Add graphical signal meter for APRS decoding

Backend changes (routes/aprs.py):
- Remove -q h flag from direwolf to enable audio level output
- Add parse_audio_level() to extract levels from direwolf output
- Add rate-limiting (max 10 updates/sec, min 2-level change)
- Push meter events to SSE queue as type='meter'

Frontend changes:
- Add signal meter widget to APRS sidebar
- Horizontal bar gauge with gradient (green->cyan->yellow->red)
- Numeric level display (0-100)
- "BURST" indicator for levels >70
- Status text (weak/moderate/strong signal)
- "No RF activity" state after 5 seconds of silence
- CSS styles in static/css/modes/aprs.css

Also added UK region to dropdown (same freq as Europe: 144.800)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

routes/aprs.py

@@ -50,6 +50,12 @@ aprs_station_count = 0
 aprs_last_packet_time = None
 aprs_stations = {}  # callsign -> station data
 
+# Meter rate limiting
+_last_meter_time = 0.0
+_last_meter_level = -1
+METER_MIN_INTERVAL = 0.1  # Max 10 updates/sec
+METER_MIN_CHANGE = 2  # Only send if level changes by at least this much
+
 
 def find_direwolf() -> Optional[str]:
     """Find direwolf binary."""
@@ -275,14 +281,64 @@ def parse_weather(data: str) -> dict:
     return weather
 
 
+def parse_audio_level(line: str) -> Optional[int]:
+    """Parse direwolf audio level line and return normalized level (0-100).
+
+    Direwolf outputs lines like:
+        Audio level = 34(18/16)   [NONE]   __||||||______
+        [0.4] Audio level = 57(34/32)   [NONE]   __||||||||||||______
+
+    The first number after "Audio level = " is the main level indicator.
+    We normalize it to 0-100 scale (direwolf typically outputs 0-100+).
+    """
+    # Match "Audio level = NN" pattern
+    match = re.search(r'Audio level\s*=\s*(\d+)', line, re.IGNORECASE)
+    if match:
+        raw_level = int(match.group(1))
+        # Normalize: direwolf levels are typically 0-100, but can go higher
+        # Clamp to 0-100 range
+        normalized = min(max(raw_level, 0), 100)
+        return normalized
+    return None
+
+
+def should_send_meter_update(level: int) -> bool:
+    """Rate-limit meter updates to avoid spamming SSE.
+
+    Only send if:
+    - At least METER_MIN_INTERVAL seconds have passed, OR
+    - Level changed by at least METER_MIN_CHANGE
+    """
+    global _last_meter_time, _last_meter_level
+
+    now = time.time()
+    time_ok = (now - _last_meter_time) >= METER_MIN_INTERVAL
+    change_ok = abs(level - _last_meter_level) >= METER_MIN_CHANGE
+
+    if time_ok or change_ok:
+        _last_meter_time = now
+        _last_meter_level = level
+        return True
+    return False
+
+
 def stream_aprs_output(rtl_process: subprocess.Popen, decoder_process: subprocess.Popen) -> None:
-    """Stream decoded APRS packets to queue.
+    """Stream decoded APRS packets and audio level meter to queue.
 
     This function reads from the decoder's stdout (text mode, line-buffered).
     The decoder's stderr is merged into stdout (STDOUT) to avoid deadlocks.
     rtl_fm's stderr is sent to DEVNULL for the same reason.
+
+    Outputs two types of messages to the queue:
+    - type='aprs': Decoded APRS packets
+    - type='meter': Audio level meter readings (rate-limited)
     """
     global aprs_packet_count, aprs_station_count, aprs_last_packet_time, aprs_stations
+    global _last_meter_time, _last_meter_level
+
+    # Reset meter state
+    _last_meter_time = 0.0
+    _last_meter_level = -1
 
     try:
         app_module.aprs_queue.put({'type': 'status', 'status': 'started'})
@@ -293,6 +349,18 @@ def stream_aprs_output(rtl_process: subprocess.Popen, decoder_process: subproces
             if not line:
                 continue
 
+            # Check for audio level line first (for signal meter)
+            audio_level = parse_audio_level(line)
+            if audio_level is not None:
+                if should_send_meter_update(audio_level):
+                    meter_msg = {
+                        'type': 'meter',
+                        'level': audio_level,
+                        'ts': datetime.utcnow().isoformat() + 'Z'
+                    }
+                    app_module.aprs_queue.put(meter_msg)
+                continue  # Audio level lines are not packets
+
             # multimon-ng prefixes decoded packets with "AFSK1200: "
             if line.startswith('AFSK1200:'):
                 line = line[9:].strip()
@@ -489,7 +557,7 @@ def start_aprs() -> Response:
         # -r 22050 = sample rate (must match rtl_fm -s)
         # -b 16 = 16-bit signed samples
         # -t 0 = disable text colors (for cleaner parsing)
-        # -q h = quiet: suppress audio level heard line (keeps packet output)
+        # NOTE: We do NOT use -q h here so we get audio level lines for the signal meter
         # - = read audio from stdin (must be last argument)
         decoder_cmd = [
             direwolf_path,
@@ -498,7 +566,6 @@ def start_aprs() -> Response:
             '-r', '22050',
             '-b', '16',
             '-t', '0',
-            '-q', 'h',
             '-'
         ]
         decoder_name = 'direwolf'

