A Low-Cost Miniaturized Optical Tracking Sensor for Vibration Frequency Measurement in IoT Sensing

Vibration frequency monitoring is important for IoT-based condition monitoring, where sensing nodes are expected to be compact, low-cost, and easy to deploy. This paper investigates a miniaturized optical tracking sensor for frequency-oriented vibration measurement. The sensor detects surface-relative motion using optical tracking and outputs incremental displacement counts through a digital interface. A prototype system based on an optical tracking sensor and an STM32 microcontroller was developed, and the vibration frequency was extracted from the accumulated count-domain signal using preprocessing and spectral analysis. Experiments were conducted under sinusoidal excitation from 10 Hz to 200 Hz with a sampling frequency of 4 kHz. The results show that the dominant vibration frequency can be identified with mean relative errors below 0.1% within the tested range. Although the time-domain count response becomes less regular at higher frequencies, the frequency component remains distinguishable. With its compact package, low power consumption, non-contact measurement capability, and unit sensor cost below USD 0.1, the proposed sensor shows potential for low-cost distributed vibration monitoring.