Design and Implementation of an Embedded System for Pipeline Inclination Monitoring in Foundation Pits

Research hypothesis: We hypothesized that a cable‑free, STM32‑based inclinometer with integrated hoisting and 180° mechanical rotation can achieve high‑precision, repeatable inclination measurements for foundation pit pipelines, while eliminating sensor zero‑drift without extra electronic circuits. What the data show: - Figure 10 Data.xlsx: Eleven consecutive inclination measurements (0–10 cycles) at the same depth point inside a fixed vertical inclinometer casing. Measured angles (°) demonstrate repeatability. - Figure 11 Data.xlsx: Three test groups at true angle 2.5°. Forward and reverse measurements are provided; compensated angle = (Forward – Reverse)/2, showing zero‑drift removal. - STM32‑CODE (Master Control Board & Probe): Complete firmware for STM32WLE5JC (master) and STM32F103C8T6 (probe). Implements FreeRTOS tasks, Bluetooth communication, finite state machine, moving average filter, and motor control. Notable findings: - Maximum deviation among 11 repeats is –0.300° (Figure 10), confirming excellent repeatability. - Compensated angles (e.g., 2.482°, 2.472°, 2.4305°) deviate <0.03° from true 2.5°, reducing zero‑drift by ≈10× (Figure 11). - The firmware enables fully automated “descend – measure – ascend – rotate – remeasure” cycles with wireless data transmission. How data were gathered: - Inclinometer tube was fixed vertically (Fig.10) or at 2.5° (Fig.11). Probe moved by hoisting mechanism; depth position monitored via microswitches. - For Fig.10: 10 automatic cycles; angle recorded at the same depth each cycle. - For Fig.11: Probe lowered to same depth → forward measurement → 180° mechanical rotation → reverse measurement. True angle verified by reference inclinometer. - All raw readings transmitted via Bluetooth to ground unit; no post‑processing filtering applied to these values. - Code developed in Keil MDK, using STM32 HAL libraries. Master board controls motors, reads sensors, runs state machine; probe board reads SCA103T sensor and responds to Bluetooth commands. How to interpret and use the data: - Figure 10: Calculate standard deviation to assess repeatability. Small variation validates mechanical and wireless stability. - Figure 11: Apply (Forward – Reverse)/2 to any opposite‑direction pair to obtain drift‑free angle. This mechanical compensation works without temperature calibration. - Firmware: Can be reused or modified for other automated inclinometer or motor‑controlled sensor platforms. The state machine and FreeRTOS task architecture are extensible. Corresponding author: Shuai Zhang ([e-mail])