FreeKG - Fun Heart Rate Monitor

A web-based experimental heart rate detector that uses your phone's microphone to detect pulse vibrations from your neck.

⚠️ DISCLAIMER: This is for entertainment purposes only and is NOT a medical device.

Features

• Clean, modular code architecture
• Microphone permission handling
• 15-second audio recording
• Bandpass filtering (0.8-3 Hz for heart rate detection)
• Real-time waveform visualization
• Heart rate calculation (BPM)

Setup

1. Upload all files to your web server:

   • index.html
   • styles.css
   • audio-processor.js
   • ui-controller.js
   • app.js

2. Add your positioning guide image as position-guide.png (optional)

   • Shows proper phone placement against neck
   • If not provided, a simple emoji placeholder will display

3. Ensure your server uses HTTPS (required for microphone access)

File Structure

├── index.html          # Main HTML structure
├── styles.css          # Styling and layout
├── audio-processor.js  # Audio capture and signal processing
├── ui-controller.js    # Interface management and visualization
├── app.js             # Main application coordinator
└── position-guide.png  # User positioning guide (to be added)

Module Breakdown

audio-processor.js

• Microphone access and permissions
• Audio recording and buffering
• Bandpass filtering (heart rate frequency isolation)
• Peak detection algorithm
• BPM calculation

ui-controller.js

• Step navigation
• Progress bar animation
• Waveform canvas rendering
• Result display
• Audio beep notification

app.js

• Event handlers for user interactions
• Coordination between audio processor and UI
• Application lifecycle management

How It Works

1. Microphone Access: Requests permission to use device microphone
2. Audio Capture: Records 15 seconds of audio data from neck vibrations
3. Signal Processing:
   • Normalizes audio data
   • Applies moving average smoothing
   • Filters to isolate 0.8-3 Hz (48-180 BPM)
4. Peak Detection: Identifies rhythmic peaks in the filtered signal
5. BPM Calculation: Analyzes peak intervals to determine heart rate
6. Visualization: Displays waveform and calculated BPM

Browser Compatibility

• Chrome/Edge: Full support
• Safari: Full support (iOS requires user interaction before microphone access)
• Firefox: Full support

Note: HTTPS is required for microphone access in all browsers.

Technical Notes

• Sample rate: Uses device's native audio sample rate (typically 44.1 kHz)
• Recording duration: 15 seconds
• BPM range: 40-200 (validated)
• Signal processing: Time-domain analysis with peak detection

Limitations

• Not a medical device
• Accuracy depends on proper positioning
• Background noise can affect results
• Works best in quiet environments
• Requires steady hand during recording

Privacy

• All processing happens locally in the browser
• No audio data is transmitted or stored
• Microphone access is used only during active recording

Future Enhancements

• Multiple measurement averaging
• Confidence score display
• Export results feature
• Historical tracking (local storage)
• Improved filtering algorithms

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Made with curiosity | Not for medical use