# Applications of the Open-Source Hardware Arduino Platform in the Mining Industry: A Review
## 3 Arduino in Wearable Systems
### Surrounding Information  
Surrounding information refers to information on the underground mine environment, such as that regarding the air quality (e.g., gas concentration, temperature, humidity, and air density), collisions, and destructive events (vibrations, ultrasonic events, and ground stability). Most studies on the development of wearable systems with Arduino for surrounding information have employed a smart helmet as an actuator. One case, using a belt, was also reported to trigger a buzzer, message, and display, in addition to other forms of alarms. Some studies have been published on the development of wearable systems for measuring the air quality in underground coal mines and providing alerts. [PERSON] [59] proposed IoT-based automation of the safety and monitoring system operations in underground coal mines, as several workers have lost their lives owing to the absence of means of communication in emergency situations inside mines. To monitor air quality and air density via a helmet-type system, various sensors have been embedded in an Arduino Nano board (ATmega328), such as gas sensors (MQ2 for combustible gas and smoke, MQ4 for methane, butane, and natural gas, and MQ135 for sulfides, benzene, and ammonia), air density, temperature, and humidity (DHT11). This study utilized ZigBee technology and the ESP8266 Wi-Fi module as a wireless transmission network for transferring the measured data from the helmets of workers to a web server (central hub station). If a sensor measurement value exceeded the threshold limit value, as in the example in Table 5 (these values may vary depending on the study), an alarm sounded in the helmet to alert the worker. Similarly, [PERSON] et al. [60] suggested a ZigBee-based intelligent helmet for coal miner safety purposes. The air quality was monitored using a gas sensor (MQ2), temperature sensor (LM35), and humidity sensor (DHT11). The three sensors were connected to an Arduino UNO board (ATmega328P) to activate a buzzer when the measurements exceeded certain levels (e.g., temperature >40 \({}^{\circ}\)C). In addition, the measured values were transmitted to a web server at a control station using ZigBee wireless communication technology, to enable further analysis and/or monitoring. Based on an air quality monitoring function, [PERSON] and [PERSON] [61] proposed a smart helmet system for indicating whether miners were wearing their helmets or not. Similar to the aforementioned study, they selected the Arduino UNO board as a microcontroller and used two gas sensors (MQ6 and MQ7 for CO and CO2, respectively). In addition, an infrared (IR) ray sensor was used to recognize the status of helmet removal. The IR sensor was laid out to transmit a continual signal from one end. If the signal was obstructed, it indicated that the mine worker was wearing a helmet; otherwise, the miner was not wearing it. For the wireless transmission of data, this study employed a GSM modem (SIM800L), a specialized type of wireless modem that works with a GSM wireless network. As actuators, a piezo buzzer on a helmet and LCD were used. To trigger the piezo buzzer, a sound generator used in electronic circuits and piezoelectric sensors were used. The measured data were displayed on the LCD. In addition to monitoring the air quality in underground mines, some studies have reported the development of wearable systems for preventing collisions with equipment or uneven roofs. [PERSON] et al. [62] developed a leather belt-type safety management system for measuring air quality and detecting collisions with various mining equipment or machines. Toward this aim, this study employed an Arduino Nano board and a prototype ultrasonic sensor (HC-SR04) for distance measurements