Mr Tagington Technical Documentation

Table of Contents

• System Architecture
• Electronic Specifications
• Power Subsystem
• Onboard Computer
• Data & Communication
• Mechanical Structure
• PCB design & modelling

System Architecture

The Mr Tagington device employs a modular dual-PCB architecture that physically separates power management from data processing functions, enabling optimized performance in challenging underwater environments. This separation allows for specialized design considerations: the power board focuses on robust energy harvesting and regulation, while the main processing board handles high-frequency sensor data acquisition and communication tasks.

Dual-PCB Design

Key Design Features:

• Power PCB: Hydraulic energy harvesting, battery management, dual-voltage regulation
• Main PCB: Sensor processing, behavioral algorithms, data storage, satellite communication
• Dedicated Power Rails: 3.3V for digital, 3.7V for analog components

Electronic Specifications

Microcontroller & Processing

Environmental Sensors

Motion & Orientation Sensors

Communication & Storage

Design Criteria & Implementation

Bus Architecture Rationale

Dedicated Communication Buses:

• I²C1: MS5837 Pressure/Temperature sensor
• I²C2: FDC1004 Capacitive sensor
• I²C3: HMC5883L Magnetometer
• SPI1: ICM-20948 IMU (high-speed data)
• SPI2: GD25Q16 Flash + Iridium module
• UART2: MAX-M10S GPS module

Benefits of Dedicated Buses:

• Eliminates bus contention and arbitration delays
• Enables simultaneous sensor operation
• Simplifies debugging and fault isolation
• Optimizes power consumption per peripheral

Key Design Innovations

1. Intelligent Sensor Activation

Pressure-Triggered GPS Wake-up:

• EXTINT pin (PC5) monitors pressure changes
• GPS activates only during surfacing events
• Eliminates constant GPS power drain underwater

2. Redundant Magnetic Sensing

Dual Magnetometer Configuration:

• Primary: ICM-20948 integrated magnetometer
• Secondary: HMC5883L dedicated sensor
• Provides orientation backup and calibration reference

3. Robust Mechanical Integration

Environmental Protection:

• MS5837 thermally exposed for accurate water temperature
• Capacitive sensors isolated from mechanical stress
• Multiple ground planes for RF performance
• Pressure-compensated enclosure design

Pin Assignment & Connectivity

Microcontroller Interface Mapping

Performance Characteristics

Data Acquisition Capabilities

Continuous Monitoring:

• IMU sampling: 100-200 Hz for biomechanical analysis
• Environmental sensors: 1-10 Hz based on state machine
• Magnetic field: 10-50 Hz for orientation tracking

Storage Capacity:

• 2MB flash storage ≈ 2-4 weeks of continuous data
• Adaptive compression based on behavioral patterns
• FIFO management for long-term deployments

Power Subsystem

Energy Harvesting & Management

The autonomous power system converts hydraulic energy to stable DC power:

Operational Modes:

• Active Generation: Water flow → Turbine → Battery charging + load power
• Battery-Only: Battery → Regulators → Load power (no-flow conditions)
• Combined: Turbine + Battery → Optimized power distribution

Key Components:

• Pelton Turbine: Hydraulic-to-electrical conversion
• CJMCU-2557: Integrated MPPT + battery management
• Dual Regulators: 3.3V (digital) and 3.7V (analog) rails

Onboard Computer

The onboard computer implements an intelligent state management system that dynamically optimizes the balance between data collection and power conservation through four distinct operational states. In Hibernation mode, the system maintains minimal power consumption by activating only the IMU for basic motion monitoring while tracking battery levels and time. This state serves as the default operational mode, consuming less than 500μA while waiting for activation triggers. When battery levels drop below 3.3V, the system transitions to Battery Saving mode, performing a complete shutdown of all non-essential systems to conserve energy until sufficient power is recovered. Activation events—either time-based (1800-second intervals) or behavior-triggered (hunting pattern detection)—prompt transition to Sensing state, where all environmental, motion, and position sensors are activated for comprehensive data collection, processing, and local storage. Finally, when conditions permit (adequate battery, surface proximity, and satellite availability), the system enters Transmission state, activating the satellite communication module and implementing a robust three-attempt retry protocol to ensure successful data delivery before returning to hibernation. This state machine architecture enables extended autonomous operation by ensuring that power-intensive components are activated only when necessary and for minimal durations.

