the assembled board cannot plug into anything until you solder a stacking header set into the four plated hole strips. Any classic Arduino R3 stacking kit fits: SparkFun PRT-11417 or Adafruit #85, about $2. This is deliberate: assembly houses don't stock stacking headers, and a flush-soldered normal header would make the shield unstackable.

The example board for this repo — the design a first-time user builds before trusting the pipeline with their own board. If this builds, routes, checks, and comes back from the fab working, the pipeline works. That is all it proves: it says nothing about whether any other design is right, and it is not a product.

What it is

A shield for the Arduino UNO Q (classic UNO outline, stacking headers):

• Screw-terminal VIN, 7–24 V — the UNO Q's own DC input range. Feeds the Q's VIN pin and a local TPS54331 buck making 5 V for shield loads, behind reverse-polarity protection (the terminal a first-timer wires backwards).
• INA226 high-side monitor on the VIN rail, upstream of everything, so the stack reports its own total consumption over I²C (address 0x40, on D20/D21; ALERT on ~D3).
• Four bidirectional level-shift channels (BSS138 + 10 k) between the headers and 5 V peripherals, on D2/D4/D7/D8. The UNO Q's headers are 3.3 V logic, not the classic UNO's 5 V — wiring 5 V gear straight in is the most common way this board gets damaged, and this circuit is the fix. Signalling limit: ~300 kHz. The 10 k pull-ups against ~30 pF of load give ~0.3 µs rise times: fine for GPIO, buttons, slow UART, and 100 kHz I²C-style traffic; not for SPI above ~300 kHz and not for NeoPixels (WS2812 timing needs edges these channels cannot produce). That is a documented property of the classic BSS138 shifter, not a defect.
• Qwiic passthrough (2× JST-SH, daisy-chain) on the same I²C bus.
• RGB status LED on ~D9/~D10/~D11, active-low, for sketches to drive.

Design record: rev-1-plan.md — every requirement cited to Arduino's own documents, every part checked against the JLCPCB library, every number with its arithmetic shown. Rules: board.toml.

What it teaches

Each board.toml rule exists here for a visible physical reason:

What it costs (estimate, 2026-08)

• 4-layer PCB, 5 pcs: ~$8–15
• JLCPCB SMT assembly (2–5 boards): setup ~$25, ~10 Extended-part feeder fees ~$30, parts ~$2.5/board, THT screw terminals hand-solder fee
• Ballpark: $70–90 for a small assembled batch
• Stacking headers are DNP — fit any Arduino stacking-header kit (~$2)

Power behavior

Attribution

The UNO Q facts in this design — pinout, electrical limits, mechanical coordinates, antenna location — come from Arduino's official documents and CAD files for the UNO Q (ABX00162), © Arduino SA, licensed CC BY-SA 4.0: datasheet, full pinout, schematics, and fab data, copies in docs/datasheets/. The antenna keepout and hole/header coordinates were extracted from the gerber and NC-drill files Arduino publishes there. This example's own design files are MIT like the rest of the repo; the CC BY-SA attribution above covers what was derived from Arduino's documents.