diff --git a/examples/netz/index.html b/examples/netz/index.html
index 2f9cda3..431a561 100644
--- a/examples/netz/index.html
+++ b/examples/netz/index.html
@@ -42,7 +42,7 @@
       }
     </style>
     <script src="https://cdn.jsdelivr.net/npm/p5@1.11.3/lib/p5.min.js"></script>
-    <script src="../../lib/WallPlotter.js?v=2.3.4"></script>
+    <script src="../../lib/WallPlotter.js?v=2.3.5"></script>
     <script src="sketch.js"></script>
   </head>
   <body>
diff --git a/examples/zickzack/index.html b/examples/zickzack/index.html
index 2f9cda3..431a561 100644
--- a/examples/zickzack/index.html
+++ b/examples/zickzack/index.html
@@ -42,7 +42,7 @@
       }
     </style>
     <script src="https://cdn.jsdelivr.net/npm/p5@1.11.3/lib/p5.min.js"></script>
-    <script src="../../lib/WallPlotter.js?v=2.3.4"></script>
+    <script src="../../lib/WallPlotter.js?v=2.3.5"></script>
     <script src="sketch.js"></script>
   </head>
   <body>
diff --git a/lib/WallPlotter.js b/lib/WallPlotter.js
index aadd8b2..c36af08 100644
--- a/lib/WallPlotter.js
+++ b/lib/WallPlotter.js
@@ -18,7 +18,7 @@ class WallPlotter {
   // Static constants
   // ---------------------------------------------------------------------------
 
-  static VERSION = '2.3.4';
+  static VERSION = '2.3.5';
   static MIN_FEED_MM_MIN = 1;
   static MAX_FEED_MM_MIN = 10000;
   /** Offline overlay size when not connected (mm) — 150×150 cm centred on origin */
@@ -32,6 +32,8 @@ class WallPlotter {
   /** If a USB write does not complete, the ACM device is usually gone. */
   static WRITE_TIMEOUT_MS = 3000;
   static RESUME_STORAGE_KEY = 'wallplotter.resume.v1';
+  /** Send a quiet M400 if the line has been silent this long (keeps USB awake). */
+  static KEEPALIVE_MS = 1200;
 
   // ---------------------------------------------------------------------------
   // Construction
@@ -118,6 +120,8 @@ class WallPlotter {
     this._okWaiter = null;
     this._sendChain = Promise.resolve();
     this._lastBusyLogAt = 0;
+    this._lastSendAt = 0;
+    this._keepaliveTimer = null;
 
     // --- Keyboard / buttons ---
     this._keysEnabled = false;
@@ -429,6 +433,7 @@ class WallPlotter {
 
     this.writer = this.port.writable.getWriter();
     this._startReadLoop();
+    this._startKeepalive();
     this._link = 'connected';
     this.onStatusChange('connected');
 
@@ -493,6 +498,7 @@ class WallPlotter {
     if (this._link === 'disconnected' && !this.port) return;
 
     this.readLoopActive = false;
+    this._stopKeepalive();
     this._cancelPendingOk();
     this._rxBuf = '';
 
@@ -538,6 +544,7 @@ class WallPlotter {
   _releaseSerialNow() {
     if (!this.port && this._link === 'disconnected') return;
     this.readLoopActive = false;
+    this._stopKeepalive();
     this._cancelPendingOk();
     this._rxBuf = '';
     const reader = this.reader;
@@ -569,7 +576,7 @@ class WallPlotter {
     }
   }
 
-  _writeLine(command) {
+  _writeLine(command, quiet = false) {
     if (!this.writer) {
       return Promise.reject(new Error('Not connected to plotter'));
     }
@@ -588,7 +595,7 @@ class WallPlotter {
           if (done) return;
           done = true;
           clearTimeout(timer);
-          this.onLog('→ ' + command);
+          if (!quiet) this.onLog('→ ' + command);
           resolve();
         },
         (err) => {
@@ -673,9 +680,9 @@ class WallPlotter {
     if (this._unloadBound) return;
     this._unloadBound = true;
     const release = () => {
-    this._stashInterruptedPath();
-    this._persistResumeState(true);
-    this._releaseSerialNow();
+      this._stashInterruptedPath();
+      this._persistResumeState(true);
+      this._releaseSerialNow();
     };
     window.addEventListener('pagehide', release);
     window.addEventListener('beforeunload', release);
@@ -806,15 +813,18 @@ class WallPlotter {
       return;
     }
 
+    this._lastSendAt = performance.now();
     const waitOk = options.waitOk !== false;
+    const quiet = options.quiet === true || /^M400\b/i.test(command);
     const okPromise = waitOk
       ? this._waitForOk(options.timeoutMs ?? WallPlotter.OK_TIMEOUT_MS, {
           command,
           waitLogAfterMs: options.waitLogAfterMs,
+          quiet,
         })
       : null;
     try {
-      const written = this._writeLine(command);
+      const written = this._writeLine(command, quiet);
       if (okPromise) {
         await Promise.all([
           written.catch((err) => {
@@ -1268,8 +1278,11 @@ class WallPlotter {
 
   _waitForOk(timeoutMs, options = {}) {
     const command = options.command || '';
-    const waitLogAfterMs = options.waitLogAfterMs ?? WallPlotter.OK_WAIT_LOG_MS;
-    const waitLabel = command ? ` (${command})` : '';
+    const quiet = options.quiet === true;
+    const waitLogAfterMs = quiet
+      ? Math.max(options.waitLogAfterMs ?? WallPlotter.OK_WAIT_LOG_MS, 8000)
+      : options.waitLogAfterMs ?? WallPlotter.OK_WAIT_LOG_MS;
+    const waitLabel = command && !quiet ? ` (${command})` : '';
 
     return new Promise((resolve, reject) => {
       if (this._okWaiter) {
@@ -1339,6 +1352,32 @@ class WallPlotter {
     waiter.reject(err);
   }
 
+  _startKeepalive() {
+    this._stopKeepalive();
+    this._keepaliveTimer = setInterval(() => {
+      this._keepaliveTick();
+    }, WallPlotter.KEEPALIVE_MS);
+  }
+
+  _stopKeepalive() {
+    if (this._keepaliveTimer != null) {
+      clearInterval(this._keepaliveTimer);
+      this._keepaliveTimer = null;
+    }
+  }
+
+  _keepaliveTick() {
+    if (this._link !== 'connected' || !this.writer) return;
+    if (this._okWaiter || this._job === 'aborting') return;
+    if (performance.now() - this._lastSendAt < WallPlotter.KEEPALIVE_MS) return;
+    this.send('M400', {
+      quiet: true,
+      allowWithoutHome: true,
+      timeoutMs: 4000,
+      waitLogAfterMs: 10000,
+    }).catch(() => {});
+  }
+
   _startReadLoop() {
     this.readLoopActive = true;
     const plotter = this;
@@ -1403,8 +1442,9 @@ class WallPlotter {
       }
       return;
     }
-    this.onLog('← ' + line);
-    if (/^(echo:\s*)?ok\b/i.test(line)) {
+    const isOk = /^(echo:\s*)?ok\b/i.test(line);
+    if (!isOk) this.onLog('← ' + line);
+    if (isOk) {
       const waiter = this._okWaiter;
       if (waiter) waiter.resolve();
     }