Project Status and Action Items
Worked for 1 min 27 sec
Done. I deleted
CN1 and moved U_MCU/Pico to the top of the board; it is now centered at about (10 mm, 88 mm) with its top edge just inside the board outline.Open item: the Pico was clamped at the board edge, so if you want more clearance from the top edge I can drop it slightly lower.
I need a power switch and some output LEDs
Thought for 5 sec
I’ll add a low-current front-panel power/enable switch rather than a high-current 12 V path switch, plus output/status LEDs with current-limiting resistors, then verify the schematic changes.
Worked for 1 min 54 sec
Added the power switch and output LEDs.
SW_PWR is a low-current front-panel switch that pulls Pico 3V3_EN to GND to turn logic off, and I added green indicators for BUS_12V and VOUT_19V5 with 4.7kΩ and 8.2kΩ series resistors.Open items:
- These are placed near the top/front-panel area but not routed yet.
- If you intended a true high-current input disconnect instead of a Pico enable switch, that needs a different switch/contactor architecture.
Route controls and verify
Use high-current switch
Route switch and LEDs
Add LED labels
Run design review
Refine this doc
Ask about this doc
Mechanical Layout Constraints — Rackmount 12V Distribution PSU
Status
Draft constraints from user-provided chassis concept and Bellwether connector documentation. Use these values to drive board outline, connector orientation, slot pitch, and airflow planning.
Chassis Envelope
- Rack height: 2U, approximately 89 mm external height.
- Planned depth: approximately 260 mm.
- Nominal width target: 10 inches / 254 mm.
- 3D printed enclosure material: ABS.
- Wall thickness target: approximately 5 mm.
- Internal usable width estimate: 254 mm - 2 × 5 mm = 244 mm.
PSU Placement
- Dell D750E-S1 PSU approximate dimensions:
- Width: 86.5 mm.
- Depth: 196.5 mm.
- Height: 38.5 mm.
- PSU(s) placed in rear corner of enclosure.
- Two PSUs can stack vertically inside 2U for future Rev B HA/failover, but Rev A remains single-PSU electrically.
- Remaining internal width next to one PSU: approximately 244 mm - 86.5 mm = 157.5 mm.
Daughterboard Orientation
- Distribution-board edge connectors run front-to-back.
- Daughterboards plug in at right angle and stand vertically, also running front-to-back.
- Daughterboards require PCB edge fingers for the slot interface; the card-edge contacts are part of the daughterboard PCB copper and must be laid out as edge-connector fingers with bevel/finish requirements, not as a separate connector component on the daughterboard.
- DC barrel output connectors are exposed toward the rear of the chassis.
- Daughterboard component height becomes horizontal slot pitch / width consumption.
- Daughterboard PCB width becomes chassis-height consumption.
- Target daughterboard width / chassis-height usage: about 50 mm, excluding edge-finger engagement and clearance.
PCB Stackup Direction
- Use 4-layer boards for both the distribution board and the 19.5 V / 180 W boost daughterboard.
- Recommended default layer assignment:
- Layer 1 / Top: components, local high-current pours, critical switching loops.
- Layer 2 / Inner 1: solid GND reference plane.
- Layer 3 / Inner 2: power plane / high-current distribution pours where practical.
- Layer 4 / Bottom: secondary routing, low-speed control, additional copper spreading.
- Do not split the main GND reference plane except for clearly justified Kelvin sense routing; prefer a single ground system.
- For the boost daughterboard, keep LM5122 gate-drive/switching loops compact on the top layer and use inner/bottom copper for heat spreading and lower impedance return paths.
Slot Count and Pitch Implications
- Target Rev A: 12 daughterboard connectors if physically feasible.
- Available bay width next to PSU: about 157.5 mm.
- Average slot pitch for 12 slots: 157.5 mm / 12 = 13.1 mm per slot.
- Average slot pitch for 10 slots: 15.8 mm per slot.
- Average slot pitch for 8 slots: 19.7 mm per slot.
Conclusion: 12 slots is probably too tight unless daughterboard components are very low-profile and airflow is ducted carefully. 8–10 slots is more mechanically realistic for high-power boost modules in the available width.
Airflow Requirements
- High-power daughterboards need clear front-to-back airflow channels.
- Avoid placing tall inductors/electrolytics so they block neighboring slots.
- Prefer consistent slot pitch with at least a few millimeters of air gap between maximum-height components.
- Add temperature sensing near the hottest daughterboard regions and at chassis exhaust.
- Consider fan mounting, intake/exhaust path, and PSU airflow direction before final connector placement.
Bellwether 70012 Connector Notes
User supplied Bellwether files:
- Product page: https://www.bellwether-corp.com/en/product/compare_show.aspx?num=1227&detail=4705
- Package Spec: HPSU Conn.-PK-70012-001_A.2.pdf
- Product Specification: HPSU Conn.-PS-70012-001_3.pdf
- 2D / sales drawing: HPSU Conn.-SD-70012-001_B.pdf
Extracted product-spec values from OCR; verify against original PDFs before creating final footprint:
- Series: Bellwether 70012 / 70019 power and signal edge-card connector.
- Pitch: 2.54 mm power and 1.27 mm signal centerlines.
- Power contact current rating: 9 A per pin.
- Signal contact current rating: 1.5 A per pin.
- Power-power voltage rating: 250 VAC RMS / DC.
- Signal-signal voltage rating: 30 VDC.
- Power-signal voltage rating: 400 VAC RMS / DC.
- Operating / storage temperature: -40°C to +105°C.
- Power contact resistance: 0.6 mΩ max, tested at 34 A DC per quad contact.
- Durability: 200 mating cycles.
- Maximum mating force: 81.6 N.
- Minimum unmating force: 14.4 N.
Connector Action Items
- Use the attached 2D/package drawings to create a custom Flux component/footprint for the exact Bellwether 70012-1111 variant.
- Verify exact pin count, keying, orientation, mounting-hole geometry, and PCB cutout/keepout from the drawing manually; OCR did not extract the footprint tables reliably.
- Mechanically align the connector to the Dell PSU shell/guide features, not just the PCB pads.
- For the daughterboard card edge, define final finger pitch, plating/finish, insertion depth, bevel angle, soldermask pullback, keepout, and retention/guide features from the mating ED32BGFBK connector documentation before fabrication.
Status LED
- Add at least one front/rear visible status LED for Rev A.
- Recommended minimum: system status RGB LED or separate POWER / FAULT LED.
- If the enclosure exposes many slots, consider one per-slot fault/enable LED later, but keep Rev A simple unless panel space allows.
Status
Chassis Envelope
PSU Placement
Daughterboard Orientation
PCB Stackup Direction
Slot Count and Pitch Implications
Airflow Requirements
Bellwether 70012 Connector Notes
Connector Action Items
Status LED
