# Real-Time Feedback in Swimming Exercises Using Embedded Devices in Water
## 2 Materials and Methods
### Battery Consumption  
The estimated battery life during continuous operation, as calculated in the previous study [8], is approximately 3.24 h.  
Figure 6: LED indicator when movement is performed.  
To enable real-time feedback, the system integrates a vibration component using a Disc Vibration Motor 1027, which is activated for 200 ms whenever an incorrect movement is detected. This motor typically consumes approximately 80 mA during operation (at 3 V power source). The additional power consumption varies based on the frequency of incorrect movements, which directly affects how often the motor is triggered.  
Three usage scenarios were considered for power consumption analysis:  
1. Frequent errors: The motor is triggered every 2 s (mistake at every attempt), resulting in 1800 activations per hour. With each activation lasting 0.2 s, the total activation time per hour is 360 s. This adds approximately 8 mAh to the hourly power consumption, increasing the total current draw to 162 mA and reducing the estimated battery life to approximately 3.09 h.
2. Moderate errors: The motor is triggered every 6 s (1 from 3 attempts is a mistake), resulting in 600 activations per hour. This adds approximately 2.66 mAh to the hourly power consumption, increasing the total current draw to 156.6 mA and reducing the estimated battery life to approximately 3.19 h.
3. Rare errors: The motor is triggered every 2 min (30 activations/h), adding just 0.14 mAh per hour to the consumption. The overall current draw becomes 154.14 mA, and battery life remains essentially unchanged at approximately 3.24 h.  
The above results were made with the following formulas:  
\[Triggers/hour=\frac{3600\;s}{Triggers\;frequency\;in\;seconds} \tag{2}\]  
\[Vibration\;time/hour=\frac{Triggers/hour\times 0.2\;s}{3600\;s} \tag{3}\]  
\[Additional\;motor\;energy\;per\;hour=80\;mA\times Vibration\;time/hour \tag{4}\]  
These results indicate that the inclusion of a vibration motor for real-time feedback has a negligible effect on power consumption under typical usage conditions [27; 28; 29]. Only in scenarios with very frequent feedback activation does the impact on battery life become noticeable. This confirms that the system remains suitable for extended testing and training sessions, while still providing meaningful real-time correction to the user.  
A typical swimming training session lasts between 1 and 3 h, depending on the swimmer's level. Since not all training time is dedicated to technique improvement exercises, the actual usage duration of the system during a session is reduced. In this context, the estimated battery life of approximately 3.24 h per charge is sufficient to support one full training session per day, after which the system can be recharged.  
To extend battery life further, several improvements are recommended: replacing the sensor with a low-power alternative (BMI270), utilizing a controller with enhanced low-power features, limiting Wi-Fi communication during the voting phase or increasing battery capacity. Implementing these enhancements would enable the system to operate across multiple training sessions before requiring a full recharge.