OpenWrt Level Meter (OWLevelMeter)

A real-time audio level meter for OpenWrt/LuCI that monitors ALSA device input channels and displays VU meters in the LuCI web interface.

Features

• ✅ Real-time VU Meters — Stereo L/R channels (easily extensible to multi-channel)
• ✅ Visual Bars — Green→Orange→Red gradient based on signal level
• ✅ Peak Hold — Holds peak level for 2.5 seconds with smooth decay
• ✅ Clipping Detection — Red flash alert when signal clips (≥0.9999)
• ✅ dB Display — Numeric display ranging -60 to 0 dB
• ✅ Device Selection — Choose any ALSA input device
• ✅ Lightweight — Pure Lua backend + HTML5 frontend, zero external dependencies
• ✅ Low Resource — Minimal CPU footprint on embedded devices

Architecture

Backend

• Daemon (levelmeter-daemon.lua) — Lua daemon using ALSA capture
  • Reads audio frames from ALSA device
  • Calculates RMS, peak, clipping detection
  • Exposes HTTP JSON API on 127.0.0.1:8765
  • Auto-restarts via procd service manager

Frontend

• LuCI Web UI — Real-time dashboard
  • RESTful polling (100ms default)
  • Canvas-based VU meter visualization
  • Device management
  • Configuration panel

Init Script

• procd Service — Managed service lifecycle

Installation

Quick Install (Auto-Script)

# On your OpenWrt router
ssh root@192.168.1.1 'bash -s' < <(curl -fsSL https://raw.githubusercontent.com/MarcoRavich/OWLevelMeter/main/install.sh)

Manual Installation

1. Install dependencies:

   opkg install alsa-utils alsa-lib

2. Copy files to router:

   git clone https://github.com/MarcoRavich/OWLevelMeter.git
   cd OWLevelMeter
   
   scp levelmeter-daemon.lua root@192.168.1.1:/usr/bin/
   ssh root@192.168.1.1 chmod +x /usr/bin/levelmeter-daemon
   
   scp etc/init.d/levelmeter root@192.168.1.1:/etc/init.d/
   ssh root@192.168.1.1 chmod +x /etc/init.d/levelmeter
   
   scp etc/config/levelmeter root@192.168.1.1:/etc/config/
   
   ssh root@192.168.1.1 mkdir -p /usr/share/luci-app-levelmeter/luasrc/{controller/admin,model/cbi/admin,view/admin}
   
   scp luci/controller/admin/levelmeter.lua root@192.168.1.1:/usr/share/luci-app-levelmeter/luasrc/controller/admin/
   scp luci/model/cbi/admin/levelmeter.lua root@192.168.1.1:/usr/share/luci-app-levelmeter/luasrc/model/cbi/admin/
   scp luci/view/admin/levelmeter_status.htm root@192.168.1.1:/usr/share/luci-app-levelmeter/luasrc/view/admin/
   
   ssh root@192.168.1.1 '/etc/init.d/levelmeter enable && /etc/init.d/levelmeter start'

3. Access the UI:

   http://192.168.1.1/luci/admin/services/levelmeter
   

Configuration

Via LuCI Web Interface

Navigate to System → Audio Level Meter to:

• Select audio input device
• Configure sample rate
• Adjust frame size
• Enable/disable service

Via UCI Command Line

# Set device (hw:0,0 = Card 0, Device 0)
uci set levelmeter.general.device="0"
uci set levelmeter.general.card="0"

# Enable service
uci set levelmeter.general.enabled="1"

# Save and restart
uci commit levelmeter
/etc/init.d/levelmeter restart

UCI Config File (/etc/config/levelmeter)

config general
    option enabled '1'
    option device 'hw:0,0'
    option card '0'
    option channels '2'
    option sample_rate '48000'
    option frame_size '1024'
    option http_port '8765'

API Endpoints

GET /api/meter

Returns current audio metrics in JSON format.

Response:

{
  "status": "ok",
  "device": "hw:0,0",
  "channels": 2,
  "dbL": -15.3,
  "dbR": -16.8,
  "peakL": -8.2,
  "peakR": -7.1,
  "clipping": false,
  "timestamp": 1704067200.123
}

GET /health

Health check endpoint.

Response:

{
  "status": "running"
}

Finding Your Audio Device

# List all ALSA devices
ssh root@192.168.1.1 'arecord -l'

# Example output:
# **** List of CAPTURE Hardware Devices ****
# card 0: PCH [HDA Intel PCH], device 0: ALC269 Analog [ALC269 Analog]
#   Subdevices: 1/1
#   Subdevice #0: subdevice #0

# Use format: hw:CARD,DEVICE
# For example: hw:0,0

Troubleshooting

Daemon not starting

# Check service status
ssh root@192.168.1.1 '/etc/init.d/levelmeter status'

# View logs
ssh root@192.168.1.1 'logread | grep levelmeter'

# Start manually with debug
ssh root@192.168.1.1 '/usr/bin/levelmeter-daemon config 0 2 48000'

No audio levels showing

1. Verify ALSA device exists:

   ssh root@192.168.1.1 'arecord -l'

2. Test direct audio capture:

   ssh root@192.168.1.1 'arecord -D hw:0,0 -f S16_LE -c 2 -r 48000 -t wav /tmp/test.wav &'
   sleep 5
   ssh root@192.168.1.1 'kill %1'

3. Check HTTP API directly:

   curl -s http://192.168.1.1:8765/api/meter | jq .

Device selection not working

Clear old configuration:

ssh root@192.168.1.1 'rm /etc/config/levelmeter && /etc/init.d/levelmeter restart'

Extending to Multi-Channel

To support more than 2 channels:

1. Edit /etc/config/levelmeter:

   option channels '6'
   

2. Modify levelmeter-daemon.lua:

   • Update channel parsing in read_and_analyze_frame()
   • Add peak tracking for each channel

3. Update luci/view/admin/levelmeter_status.htm:

   • Add more VU meter bars in JavaScript renderMeters()

Performance

• CPU Usage: ~2-5% on typical OpenWrt router (MT7621)
• Memory: ~5-10 MB (daemon + LuCI process)
• Update Rate: 100ms default (configurable)
• Latency: ~200-300ms (arecord buffering + HTTP polling)

License

Based on LevelMeter by MrMazure

Contributing

Pull requests welcome! Areas for improvement:

• Multi-channel support
• Spectrum analyzer
• LUFS metering
• WebSocket streaming (lower latency)
• Mobile app

Support

For issues and feature requests, open an issue on GitHub.