Fire Cabinet Monitoring Device Design
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Cabinet Eye Redesign Brief
Why the current board is wrong
The current project is still an ESP32 environmental sensor board with a large default 160 mm x 100 mm layout. It does not match the revised product direction:
- not Raspberry Pi Zero W based
- no camera-ready carrier layout
- no battery charging path
- no NFC reader area on the underside
- no reed-switch-oriented edge I/O concept
- physically much larger and less intuitive than the desired product
This should be treated as a redesign, not an incremental cleanup.
Revised product architecture
Core approach
Use the PCB as a thin carrier/backplane for a Raspberry Pi Zero W.
The Pi should be able to be placed directly onto the carrier PCB using the 2x20 GPIO hole pattern with low-profile male pins soldered into the carrier board. The user can then:
- place the Pi onto the board
- plug in the camera flex
- plug in the battery
- connect the reed switch
- charge via USB-C
This gives a simpler and more intuitive assembly flow.
Recommended functional blocks
1) Pi Zero W mounting block
- 2x20 low-profile through-hole header pattern
- Pi outline and keepout shown in layout
- Keep Pi antenna end clear of metal and large copper features
- Avoid tall components under the Pi except where intentionally cleared
2) Battery + USB-C charging block
- USB-C 5 V sink input
- single-cell Li-ion/LiPo charger
- power-path or load-sharing so the unit can run while charging
- battery connector positioned for easy internal cable routing
- battery protection either in cell pack or on-board depending battery choice
3) 5 V / Pi power delivery block
- clean 5 V rail to the Pi from USB/load-share path or boost path if needed
- bulk capacitance near Pi power entry
- reverse/current protection sized from actual Pi + camera + NFC + LED + accessory load budget
4) Camera block
- preserve a straight flex-cable corridor from Pi camera connector to lens location
- no tall parts in the cable bend path
- front alignment corridor must be treated as a mechanical feature, not leftover space
5) Reed switch block
- 2-pin connector near the edge closest to the cabinet wire entry
- ESD/filtering and pull-up/pull-down strategy
- input routed as a low-speed external cable interface
6) NFC block on bottom side
- bottom-mounted NFC antenna/reader region
- keep copper and ground plane appropriately cleared beneath/around the antenna region per selected reader/antenna guidance
- avoid batteries, screws, and Pi shielding directly over the antenna zone
- place reader IC close to antenna feed but keep the antenna area itself clean
7) Status / service block
- small front-edge LED aligned to the enclosure indicator opening
- optional debug/test pads
Slim-board layout direction
Placement strategy
- Make the PCB only slightly larger than the Pi footprint.
- Add a narrow extension zone for USB-C, battery connector, and reed-switch connector.
- Put the NFC reader/antenna on the bottom side toward the outside-facing surface.
- Keep the Pi on the top side as the dominant mass.
- Keep battery low and close to the center to reduce inertia if the unit is knocked loose.
Geometry direction
Target a narrow rectangular board, roughly Pi-sized plus one connector wing. The design should feel like a dedicated appliance carrier, not a generic dev board.
Intuitive connector arrangement
- USB-C on one accessible edge
- battery JST nearby but tucked inward
- reed switch connector on the side facing cabinet wiring
- LED on front edge
- camera corridor straight to the lens opening
Important design constraints
- The Pi Zero W itself is larger and heavier than a small MCU board, so the carrier must minimize extra board area and tall parts.
- NFC performance will suffer if the antenna sits directly behind a battery or large ground plane.
- The Pi Zero W is a 5 V system; battery operation likely requires a proper power-path and possibly a regulated 5 V rail depending architecture.
- USB-C charging requires a real charger/load-sharing strategy, not just a battery connector.
Recommended next execution plan
- Remove the current ESP32-centric architecture from the schematic.
- Build a new Pi Zero W carrier schematic around:
- USB-C power/charging
- battery input
- Pi header interface
- reed switch input
- status LED
- NFC reader interface
- Resize the PCB to a compact Pi-centric rectangle.
- Place by mechanical priority first:
- USB-C edge
- Pi footprint
- camera corridor
- battery connector
- reed switch connector
- bottom NFC zone
- Review placement before any routing.
Open items before detailed schematic capture
- exact battery type and connector preference
- selected Pi camera version / lens position
- desired NFC mode (simple tag read, phone tap config, etc.)
- whether the system must operate while charging and while battery is disconnected
- enclosure maximum thickness and mounting-hole/tabs positions
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