fix(envea): add retry logic for sensor read failures

- Retry up to 3 times if no valid frame is received
- Reduced wait time per attempt to 0.8s (total max ~3s with retries)
- Small delay between retries (0.2s)
- Only logs command on first attempt to reduce noise

This should eliminate the occasional 0 values caused by timing issues.

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

envea/read_value_v2.py

@@ -106,67 +106,69 @@ try:
                 try:
                     debug_print(f"Reading from {name}...")
 
-                    # Flush input buffer to clear any stale data
+                    calculated_value = None
-                    serial_connection.reset_input_buffer()
+                    max_retries = 3
 
-                    # Send command to sensor
+                    for attempt in range(max_retries):
-                    command = b"\xFF\x02\x13\x30\x01\x02\x03\x04\x05\x06\xFF\xFF\xFF\xFF\xFF\xFF\xFF\xFF\x12\xAF\x88\x03"
+                        # Flush input buffer to clear any stale data
-                    serial_connection.write(command)
+                        serial_connection.reset_input_buffer()
-                    debug_print(f"  → Sent command: {command.hex()}")
 
-                    # Wait for complete sensor response (sensor needs time to process and reply)
+                        # Send command to sensor
-                    time.sleep(1.5)
+                        command = b"\xFF\x02\x13\x30\x01\x02\x03\x04\x05\x06\xFF\xFF\xFF\xFF\xFF\xFF\xFF\xFF\x12\xAF\x88\x03"
+                        serial_connection.write(command)
+                        if attempt == 0:
+                            debug_print(f"  → Sent command: {command.hex()}")
 
-                    # Read all available data from buffer
+                        # Wait for sensor response
-                    bytes_available = serial_connection.in_waiting
+                        time.sleep(0.8)
-                    debug_print(f"  ← Bytes available in buffer: {bytes_available}")
 
-                    if bytes_available > 0:
+                        # Read all available data from buffer
-                        data_envea = serial_connection.read(bytes_available)
+                        bytes_available = serial_connection.in_waiting
-                    else:
+                        debug_print(f"  ← Attempt {attempt + 1}: {bytes_available} bytes available")
-                        # Fallback: try reading with timeout
-                        data_envea = serial_connection.read(32)
 
-                    debug_print(f"  ← Received {len(data_envea)} bytes: {data_envea.hex() if data_envea else 'empty'}")
+                        if bytes_available > 0:
-                    
+                            data_envea = serial_connection.read(bytes_available)
-                    # Find frame start (0xFF 0x02) in received data - may have echo/garbage before it
-                    frame_start = -1
-                    for i in range(len(data_envea) - 1):
-                        if data_envea[i] == 0xFF and data_envea[i + 1] == 0x02:
-                            frame_start = i
-                            debug_print(f"  → Found frame header at position {i}")
-                            break
-
-                    if frame_start >= 0:
-                        # Extract frame from header position
-                        frame_data = data_envea[frame_start:]
-                        debug_print(f"  → Frame data ({len(frame_data)} bytes): {frame_data.hex()}")
-
-                        if len(frame_data) >= 20:
-                            byte_20 = frame_data[19]
-                            raw_value = byte_20
-                            calculated_value = byte_20 * coefficient
-                            debug_print(f"  → Byte 20 value: {raw_value} (0x{raw_value:02X})")
-                            debug_print(f"  → Calculated value: {raw_value} × {coefficient} = {calculated_value}")
-
-                            if name == "h2s":
-                                data_h2s = calculated_value
-                            elif name == "no2":
-                                data_no2 = calculated_value
-                            elif name == "o3":
-                                data_o3 = calculated_value
-                            elif name == "co":
-                                data_co = calculated_value
-                            elif name == "nh3":
-                                data_nh3 = calculated_value
-                            elif name == "so2":
-                                data_so2 = calculated_value
-
-                            debug_print(f"  ✓ {name.upper()} = {calculated_value}")
                         else:
-                            debug_print(f"  ✗ Frame too short ({len(frame_data)} bytes after header, expected ≥20)")
+                            data_envea = serial_connection.read(32)
+
+                        if len(data_envea) > 0:
+                            debug_print(f"  ← Received {len(data_envea)} bytes: {data_envea.hex()}")
+
+                        # Find frame start (0xFF 0x02) in received data
+                        frame_start = -1
+                        for i in range(len(data_envea) - 1):
+                            if data_envea[i] == 0xFF and data_envea[i + 1] == 0x02:
+                                frame_start = i
+                                break
+
+                        if frame_start >= 0:
+                            frame_data = data_envea[frame_start:]
+                            if len(frame_data) >= 20:
+                                byte_20 = frame_data[19]
+                                calculated_value = byte_20 * coefficient
+                                debug_print(f"  → Found valid frame at position {frame_start}")
+                                debug_print(f"  → Byte 20 = {byte_20} × {coefficient} = {calculated_value}")
+                                break  # Success, exit retry loop
+
+                        debug_print(f"  ✗ Attempt {attempt + 1} failed, {'retrying...' if attempt < max_retries - 1 else 'giving up'}")
+                        time.sleep(0.2)
+
+                    if calculated_value is not None:
+                        if name == "h2s":
+                            data_h2s = calculated_value
+                        elif name == "no2":
+                            data_no2 = calculated_value
+                        elif name == "o3":
+                            data_o3 = calculated_value
+                        elif name == "co":
+                            data_co = calculated_value
+                        elif name == "nh3":
+                            data_nh3 = calculated_value
+                        elif name == "so2":
+                            data_so2 = calculated_value
+                        debug_print(f"  ✓ {name.upper()} = {calculated_value}")
                     else:
-                        debug_print(f"  ✗ No valid frame header (FF 02) found in response")
+                        debug_print(f"  ✗ Failed to read {name} after {max_retries} attempts")
                         
                 except serial.SerialException as e:
                     debug_print(f"✗ Error communicating with {name}: {e}")