## 2 Materials and Methods
### Equipment of Experimental Research
Data in the slave microcontrollers were not processed. This data set was transmitted to the master microcontroller through the local ad hoc Wi-Fi network. Each slave device was powered by a 3.6 V Li-Ion battery (Howell Energy Co., Ltd., Shenzhen, China). The supply voltage level was kept constant using an internal microcontroller stabilizer. Direct raw data from the sensor arrays needed mathematical processing. In this case, the best solution was to normalize the data placed in each slave microcontroller, where the analog signal from the sensors was transformed into a digital one using internal ADC. The median filter with a median width of three samples was implemented for the conditioning of the sensor data values. Therefore, high peaks and nonessential data distortions were filtered out. Implementing advanced filters was unreasonable due to the relatively low frequency of the signal. The master ESP32 microcontroller, which was connected to cloud storage via another network, served as the central network unit. Its primary function is to serve as the main data-collection point to collect information transmitted from the separate microcontrollers. However, it can only reliably receive data at intervals of approximately 26 ms. While this rate meets the requirements for the data acquisition and transmission process, it does impose a limitation on the overall speed of the data-acquisition system. In addition to cloud storage, there is an alternative option of using local storage on a connected PC. Such an option is helpful in the case of a short series of measurements. Electronic control measurements of the system latency were performed using a Rigol DS1052E oscilloscope (RIGOL Technologies EU GmbH., Gilching, Germany). The sensor data from both feet were streamed to the microcontrollers through the network interface, which is a communication protocol designed to handle data transfer between different components on the same board. Synchronization algorithms were used to solve the problem of proper synchronization of data collected from different sources (Figure 3). These algorithms help identify and adjust delays between data to achieve a sufficient level of data synchronization. The microcontrollers, in turn, transmit data wirelessly to the main ESP32 using Wi-Fi protocols. In this case, wireless communication operates at a frequency of 2.4 GHz. The main ESP32 is connected to the cloud storage, serving as the central data repository and analysis hub. The network structural operation algorithm provided in Figure 1 presents the network members within the local wireless network with two ESP32 slave microcontrollers and the master ESP32 microcontroller acting as an access point (AP). Each slave microcontroller (ESP32-1 and ESP32-2) acquires a pressure-sensor array, gyroscope, and accelerometer sensors. The master microprocessor controls a wireless Wi-Fi network, stores data internally, and transmits it to a PC or cloud, depending upon the request. This structure allowed us to perform the desired data-flow control using network capabilities. The synchronization method proposed for data collection involves slave boards and a master board operating synchronously. Slave boards remain idle (do not collect or send any data) until a command message is received from the master board instructing it to start acquiring sensor readings. A command message acts as a synchronizing message that is sent once per each data-acquisition cycle, which spans from timestamp generation to data export to cloud storage. Due to a comprehensive synchronization of the entire system, the master board is authorized to create a timestamp resembling the state of the overall system. Under the generated timestamp, the collected data are exported to cloud storage. As the system gets synchronized each time command messages are sent out, the synchronization quality does not depend upon the quality of a single synchronization signal. On the other hand, the overall synchronization quality declines as the quality of the wireless connection declines.