## 3 Experimental Results
### Measurements of Mat Pressure Sensor
#### 3.1.4 Fourth Experimental Test  
In the last test experiment, the electrical properties of the mat sensors were analyzed using the Arduino embedded system and the force gauge FB200 200 N (20 kg) 0.05 N (Figure 5b). In order to acquire the electrical signals from the pressure sensor mat, the interface between the measuring mat pressure, electronic components, and circuits was developed. The active mat sensor cells are arranged in columns and rows connected to the output of the shift register, which adds I/O pins to the Arduino system. The SN74 HC595 device contains an 8-bit, serial-in, parallel-out shift register that feeds an 8-bit D-type storage register. The shift register has a direct overriding clear input, serial input, and serial outputs for cascading. When the output-enabled input is high, the outputs are in the high-impedance state. The diodes were connected to SN74 HC595 outputs to block the  
Figure 11: Resistance in the function of the force applied on Velostat pressure sensing mat n.1 for different points. Figure 10: Resistance in the function of the force applied on the Velostat pressure sensing mat n.2 for different points. possibility of the returning voltage from the mat to the system switching to the next levels. The Multiplexer CD4051D was used to read the resistance values. The SN74 HC595 device controls the response signal and switches on one active column of the sensitive mat. The Multiplexer CD4051D controls the signal response of the mat and selects the active row of the mat connected to ADC and provides the reading (Figure 12a). Its operation resembles a normally open switch that is activated by specifying the appropriate binary value. The signal from the mat is amplified by an operational amplifier. The op-amp is connected as well to the Arduino board (Figure 12b). The purpose of the code-program in Arduino is to control the shift register and the multiplexer for retrieving serial data input from the mat. The first part of the software program provides the changing of the time between the data samples, expressed in milliseconds, and the input/output pins on the microcontroller, for which the digital states can be read and the values assigned and changed. The program code (Supplementary Materials) can provide continuous measurements and establish serial communication with LabVIEW-Arduino using UART to transfer continuous stream data. The variables indicate the physical position of the pins; the time interval (minimum jump time is 50 ms) and the size of the matrix represent the mat expressed in rows and columns. In particular, the analog pin is used to read data downloaded from the mat, the digital pin is used to control the multiplexer, and the SRCLK shift register clock pin is changed (set to 1-high 0-low) according to the microcontroller connection and information transfer. The following statements and declarations are executed in the program code (Supplementary Materials):  
* number of rows and columns measurement
* declaration of pin settings on the shift register, in case of a changing number of columns
* position in the matrix
* declaration of connection via UART
* declaration of pin operation  
Figure 12: (**a**) Schematic of the electrical circuit in the Autodesk Eagle program using the ESP system, (**b**) LabVIEW Front Panel. As reported in the S1. The Arduino has a USB interface used for sending data from the mat sensor to the host computer. The mat sensor data received from the Arduino hardware are displayed using the LabVIEW 2021 Q interface. The front panel window (Figure 12b) presents the interactive input and output terminals of the user interface for LabVIEW code VI. The front panel window is the user interface for the VI and exhibits controls and indicators, which are the interactive input and output terminals, respectively, of the VI. The mat matrix (14 \(\times\) 14) is connected to Arduino platform and LabVIEW 2021 Q in order to read and properly detect the data of pressure force on mat in real time for each cells of mat as shown in the LabVIEW front panel (Figure 12b).