## 3 Materials and Methods
### Blackbox Devices' Concept and Development  
The Blackbox devices within the Monit4 Healthy system follow a modular sensor-fusion framework, integrating low-power microcontrollers (ESP32, STM32) for energy-efficient processing. Edge computing optimizes local data analysis, reducing bandwidth usage and improving response times. To ensure data security, encryption protocols and secure communication channels are implemented, aligning with regulatory standards. For precise integration and manufacturability, Autodesk Fusion 360 [57; 58] was chosen due to its all-in-one 3D modeling, parametric design, simulation, and real-time collaboration capabilities. This cloud-based platform enabled efficient transitions from concept to production. Development began with manual measurements and hand sketches, later digitized in Autodesk Fusion 360 to ensure accuracy in geometric constraints, tolerances, and material properties. This structured workflow, applied to all Blackbox devices, minimized design inconsistencies and optimized fabrication processes. The design process included defining functional specifications, developing 2D sketches, and transitioning to parametric 3D models with manufacturability optimizations (e.g., fileting, draft angles, sensor housings). High-fidelity simulations (FEA, thermal analysis) ensured structural robustness and hardware integration. Iterative refinements addressed discrepancies, optimizing material use and production feasibility. Final designs were formalized in STL format for seamless fabrication, ensuring scalability and real-world deployment. The combination of manual sketching, digital modeling, and iterative validation enhanced reliability and performance, as illustrated in subsequent figures. The finalized prototype of the EMG Blackbox is illustrated in Figure 2, showcasing its compact design, component layout, and integration of core hardware elements such as the Arduino Mega, NodeMCU ESP8266, and Li-Po battery. This configuration supports real-time data acquisition, wireless transmission, and portable biomedical monitoring capabilities. Figure 2 illustrates the 3D extruded model derived from a 2D sketch in Autodesk Fusion 360. The enclosure is designed for housing electronic or medical sensors and features:  
* Corner mounting holes for secure fastening. * Side cutout ventilation and USB-C connectivity. * A circular opening on the angled face, for sensor integration. * _Geometric features_: Rectangular base with an inclined edge for structural compatibility; the chamfered surface enhances ergonomics and esthetics. * _Mounting points_: Four precisely positioned screw holes ensure secure fastening and stability. * _Recessed cavity_: Central section accommodates a display, sensor, or functional interface. * _Manufacturing considerations_: Optimized for 3D printing, balancing material efficiency and structural integrity. Figure 3 illustrates the fully developed 3D model of the Medical Blackbox, designed in Autodesk Fusion 360 for the Monit4 Healthy system. The enclosure integrates structural, functional, and ergonomic optimizations for housing medical-grade electronics and sensors. _Technical and functional design considerations_  
* _Structural optimization_: Rigid, lightweight construction ensuring mechanical protection and spatial efficiency. * _Ventilation system_: Engineered side slots for effective heat dissipation and sensor accuracy. Figure 3: The final model of the Medical Blackbox. The finalized prototype of the Medical Blackbox device used in the Monit4 Healthy system. The image shows the internal layout of key components, including the Arduino Mega microcontroller, signal conditioning circuits, NodeMCU ESP8266 for wireless communication, and the Li-Po battery pack. The device integrates multiple biomedical sensors (ECG, EMG, photoplethysmography (PPG), GSR) for real-time physiological data acquisition and processing.