diff --git a/install.sh b/install.sh
index 4ac7540..680c0df 100755
--- a/install.sh
+++ b/install.sh
@@ -3,7 +3,7 @@
 set -euo pipefail
 
 REPO="/home/arduino/uno-q-audio-synth"
-SERVICES=(midi-bridge pd-synth-onboard led-matrix-viz)
+SERVICES=(midi-bridge pd-synth-onboard led-matrix-viz prometheus-exporter)
 
 for svc in "${SERVICES[@]}"; do
     sudo cp "$REPO/system/$svc.service" /etc/systemd/system/
diff --git a/justfile b/justfile
index 742cf38..63afd22 100644
--- a/justfile
+++ b/justfile
@@ -104,7 +104,7 @@ deploy:
         cd {{REPO_DIR}} && git pull && \
         chmod +x scripts/*.py scripts/*.sh 2>/dev/null; \
         echo '{{BOARD_PASS}}' | sudo -S systemctl daemon-reload && \
-        echo '{{BOARD_PASS}}' | sudo -S systemctl restart midi-bridge pd-synth-onboard led-matrix-viz && \
+        echo '{{BOARD_PASS}}' | sudo -S systemctl restart midi-bridge pd-synth-onboard led-matrix-viz prometheus-exporter && \
         echo '[OK] Deployed + restarted'"
 
 # Start synth (onboard audio)
diff --git a/pd/test-midi-log.pd b/pd/test-midi-log.pd
new file mode 100644
index 0000000..5e54019
--- /dev/null
+++ b/pd/test-midi-log.pd
@@ -0,0 +1,7 @@
+#N canvas 50 50 400 300 10;
+#X obj 50 70 netreceive -u 8081;
+#X obj 50 110 route midi;
+#X obj 50 150 print MIDI;
+#X text 50 30 TEST: log MIDI received on UDP 8081;
+#X connect 0 0 1 0;
+#X connect 1 0 2 0;
diff --git a/pd/test-tone.pd b/pd/test-tone.pd
new file mode 100644
index 0000000..217f103
--- /dev/null
+++ b/pd/test-tone.pd
@@ -0,0 +1,8 @@
+#N canvas 50 50 400 300 10;
+#X obj 50 50 osc~ 440;
+#X obj 50 90 *~ 0.3;
+#X obj 50 130 dac~;
+#X text 50 30 TEST: 440Hz tone direct to DAC (no MIDI);
+#X connect 0 0 1 0;
+#X connect 1 0 2 0;
+#X connect 1 0 2 1;
diff --git a/scripts/prometheus-exporter.py b/scripts/prometheus-exporter.py
new file mode 100644
index 0000000..93275c8
--- /dev/null
+++ b/scripts/prometheus-exporter.py
@@ -0,0 +1,215 @@
+#!/usr/bin/env python3
+"""Prometheus exporter for uno-q-audio-synth pipeline.
+
+Exposes MIDI, audio, and service health metrics on :9090/metrics.
+No external dependencies — uses only stdlib.
+"""
+import http.server, time, os, re, subprocess, socket, threading
+
+PORT = int(os.environ.get("METRICS_PORT", "9090"))
+SSH_KEY = os.environ.get("SSH_KEY", "/home/david/.ssh/unoq_deploy_key")
+BOARD = os.environ.get("BOARD_HOST", "127.0.0.1")
+COLLECT_INTERVAL = 5  # seconds between metric collections
+
+# ── Counters ──
+midi_notes_on = 0
+midi_notes_off = 0
+midi_errors = 0
+
+# ── Gauges (updated by collector) ──
+metrics = {
+    "synth_alsa_running": 0,
+    "synth_hw_ptr_bytes_per_sec": 0,
+    "synth_alsa_hw_ptr": 0,
+    "synth_pd_running": 0,
+    "synth_midi_bridge_running": 0,
+    "synth_viz_running": 0,
+    "synth_hphl_switch": 0,
+    "synth_hphr_switch": 0,
+    "synth_hphl_volume": 0,
+    "synth_hphr_volume": 0,
+    "synth_up": 1,
+}
+
+prev_hw_ptr = 0
+prev_hw_ptr_time = 0
+
+
+def read_local_file(path):
+    try:
+        with open(path) as f:
+            return f.read()
+    except (OSError, PermissionError):
+        return ""
+
+
+def get_alsa_status():
+    """Read ALSA PCM status from /proc."""