static/css/modes/aprs.css

@@ -46,3 +46,86 @@
 .aprs-stat-label {
     color: var(--text-muted);
 }
+
+/* Signal Meter Styles */
+.aprs-signal-meter {
+    margin-top: 12px;
+    padding: 10px;
+    background: rgba(0,0,0,0.3);
+    border: 1px solid var(--border-color);
+    border-radius: 4px;
+}
+.aprs-meter-header {
+    display: flex;
+    align-items: center;
+    gap: 8px;
+    margin-bottom: 8px;
+}
+.aprs-meter-label {
+    font-size: 10px;
+    font-weight: bold;
+    letter-spacing: 1px;
+    color: var(--text-secondary);
+}
+.aprs-meter-value {
+    font-size: 12px;
+    font-weight: bold;
+    font-family: monospace;
+    color: var(--accent-cyan);
+    min-width: 24px;
+}
+.aprs-meter-burst {
+    font-size: 9px;
+    font-weight: bold;
+    color: var(--accent-yellow);
+    background: rgba(255, 193, 7, 0.2);
+    padding: 2px 6px;
+    border-radius: 3px;
+    animation: burst-flash 0.3s ease-out;
+}
+@keyframes burst-flash {
+    0% { opacity: 1; transform: scale(1.1); }
+    100% { opacity: 1; transform: scale(1); }
+}
+.aprs-meter-bar-container {
+    position: relative;
+    height: 16px;
+    background: rgba(0,0,0,0.4);
+    border-radius: 3px;
+    overflow: hidden;
+    margin-bottom: 4px;
+}
+.aprs-meter-bar {
+    height: 100%;
+    width: 0%;
+    background: linear-gradient(90deg,
+        var(--accent-green) 0%,
+        var(--accent-cyan) 50%,
+        var(--accent-yellow) 75%,
+        var(--accent-red) 100%
+    );
+    border-radius: 3px;
+    transition: width 0.1s ease-out;
+}
+.aprs-meter-bar.no-signal {
+    opacity: 0.3;
+}
+.aprs-meter-ticks {
+    display: flex;
+    justify-content: space-between;
+    font-size: 8px;
+    color: var(--text-muted);
+    padding: 0 2px;
+}
+.aprs-meter-status {
+    font-size: 9px;
+    color: var(--text-muted);
+    text-align: center;
+    margin-top: 6px;
+}
+.aprs-meter-status.active {
+    color: var(--accent-green);
+}
+.aprs-meter-status.no-signal {
+    color: var(--accent-yellow);
+}

templates/index.html

@@ -5949,6 +5949,9 @@
         let isAprsRunning = false;
         let aprsPacketCount = 0;
         let aprsStationCount = 0;
+        let aprsMeterLastUpdate = 0;
+        let aprsMeterCheckInterval = null;
+        const APRS_METER_TIMEOUT = 5000; // 5 seconds for "no signal" state
 
         function checkAprsTools() {
             fetch('/aprs/tools')
@@ -6052,6 +6055,10 @@
                     updateAprsStatus('listening', data.frequency);
                     document.getElementById('aprsStatusStations').textContent = '0';
                     document.getElementById('aprsStatusPackets').textContent = '0';
+                    // Show signal meter
+                    document.getElementById('aprsSignalMeter').style.display = 'block';
+                    resetAprsMeter();
+                    startAprsMeterCheck();
                     startAprsStream();
                 } else {
                     alert('APRS Error: ' + data.message);
@@ -6071,10 +6078,13 @@
                     isAprsRunning = false;
                     document.getElementById('startAprsBtn').style.display = 'block';
                     document.getElementById('stopAprsBtn').style.display = 'none';
-                    // Hide sidebar status bar
+                    // Hide sidebar status bar and signal meter
                     document.getElementById('aprsStatusBar').style.display = 'none';
+                    document.getElementById('aprsSignalMeter').style.display = 'none';
                     document.getElementById('aprsMapStatus').textContent = 'STANDBY';
                     document.getElementById('aprsMapStatus').style.color = '';
+                    // Stop meter check interval
+                    stopAprsMeterCheck();
                     if (aprsEventSource) {
                         aprsEventSource.close();
                         aprsEventSource = null;
@@ -6099,6 +6109,9 @@
                         updateAprsStatus('tracking');
                     }
                     processAprsPacket(data);
+                } else if (data.type === 'meter') {
+                    // Update signal meter
+                    updateAprsMeter(data.level);
                 }
             };
 
