diff --git a/controller/protocol.py b/controller/protocol.py
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--- /dev/null
+++ b/controller/protocol.py
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+"""
+protocol.py - Command builder for common cheap BLE LED controller protocols.
+
+These controllers all speak one of a handful of similar protocols.
+We'll confirm which format the KAIYU uses after sniffing/probing.
+
+Supported protocol families:
+  - 0x7E family  (most common, used by ELK-BLEDOM, LEDBLE, etc.)
+  - 0x56 family  (older MagicLight / JACKYLED style)
+"""
+
+
+class Protocol7E:
+    """
+    The 0x7E protocol family.
+
+    Packet format: 7e 00 <CMD> <P1> <P2> <P3> <P4> <LED> ef
+    CMD 0x04 = power on/off
+    CMD 0x05 = set colour (P1=mode, P2=R, P3=G, P4=B)
+    CMD 0x01 = set brightness (P1=0x00–0x64)
+    CMD 0x03 = set effect/speed
+    """
+
+    # Colour mode byte for CMD 0x05
+    MODE_STATIC = 0x03
+    MODE_EFFECT = 0x02
+
+    # LED channel — 0xFF = all channels
+    LED_ALL = 0xFF
+
+    @staticmethod
+    def set_color(r: int, g: int, b: int) -> bytes:
+        r, g, b = _clamp(r), _clamp(g), _clamp(b)
+        return bytes([0x7e, 0x00, 0x05, Protocol7E.MODE_STATIC, r, g, b, 0x00, 0xef])
+
+    @staticmethod
+    def set_brightness(level: int) -> bytes:
+        """level: 0–100"""
+        level = max(0, min(100, level))
+        return bytes([0x7e, 0x00, 0x01, level, 0x00, 0x00, 0x00, Protocol7E.LED_ALL, 0xef])
+
+    @staticmethod
+    def turn_on() -> bytes:
+        return bytes([0x7e, 0x00, 0x04, 0x00, 0x00, 0x00, 0x00, Protocol7E.LED_ALL, 0xef])
+
+    @staticmethod
+    def turn_off() -> bytes:
+        return bytes([0x7e, 0x00, 0x04, 0x00, 0x00, 0x00, 0x00, 0x00, 0xef])
+
+    @staticmethod
+    def set_effect(effect_id: int, speed: int = 0x03) -> bytes:
+        """
+        effect_id: 0x80–0x8b (varies by controller)
+        speed: 0x01 (fast) – 0x0a (slow)
+        """
+        return bytes([0x7e, 0x00, 0x03, effect_id, speed, 0x00, 0x00, Protocol7E.LED_ALL, 0xef])
+
+
+class Protocol56:
+    """
+    The 0x56 protocol family (older MagicLight style).
+
+    RGB command : 56 RR GG BB 00 f0 aa
+    White cmd   : 56 00 00 00 WW 0f aa
+    Power on    : cc 23 33
+    Power off   : cc 24 33
+    """
+
+    @staticmethod
+    def set_color(r: int, g: int, b: int) -> bytes:
+        r, g, b = _clamp(r), _clamp(g), _clamp(b)
+        return bytes([0x56, r, g, b, 0x00, 0xf0, 0xaa])
+
+    @staticmethod
+    def set_white(level: int) -> bytes:
+        level = _clamp(level)
+        return bytes([0x56, 0x00, 0x00, 0x00, level, 0x0f, 0xaa])
+
+    @staticmethod
+    def turn_on() -> bytes:
+        return bytes([0xcc, 0x23, 0x33])
+
+    @staticmethod
+    def turn_off() -> bytes:
+        return bytes([0xcc, 0x24, 0x33])
+
+
+def _clamp(v: int) -> int:
+    return max(0, min(255, v))
+
+
+# ── Convenience ───────────────────────────────────────────────────────────────
+# Default to 7E family — update after confirming with scanner
+ActiveProtocol = Protocol7E