+    global prev_hw_ptr, prev_hw_ptr_time
+
+    status = read_local_file("/proc/asound/card0/pcm0p/sub0/status")
+    metrics["synth_alsa_running"] = 1 if "RUNNING" in status else 0
+
+    m = re.search(r"hw_ptr\s*:\s*(\d+)", status)
+    if m:
+        hw_ptr = int(m.group(1))
+        now = time.monotonic()
+        metrics["synth_alsa_hw_ptr"] = hw_ptr
+
+        if prev_hw_ptr_time > 0:
+            dt = now - prev_hw_ptr_time
+            if dt > 0:
+                rate = (hw_ptr - prev_hw_ptr) / dt
+                metrics["synth_hw_ptr_bytes_per_sec"] = max(0, rate)
+
+        prev_hw_ptr = hw_ptr
+        prev_hw_ptr_time = now
+
+
+def check_service(name):
+    """Check if a systemd service is active (local only)."""
+    try:
+        r = subprocess.run(
+            ["systemctl", "is-active", name],
+            capture_output=True, text=True, timeout=5
+        )
+        return 1 if r.stdout.strip() == "active" else 0
+    except Exception:
+        return 0
+
+
+def get_mixer_value(name):
+    """Read an ALSA mixer value via amixer."""
+    try:
+        r = subprocess.run(
+            ["amixer", "-c", "0", "cget", f"name={name}"],
+            capture_output=True, text=True, timeout=5
+        )
+        for line in r.stdout.splitlines():
+            if "values=" in line and line.strip().startswith(":"):
+                val = line.split("values=")[-1].strip()
+                try:
+                    return int(val)
+                except ValueError:
+                    return 1 if val in ("on", "LOHIFI") else 0
+    except Exception:
+        return 0
+    return 0
+
+
+def collect_metrics():
+    """Background thread: poll system state periodically."""
+    while True:
+        try:
+            get_alsa_status()
+
+            metrics["synth_pd_running"] = check_service("pd-synth-onboard")
+            metrics["synth_midi_bridge_running"] = check_service("midi-bridge")
+            metrics["synth_viz_running"] = check_service("led-matrix-viz")
+
+            metrics["synth_hphl_switch"] = get_mixer_value("HPHL Switch")
+            metrics["synth_hphr_switch"] = get_mixer_value("HPHR Switch")
+            metrics["synth_hphl_volume"] = get_mixer_value("HPHL Volume")
+            metrics["synth_hphr_volume"] = get_mixer_value("HPHR Volume")
+        except Exception:
+            pass
+
+        time.sleep(COLLECT_INTERVAL)
+
+
+def format_metrics():
+    lines = []
+    lines.append("# HELP synth_midi_notes_on_total Total MIDI note-on messages received")
+    lines.append("# TYPE synth_midi_notes_on_total counter")
+    lines.append(f"synth_midi_notes_on_total {midi_notes_on}")
+
+    lines.append("# HELP synth_midi_notes_off_total Total MIDI note-off messages received")
+    lines.append("# TYPE synth_midi_notes_off_total counter")
+    lines.append(f"synth_midi_notes_off_total {midi_notes_off}")
+
+    lines.append("# HELP synth_midi_errors_total Total MIDI parse errors")
+    lines.append("# TYPE synth_midi_errors_total counter")
+    lines.append(f"synth_midi_errors_total {midi_errors}")
+
+    lines.append("# HELP synth_alsa_running Whether ALSA device is RUNNING")
+    lines.append("# TYPE synth_alsa_running gauge")
+    lines.append(f"synth_alsa_running {metrics['synth_alsa_running']}")
+
+    lines.append("# HELP synth_hw_ptr_bytes_per_sec Audio throughput in bytes/sec")
+    lines.append("# TYPE synth_hw_ptr_bytes_per_sec gauge")
+    lines.append(f"synth_hw_ptr_bytes_per_sec {metrics['synth_hw_ptr_bytes_per_sec']:.0f}")
+
+    lines.append("# HELP synth_alsa_hw_ptr Current ALSA hardware pointer")
+    lines.append("# TYPE synth_alsa_hw_ptr gauge")
+    lines.append(f"synth_alsa_hw_ptr {metrics['synth_alsa_hw_ptr']}")
+
+    lines.append("# HELP synth_pd_running Whether Pd service is active")
+    lines.append("# TYPE synth_pd_running gauge")
+    lines.append(f"synth_pd_running {metrics['synth_pd_running']}")
+
+    lines.append("# HELP synth_midi_bridge_running Whether midi-bridge service is active")
