# Smart Helmet-Based Personnel Proximity Warning System for Improving Underground Mine Safety
## 2 Design of the Proximity Warning System (PWS) Based on Bluetooth Beacons and Smart Helmets
### Design of BLE Receiver Units Using an Arduino Board  
Arduino is an open source electronic platform based on easy-to-use hardware and software (Table 2). The Arduino board reads the input data, including sensor illumination and button pressing and converts it into output data. Because the Arduino board and software are open sources, users can independently build boards to adjust the system to meet specific needs [48].  
In this study, a smart helmet was developed to develop a wearable personal PWS for workers. The smart helmet was made by combining an Arduino Uno board, Bluetooth BLE module (FBL780 BC, Table 3), LED strap, and two-leg LEDs with the safety helmet worn by mining workers. Figure 3a,b show the exterior shape of the equipment divided into front and rear parts. The smart helmet provides visual warnings through LED straps (using two-leg LEDs), and receiving power through portable batteries. The Bluetooth BLE module (FBL780 BC) supports Bluetooth Low Energy, a low-power function based on Bluetooth 4.1.  
The circuit diagram was used to visualize the connection method of the Arduino board, LED, and Bluetooth module as shown in Figure 4. The process of the operating algorithm of the smart-helmet PWS is illustrated in Figure 5. After the BLE signal was received via the Bluetooth BLE module attached to the smart helmet, it was compared to the MAC address of the Bluetooth beacon stored in the database. If the MAC addresses of  
\begin{table}
\begin{tabular}{c c} \hline
**Item** & **Value** \\ \hline Model & Arduino Uno R3 \\ Microcontroller & ATmega328P \\ Length & 68.6 mm \\ Width & 53.4 mm \\ Weight & 25 g \\ Operating Voltage & 5 V \\ Input Voltage & 7–12 V (recommended), 6–20 V (limit) \\ Digital I/O Pins & 14 (of which 6 provide PWM output) \\ PWM Digital I/O Pins & 6 \\ Analog Input Pins & 6 \\ DC Current per I/O Pin & 20 mA \\ DC Current for 3.3V Pin & 50 mA \\ Flash Memory & 32 KB (ATmega328P) of which 0.5 KB used by bootloader \\ SRAM & 2 KB (ATmega328P) \\ EEPROM & 1 KB (ATmega328P) \\ Clock Speed & 16 MHz \\ LED\_BUILTIN & 13 \\ \hline \end{tabular}
\end{table}
Table 2: Specifications of the Arduino Uno board [49].  
\begin{table}
\begin{tabular}{c c} \hline
**Item** & **Value** \\ \hline Model & FBL780 BC \\ Bluetooth specification & Bluetooth4.1 Low Energy Support \\ Communication distance & 10 m \\ Frequency range & 2402–2480 MHz ISM Band \\ Sensitivity & \(-94\) dBm \\ Transmit power & 2 dBm (\(-3\) dBm: Actual value after matching) \\ Size & 15.5 mm \(\times\) 18.5 mm \\ Input power & 3.3 V \\ Current consumption & Peripheral: 3 mA (Max), Central: 21 mA (Max: Scanning) \\ Operating temperature & Min: \(-10\)\({}^{\circ}\)C, Max: 50 \({}^{\circ}\)C \\ Communication speed & 2400 bps-230,400 bps \\ Antenna & Chip Antenna \\ Interface & UART \\ \hline \end{tabular}
\end{table}
Table 3: Specifications of Bluetooth module [50].  
the Bluetooth beacons are matched, the LED wrap and two leg LEDs are turned on for 30 s to provide a visual alert to the worker and the driver and, if not, they are not turned on. The system is designed to operate repeatedly through infinite loops when power to the Arduino board is turned on.  
Figure 4: Circuit diagram of Arduino application.  
Figure 3: The component of the smart helmet. The rear part (**a**) and the front part (**b**) of the helmet.