A Wireless Optical Gate and IMU System for Agility Assessment: Architecture, Synchronization and Validation

Abstract

Accurate, field-ready timing and motion capture are essential for assessing agility beyond the limits of manual stopwatches. We present a modular measurement system that fuses infrared (IR) optical gates for robust event detection with a trunk-worn inertial measurement unit (IMU) for kinematic profiling. Each sensing node is built on an Adafruit Feather M0 Wi-Fi microcontroller and communicates via UDP to a laptop server. Time alignment is accomplished without internet connectivity: the server establishes a relative epoch and executes a triple-handshake broadcast protocol, while timestamps are generated at the edge to avoid latency bias from transport or processing. Module- and device-level characterization shows that IR-receiver processing combined with interrupt service routine latency yields a per-event timestamp error of 0.54 ms ± 0.14 ms (latency ± uncertainty), and local clocks remain stable over the durations relevant to agility trials. In wireless operation, accepted synchronization attempts form tight response clusters in favorable RF conditions, whereas congested environments may require retries; for section times across different gates, we therefore report a conservative inter-node uncertainty. End-to-end validation across laboratory, entry-hall, and gym venues using the Agility T-test confirms that total test time measured on the same start/finish gate remains below 1 ms error over 10–20 s trials. Synchronized IMU waveforms add explanatory value beyond total and split times by revealing braking, change-of-direction, and re-acceleration phases. The system provides a deployable workflow with substantially improved precision over manual timing. Future work will target more robust synchronization and expanded analytics, including automated phase detection, asymmetry indices, and optional integration with indoor positioning.