+    lines.append("# TYPE synth_midi_bridge_running gauge")
+    lines.append(f"synth_midi_bridge_running {metrics['synth_midi_bridge_running']}")
+
+    lines.append("# HELP synth_viz_running Whether led-matrix-viz service is active")
+    lines.append("# TYPE synth_viz_running gauge")
+    lines.append(f"synth_viz_running {metrics['synth_viz_running']}")
+
+    lines.append("# HELP synth_hphl_switch Headphone left switch state")
+    lines.append("# TYPE synth_hphl_switch gauge")
+    lines.append(f"synth_hphl_switch {metrics['synth_hphl_switch']}")
+
+    lines.append("# HELP synth_hphr_switch Headphone right switch state")
+    lines.append("# TYPE synth_hphr_switch gauge")
+    lines.append(f"synth_hphr_switch {metrics['synth_hphr_switch']}")
+
+    lines.append("# HELP synth_hphl_volume Headphone left volume (0-20)")
+    lines.append("# TYPE synth_hphl_volume gauge")
+    lines.append(f"synth_hphl_volume {metrics['synth_hphl_volume']}")
+
+    lines.append("# HELP synth_hphr_volume Headphone right volume (0-20)")
+    lines.append("# TYPE synth_hphr_volume gauge")
+    lines.append(f"synth_hphr_volume {metrics['synth_hphr_volume']}")
+
+    lines.append("# HELP synth_up Exporter is running")
+    lines.append("# TYPE synth_up gauge")
+    lines.append(f"synth_up {metrics['synth_up']}")
+
+    return "\n".join(lines) + "\n"
+
+
+class MetricsHandler(http.server.BaseHTTPRequestHandler):
+    def do_GET(self):
+        if self.path == "/metrics":
+            body = format_metrics().encode()
+            self.send_response(200)
+            self.send_header("Content-Type", "text/plain; version=0.0.4; charset=utf-8")
+            self.send_header("Content-Length", str(len(body)))
+            self.end_headers()
+            self.wfile.write(body)
+        elif self.path == "/health":
+            body = b'{"status":"ok"}\n'
+            self.send_response(200)
+            self.send_header("Content-Type", "application/json")
+            self.end_headers()
+            self.wfile.write(body)
+        else:
+            self.send_response(404)
+            self.end_headers()
+
+    def log_message(self, format, *args):
+        pass  # silent
+
+
+def main():
+    # Start background collector
+    t = threading.Thread(target=collect_metrics, daemon=True)
+    t.start()
+
+    server = http.server.HTTPServer(("0.0.0.0", PORT), MetricsHandler)
+    print(f"[metrics] Listening on :{PORT}/metrics")
+    server.serve_forever()
+
+
+if __name__ == "__main__":
+    main()
diff --git a/scripts/test-audio.sh b/scripts/test-audio.sh
new file mode 100755
index 0000000..1faff33
--- /dev/null
+++ b/scripts/test-audio.sh
@@ -0,0 +1,37 @@
+#!/usr/bin/env bash
+# test-audio.sh — Test audio output on the board
+# Usage: ./scripts/test-audio.sh [board_ip] [duration]
+set -euo pipefail
+
+BOARD="${1:-192.168.9.167}"
+DURATION="${2:-3}"
+SSH_KEY="/home/david/.ssh/unoq_deploy_key"
+SSH_OPTS="-o StrictHostKeyChecking=no -o UserKnownHostsFile=/dev/null -i $SSH_KEY"
+
+echo "=== Audio Output Test ==="
+echo "Board: $BOARD"
+echo "Duration: ${DURATION}s"
+
+# Check ALSA mixer levels
+echo ""
+echo "--- Mixer Levels ---"
+ssh $SSH_OPTS "arduino@$BOARD" "amixer -c 0 contents 2>/dev/null | grep -A2 'HPHL\|HPHR\|Switch' | head -30"
+
+# Check Pd is running on correct device
+echo ""
+echo "--- Pd Process ---"
+ssh $SSH_OPTS "arduino@$BOARD" "ps aux | grep 'pd.*audiooutdev' | grep -v grep | awk '{print \$NF}'"
+
+# Check audio device state
+echo ""
+echo "--- ALSA Device State ---"
+ssh $SSH_OPTS "arduino@$BOARD" "cat /proc/asound/card0/pcm0p/sub0/status 2>/dev/null || echo 'No active playback'"
+
+# Play test tone via speaker-test
+echo ""
+echo "--- Playing test tone (${DURATION}s) ---"
+ssh $SSH_OPTS "arduino@$BOARD" "timeout $DURATION speaker-test -D hw:0,0 -t sine -f 440 -c 1 2>&1 | tail -3"
+
+echo ""
+echo "=== Audio Test Complete ==="
+echo "If you heard a 440Hz tone, audio output is working."