State Management System

The control system implements an intelligent state machine for optimal power and data management:

Operational States:

• Hibernation: IMU-only monitoring, ultra-low power
• Battery Saving: Complete shutdown, emergency conservation
• Sensing: Full sensor activation and data collection
• Transmission: Satellite communication with retry logic

Data & Communication

The data and communication system integrates a comprehensive sensor suite—including pressure, temperature, motion, magnetic field, and GPS sensors—that captures both environmental conditions and behavioral metrics. Raw sensor data is processed into calculated parameters such as depth, speed, and hunting probability, then encoded into efficient 64-character plain text strings for transmission. The system employs adaptive transmission modes, scaling from full datasets during optimal conditions to essential-only data during power conservation.

Sensor Suite & Processing

Calculated Behavioral Metrics:

• Depth: (pressure - 1013.25) / 100 meters
• Speed: Position delta over time (m/s)
• Hunting Score: Multi-parameter movement analysis
• Activity Index: Acceleration magnitude and patterns

Data Transmission Protocol

The following pipeline is designed for data transmission:

Fixed-Width Encoding (64-character):

TTTTSSSSPPPPBBBBGGGGLLLLAAAAIIIIMMMMDDDDHHHHXXXXYYYYZZZZRRRRCCCC

Data Structure:

• TTTT: Time (HHMM), SSSS: Seconds, PPPP: Pressure (mbar×10)
• BBBB: Battery (mV), GGGG/LLLL: Latitude/Longitude (degrees×1000)
• AAAA: Acceleration (g×1000), CCCC: Checksum

Adaptive Transmission Modes:

• Normal (64 chars): Full dataset when surfacing + good power
• Low Power (32 chars): Essential data during conservation
• Emergency (16 chars): Critical status during faults

Design Innovations

Bus Architecture:

• Dedicated I²C/SPI buses per sensor eliminate contention
• Simultaneous operation and simplified debugging
• Optimized power consumption per peripheral

Intelligent Activation:

• Pressure-triggered GPS wake-up (EXTINT pin)
• Dual magnetometer configuration for redundancy
• Event-driven sensor activation based on behavioral triggers

Environmental Robustness:

• IP68-rated pressure-compensated enclosure
• Thermally exposed sensors for accurate measurements
• Corrosion-resistant materials for marine deployment

This integrated system enables long-term autonomous monitoring of shark behavior through optimized power management, comprehensive sensing, and reliable satellite communication.

Mechanical Design

Structural Components

• Hull: Base of the FDM-3D printed structural core. Manufactured in PLA with 100% infill for structural integrity and water-proofed with a coat of Vinyl Ester Resin. Holds the electrical components on the inside and the attatchment to the torsional spring on the outside.
  
• Cover: Cover of the FDM-3D printed structural core, complimentary to teh Hull with lip interlocking. Manufactured in PLA with 100% infill for structural integrity and water-proofed with a coat of Vinyl Ester Resin. Holds the snesors in contact to the outside and both the housing and rotational seal for the pelton turbine axle.
  
• Pad Holds: FDM-3D printed supports for the grip pads that non-invasively attatch to the sharks dorsal fin. Manufactured in PLA with 100% infill and water-proofed with a coat of Vinyl Ester Resin, these recieve the torsional spring and attatch to the silicone pads through an cyanoacrylate adhesive.
  
• Pelton Turbine: FDM-3D printed Pelton turbina compatible with dc motor axle. Manufactured in PLA with 100% infill and and water-proofed with a coat of Vinyl Ester Resin, this component transforms the water flow along the surface of the tag into energy for the tag through a DC motor and the power system.
  
