# Applications of Smart Helmet in Applied Sciences: A Systematic Review
## 3 Results
### Types of Microcontroller Used in Smart Helmets  
Different types of microcontroller have been used to develop smart helmets. By analyzing 103 articles, this study classified the microcontrollers into four categories.  
- Chip modular concept unit (MCU): a single computer chip designed for embedded applications (e.g., PIC 18F8720) [110]  
- Single-board MCU: a microcontroller built onto a single printed circuit board (e.g., Arduino) [111]  
- Single-board computer: a complete computer built on a single circuit board, with microprocessor(s), memory, input/output, and other features required for a functional computer (e.g., Raspberry Pi) [112]  
- Smart device: an electronic device, generally connected to other devices or networks by means of different wireless protocols that can operate to some extent interactively and autonomously (e.g., smartphone) [113]  
\begin{table}
\begin{tabular}{l l l} \hline \hline
**Human Health Monitoring** & \multicolumn{1}{c}{**Environmental Monitoring**} & \multicolumn{1}{c}{**Machine Monitoring**} \\ \hline - Accident detection (50 papers) & - Harmful gas detection (11 papers) & - Speed detection (7 papers) \\ - Helmet wear detection & - Video shooting (11 papers) & - Proximity warning (2 papers) \\ (46 paper) & - Temperature detection (11 papers) & - Fuel level detection (1 papers) \\ - Alcohol detection (42 papers) & - Humidity detection (7 papers) & - Fuel level detection (1 papers) \\ - Drowsiness detection & - Brightness detection (3 papers) & \\ (6 papers) & - Barometric pressure detection & \\ - Brainwave detection (4 papers) & (2 papers) & \\ - Heart rate detection (4 papers) & - Fire detection (2 papers) & \\ - Head motion detection & - Pothole detection (1 papers) & \\ (3 papers) & & \\ \hline \hline \end{tabular}
\end{table}
Table 4: Types of sensor depending on the purpose used in smart helmet studies.  
Figure 7: Trend of sensor uses in smart helmet studies. (**a**) Cumulative number of uses of sensor types according to year. Usage percentage of sensors for (**b**) human health monitoring, (**c**) environmental monitoring, and (**d**) machine monitoring.  
The number of studies that used each of the four types is presented in Figure 8. Among the 103 articles analyzed in this study, the single-board MCU was the most used (56 studies), followed by the chip MCU (28 studies). The number of single-board computers and smart devices used was relatively small (11 and 8 articles, respectively). The use of single-board MCUs has increased rapidly since 2016. Although there have not been many uses of single-board computers so far, their use for smart helmets has increased since 2017. The use of smart devices has been minimal, which is believed to be because of the relatively high cost compared with other devices.  
Figure 9 shows the use of sensors according to the type of microcontroller in smart helmet studies. Accident, helmet wear, and alcohol detection sensors have been frequently used with the chip MCU and single-board MCU. As shown in Figure 7, the uses of accident, helmet wear, and alcohol detection sensors make up a large part of smart helmet applications. Therefore, it is judged that the uses of chip MCU and single-board MCU were rapidly increased due to the increased development of smart helmets for accident, helmet wear, and alcohol detections. In the case of using a sensor that processes a large amount of data such as video shooting, it can be seen that a single-board computer or a smart device is being used. If the use of sensors based on images or videos increases in smart helmet studies, the single-board computers or smart devices are expected to be used more as microcontrollers.