## 4 Results and Discussion  
Current was measured with a basic function oscilloscope and a shunt resistor while the system was operating. OTA's power consumption was not calculated to estimate total power consumption. The power consumption was calculated based on four conditions: tissue is used, and the value is transmitted; tissue is not used; battery voltage measurement; and the deep sleep. When the tissue is not used, the system would sleep for 10 min. When tissue is used, the system would go to sleep for 10 min after changing or updating the data on the dashboard. In the sleep mode, 20 mA was consumed. The current profiles of some cases are shown in Figure 14. \begin{table}
\begin{tabular}{c c c} \hline \hline
**No.** & **Components** & **Cost (USD)** \\ \hline
1. & Laser ToF distance sensor & 5.00 \\
2. & ESP32 SoC & 6.00 \\
3. & Battery Li-Po 420 mA & 4.00 \\
4. & MCP 1700 low dropout (LDO) regulator & 0.50 \\
5. & T4056 charger module & 1.00 \\
6. & Light emitting diode (LED) and the other accessories & 1.00 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Estimated price. Figure 14: Current profiles. (**a**) Current profile when the system is in OTA mode, (**b**). Current profile when tissue is not used and (**c**) Current profile when tissue is used and transmitting. We illustrate the performance of the system when installed in a bathroom in a house that has four people. Based on our survey, a family with four members spends a week to use up all their tissue (80 cm radius). Each member uses tissue five times per day, on average. In a day, the system has to be updated on the dashboard 20 times, and it checks the amount of tissue 144 times. The device's power profile is shown in Figure 15. The different colors represent the different cases. In Table 3, \(C_{1}\) is the average current consumption for measuring the tissue value and transmitting, \(C_{2}\) is the average current consumption for measuring the tissue value, \(C_{3}\) is the average current consumption for measuring the tissue value and ADC reading for battery voltage, and \(C_{4}\) is the average deep sleep current. The battery deterioration factor needs to be taken into consideration, because the battery is self-discharging over time. In this work, we selected a deterioration factor of 0.8 per year from the battery datasheet [35]. In this model, sleep time is 10 min, and battery life is calculated, as can be seen in Table 3. The battery will last around 120 days. Power budget for the tissue monitoring application is calculated from Table 4 and shows in Figure 16. The battery can be fully recharged within an hour. For battery testing conditions, the system is set to a sleep duration of 15 s. In one day, the system is triggered 5760 times. The system transmits data, on average, 69 times per day (C1), measures battery level (C3), measures the actual amount of tissue an average of 5691 times (C2), and spends the rest of time in deep sleep mode (C4). The estimated battery life is calculated according to Equations (6) and (11) as shown in Table 5. The power budget for testing conditions is calculated in Table 6 and shown in Figure 17. The constant battery voltage of 3.3 V was assumed for all the power budget calculations. The battery usage graph is shown in Figure 18.  
A sample visualization of the two-sensor data received for toilet and kitchen as shown in Figure 1b. The tissue readings are displayed in red, orange, yellow, or green to indicate the levels are too low, adequate, a quarter, and high, respectively. It sends notification emails when tissue or battery voltage is low. The user can easily find out the tissue status or battery voltage via email when they are low. When the system in active mode, the LED blinks. Hence, users are assured that the system is in active mode from the visual feedback. The application energy parameters shown in Figure 11 are measured using software tools in [36] and summarized in Table 7.  
Figure 15: Power profile of the paper monitoring device related to the selected application scenario.