MustafaMulla29/rp2040-bldc-motor-controller-new

docs/compact-layout.md

# Compact 9 V USB-PD layout — 12 October 2026

The current board is **73 × 72 mm**. The sixth review below records the latest 1 mm height reduction. Earlier revisions are retained here for context.

This page records the previous outline reduction. The subsequent [power-layout review](routing.md) retains the 73 × 75 mm outline, updates 47 positions/orientations, places main power routes on outer copper, and expands the required path checks from 53 to 69. Current validation is recorded in [validation](validation.md).

The PCB is reduced from **77 × 78 mm to 73 × 75 mm**: 531 mm² less area, an **8.8% reduction**. It is 24.0% smaller than the earlier 80 × 90 mm board. The left USB edge and upper motor-socket edge stay in place. The right edge moves inward another 4 mm and the lower edge another 3 mm. Native outline center: (−3.5, 10) mm.

Thirty-seven component/test-pad placements change. The three outward-facing motor sockets shift left 3.3 mm. BOOT and RESET move beside the speed knob; ARM moves inward along the lower edge. The power switch, current-limited power circuit and service pads move into the remaining usable space. The processor, PD circuit, bridge, knob and USB receptacles retain their positions apart from affected peripheral parts. All 152 fitted parts remain on top. The four copper layers and 1.6 mm thickness are unchanged.

Mounting-hole centers are (−37, −24), (29.5, −24), (−37, 44) and (29.5, 44) mm. Each hole has a 3.2 mm drill. Component courtyards and 6.4 mm screw-head envelopes were checked for overlap. Necessary connector, control, assembly and routing space remains.

The authored route plan is regenerated for the new geometry and rebuilt through native tscircuit. The exact-routing-input guard remains active. Trace widths, copper clearances, drill dimensions and the 53 required power/gate/bypass path checks are unchanged. Obsolete branches and isolated vias are removed from the source plan. The new motor-fault connection is shortened to 56.7 mm. Generated circuit data and DRC findings are never filtered or patched.

The electrical pin/net mapping is unchanged across all 527 component pins. Schematic placement is unchanged and retains only the reviewed heuristic advisories documented in [validation](validation.md). Current PCB checks and artifact hash are recorded in `../assembly/dist/results/pcb-validation.json`; the assembly must match that certificate. Ten assembly tests and the smaller board's 3D inspection pass.

This version was developed and checked in a separate copy before promotion to main. This is a CAD-checked prototype. It does not establish a minimum possible size or physical operating/thermal qualification. Motor-control firmware and physical adapter fit remain separate outstanding work.

## Fourth review: 73 × 74 mm

The upper edge moves inward 1 mm, from y=47.5 to 46.5 mm. The board center is
now (-3.5, 9.5) mm. Width and the other three edges are unchanged. This saves
73 mm², or **1.33%** relative to 73 × 75 mm; total area is 5402 mm².

J10/J11/J12, RV1, BOOT/RESET and the upper service pads move down 1 mm. The top
mounting holes move to (-37, 43) and (29.5, 43) mm; the lower holes stay at y=-24.
C140 moves 0.65 mm toward U11. Its direct supply trace decreases from 3.44 to
3.08 mm and its ground connection from 2.26 to 1.63 mm, at their original
0.30/0.20 mm widths. C140's courtyard clears J10 by 0.155 mm. User labels follow
the controls, and SWD TEST is placed above the service row.

The initial compressed routing was rejected for real clearance conflicts.
The corrected source plan reroutes the 1.20 mm U-phase path and two service-area
traces, and relocates two existing routing vias. No trace-width rule is reduced,
no new vias are added, and all 22 explicit ground/thermal vias are unchanged.
The smaller board retains all 152 fitted parts and all functions.

A 73 × 73 mm trial with this arrangement overlaps J10/C140 and J11/R91/C90
courtyards. The bottom and side edges already have close copper or components.
More reduction would require a broader placement/routing change or smaller
connectors, rather than further outline trimming. This is a tested local
reduction, not proof of the minimum possible board size.


## Fifth review: 73 × 73 mm — 11 October

This pass saves another 73 mm² (1.35%) versus 73 × 74 mm. The outline is
x=[-40, 33], y=[-27.5, 45.5] mm, with center (-3.5, 9) mm. The upper mounting
holes move to (-37, 42) and (29.5, 42) mm. Lower holes and both USB ports stay put.
All 152 fitted components remain on top, with the same parts and electrical nets.