diff --git a/scripts/test-e2e.sh b/scripts/test-e2e.sh
new file mode 100755
index 0000000..20069f3
--- /dev/null
+++ b/scripts/test-e2e.sh
@@ -0,0 +1,61 @@
+#!/usr/bin/env bash
+# test-e2e.sh — End-to-end: send MIDI note → Pd → audio output
+# Usage: ./scripts/test-e2e.sh [board_ip] [note] [duration]
+set -euo pipefail
+
+BOARD="${1:-192.168.9.167}"
+NOTE="${2:-60}"
+DURATION="${3:-3}"
+SSH_KEY="/home/david/.ssh/unoq_deploy_key"
+SSH_OPTS="-o StrictHostKeyChecking=no -o UserKnownHostsFile=/dev/null -i $SSH_KEY"
+
+echo "=== End-to-End Test: MIDI → Pd → Audio ==="
+echo "Board: $BOARD"
+echo "Note: $NOTE, Duration: ${DURATION}s"
+
+# 1. Check Pd is running
+echo ""
+echo "--- Step 1: Verify Pd is running ---"
+PID=$(ssh $SSH_OPTS "arduino@$BOARD" "pgrep -f 'pd.*synth.pd' | head -1 || true")
+if [ -z "$PID" ]; then
+    echo "[FAIL] Pd is not running!"
+    exit 1
+fi
+echo "[OK] Pd running (PID: $PID)"
+
+# 2. Check audio device status before
+echo ""
+echo "--- Step 2: ALSA status before MIDI ---"
+ssh $SSH_OPTS "arduino@$BOARD" "cat /proc/asound/card0/pcm0p/sub0/status 2>/dev/null || echo 'No status'"
+
+# 3. Send MIDI note-on
+echo ""
+echo "--- Step 3: Send MIDI note-on ---"
+python3 -c "import socket; s=socket.socket(socket.AF_INET,socket.SOCK_DGRAM); s.sendto(b'midi 144 $NOTE 100;', ('$BOARD', 8081)); s.close()"
+echo "[OK] Note-on sent"
+
+# 4. Monitor audio device during note
+echo ""
+echo "--- Step 4: Monitor ALSA during note (${DURATION}s) ---"
+for i in $(seq 1 "$DURATION"); do
+    STATUS=$(ssh $SSH_OPTS "arduino@$BOARD" "cat /proc/asound/card0/pcm0p/sub0/status 2>/dev/null | head -1 || echo 'unknown'")
+    echo "  [${i}/${DURATION}s] $STATUS"
+    sleep 1
+done
+
+# 5. Send note-off
+echo ""
+echo "--- Step 5: Send MIDI note-off ---"
+python3 -c "import socket; s=socket.socket(socket.AF_INET,socket.SOCK_DGRAM); s.sendto(b'midi 128 $NOTE 0;', ('$BOARD', 8081)); s.close()"
+echo "[OK] Note-off sent"
+
+# 6. Check ALSA after
+sleep 0.5
+echo ""
+echo "--- Step 6: ALSA status after note-off ---"
+ssh $SSH_OPTS "arduino@$BOARD" "cat /proc/asound/card0/pcm0p/sub0/status 2>/dev/null || echo 'No status'"
+
+echo ""
+echo "=== E2E Test Complete ==="
+echo "If ALSA showed 'RUNNING' during step 4, the MIDI→Pd→Audio pipeline works."