• GFRP Skin: 2mm thick skin of Glass Fiber Reinforced Polymer applied over the hole structured and binded to the nucleus through Vinyl Ester Resin. Manufactured from glass fiber symmetric plain weave and a Vinyl Ester Resin matrix, it handles the direct structural load due to external pressure and is supported angainst bukling by the PLA 3D printed nucleus.

Design Criteria

Marine Environment Considerations

• Corrosion Resistance: Saltwater surface flow exposure is prone to corrosively degrade materials, this reduces ultimate product life and could cause loss of the electrical components due to structural failure as a result of the corrosion of the structure
• Pressure Tolerance: Water depth requires the exposure to equivalent external pressures for sealed bodies (such as our tag), approximations dictate 1 bar of pressure pero 10 meters of depth, however for depths of around 300 meters (current working limits of this prototype) the tag must be able to withstand approximately 30 bar or 3 MPa. Applying a safety factor of 1.25.
• Biofouling Mitigation: Crevice presence in bodies exposed to seawater often experience marine growth, smooth surfaces mitigates this.

Operational Requirements

• Attachment Security: Tag attatchment must adhere to non-invasive methods and avoid both securing through penetration (fin or skin) and excessive pressure on the animal's limbs.
• Hydrodynamic Efficiency: The tag must maintain a minimal drag coefficient and avoid impeding the animal's movement as much as possible.
• Durability: The tag must be able to withstand deployment and functionality for extended periods of time, managing dtructural durability and energy generation.
• Manufacturing Scalability: The tag must be easy to manufacture via 3D printing prototyping and scalable to mission requirements.
• Structual Stability: The tag must be able to withstand structurally the calculated pressure of 3 MPa with a safety factor of 1.25, resulting in a design pressure of 3.77 MPa.

Design Constraints

• Size Limitations: The tag must allow space for all the electronic components while maintaining the smalles dimensions possible in order to lessen the impact on the animal's mobility.
• Hydrodynamic Interaction: The hydrodynamic profile of the tag must minimize drag while allowing for power generation through a pelton turbine.
• Manufacturing Feasibility: The use of 3D printing in the tag's manufacturing must allow foir rapid prototyping and adaptability to changing requirements.
• Regulatory Compliance: The tag must minimize of outright end any potential negative impact on animal welfare and enviromental safety, this can be done through non-invasive approaches to tag attatchment and the use of non polutting materials.

Mechanical Design - Enclosure Structure

Structural Approach with Reinforcement

• Structural Concept: The enclosure is composed of an FDM 3D-printed PLA nucleus with a 3 mm wall thickness, impregnated and sealed with a vinyl ester resin to eliminate inter-layer porosity and improve compressive strength.
• Reinforcement Layer: A 2 mm Glass Fiber Reinforced Polymer (GFRP) skin is applied over the impregnated surface using vacuum-assisted layup. The composite layup follows a symmetric [±45/0/0/±45] stacking sequence of plain weave glass fiber, prioritizing circumferential stiffness for external pressure loads.
• Material Rationale: GFRP was selected instead of CFRP to ensure magnetic transparency for the onboard magnetometer and to prevent conductive interference.
• Interfacial Bonding: The PLA–GFRP interface is bonded using the same vinyl ester resin matrix, providing continuous shear load transfer and improved delamination resistance.
• Sealing Method: All joints use static O-ring seals—two circular (18 mm diameter) and one square (3.9 × 4.9 mm), these are made from EPDM/Viton (75–90A) for marine-grade sealing.
• Surface Treatment: A smooth resin finish mitigates marine biofouling and facilitates laminar boundary flow across the hull surface.

Aerodynamic (Hydrodynamic) Profile Design

• Streamlined Geometry: The tag’s cross-section combines a semicircular leading edge external to de clamp on the animal's dorsal fin and a rectangular base section, yielding an approximate frontal area of 0.00256 m² (25.6 cm²). The external GFRP coating and rounded transitions reduce local flow separation.
  
