System Requirements Specification: Bunk & Desk Node

Project: bunk-and-desk-node
Company / Entity: Nomad (open-circuit-nomad)
Revision: v0.1

1. Use Cases & Functional Requirements (`REQ-FUNC`)

ID	Use Case / Requirement	Acceptance Criteria	Verification Method	Linked Artifact
REQ-FUNC-01	Unified Dual-Mode Hardware: One common PCB supports both bunk-bed stair lighting and study desk automation.	Hardware mode selection via 2-pin jumper (`J_MODE` closed = Stair, open = Desk).	Bench test in both modes	`hardware/sheet_mcu_core.kicad_sch`
REQ-FUNC-02	Night-Time Stair Guidance: Smoothly illuminate bunk stairs when a child approaches at night.	Drive 5V WS2812B LED strip via 3.3V-to-5V logic level shifter; fade on/off over 1.5s.	Oscilloscope & LED strip test	`hardware/sheet_outputs.kicad_sch`
REQ-FUNC-03	Automatic Motion Trigger: Detect movement near bunk stairs without false triggers.	Support 3.3V PIR/mmWave sensor (`J_PIR`) with hardware RC noise filter.	Motion trigger latency test	`hardware/sheet_sensors.kicad_sch`
REQ-FUNC-04	Study Desk Light & Break Chime: Provide desk task lighting, ambient monitoring, and 45-min study break alerts.	Support external push button (`J_BTN`), piezo buzzer, and I2C sensors (`J_I2C`).	Functional button, buzzer & I2C scan	`hardware/sheet_sensors.kicad_sch`
REQ-FUNC-05	Home Assistant & Bedtime Cue: Allow wireless control and scheduled evening amber wind-down lighting.	2.4 GHz Wi-Fi connectivity via ESP32 module with OTA firmware updates.	Home Assistant integration test	`firmware/`

ID	Requirement	Acceptance Criteria	Verification Method	Linked Artifact
REQ-SAFE-01	Direct Mains Operation: Operate directly from 230V AC 50Hz bedroom wiring without external wall adapters.	Integrated isolated AC-DC module (`HLK-PM01` / `HLK-5M05`) outputting 5V DC + 3.3V LDO.	Load regulation & thermal check	`hardware/sheet_power_hv.kicad_sch`
REQ-SAFE-02	Primary Overcurrent & Surge Protection: Protect against short circuits and Indian grid voltage spikes.	1A/250V slow-blow PCB fuse (`F1`) + `10D471K` MOV (`RV1`) on AC input.	Schematic ERC & BOM inspection	`hardware/sheet_power_hv.kicad_sch`
REQ-SAFE-03	Reinforced Primary-to-Secondary Isolation: Prevent electric shock hazard between 230V AC and low-voltage touch circuits.	Minimum `>= 5.0 mm` creepage/clearance gap + `1.5 mm` milled isolation slot (`Edge.Cuts`).	KiCad DRC (`Mains_HV` custom rule)	`hardware/bunk-and-desk-node.kicad_pcb`
REQ-SAFE-04	Child-Safe Enclosure: Prevent accidental finger contact with live mains terminals.	Fully enclosed 3D-printed housing secured with M3 screws and cable strain relief.	Mechanical fit & STEP inspection	`enclosure/bunk-and-desk-node.step`

ID	Requirement	Acceptance Criteria	Verification Method	Linked Artifact
REQ-EMC-01	Conducted EMI Suppression: Prevent switching supply noise from radiating onto house AC wiring.	`0.1 uF` X2 safety capacitor + `10 mH` common-mode choke before AC-DC module.	Schematic & layout review	`hardware/sheet_power_hv.kicad_sch`
REQ-EMC-02	Low-Impedance Ground Return: Minimize radiated emissions on the low-voltage digital section.	Unbroken `B.Cu` ground plane (`GND`) under secondary side with perimeter stitching vias.	PCB layout inspection	`hardware/bunk-and-desk-node.kicad_pcb`
REQ-EMC-03	Local Power Decoupling & Data Damping: Prevent high-frequency ringing on MCU and LED lines.	`100 nF + 10 uF` ceramic caps within 3 mm of VDD pins; `330 ohm` series resistor on LED data.	PCB layout & waveform check	`hardware/sheet_mcu_core.kicad_sch`