## 1 Theoretical Background
Thus, this system is beneficial for noncontact distance measurements and the dynamic behavior of the structure under study [45]. On the contrary, VL53l0X VL53l1X (ToF tech) sensors typically use harmless light emission for the bare eyes and provide a high reading frequency at an affordable price. Therefore, by considering the advantages and disadvantages of various sensors, HC-SR04, VL53L0X, and VL53L1X technologies have been selected for the experiments of this paper because of their price, range, eye safety, and sampling frequency. All the sensors listed in Table 1 can be connected to low-cost microcontrollers such as an Arduino. It is essential to mention that currently, many researchers are using Field Programmable Gate Array (FPGA) circuits instead of microcontrollers (such as Arduino) and minicomputers (such as Raspberry Pi) [46]. FPGA is a programmable semiconductor integrated circuit in which the majority of its electrical functionality is configurable even after the chipset production [47; 48]. On the one hand, the function ability of microcontrollers (such as Arduino) is like a normal CPU. A code is written in a programming language that gets compiled to machine code. Then, this machine code gets executed by the processor one line at a time. On the other hand, the configurable logic cells of FPGA make it more versatile, faster and optimizable. However, designing a system based on FPGA is more complex. In addition, indicated by many scholars (such as [49]), the coding language of Arduino (C programming) is less complicated than that of FPGA (Verilog). Low-cost microcontrollers can control many low-cost sensors. Arduino is an incredibly cheap microcontroller that is easy to use and based on an open-source electronic prototyping platform with a highly active online community. In fact, many great circuit producers (such as SparkFun Electronics) sell their sensors with open-source Arduino libraries and examples. The sensors are usually connected to Arduino through four methods:  
(1) Digital pins: these pins can be configured to function as either input or output. (2) Analog pins: the primary function of these pins is to read analog sensor data and return integers between 0 and 1023 with 10-bit resolution. Additionally, analog pins can be configured and used like the digital pins and function as either input or output, as well. (3) Integrated Circuit Bus (I2C): serial data exchange between specialized integrated circuits and the microcontroller. Multiplexors are needed for connecting multiple similar sensors to this port [50]. (4) Serial Peripheral Interface (SPI): ports synchronous serial data protocol so the microcontroller can communicate with one or more peripheral devices [51; 52]. Today, low-cost sensors based on Arduino devices are getting widespread attention from civil engineers due to their affordable price and the increased possibility of long-term monitoring with reasonable budgets [25; 37; 53]. However, the most significant drawbacks of low-cost sensors are their resolution and accuracy compared to traditional commercial solutions. To solve this issue for the first time on record, Komarizadehasl et al. [50] found that the average result of multiple low-cost sensors aligned in the same place is more accurate, has less noise density, and has a better resolution than the output of a single sensor for measuring an environmental variation or a structural response. To verify this concept, the researchers connected five similar low-cost accelerometers to an Arduino Uno with a multiplexor through an I2C port. The results were compared with commercial accelerometers and show that an increasing number of randomly selected similar sensors working together is always beneficial. However, data acquisition of this paper required a connected laptop for saving the data. The literature analysis shows that the methodology proposed in this paper has not been examined with low-cost distance sensors.