## 2 Design Method  
The proposed miniaturized IV detection and monitoring system consists of a load cell and photosensor, as shown in Figure 1. As shown in the figure, the load cell consistently monitors changes in the IV fluid's volume. It can display the amount of infused IV fluid, as the laser module and photoresistor count the drops of IV fluid. This can improve the accuracy of monitoring and provide increased resistance against external interferences. Immediately after the micro controller unit processes the data, all the information on the infused IV fluid is sent via Wi-Fi to the NS's mobile devices. By using dedicated applications, medical staff can monitor a patient's IV infusion rate in real time. Each sensor is attached to one body. The red laser module emits a broad range of wavelengths with the peak power occurring at 650 nm, as shown in Figure 2 (minimum wavelength: 640 nm and maximum wavelength: 670 nm). This laser module has a narrow beamwidth of 5 mrad, which is able to accurately detect the fluid drops [18]. The laser has its own beam size, which was 5 mm in this study. The volume of each drop is approximately 1 mL [19]. This means that the dropsfall within the laser module's coverage range. Additionally, the photoresistor has a high sensitivity in the range of 600-700 nm, in order to detect light at a specific wavelength. An experiment was conducted to prove that these concepts work. The irradiated and received powers were measured from the saline drop captured in the chamber. The irradiation power from the laser module was 5.00 mW, and the received power, passing through the fluid chamber, was 4.04 mW. To count each drop in the chamber, we divided the time period into segments T\({}_{1}\)-T\({}_{4}\), as shown in Figure 3. The photoresistor voltage outputs change according to the drops. T\({}_{1}\) represents the ideal voltage variation, while T\({}_{2}\) and T\({}_{3}\) denote real voltages. T\({}_{2}\) is the time interval required for the formed drop to fall. Voltage changes begin immediately after the drop is formed. This is because the drop reflects light, which screens the photoresistor. The larger the fluid drop (from the starting point of T\({}_{2}\) to T\({}_{21}\)), the smaller the amplitude of the voltage. IV fluid drops continue forming from T\({}_{21}\) to T\({}_{22}\). After T\({}_{2}\), the voltage recovers to its initial value, which follows T\({}_{31}\), and is represented by T\({}_{3}\). T\({}_{4}\) represents the time during which the chamber is empty. Thus, T\({}_{1}\) after T\({}_{2}\) indicates the drop of a single droplet. Figure 1: Work process and communication between the proposed system and mobile devices via Wi-Fi. Figure 2: Characteristics of the laser module with its beam pattern chart. Figure 3 demonstrates this entire mechanism. Additionally, the load cell counts every loss in weight, which can be converted to determine the overall infused volume of IV fluid. When light passes through a block, which comprises a homogeneous medium, it causes a loss of light, denoted by \(\Delta\phi\). In this case, the proportionality constant represents absorption (\(\alpha\)), loss of light (\(\Delta\phi\)), incident light (\(\phi_{0}\)), the thickness of the block (\(\Delta x\)), and the intensity of the penetrated light (\(\phi\)). We can represent these with the following equations based on the exponential law of absorption. \[\Delta\phi=-\phi_{0}\,\alpha\Delta x \tag{1}\]  
\[\frac{d\phi}{\phi_{0}}=-\alpha dx \tag{2}\]  
\[\int_{\phi_{0}}^{\phi}\frac{d\phi}{\phi}=-\alpha\int_{0}^{x}dx \tag{3}\]  
\[\log_{e}\biggl{(}\frac{\phi\prime}{\phi_{0}}\biggr{)}=-\alpha x \tag{4}\]  
\[\phi\prime=\phi_{0}e^{-\alpha x} \tag{5}\]  
Figure 3: Working mechanism of the photosensors. (**a**) T\({}_{2}\), (**b**) T\({}_{3}\), and (**c**) T\({}_{4}\) of a chamber. (**d**) Graph describing the variation gap between the ideal and real voltages. Thus, the coefficient of light absorption can be described as the equation relating medium and wavelength.