@@ -6108,6 +6121,91 @@
             };
         }
 
+        // Signal Meter Functions
+        function resetAprsMeter() {
+            aprsMeterLastUpdate = 0;
+            const bar = document.getElementById('aprsMeterBar');
+            const value = document.getElementById('aprsMeterValue');
+            const burst = document.getElementById('aprsMeterBurst');
+            const status = document.getElementById('aprsMeterStatus');
+            if (bar) {
+                bar.style.width = '0%';
+                bar.classList.remove('no-signal');
+            }
+            if (value) value.textContent = '--';
+            if (burst) burst.style.display = 'none';
+            if (status) {
+                status.textContent = 'Waiting for signal...';
+                status.className = 'aprs-meter-status';
+            }
+        }
+
+        function updateAprsMeter(level) {
+            aprsMeterLastUpdate = Date.now();
+            const bar = document.getElementById('aprsMeterBar');
+            const value = document.getElementById('aprsMeterValue');
+            const burst = document.getElementById('aprsMeterBurst');
+            const status = document.getElementById('aprsMeterStatus');
+
+            if (bar) {
+                bar.style.width = level + '%';
+                bar.classList.remove('no-signal');
+            }
+            if (value) value.textContent = level;
+
+            // Show burst indicator for high levels (>70)
+            if (burst) {
+                if (level > 70) {
+                    burst.style.display = 'inline';
+                    // Remove and re-add to trigger animation
+                    burst.style.animation = 'none';
+                    burst.offsetHeight; // Trigger reflow
+                    burst.style.animation = null;
+                } else {
+                    burst.style.display = 'none';
+                }
+            }
+
+            // Update status text
+            if (status) {
+                status.className = 'aprs-meter-status active';
+                if (level < 10) {
+                    status.textContent = 'Low signal / noise floor';
+                } else if (level < 30) {
+                    status.textContent = 'Weak signal detected';
+                } else if (level < 60) {
+                    status.textContent = 'Moderate signal';
+                } else {
+                    status.textContent = 'Strong signal / packet burst';
+                }
+            }
+        }
+
+        function startAprsMeterCheck() {
+            // Check for no-signal state every second
+            aprsMeterCheckInterval = setInterval(function() {
+                if (aprsMeterLastUpdate > 0 && (Date.now() - aprsMeterLastUpdate) > APRS_METER_TIMEOUT) {
+                    // No meter updates for 5 seconds - show no-signal state
+                    const bar = document.getElementById('aprsMeterBar');
+                    const status = document.getElementById('aprsMeterStatus');
+                    const burst = document.getElementById('aprsMeterBurst');
+                    if (bar) bar.classList.add('no-signal');
+                    if (burst) burst.style.display = 'none';
+                    if (status) {
+                        status.textContent = 'No RF activity / silence';
+                        status.className = 'aprs-meter-status no-signal';
+                    }
+                }
+            }, 1000);
+        }
+
+        function stopAprsMeterCheck() {
+            if (aprsMeterCheckInterval) {
+                clearInterval(aprsMeterCheckInterval);
+                aprsMeterCheckInterval = null;
+            }
+        }
+
         function processAprsPacket(packet) {
             // Update packet log
             const logEl = document.getElementById('aprsPacketLog');

templates/partials/modes/aprs.html

@@ -17,6 +17,7 @@
                             <select id="aprsRegion">
                                 <option value="north_america">North America (144.390)</option>
                                 <option value="europe">Europe (144.800)</option>
+                                <option value="uk">UK (144.800)</option>
                                 <option value="australia">Australia (145.175)</option>
                                 <option value="japan">Japan (144.640)</option>
                             </select>
@@ -48,4 +49,23 @@
                             <span class="aprs-stat"><span class="aprs-stat-label">PACKETS:</span> <span id="aprsStatusPackets">0</span></span>
                         </div>
                     </div>
+                    <!-- Signal Meter -->
+                    <div id="aprsSignalMeter" class="aprs-signal-meter" style="display: none;">
+                        <div class="aprs-meter-header">
+                            <span class="aprs-meter-label">SIGNAL</span>
+                            <span class="aprs-meter-value" id="aprsMeterValue">--</span>
+                            <span class="aprs-meter-burst" id="aprsMeterBurst" style="display: none;">BURST</span>
+                        </div>
+                        <div class="aprs-meter-bar-container">
+                            <div class="aprs-meter-bar" id="aprsMeterBar"></div>
+                            <div class="aprs-meter-ticks">
+                                <span>0</span>
+                                <span>25</span>
+                                <span>50</span>
+                                <span>75</span>
+                                <span>100</span>
+                            </div>
+                        </div>
+                        <div class="aprs-meter-status" id="aprsMeterStatus">Waiting for signal...</div>
+                    </div>
                 </div>