Submerged Unit
The submerged unit lives inside the crab pot, handling all vision, detection, size measurement, and door control operations.
Core Hardware
Section titled “Core Hardware”Compute Module: Waveshare ESP32-P4-NANO
- Espressif ESP32-P4 (dual RISC-V HP cores, 400MHz)
- 768KB SRAM + 32MB OPI PSRAM (200MHz)
- MicroSD card slot (model storage, image logging, calibration data)
- USB-C programming interface
- ESP32-C6 companion chip (bench testing and diagnostics only — not used in deployment)
Camera: OV5647 NoIR (MIPI CSI)
- 5MP (2592×1944), no IR-cut filter
- MIPI CSI-2 (2-lane) interface
- Hardware ISP: debayering, white balance, noise reduction, lens distortion correction
- IR-sensitive natively (NoIR variant)
Vision Pipeline
Section titled “Vision Pipeline”- Trigger: LP-Core detects motion via frame differencing (main CPU sleeps until woken)
- Capture: MIPI CSI frame with IR illumination, processed through hardware ISP
- Detect: ESP-DL YOLO inference (320×320 input, INT8 quantized)
- Output: bounding boxes + class scores + confidence
- Inference time: TBD (estimated <200ms based on esp-detection benchmarks)
- Measure: Pinhole camera model converts bounding box pixels to physical size (mm)
- Uses camera calibration data + known pot floor distance
- Accuracy target: ±5–10mm at typical pot dimensions
- Decide: Compare species + measured size against regulatory minimums
- Act: Lock door (keeper) or unlock door (release bycatch)
- Report: Send
CATCH_EVENTup the tether to the smart buoy
IR Illumination
Section titled “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
Section titled “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
Section titled “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-P4. 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
Section titled “Power Budget”| State | Current Draw | Duration |
|---|---|---|
| Deep sleep | TBD (datasheet v0.5) | Most of the time |
| Idle monitoring (LP-Core, 1 fps) | ~5–10mA (estimated) | ~200ms per second |
| Active inference | ~400–500mA (estimated) | ~300ms 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.