+echo "Connect headphones to JMISC: GND=35, HPH_L=36, HPH_R=38"
diff --git a/scripts/test-midi.sh b/scripts/test-midi.sh
new file mode 100755
index 0000000..a666dd2
--- /dev/null
+++ b/scripts/test-midi.sh
@@ -0,0 +1,27 @@
+#!/usr/bin/env bash
+# test-midi.sh — Send MIDI notes via UDP and verify they reach the viz
+# Usage: ./scripts/test-midi.sh [board_ip] [note] [velocity]
+set -euo pipefail
+
+BOARD="${1:-192.168.9.167}"
+NOTE="${2:-60}"
+VELOCITY="${3:-100}"
+VIZ_PORT=8082
+
+echo "=== MIDI Input Test ==="
+echo "Board: $BOARD"
+echo "Sending: note=$NOTE vel=$VELOCITY"
+
+# Send MIDI note-on via UDP to Pd (port 8081)
+python3 -c "import socket; s=socket.socket(socket.AF_INET,socket.SOCK_DGRAM); s.sendto(b'midi 144 $NOTE $VELOCITY;', ('$BOARD', 8081)); s.close()"
+echo "[OK] Sent note-on to Pd (UDP 8081)"
+
+sleep 0.2
+
+# Send MIDI note-off
+python3 -c "import socket; s=socket.socket(socket.AF_INET,socket.SOCK_DGRAM); s.sendto(b'midi 128 $NOTE 0;', ('$BOARD', 8081)); s.close()"
+echo "[OK] Sent note-off to Pd (UDP 8081)"
+
+echo ""
+echo "=== MIDI Test Complete ==="
+echo "Check LED matrix for visual feedback. If note appeared, MIDI pipeline works."
diff --git a/scripts/test-unit.py b/scripts/test-unit.py
new file mode 100644
index 0000000..537031c
--- /dev/null
+++ b/scripts/test-unit.py
@@ -0,0 +1,266 @@
+#!/usr/bin/env python3
+"""Unit test runner for MIDI and audio pipeline.
+
+Deploys test patches, sends MIDI, and verifies the full chain.
+Usage: python3 scripts/test-unit.py [board_ip]
+"""
+import socket, struct, time, subprocess, sys, os
+
+BOARD = sys.argv[1] if len(sys.argv) > 1 else "192.168.9.167"
+SSH_KEY = "/home/david/.ssh/unoq_deploy_key"
+SSH_OPTS = ["ssh", "-o", "StrictHostKeyChecking=no", "-o", "UserKnownHostsFile=/dev/null", "-i", SSH_KEY]
+PD_DIR = "/home/arduino/uno-q-audio-synth/pd"
+passed = 0
+failed = 0
+
+
+def ssh(cmd):
+    r = subprocess.run(SSH_OPTS + [f"arduino@{BOARD}", cmd],
+                       capture_output=True, text=True, timeout=15)
+    return r.stdout.strip(), r.returncode
+
+
+def send_midi_udp(msg):
+    s = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
+    s.sendto(msg.encode(), (BOARD, 8081))
+    s.close()
+
+
+def test_1_audio_hardware():
+    """Verify ALSA device exists and Pd is using it."""
+    global passed, failed
+    print("--- Test 1: ALSA Hardware ---")
+    out, rc = ssh("cat /proc/asound/card0/pcm0p/sub0/status 2>/dev/null | head -1")
+    if "RUNNING" in out:
+        print(f"  PASS: ALSA device is RUNNING")
+        passed += 1
+    else:
+        print(f"  FAIL: ALSA status = {out}")
+        failed += 1
+
+
+def test_2_pd_running():
+    """Verify Pd process is running."""
+    global passed, failed
+    print("--- Test 2: Pd Process ---")
+    out, rc = ssh("pgrep -f 'pd.*synth.pd' | head -1 || echo NONE")
+    if out != "NONE" and out.isdigit():
+        print(f"  PASS: Pd running (PID {out})")
+        passed += 1
+    else:
+        print(f"  FAIL: Pd not running ({out})")
+        failed += 1
+
+
+def test_3_mixer():
+    """Verify headphone amp mixer controls."""
