# Real-Time Feedback in Swimming Exercises Using Embedded Devices in Water
## 2 Materials and Methods  
Studies involving real-time guidance of human movement during activities are relatively rare [6,7]. This paper proposes a novel approach for delivering live feedback in aquatic environments. The hardware utilized in this study was previously tested on dry land, as presented in the work titled \"Learning Swimming Techniques by Means of Real-Time Monitoring with Embedded Devices\" [8]. For the current study, the system was enhanced with a vibration motor integrated into each device and was modified for waterproof operation to enable use in water-based testing. The vibration motor employed is the Disc Vibration Motor 1027 (Shenzhen ChuangXinDa Micro Motor Co., Shenzhen, China),which is connected to an output pin of the ESP32 Lolin Lite microcontroller (Espressif Systems, Shanghai, China). This setup allows the motor to be activated or deactivated as needed, providing vibration-based (tactile) feedback to the user when specific movement triggers are detected. A vibration motor is well-suited for this type of feedback, due to its ability to deliver precise tactile feedback at specific locations on the skin, allowing the user to identify the exact point of error through direct skin contact [9]. Given the aquatic environment, vibration feedback remains effective, as it is perceptible even underwater. In contrast, using an acoustic buzzer [10] as an alternative feedback modality would require a sound level high enough for the user to hear, which could disturb other swimmers during training sessions due to its audibility in the surrounding area. Moreover, with multiple devices operating simultaneously, acoustic feedback may introduce ambiguity, making it difficult for the user to discern which specific body part is not moving correctly, based on the received feedback from the devices. An alternative method for providing feedback is through the use of smart goggles, which can visually display information directly to the swimmer [11,12]. To achieve waterproofing, hot glue was applied to seal the device, with careful attention to leave access to the battery socket for charging and the programming interface. As a result, the device is not fully waterproof. Therefore, it was enclosed in a resealable plastic bag, which was sealed before placement on the user's arm [13]. The updated device is present in Figure 1 below. Alternative waterproofing methods were also explored. These included the use of waterproof cases designed for action cameras and waterproof smartphone pouches, both of which offer sealed enclosures to protect the electronics from water ingress. Both waterproofing approaches are illustrated in Figures 2 and 3 below. Using the enclosures shown in Figure 1, it was necessary to apply additional tape inside the cases to stabilize the device. Without this, the device tended to shift during gesture execution. In contrast, the plastic bags shown in Figure 2 holds closely to the device, securing it firmly to the arm. In both configurations, strong waterproof duct tape was employed to maintain the device in the desired position on the arm [14]. An ideal enclosure consists of a custom-designed waterproof case, which can be fabricated using 3D printing. However, as the prototype is still under continuous development, including hardware modifications, premature acquisition of a prefabricated solid enclosure would increase costs. Once the enclosure design is finalized, it can incorporate straps similar to those used in other wearables, such as smartwatches, thereby eliminating the need for temporary solutions like duct tape. As a software side, the system keeps in majority the implementation from \"Learning Swimming Techniques by Means of Real-Time Monitoring with Embedded Devices\" paper.