## 1 Introduction
The same method was also used to determine the prestressing forces of external post-tensioning tendons at a highway bridge [15]. Mechanical vibrations of stay cables were also investigated by utilizing the integrated camera of the smartphone, whereby the natural frequencies were evaluated from stationary as well as handheld smartphone cameras by tracking the displacement of the cables [16]. Since the operating system can influence the achievable measurement quality, e.g., depending on battery status or the number of processes running in parallel, external sensors have also been used for data collection. The connection between smartphone and external sensors has been established wired [13] or wirelessly via microcontroller [6]. In order to collect, store, process, and visualize acceleration data, smartphone applications have been developed for Android [6; 10] as well as for iOS [13; 14] operating systems, which allow data handling within a single device. Smartphone-based vibration measurements were applied in [17] for the identification of dynamic properties on rural bridges. The application of smartphones for damage detection was studied in [18]. There, a small-scale steel frame model was subjected to base excitation, and peak acceleration data obtained from an internal sensor was in good agreement with the one determined from traditional piezoelectric sensors, though greater variance was found for the displacements. The enormous increase in applications of sensor-based technology in the scope of SHM demonstrates the necessity of improved, high-performance, mobile technologies. With the rapid development and popularization of smartphones, the adoption of these became increasingly interesting to the SHM community. The presented work concentrates on the properties and advantages of the software framework designed for single-board computers to measure vibrations via sensors attached to microcontrollers or nested in mobile devices. Such modern devices include smartphones and tablets equipped with considerable computational resources and large memory capacity. Unlike traditional monitoring systems, these widely available devices combine the recording, storage, processing, transfer, and visualization of data within one unit. Due to vast differences in measurement properties arising from the various built-in sensors on the market and their qualities, external, low-cost sensors connected to RPi are included complementary to the mentioned hardware components for additional data acquisition. All aforementioned systems utilize the MEMS-based acceleration sensors to determine the system properties of structures by measuring structural vibrations. As past studies have already shown, the sensor resolution and sampling rate, which result from differences in accelerometers and sensor driver software configuration, affect the properties of measurement data directly [6]. Based on this fact, sensor characteristics are further investigated with respect to the hardware used. To demonstrate the performance of the technology platform, two types of application areas are showcased. Preliminary work included an evaluation of measurements on stay-cables during the construction of Queensferry Crossing [6], where tension forces were determined and compared with direct force measurements. Vibration measurements on bridge piers were performed on the Schindgraben bridge during blasting activities to determine vibration velocities. The technology platform presented here employs standard mass market hardware and features a software framework specifically geared towards optimum utilization of system resources in the context of WiFi-based meshed sensor network transient measurements. In contrast to existing methods [19], the approach presented in this paper deliberately refrains from using additional microcontroller hardware to facilitate data acquisition from sensor hardware. A primary design goal was the implementation in Python as a high level programming language to provide transparency and facilitate future extensions.