Submerged Unit

The submerged unit lives inside the crab pot, handling all vision, classification, and door control operations.

Core Hardware

Microcontroller: ESP32-CAM (Ai-Thinker module)

• Espressif ESP32-S (dual-core 240MHz, 520KB SRAM)
• OV2640 camera (2MP, 1600×1200 max)
• MicroSD card slot (used for model storage and image logging)
• 4MB flash + 4MB PSRAM

Vision Pipeline

1. Trigger: Motion detected via frame differencing (camera captures at 1 fps idle)
2. Capture: Full-resolution frame with IR illumination
3. Classify: TFLite Micro inference (quantized MobileNet v2, INT8)
   • Input: 96×96 RGB (downscaled from capture)
   • Output: species class + confidence score
   • Inference time: ~300ms on ESP32
4. Measure: Size estimation from known camera-to-subject distance
5. Decide: Compare species + size against keeper thresholds
6. Act: Lock door (keeper) or unlock door (release bycatch)
7. Report: Send CATCH_EVENT up the tether to the smart buoy

IR Illumination

• Wavelength: 850nm (invisible to crabs, effective underwater)
• Array: 3–5 IR LEDs, forward-facing
• Power: Pulsed only during capture (100ms pulse, ~500mA peak draw)
• Range: Effective at 30–50cm (typical pot interior dimensions)

Door Mechanism

• Actuator: MG90S metal gear micro servo (stall torque 1.8kg·cm)
• Mechanism: Cam-locked sliding bolt
• States: Locked (retain catch), Unlocked (release)
• Feedback: Position sensor confirms door state
• Failsafe: Door defaults to unlocked on power loss (releases all catch rather than trapping indefinitely)

Tether Interface

The submerged unit connects to the smart buoy via a 4-conductor shielded cable:

Wire	Function
Red	V+ (24V from buoy boost converter)
Black	GND (power return)
Yellow	UART TX (submerged -> buoy)
White	UART RX (buoy -> submerged)

The submerged unit includes an MP1584 buck converter stepping 24V tether power down to 5V, plus a 3.3V LDO for the ESP32. This PoE approach reduces voltage drop over 10-20m cable lengths from ~0.85V (at 5V/500mA) to ~0.18V (at 24V/104mA), providing clean power at any practical tether length.

• Baud rate: 115200
• Protocol: SLIP-framed packets (same format as LoRa packets, minus encryption)
• Cable length: 10–20m depending on deployment depth

Power Budget

State	Current Draw	Duration
Deep sleep	10µA	Most of the time
Idle monitoring (1 fps)	80mA	~200ms per second
IR capture + inference	350mA	~500ms per event
Servo actuation	500mA	~1s per event

All power is supplied as 24V PoE via tether, stepped down locally. The submerged unit has no local battery.