rebuilt the arduino code and website, since i had lost it like an idiot.

app.py

@@ -1,13 +1,21 @@
 #!/usr/bin/env python3
-from flask import Flask, render_template, jsonify
+"""
+Flask web UI for ultra-responsive fan control.
+Works with the Arduino sketch above (pin 11 PWM).
+"""
+
+from flask import Flask, render_template, jsonify, request
 import serial
 import serial.tools.list_ports
 import threading
 import time
+import sys
 
 app = Flask(__name__)
 
-# --- Auto-find Arduino ---
+# -------------------------------------------------
+# Auto-detect Arduino
+# -------------------------------------------------
 def find_arduino():
     for p in serial.tools.list_ports.comports():
         if 'Arduino' in p.description or 'ACM' in p.device or 'USB' in p.device:
@@ -17,57 +25,99 @@ def find_arduino():
 PORT = find_arduino()
 BAUD = 115200
 
-# Global serial object
+# Global serial
 ser = None
 serial_lock = threading.Lock()
 
+# -------------------------------------------------
+# Serial init with retry on "busy"
+# -------------------------------------------------
 def init_serial():
     global ser
-    try:
-        ser = serial.Serial(PORT, BAUD, timeout=0)
-        time.sleep(2)  # wait for Arduino reset
-        print(f"Connected to {PORT}")
-    except Exception as e:
-        print(f"Serial error: {e}")
-        ser = None
+    for attempt in range(6):
+        try:
+            ser = serial.Serial(PORT, BAUD, timeout=0)
+            time.sleep(2)  # Arduino reset
+            print(f"[OK] Connected to {PORT}")
+            return
+        except serial.SerialException as e:
+            if 'Device or resource busy' in str(e):
+                print(f"[BUSY] Port busy, retry {attempt+1}/6 in 1s...")
+                time.sleep(1)
+            else:
+                print(f"[ERROR] Serial: {e}")
+                sys.exit(1)
+    sys.exit("[FATAL] Could not open serial port after retries")
 
 init_serial()
 
-# --- Send command safely ---
-def send_command(cmd):
+# -------------------------------------------------
+# Safe send
+# -------------------------------------------------
+def send_command(cmd: str):
     with serial_lock:
         if ser and ser.is_open:
             try:
                 ser.write(cmd.encode())
                 ser.flush()
-            except:
-                print("Serial write failed")
-        else:
-            print("Serial not open")
+            except Exception as e:
+                print(f"[WRITE FAIL] {e}")
+
+# -------------------------------------------------
+# Background reader – pushes feedback to browser via SSE
+# -------------------------------------------------
+from collections import deque
+feedback_buffer = deque(maxlen=50)  # last 50 messages
 
-# --- Background reader (optional: show live feedback) ---
 def serial_reader():
     while True:
         if ser and ser.in_waiting:
-            line = ser.readline().decode(errors='ignore').strip()
-            if line:
-                print(f"Arduino: {line}")
-        time.sleep(0.01)
+            try:
+                line = ser.readline().decode(errors='ignore').strip()
+                if line:
+                    feedback_buffer.append(line)
+            except:
+                pass
+        time.sleep(0.005)
 
 threading.Thread(target=serial_reader, daemon=True).start()
 
-# --- Routes ---
+# -------------------------------------------------
+# Routes
+# -------------------------------------------------
 @app.route('/')
 def index():
     return render_template('index.html')
 
 @app.route('/cmd/<key>')
 def command(key):
-    if len(key) == 1 and key in '0123456789fFsS':
+    if len(key) == 1 and key.lower() in '0123456789fs':
         send_command(key)
         return jsonify(status="ok", key=key)
     return jsonify(status="invalid"), 400
 
+# -------------------------------------------------
+# Server-Sent Events (SSE) – live Arduino feedback
+# -------------------------------------------------
+from flask import Response
+
+@app.route('/stream')
+def stream():
+    def event_stream():
+        last_len = 0
+        while True:
+            if len(feedback_buffer) > last_len:
+                msg = feedback_buffer[-1]
+                last_len = len(feedback_buffer)
+                yield f"data: {msg}\n\n"
+            time.sleep(0.05)
+    return Response(event_stream(), mimetype="text/event-stream")
+
+# -------------------------------------------------
+# Run
+# -------------------------------------------------
 if __name__ == '__main__':
-    # Allow access from your phone/tablet on same WiFi
-    app.run(host='0.0.0.0', port=5000, debug=False)
+    # Accessible from phone/tablet on same WiFi
+    print(f"\nWeb UI: http://YOUR_IP:5000")
+    print("   (Find YOUR_IP with: ip addr show | grep inet)")
+    app.run(host='0.0.0.0', port=5000, debug=False, threaded=True)