# Airbag Protection and Alerting System for Elderly People
## 2 Methodology
which is too high to be driven by the Arduino 5-volt supply, so the value receives its voltage from the boost converter. Then, a transistor is utilized to control the valve [23]. The flow rate of the air valve is calculated using the following formula:  
\[Flow\ Rate\ (L/min)=SCFM\times 28.32 \tag{3}\]  
\[Flow\ Rate\ (L/min)=22\times 28.32=623.04\ L/min\]  
where \(SCFM\) is the flow rate of gas under standard pressure and temperature conditions (standard cubic feet per minute). * MOSFET (metal oxide semiconductor field-effect transistor): To supply the air valve, a driving transistor should be used. That is because the Arduino cannot provide the valve with enough power to operate. The chosen MOSFET is the IRF520 module. The transistor breakout board is contained in this little module (HCMODU0083). The module is made to switch large DC loads from a single microcontroller digital pin. To connect the load and an external power supply, screw terminals are provided [21]. * A Bluetooth BLE module: It establishes a protocol for data transmission between devices and serves as an interface for wireless Bluetooth low energy connections between any two devices. The average mediated data communication range of a Bluetooth low energy module is typically tens of meters, and data are transmitted in designated frequency bands. The chosen Bluetooth module is HC-06. It is a class-2 slave Bluetooth module designed to allow wireless serial communications between microcontrollers like Arduino and other Bluetooth-enabled devices [24]. * Battery: As the system is proposed to be wearable, a high capacity and lightweight rechargeable battery should be used. The lithium-ion battery was selected with a charge controller to protect it from overcharging and over discharging limits. The lithium battery charger TP4056 module can charge lithium-ion rechargeable batteries and offers the necessary protection needed by lithium-ion batteries in addition to safe charging. The module's input voltage is 5 V, and the maximum charging current is 1000 mA (1A) [25]. The battery used is 3.7 volt and its capacity is 3000 mAh. The power consumption is calculated as:  
\[ \begin{split} Battery\ Power\ Consumption\ (P)=V\times I\\ =3.7\times\ 3=11.1\ \text{Watt-h}\end{split}  \tag{4}\]  
The battery charging time to the maximum is given by:  
\[ \begin{split} Battery\ Charging\ time=\frac{Battery\ watt-hour}{Charger\ Power\ (watt)}\end{split}  \tag{5}\]  
The charger used is 5 volt and 1 A, then:  
\[ \begin{split} Charger\ power=V\times I\\ \text{Charger power}=5\ \times\ 1=5\ \text{Watt}\\ \text{System's battery charging time}=\frac{11.1}{5}=2.22\ \text{h}\end{split}  \tag{6}\]
* The boost converter MT3608 module was used to supply the Arduino Nano with the needed voltage and to operate the 12-volt DC valve directly. It is a cheap module that can step-up a 2 to 24 V input voltage up to a 5 to 28 V output at up to 2 A. Since the module cannot output more power than its inputs, DC-DC boost converters scale up the input voltage to a higher voltage while also ramping down the available current [26]. * Air tank: The two sides of the pipe were closed by a plastic gland using specialized glue made and sold for these pipes, a hole was made at one of its sides for the air inlet usinga stem (tire valve), and the pipe will be filled with air by an air compressor through the stem, and another hole was made for the air outlet by connecting a pneumatic fitting, which will be connected with the solenoid valve inlet using an 8 mm pneumatic pipe, while another fitting will be utilized to connect the valve outlet with the airbag via another 8 mm pneumatic pipe. * Airbag: A bubble wrap sheet shaped as an airbag and sealed using durable duct tape, covered with a fabric case, that is closed around it using a zipper, and the cloth has three fabric slits used to attach it to the user's pants using the user's belt. Figures 3-6 illustrate the detailed layout views of the scheme that was designed using SolidWorks.