agamrossen/VolAnti

What it solves

VolAnti is an open-source acoustic drone detection system designed to identify multirotor drones by the sound of their propellers. Unlike traditional detection systems that rely on radio signals—which can be silent in the case of fiber-optic FPV drones—VolAnti listens for the specific physical harmonic comb produced by spinning propellers.

How it works

The system uses an ESP32-S3 and four MEMS microphones arranged in a plus-pattern to increase signal-to-noise ratio and create an omnidirectional sensitivity device. It processes audio in 32ms slices using a 2048-point FFT to analyze the spectrum.

Key technical components include:

• Adaptive Floor: It maintains a running model of background noise and subtracts it to avoid false alarms from steady sounds like traffic.
• Comb Score: It calculates a rate between 70 and 2000 Hz and measures the energy on the "teeth" of the harmonic comb versus the gaps.
• Track and Hold: A detection is only triggered if the same rate wins six consecutive frames.
• Four Detection Tiers: It employs four independent detectors (Fast comb, Slow comb, Envelope wash, and No-floor comb) to catch drones whether they are approaching, hovering, or flying at high thrust.

Who it’s for

It is intended for schools, farms, and small communities who need a cheap, local "tripwire" for the last few hundred meters of their property. It is designed to be built and repaired by the user, with options for a breadboard build or a full custom PCB unit.

Highlights

• Acoustic-only detection: Works when radio spectrum is empty.
• Low latency: Detection can occur in as little as 0.23 seconds.
• Multi-alert system: Triggers a beeper, flashing red LED, haptic motor, e-paper screen, and LoRa radio packets to notify other units.
• Long range: Demonstrated detection at 104 meters in field tests.
• Low cost: Full units can be built for £50 to £80.