Hardware and Software of the ‘Smart’ Boat Oar for the Applied Force Measurement System

Assessment of the volume and quality of a rower's efforts during training plays an important role in preparing for competitions and improving his results. The article reviews existing commercial solutions, such as rowing simulators and individual sensor devices. It was determined that such proposals allow recording the frequency or trajectory of movement, but do not measure force. They also have limited functionality in real water conditions or high cost. Therefore, it is proposed to bring rowers' training into the realm of modern technologies for measuring and analyzing information in real time. For this purpose, a device mounted on an oar for numerically assessing individual aspects of rowing technique and corresponding software are proposed. Approaches to creating an embedded system for measuring force, orientation, and vibration response of an oar are investigated. The hardware part of the device is developed based on the Seeed XIAO nRF52840 board with low power consumption, built-in Bluetooth, accelerometer, and gyroscope. A strain gauge in combination with an analog-to- digital converter HX711 was used as a force sensor. The disadvantages of previous solutions based on Arduino Nano and the HC-05 module are described, in particular, high power consumption, unstable communication, and non-compliance with modern requirements.  The choice of a real-time operating system is described. The capabilities of Zephyr OS, FreeRTOS, and Mbed OS are compared. FreeRTOS is preferred as a system with a minimalist kernel sufficient for flow control and stable operation of sensors in real time. The device's power consumption in different modes is analyzed. The use of sleep modes for the microcontroller, sensors, and other components is proposed. A battery discharge curve is constructed that takes into account the nonlinear relationship between voltage and residual charge, which allows for accurate determination of the charge level in field conditions without external indicators. The article also describes the principle of device calibration. A multi-point force calibration method with interpolation between key points is presented.