SvayamV3 IIK

SvayamV3_IIK — STM32H743 Flight Controller

6-layer · 125 × 90 mm · STM32H743IIK6 · 16 servo channels · 9 protected peripheral ports

⚠️ Design status: layout in progress — not fabrication-ready

Schematic is complete and frozen (ERC 0 errors). Placement is finalised and every functional net is electrically connected (unconnected_items = 0), but DRC still reports 2 shorts — both vias sitting inside one unassigned connector MP pad — plus vias and drills outside the current rule set. Do not order boards from this revision. See docs/STATUS.md.

Contents

What this is

A servo-based UAV flight controller built around the STM32H743IIK6 (Cortex-M7, UFBGA-201, 0.65 mm pitch). The board distributes power to a fixed-wing/multirotor airframe with 16 PWM servo outputs, redundant IMU and barometer sensing, dual CAN, USB-C, micro-SD logging, and nine current-limited peripheral ports for GPS, telemetry radios, and external sensors.

Design priorities, in order:

1. Repairability — silkscreen carries function labels (Channel 1…Channel 16, TELEM1, GPS, SBUS, …) instead of values; component values live on the F.Fab layer so they stay readable in the editor and in fab documentation without cluttering the assembled board.
2. Survivability — every external port sits behind a TPS2553 current limiter; TVS diodes on the battery and servo rails; separate LDO domains for FMU and sensors.
3. Do-no-harm to the airframe — the +VSERVO rail is fail-last: it has no on-board source and no series fuse, so a failed BEC cannot brown out the flight controller.

Board specifications

Hardware architecture

Compute and storage

Sensing — redundant by design

The sensor block is laid out as its own quiet zone with a dedicated +3V3_SENS domain and local copper pour, kept away from the switching regulator.

Power chain

POWER1 (J9) ─┐
             ├─► U10 TPS2120  power mux ─► U11 TPS63070  buck-boost 5 V ─► U14 AP22804 ─► +5V_PERIPH
POWER2 (J16)─┘        (ILIM R24 = 33k)          (R27/R28 → 4.99 V)                        │
                                                                                          ├─► U16…U24  9× TPS2553 current limiters
                                                                                          │     GPS · TELEM1 · TELEM2 · SERIAL4 ·
                                                                                          │     SERIAL5 · I2C · CAN · CAN2 · SPI
                                              U12 RT9080 ─► +3V3_FMU  (MCU, IO)            │
                                              U13 RT9080 ─► +3V3_SENS (sensor zone)        │
                                              U15 USBLC6-2SC6 ─► USB-C ESD              +VSERVO
                                                                                          (external BEC, fail-last)

• TVS: D4/D5 on +VBRICK1/+VBRICK2, D8 SMAJ6.0A on +VSERVO.
• +VSERVO reservoir: C78 220 µF bulk + 16 × 1 µF per channel.
• Per-port trip current is set by each limiter's RILIM: U16 R84 33k, U17 R85 33k, U18 R86 75k, U19 R87 75k, U20 R88 110k, U21 R89 47k, U22 R90 56k, U23 R91 110k, U24 R92 47k.

Connectors

Servo outputs J19–J34 (JST-XH B3B-XH-A, 2.50 mm, pin order S / V+ / GND) map Channel 1…Channel 16 in physical order along the board edge.

Repository layout

.
├── SvayamV3_IIK.kicad_pro      # KiCad 10 project
├── SvayamV3_IIK.kicad_sch      # root sheet
│   ├── microcontroller.kicad_sch
│   ├── sensor.kicad_sch
│   ├── power.kicad_sch
│   └── connector.kicad_sch
├── SvayamV3_IIK.kicad_pcb      # 6-layer board
├── SvayamV3_IIK.kicad_dru      # custom DRC rules (global + BGA rule area)
├── fp-lib-table                # project footprint table (${KIPRJMOD})
├── sym-lib-table               # project symbol table (${KIPRJMOD})
├── Library/                    # custom + converted libraries (symbols, footprints, 3D)
├── docs/
│   ├── schematic.pdf           # full multi-sheet schematic (exported)
│   ├── STATUS.md               # live status + open DRC items
│   ├── DESIGN.md               # design decisions and their rationale
│   ├── STACKUP.md              # layer stackup and impedance notes
│   ├── board-stats.txt         # kicad-cli board statistics
│   ├── bom.csv                 # BOM (grouped by value + footprint)
│   ├── images/                 # PCB previews for this README
│   └── reports/                # dated ERC / DRC reports
└── fabrication/
    └── README.md               # fab gate, export commands, JLCPCB notes

Machine-local working files (.history/, output/, *-backups/, *.kicad_prl, .deepseek-sources/) are deliberately not tracked — see .gitignore.

Documentation

Opening the project

1. KiCad 10.0 or newer (generator_version 10.0, format 20260206). Older KiCad cannot open the project.
2. Open SvayamV3_IIK.kicad_pro. Both library tables resolve through ${KIPRJMOD}, so the project is self-contained — no global library setup required.
3. Run Tools → Update PCB from Schematic (F8) only if the PCB and schematic have drifted; on a clean checkout they are in parity (0 issues).

Known limitation: sym-lib-table registers the custom library under the nickname Svayam_Symbol, while the schematic references it as Svayam, and a stale tps63070 entry points at a footprint directory. Symbols are embedded in the sheets, so the project opens and plots correctly — but ERC will report 9 lib_symbol_issues warnings until the table nickname is aligned. See docs/STATUS.md.

Board statistics

Numbers below come straight from kicad-cli pcb export stats and the ERC/DRC reports in docs/reports/:

Fabrication

No gerbers are published for this revision — the design is not ready to order. The release gate and exact commands live in fabrication/README.md.

Intended process: JLCPCB, 6 layers, 1.6 mm, ENIG, stackup JLC06161H-3313.

Open items before fabrication

Full detail: docs/reports/drc-2026-10-25.txt.

Design references

• PCB Design Tutorial, Rev. A — David L. Jones — track width / current tables, copper pour practice, silkscreen conventions.
• IPC-2221 — conductor spacing and current capacity.
• JST XH series datasheet — 3 A per contact (AWG22) limit used to size the servo stubs.
• Component datasheets: STM32H743II, TPS63070, TPS2120, TPS2553-Q1, AP22804, RT9080, BMI088, BMI270, BMP388, DPS310, BMM150, FM25CL64B, TJA1051.

License

Hardware design files are released under CERN-OHL-S-2.0 — see LICENSE. You may study, modify, manufacture and distribute the design, provided derivative hardware is released under the same licence.

Credits

Designed and routed in KiCad 10.0. Schematic symbols and footprints for the custom sensors and connectors were converted with easyeda2kicad and vendored into Library/.