• Energy Generation Integration: The body includes an aperture for a Pelton turbine on the lateral section. The opening is filleted and flow-aligned to minimize disturbance and separation bubbles, allowing the turbine to harness part of the passing flow for onboard energy generation through a 9V DC motor.
• Flow Optimization: The combined hull and cover form a smooth, continuous hydrodynamic contour which fades of to an end tail. The addition of the turbine increases the total drag coefficient to an estimated Cd ≈ 0.6, accounting for flow interference, while maintaining overall directional stability.

Pressure Design Calculations

Hydrostatic external pressure at 300 m depth is estimated using the standard seawater relation:

$$p = \rho g h$$

where:

• $\rho = 1025\ \mathrm{kg/m^3}$ (seawater density)
• $g = 9.81\ \mathrm{m/s^2}$ (gravitational acceleration)
• $h = 300\ \mathrm{m}$ (depth)

$$p = 1025 \times 9.81 \times 300 = 3{,}016{,}575\ \mathrm{Pa} \approx 3.02\ \mathrm{MPa}$$

Applying a safety factor of 1.25:

$$p_\text{design} = 1.25 \times 3.02\ \mathrm{MPa} = 3.77\ \mathrm{MPa}$$

Thus, the enclosure must resist a design pressure of 3.77 MPa (≈37.7 bar) without yielding or delamination.
The GFRP skin handles the primary compressive load, while the PLA core prevents buckling through internal support.
The resulting 5 mm composite wall (3 mm core + 2 mm GFRP) provides an ample margin against both collapse and wrinkling failure.

3D Printing Development

• Process Parameters: Printed using 0.2 mm nozzle, 0.12–0.16 mm layer height, and 100% infill for maximum density.
• Tolerances: Nominal ±0.2 mm, with post-processing (fine sanding and resin impregnation) to achieve sealing-grade surfaces for O-rings.
• Impregnation Phase: The printed hull is first coated in low-viscosity vinyl ester resin under vacuum to seal print lines before GFRP layup.
• Layup Phase: The 2 mm GFRP skin is applied using vacuum bagging, ensuring <2% void content and high fiber–resin adhesion.
• Final Assembly: Mating surfaces (hull–cover interface and sensor port) are machined or sanded to fit standard marine seal grooves per Parker specifications.

Mechanical Design - Attachment System

Non-Invasive Coupling Approach

[Clamp mechanism design philosophy, padding materials, and animal safety features will be described]

Torsional Spring Mechanism

• Non-Invasive Retention: Torsional spring avoids resorting to invasive attachment methods
• Controlled Pressure: Silicon grip pads ensure low crushing pressure prevents detachment by drag
• Animal Safety: Designed to guarantee no unnecessary harm to sharks while maintaining secure attachment

Spring Calculations and Grip Pad Sizing

[Mechanical spring design, force calculations, contact pressure distribution, and pad dimensioning will be detailed]

Mechanical Design - Pelton Turbine

Turbine Configuration

[Turbine blade design, flow optimization, and energy conversion efficiency analysis will be presented]

PCB Design & Modeling

The electronic systems were implemented through comprehensive PCB design and 3D modeling, following the modular dual-PCB architecture described in the system specifications. Both boards were fully designed, routed, and validated virtually, with detailed 3D models created to verify mechanical integration and environmental compatibility.

Main Processing PCB Design

The main board design integrates the complete sensor suite, processing core, and communication systems with emphasis on signal integrity and EMI mitigation in the virtual environment.

Schematic Design

Comprehensive schematic showing microcontroller implementation and sensor interfaces

3D Model

3D model illustrating component clearance and mechanical mounting points

Power PCB

The power board design integrates the complete energy harvesting system, MPPT and BMS.

Schematic Design

Comprehensive schematic showingpower subsystem

3D Model

3D model illustrating component clearance and mechanical mounting points

Both PCB designs underwent extensive design rule checking, signal integrity simulation, and 3D mechanical validation to ensure the theoretical design meets all electrical and mechanical requirements for marine environment operation. The virtual prototyping approach allowed for comprehensive optimization of the system architecture before physical implementation.