24 GHz FMCW-Based Radar Occupancy Detector with Embedded Firmware and Configurable GUI
Keywords:
ATmega32U4, Embedded firmware, FMCW radar, GUI interface, Occupancy sensing, Presence detection, Stepper motor scanningAbstract
Common presence sensors such as Passive Infrared (PIR) sensors and ultrasonic modules exhibit critical performance gaps when tasked with detecting stationary occupants, operating in thermally variable environments, or providing user-configurable detection parameters. This paper reports the architecture, firmware design, and experimental validation of a small-form-factor presence detector built around a 24 GHz Frequency-Modulated Continuous Wave (FMCW) radar, aimed at overcoming these limitations. The system integrates the LD2420 single-chip radar module with an ATmega32U4 microcontroller deployed on the RFME P567858 custom printed circuit board, communicating via UART at 256,000 bps. An ATmega32U4-to-PC USB CDC bridge at 115,200 bps enables real-time data streaming to a feature-rich Windows desktop GUI developed in C# (Microsoft Visual Studio). Zone-based detection logic partitions the sensing field into three spatial regions: Zone A (0–50 cm, Critical Alert), Zone B (50–200 cm, Near Presence), and Zone C (200–500 cm, Far Presence). Angular scanning coverage is extended through a NEMA 17 stepper motor driven by an A4988 microstepping driver at 1/16 resolution, achieving 0.1125° per step. Experimental results demonstrate reliable human presence detection from 50 to 500 cm with a maximum absolute error of 3.7 at 350 cm, 100% zone classification accuracy across 300 test frames, and an end-to-end GUI update latency of 64 ms ± 12 ms. The proposed platform represents a cost-effective, configurable, and privacy-preserving alternative to existing occupancy sensing solutions.
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