Metal Detector Signal Flow Diagram

METAL DETECTOR - SIGNAL FLOW DIAGRAM

HARDWARE LAYER

METAL TARGET

↓

EM Field Distortion

↓

RECEIVE COIL

↓

Analog Signal

↓

MICROPHONE INPUT

AUDIO OUTPUT
(Speaker/Headphones)

↑

TRANSMIT COIL

SOFTWARE LAYER - AudioEngine (44.1 kHz)

STEREO OUTPUT
(AudioTrack)

↓

LEFT
Multi-Tone
Generator

TX Signal
1-24 tones
1000-20000 Hz

RIGHT
Target Audio
Generator

Feedback
Audio

MONO INPUT
(AudioRecord)
1920 samples

RX Signal (Left channel only)

Callback: 23.2 Hz
Latency: 43.5 ms

DSP PROCESSING LAYER

IQ DEMODULATOR DSP
(Real-time processing)

For each frequency:
• Quadrature mixing: I = sample × cos(phase), Q = -sample × sin(phase)
• Single-pole IIR low-pass filter (α = 0.01, ~10 Hz cutoff)
• Amplitude calculation: √(I² + Q²) × 2
• Phase calculation: atan2(Q, I)

↓

Ground Balance
Manager

Remove ground
interference

VDI Calculator

Multi-tone
discrimination

↓

Callback to UI
(30 Hz update rate)

ToneAnalysis List + VDI Result

UI LAYER

Waveform Display

VDI Display &
Tone Info

KEY SIGNAL PARAMETERS

Sample Rate: 44,100 Hz
Buffer Size: 1920 samples (device-dependent)
Audio Callback Rate: 23.2 Hz (measured on device)
Buffer Latency: 43.5 ms
Update Rate: 30 Hz (configurable, max ~23 Hz)
TX Frequencies: 1-24 tones, logarithmically spaced
Frequency Range: 1000 Hz (fixed min) to 20000 Hz (max)
RX Processing: IQ demodulation with α=0.01 IIR filter

CODE REFERENCES

AudioEngine.kt:274 - playbackLoop() generates stereo output
AudioEngine.kt:326 - recordLoop() captures mono input
IQDemodulator.kt:195 - processMono() called every 43.5 ms
IQDemodulator.kt:77 - analyze() performs IQ demodulation