# Identifying Earthquakes in Low-Cost Sensor Signals Contaminated with Vehicular Noise
## 3 Proposed Methodology
### Low-Cost Seismic Sensory Equipment  
The low-cost sensor mentioned in Section 3.1 was created in the CMODLab of Ionian University, Corfu, Greece; it consists of low-cost hardware and a data logger system. Originally, it was created for detecting seismic events and was placed in various areas, mostly near traffic roads. This placement is a part of the low-cost concept, so the sensors are easily accessible and replaceable in case of malfunction. The system employs a 3-axis geophone, operating at 4.5 Hz and 380 Ohm, serving as the main data logger to record signals. A sampling rate of 225 Hz is archived from the data logger and an accurate timestamp is added to each sample from a precise real-time clock circuit. This clock is checked and corrected every hour by using internet information. The recorded data are stored internally at the system in 5 min chunks (coinciding with files); subsequently, these are transmitted to the database server every 5 min by using internet connectivity. The low-cost system consists of low-cost hardware and open-source software. The system uses Raspberry Pi 3 B+, which is a credit-card-sized microcomputer board (see Figure 2). In addition, the system uses an analog-to-digital board with 24-bit high speed (ADS1256) precision, specialized for interconnection with the microcomputer and the real-time clock circuit breakout board DS3231. To support the system's energy needs, it uses a step-down converter with +5 Volt power, up to 3 Amps. The system is also fitted with a solar panel, battery, and a solar charg controller to make the system autonomous. Moreover, the system utilized additional accessories, such as a USB GSM-GPRS 4G modem to support the system's internet connection, a 3-axis geophone sensor with a cutoff frequency _fc_ set at 4.5 Hz, and a micro-SD 32 GB memory card that functions as the hard disk of the microcomputer board and stores all the necessary software needed to support the system (e.g., Python, data, etc.). The operating system used in the sensor is a Linux-based operational system for Raspberry Pi. We also used Python and C++ to write and execute scripts, depending on the needs of the task. The microcomputer board Raspberry Pi 3 B+, is the heart of the data logger system, and was selected for its high adaptability to integrate with various additional boards, like (I2c Bus, UART, SPI, GPIO, etc. ), and it provides the data logger with multiple capabilities. Figure 2: Full data logger system setup with housing in a plastic waterproof IP67 box. In addition, as mentioned above, a 24-bit A/D high-speed analog-to-digital precision board (ADS1256), as shown in Figure 3, is connected to the microcomputer board using the 40-pin GPIO connector. The A/D board has 24 bits of accuracy and has a quantization error 1/2 LSB of 22\({}^{24}\)/max input voltage. It can be adjusted to operate with a max input voltage of 3.3 or 5 volts. In our case, the max input voltage is 5 volts, which means we have a quantization error of 1/2 of 5 volts/2\({}^{24}\). The board has 8 analog inputs, which can work in a simple mode (8 input channels) or in a differential mode (4 input channels), similar to our data logger. It can accommodate sample rates of up to 30K samples per second (in a single channel--simple mode) and features an internal amplifier with an amplification factor of up to 64. In the proposed system, it uses a sampling rate of 3750 Hz and an amplification factor of 64. As per the datasheet ([[https://www.ti.com/lit/ds/symlink/ads1256.pdf](https://www.ti.com/lit/ds/symlink/ads1256.pdf)]([https://www.ti.com/lit/ds/symlink/ads1256.pdf](https://www.ti.com/lit/ds/symlink/ads1256.pdf)), accessed on 13 September 2023) of the ADS1256, the noise level is up to 6 bits, while the effective number of bits (ENOB) with the buffer off is essentially the remaining 18 bits. The output of the A/D card is given in counts. According to the amplification factor of 64, the differential max input voltage that can be measured from the A/D card cannot be higher than \(\pm\)78.125 mV.