PSI - Issue 64

M. Komary et al. / Procedia Structural Integrity 64 (2024) 693–699

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Mahyad Komary/ Structural Integrity Procedia 00 (2019) 000 – 000

1. Introduction The integrity and safety of civil infrastructures, especially bridges, are of paramount importance. Structural Health Monitoring (SHM) systems play a crucial role in diagnosing and prognosticating the health of these structures. Traditional SHM systems often involve high-cost sensors, limiting widespread application [1]. This study introduces a paradigm shift by employing the NodeMCU microcontroller as a central hub to integrate various low-cost sensors for effective SHM, democratizing access to advanced monitoring technologies. This paper explores the integration of several low-cost sensors into SHM applications, specifically for bridges, and demonstrates the results obtained from their deployment in various tests. The main objective is to unveil the potential of low-cost sensors as economical alternatives to expensive commercial sensors, broadening accessibility and enhancing measurement points for more robust results. 2. Low-cost Sensors for SHM Applications Recently, the integration of low-cost sensors into SHM for bridges has shown promising potential to make these systems more accessible and widespread [2][3]. This section initially delves into the specifics the NodeMCU microcontroller used in this study as well as each sensor type, highlighting their main features and applications in SHM programs. 2.1. NodeMCU as the Central Hub in SHM Applications NodeMCU is an open-source IoT platform that includes a firmware that runs on the ESP8266 Wi-Fi SoC (System on Chip) and hardware based on the ESP-12 module [4]. It is produced by Espressif Systems (China), is equipped with digital input/output pins, analog inputs, and integrated Wi-Fi, making it highly suitable for connecting and controlling sensors over the internet [5]. Its capacity to support various communication protocols coupled with its programmable nature makes NodeMCU an ideal central hub for low-cost SHM systems. Figure 1 is the schematic of the NodeMCU circuit .

Fig. 1. NodeMCU microcontroller.

2.2. Ultrasonic Sensor (HC-SR04) The HC-SR04 ultrasonic ranging module manufactured by MULTICOMP (China) offers a 20 mm – 4000 mm non-contact measurement function (figure 2). The accuracy of ranging for this sensor can be as high as 3 mm [6]. The fundamental idea behind the work is to use an I/O trigger for a high-level signal that lasts at least 10µs (microseconds). The module automatically transmits at a frequency of 40 kHz and detects the presence of a return pulse signal. Ultimately, the range can be computed using the time difference between the trigger signal's transmission and reception of the echo signal. Test length equals (time × sound velocity (340 m/s)).

Fig. 2. Schematic of an Ultrasonic ranging module HC-SR04.