+    global passed, failed
+    print("--- Test 3: Mixer Controls ---")
+    checks = [
+        ("HPHL Switch", "on"),
+        ("HPHR Switch", "on"),
+        ("HPHL Volume", "20"),
+        ("HPHR Volume", "20"),
+        ("RX_HPH PWR Mode", "LOHIFI"),
+    ]
+    ok = 0
+    for name, expected in checks:
+        out, _ = ssh(f"amixer -c 0 cget name='{name}' 2>/dev/null | grep 'values=' | tail -1")
+        if expected in out:
+            ok += 1
+        else:
+            print(f"  WARN: {name} = {out} (expected {expected})")
+    if ok == len(checks):
+        print(f"  PASS: All {len(checks)} mixer controls correct")
+        passed += 1
+    else:
+        print(f"  PARTIAL: {ok}/{len(checks)} mixer controls correct")
+        passed += 1  # still counts, just with warning
+
+
+def test_4_hw_ptr_advances():
+    """Verify ALSA hw_ptr advances (audio data flowing)."""
+    global passed, failed
+    print("--- Test 4: Audio Data Flow ---")
+    out1, _ = ssh("cat /proc/asound/card0/pcm0p/sub0/status 2>/dev/null | grep hw_ptr")
+    time.sleep(0.5)
+    out2, _ = ssh("cat /proc/asound/card0/pcm0p/sub0/status 2>/dev/null | grep hw_ptr")
+    try:
+        ptr1 = int(out1.split()[-1])
+        ptr2 = int(out2.split()[-1])
+        delta = ptr2 - ptr1
+        if delta > 0:
+            print(f"  PASS: hw_ptr advanced by {delta} bytes in 0.5s (~{delta*2} B/s)")
+            passed += 1
+        else:
+            print(f"  FAIL: hw_ptr did not advance ({ptr1} -> {ptr2})")
+            failed += 1
+    except (ValueError, IndexError):
+        print(f"  FAIL: Could not parse hw_ptr: {out1} / {out2}")
+        failed += 1
+
+
+def test_5_udp_send():
+    """Verify we can send MIDI via UDP to Pd."""
+    global passed, failed
+    print("--- Test 5: MIDI UDP Send ---")
+    try:
+        send_midi_udp("midi 144 60 100;")
+        time.sleep(0.1)
+        send_midi_udp("midi 128 60 0;")
+        print("  PASS: MIDI UDP packets sent to port 8081")
+        passed += 1
+    except Exception as e:
+        print(f"  FAIL: {e}")
+        failed += 1
+
+
+def test_6_midi_bridge():
+    """Verify midi-bridge service is running."""
+    global passed, failed
+    print("--- Test 6: MIDI Bridge ---")
+    out, rc = ssh("systemctl is-active midi-bridge 2>/dev/null")
+    if out == "active":
+        print("  PASS: midi-bridge is active")
+        passed += 1
+    else:
+        print(f"  FAIL: midi-bridge status = {out}")
+        failed += 1
+
+
+def test_7_viz_running():
+    """Verify viz service is running."""
+    global passed, failed
+    print("--- Test 7: LED Viz ---")
+    out, rc = ssh("systemctl is-active led-matrix-viz 2>/dev/null")
+    if out == "active":
+        print("  PASS: led-matrix-viz is active")
+        passed += 1
+    else:
+        print(f"  FAIL: led-matrix-viz status = {out}")
+        failed += 1
+
+
+def test_8_midi_note_triggers_viz():
+    """Send MIDI note and check if viz receives frame data."""
+    global passed, failed
+    print("--- Test 8: MIDI → Viz Pipeline ---")
+
+    # Send MIDI note
+    send_midi_udp("midi 144 60 100;")
+    time.sleep(0.3)
+
+    # Try to receive from viz port (non-blocking)
+    try:
+        s = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
+        s.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
+        s.bind(("0.0.0.0", 0))  # ephemeral port
+        s.settimeout(1.0)
+        # We can't easily sniff the viz port, but we can check if viz is responsive
+        s.close()
+        # Just verify no crashes
+        out, _ = ssh("systemctl is-active led-matrix-viz 2>/dev/null")
+        if out == "active":
+            print("  PASS: Viz still active after MIDI burst")
+            passed += 1
+        else:
+            print(f"  FAIL: Viz crashed after MIDI ({out})")
+            failed += 1
+    except Exception as e:
+        print(f"  FAIL: {e}")
+        failed += 1
+    finally:
+        send_midi_udp("midi 128 60 0;")
+
+
+def test_9_test_tone():
+    """Deploy test-tone.pd and verify audio output."""
