# Development of Digital Device Using ZigBee for Environmental Monitoring in Underground Mines
###### Abstract  
In underground mines, various mining activities may generate dust or vibrations, affecting workers' health and safety. Therefore, for worker safety, we must monitor the environment and identify possible risks. However, it is difficult to install multiple sensors and acquire data simultaneously because of the difficulties of connecting to an external network in underground mines. This study developed a digital device to share acquired data by combining ZigBee communication technology with an accelerometer and dust sensor. In total, 29 vibration modules, 14 dust modules, and 2 coordinator modules were installed at Taeyoung EMC's Samdo Mine in Samcheok, Republic of Korea. Because of its application, we could detect changes in vibration and dust before and after blasting. The dust density of the devices close to the blasting point increases rapidly up to about 230 \(\mathrm{\SIUnitSymbolMicro m}^{3}\) and then decreases to about 180 \(\mathrm{\SIUnitSymbolMicro m}/\mathrm{m}^{3}\), and the dust density of the devices further increases over time. The dust density was usually maintained at a value of about 100 to 150 \(\mathrm{\SIUnitSymbolMicro m}/\mathrm{m}^{3}\) before blasting. The spatial distribution of the dust density of multiple devices was visualized using ArcGIS Pro. Although the wireless sensor network is well-established, some modules were temporarily disconnected from the network. In order to solve the problem of unstable network connection in some modules, change of network settings and line of sight analysis are required. Improvements in the technology developed in this study may help prevent potential hazards in underground mines. ZigBee; wireless sensor network; accelerometer; dust sensor; underground mine +
Footnote †: journal: Medical Engineering  
a good connection to existing networks, underground mines have difficulty connecting to networks outside the mine [8]. Recently, with the development of Internet of Things (IoT) technology, attempts to combine various sensors and IoT to monitor the environment in mines have been increasing. [PERSON] et al. [9] combined IoT and cloud computing with various sensors that can measure the water level, deformation, and pressure of tailings dams to prevent collapse accidents that may occur in tailings dams. [PERSON] and [PERSON] [10] observed vibrations caused by blasting in open-pit mines using an accelerometer and radio frequency (RF) module. [PERSON] et al. [11] provided a miniaturized antenna system that uses a global system for mobile communication (GSM) to enable communication between miners in an underground mine. In addition, numerous studies have been conducted on air monitoring in mines using IoT technologies such as Bluetooth, Wi-Fi, and ZigBee [12; 13; 14; 15]. IoT technologies, including Bluetooth, near-field communication (NFC), Wi-Fi, and ZigBee, can be utilized for wireless communication depending on the environment and application. Bluetooth is a short-range wireless communication technology with a range of approximately 10 m that consumes barely any power. For the recently developed Bluetooth 5.0, the transmission distance was approximately 40 m, and the transmission speed was increased to 2 Mbps. However, it is not suitable for real-time monitoring because the communication distance is extremely short for use in mines, and the maximum number of devices that can be connected is relatively small. NFC is also a short-distance wireless communication technology that can exchange data at a short distance of within 10 cm, and because it uses a one-to-one tagging method, it is not suitable for the real-time monitoring of multiple points. Wi-Fi is useful for monitoring because of its wide communication range and fast data transmission speed, but it is power- and cost-extensive for routers to build Wi-Fi networks.