Fourteen placements change. J10/J11/J12, the knob, BOOT/RESET and TP11–TP14 move
inward 1 mm. U11 moves down 0.85 mm together with its eight thermal vias and
local ground pours. C140 moves down 1 mm; its supply/ground traces are now
3.01/1.49 mm long at the same 0.30/0.20 mm widths. R91 moves down 1 mm. C90 moves
beside C91, between the first two half bridges, and rotates 180 degrees while
preserving its pin-to-net mapping. Its two ground vias move with it.

The main supply path shortens from 23.64 to 22.23 mm at 1.50 mm width. U/V socket
paths shorten from 36.51/26.40 to 35.72/25.10 mm at 1.20 mm width. C90's supply
trace shortens from 5.35 to 4.72 mm; its ground stub grows from 0.70 to 1.25 mm.
Both remain 0.60 mm wide, with paired ground vias. Existing current-sense and
short reset routing are preserved. No trace widths were reduced.

The via count remains 473. Individual deletion trials on 173 signal/control
vias found none removable while retaining all remaining copper connectivity.
Ground/thermal and power vias were excluded from this deletion experiment;
all 22 explicit ground/thermal vias and 42 power-via pairs remain.

A 73 × 72 mm candidate cleared component courtyards but forced long power and
control routing detours. It was rejected in favor of the shorter routes above.
This does not prove 73 × 73 mm is the absolute minimum: further reduction needs
a broader redesign, rather than more trimming of the tested placement.

The expanded audit checks 88 width paths, including all three half-bridge
bypass capacitors, 526 pad anchors and 152 component/screw clearances. Native
PCB DRC, physical connectivity and independent manufacturing-clearance checks
pass. Assembly and factory outputs must be regenerated from this same source.


## Sixth review: 73 × 72 mm — 12 October 2026

The lower edge moves from y=-27.5 to -26.5 mm. The other three edges stay in
place, giving center (-3.5, 9.5) mm and 5256 mm² area: another **1.37%** saved
versus 73 × 73 mm. The lower mounting holes move up to (-37, -23) and
(29.5, -23) mm. The top holes remain at y=42.

Twelve placements change: ARM (SW3), R47, R86, R134, R144 and seven lower
service pads (TP6–TP10/TP15/TP16). R134 turns 90 degrees to fit beside ARM.
The label positions follow the moved controls and pads. All 152 fitted parts
remain on top; components, functions and electrical pin/net mapping are unchanged.
The motor sockets, USB ports and power stage retain their reviewed positions.

Lower signal routes are repaired at their existing widths. The LED signal gains two necessary transitions; total vias change from 473 to **475**.
Eight existing routing vias move to clear the new pad positions or board edge.
All 22 explicit ground/thermal vias are unchanged, and all 42 parallel power
via pairs remain. Individual removal trials on 175 signal/control vias find
none removable while preserving all remaining copper connectivity.

No trace widths are reduced. All 88 required power/gate/bypass paths pass.
The full-segment width scan now covers **11 local supply rails**, adding
MCT_AVDD, MCT_DVDD, MCT_GVDD, PD_1V2 and PD_2V7 at the existing 0.20 mm
minimum. It found no undersized branches. The power-switch control route
shortens from 38.44 to 31.15 mm; the local 3.3 V route under the processor
shortens from 33.36 to 30.82 mm. The LED signal remains 0.20 mm and uses top/bottom/inner2,
40.85 mm versus 38.69 mm previously. The inner1 ground-reference layer remains
free of non-ground traces. The USB-presence resistor branch is shortened to
0.525 mm; its MCU connection stays on top. Total USB-presence copper grows
from 28.54 to 33.41 mm, while total LED-signal copper grows from 41.67 to
43.13 mm. Main power routes and widths are unchanged.

Native PCB DRC, independent copper connectivity/clearance, 526 pad anchors,
152 component/screw envelopes and control-label spacing pass. The assembly
and factory export are regenerated from this same source. This is a local
reduction that preserves the power layout, not proof of the smallest possible
board or physical current/thermal qualification.