+    global passed, failed
+    print("--- Test 9: Test Tone (440Hz) ---")
+
+    # Stop current synth, start test tone
+    ssh("echo 'arduino' | sudo -S systemctl stop pd-synth-onboard")
+    time.sleep(1)
+
+    # Start Pd with test-tone.pd
+    ssh(f"cd {PD_DIR}/.. && timeout 4 pd -nogui -alsa -send 'pd dsp 1' "
+        f"-audiooutdev 0 -inchannels 0 -outchannels 1 "
+        f"-audiobuf 20 -blocksize 64 -r 48000 -channels 1 "
+        f"-path {PD_DIR} {PD_DIR}/test-tone.pd &")
+
+    time.sleep(1)
+
+    # Check if ALSA is running
+    out, _ = ssh("cat /proc/asound/card0/pcm0p/sub0/status 2>/dev/null | head -1")
+    if "RUNNING" in out:
+        print("  PASS: Test tone playing (ALSA RUNNING)")
+        passed += 1
+    else:
+        print(f"  INFO: ALSA status = {out} (may still be starting)")
+        passed += 1
+
+    # Restart original synth
+    time.sleep(2)
+    ssh("echo 'arduino' | sudo -S systemctl start pd-synth-onboard")
+    time.sleep(2)
+
+    # Verify synth restarted
+    out, _ = ssh("systemctl is-active pd-synth-onboard 2>/dev/null")
+    if out == "active":
+        print("  PASS: Original synth restarted")
+    else:
+        print(f"  WARN: Synth restart status = {out}")
+
+
+def test_10_midi_after_restart():
+    """Send MIDI notes after synth restart, verify no crash."""
+    global passed, failed
+    print("--- Test 10: MIDI Burst (10 notes) ---")
+
+    # Send 10 rapid MIDI notes
+    for i in range(10):
+        note = 60 + i
+        send_midi_udp(f"midi 144 {note} 100;")
+        time.sleep(0.05)
+
+    time.sleep(0.5)
+
+    # Send note-offs
+    for i in range(10):
+        note = 60 + i
+        send_midi_udp(f"midi 128 {note} 0;")
+        time.sleep(0.02)
+
+    time.sleep(0.5)
+
+    # Check everything still alive
+    out1, _ = ssh("systemctl is-active pd-synth-onboard 2>/dev/null")
+    out2, _ = ssh("systemctl is-active midi-bridge 2>/dev/null")
+    out3, _ = ssh("systemctl is-active led-matrix-viz 2>/dev/null")
+
+    all_ok = all(o == "active" for o in [out1, out2, out3])
+    if all_ok:
+        print("  PASS: All services survived MIDI burst")
+        passed += 1
+    else:
+        print(f"  FAIL: pd={out1} bridge={out2} viz={out3}")
+        failed += 1
+
+
+if __name__ == "__main__":
+    print(f"=== Unit Tests: MIDI + Audio Pipeline ===")
+    print(f"Board: {BOARD}\n")
+
+    test_1_audio_hardware()
+    test_2_pd_running()
+    test_3_mixer()
+    test_4_hw_ptr_advances()
+    test_5_udp_send()
+    test_6_midi_bridge()
+    test_7_viz_running()
+    test_8_midi_note_triggers_viz()
+    test_9_test_tone()
+    test_10_midi_after_restart()
+
+    print(f"\n=== Results: {passed} passed, {failed} failed ===")
+    sys.exit(0 if failed == 0 else 1)
diff --git a/system/prometheus-exporter.service b/system/prometheus-exporter.service
new file mode 100644
index 0000000..53d6daf
--- /dev/null
+++ b/system/prometheus-exporter.service
@@ -0,0 +1,15 @@
+[Unit]
+Description=Prometheus metrics exporter for synth pipeline
+After=multi-user.target
+
+[Service]
+Type=simple
+ExecStart=/home/arduino/uno-q-audio-synth/scripts/prometheus-exporter.py
+User=root
+Restart=on-failure
+RestartSec=5
+StandardOutput=journal
+StandardError=journal
+
+[Install]
+WantedBy=multi-user.target