## 2 Materials and Methods  
The basic idea behind this work is to design a ubiquitous, cost effective, convenient, and easy to use prototype as an all-in-one approach to support people identifying their health status as well as to predict and prevent adverse events. Hence, we design our prototype according to four principle pillars. Comprehensive, Convenience, Continuous, and Cost-effective (4C) are taken into consideration as the principles. We provide the strict definitions for each component of this term as: Comprehensive--indicates multi-parameters monitoring and the combination of the effective areas in personalized healthcare [52]. Convenience--discusses and addresses the mode of wearability including the size and weight of the prototype [53]. Continuous--refers to prolonged monitoring which is a serious concern in wearable monitoring [40]. Cost-effective--targets the final cost of the prototype which is a concern. The personalized healthcare becomes more and more important and popular and wearables as the main means are receiving more attention. Thus to encourage the users to use them, these devices must be affordable [54]. The fundamental concept is to construct the hardware in \(z\)-direction (3D-MPL approach). Each task and parameter is implemented through mounting the sensor/actuator (or number of sensors from the same domain) on the same physical layer. These layers are located one on top of another through a board-to-board connector. Therefore, \((x,y)\)-plane remains unchanged (in contrast to other prototypes/products) but the height of the prototype is expanded slightly--but still appropriate for a wrist-worn device. The connectors provide signaling between layers and the main platform. The measurements are displayed on the prototype and transmitted to the smartphone in real-time. The smartphone is used as mid-term storage and gateway to a server for permanent storage and data analysis. We support the prototype configuration in BLE connected mode by sensor activation/deactivation. Thus, we develop a smartphone application for bidirectional data communication between the prototype and the smartphone. User activates the intended sensor by pressing the respective button on the application and the data are measured, processed, and transmitted to the smartphone. Upon the pressing the button, a string including the sensor's name is transmitted from the smartphone which is handled on the prototype. This string is used as a condition for sensor activation. We apply centralized data processing and a strict data protection policy. All sensors are connected and communicate to microcontroller via Inter-Integrated Circuit (IIC), Analogue to Digital Converter (ADC), or a combination of both interfaces. Behavioral sensors, air condition sensors, and skin temperature are supported with IIC, PPG sensor, loudness, and UV are supported with ADC, and gas sensors are taking the combination of both for initialization and configuration. The data from all sensors are pre-processed and processed on the prototype prior than transmission to the smartphone. This includes filtering the noise, pattern creation, and data conversion to the target data unit. All data are either transmitted directly via BLE or stored in the integrated memory, if BLE connection temporarily is unavailable (see Figure 1 and Algorithm 1). ```
Input: Commands to activate the sensors, sampling rates, i: buffering counter Result: Measurements, data transmission, storage, and display
1 Procedure: General Strategy of Operation; Begin (Device is powered on): Hardware & Software check; Communication interfaces initialization: IIC, ADC ;// IIC: 100 kHz, ADC: 10-bit resolution Sensors initialization ;// Not necessarily configured nor started Internal memory initialization; Display initialization; BLE status check; if(\(BLE==Connected\))then
2\(Default1:sampling\ rate=50\ Hz\); Physical activity sensors are on operation \(\rightarrow\) measurement \(\rightarrow\) F1 is transmitted; \(Default2:sampling\ rate=1\ Hz\); Air humidity, pressure, and temp.