On-Device tilt and symmetry sensing with a MEMS Accelerometer

Abstract

Field measurement of structural displacement and inclination is hindered by drift in double integration, stringent filtering needs, and the limited compute/bandwidth of low-cost microcontrollers. This work presents node based on an ADXL345 tri-axial accelerometer with on-board processing that estimates dynamic tilt and symmetry in real time without double integration. Three real-time filters, Butterworth IIR (BWF), finite impulse response (FIR), and moving average (MAF, uniform-tap FIR), were implemented on the device and benchmarked against an offline Savitzky–Golay reference. A rigid-body rotation model links off-centre acceleration to inclination and defines a dimensionless rotation index for symmetry assessment. Calibration against analytical motion identified a linear-phase FIR as optimal, yielding the lowest RMSE over 0.5–8 Hz while preserving waveform shape. Computational profiling on an 11.0592 MHz microcontroller measured average per-sample execution of 2.5 µs (MAF), 6 µs (FIR), and 12 µs (BWF), enabling 800 Hz local sampling with ≥ 100 Hz wireless streaming and an 8 × reduction via on-device decimation (no compression). Under cyclic tension, lateral acceleration quantified asymmetry: non-cracked and two-sided-cracked specimens showed comparable lateral levels, whereas one-sided-cracked specimens exhibited markedly higher values consistent with crack-induced rotation. Vertical acceleration agreed with acceleration reconstructed from displacement, with peak deviations of ∼ 9–14%; accuracy decreased at the lowest acceleration levels, consistent with stronger low-frequency spectral content. Tilt from acceleration tracked displacement-based tilt with minor underestimation at the smallest amplitudes. Overall, the node delivers embedded, phase-faithful filtering and tilt/symmetry estimation with quantified computational cost, making acceleration-based monitoring practical on resource-constrained hardware while avoiding big-data burdens.