diff --git a/fw/Core/Src/main.c b/fw/Core/Src/main.c
index aaf8352..cb9ac02 100644
--- a/fw/Core/Src/main.c
+++ b/fw/Core/Src/main.c
@@ -111,6 +111,7 @@ config_t sensor_config;
 uint8_t sensor_config_pending_write = 0;
 uint8_t baudrate_changed = 0;
 uint8_t modbus_address_changed = 0;
+uint8_t co2_valid = 0;
 /* USER CODE END PV */
 
 /* Private function prototypes -----------------------------------------------*/
@@ -179,7 +180,7 @@ int main(void)
 
   /* Turn on MAGENTA LED to signal startup state */
   LL_GPIO_ResetOutputPin(LED_R_GPIO_Port, LED_R_Pin);
-  LL_GPIO_SetOutputPin(LED_G_GPIO_Port, LED_G_Pin);
+  LL_GPIO_ResetOutputPin(LED_G_GPIO_Port, LED_G_Pin);
   LL_GPIO_ResetOutputPin(LED_B_GPIO_Port, LED_B_Pin);
 
   /* Enable I2C for sensors */
@@ -297,6 +298,11 @@ int main(void)
 			  scd4x_read_measurement(&CO2,
 					  	  	  	  	 &T_SCD4x,
 									 &RH_SCD4x);
+			  if (CO2 > 0) {
+				  co2_valid = 1;
+			  } else {
+				  co2_valid = 0;
+			  }
 		  }
 
 		  /* Read SPS30 data (if connected) */
@@ -312,6 +318,7 @@ int main(void)
 	  }
 	  /* TEST END */
 	  if (sensor_config.led_on) {
+		  if (co2_valid == 1) {
 			  if (CO2 <= sensor_config.led_co2_alert_limit1) {
 				  /* CO2 is OK -> GREEN */
 				  LL_GPIO_SetOutputPin(LED_R_GPIO_Port, LED_R_Pin);
@@ -331,10 +338,17 @@ int main(void)
 				  LL_GPIO_SetOutputPin(LED_B_GPIO_Port, LED_B_Pin);
 			  }
 		  } else {
-			  LL_GPIO_SetOutputPin(LED_R_GPIO_Port, LED_R_Pin);
+
+			  LL_GPIO_ResetOutputPin(LED_R_GPIO_Port, LED_R_Pin);
 			  LL_GPIO_SetOutputPin(LED_G_GPIO_Port, LED_G_Pin);
-			  LL_GPIO_SetOutputPin(LED_B_GPIO_Port, LED_B_Pin);
+			  LL_GPIO_ResetOutputPin(LED_B_GPIO_Port, LED_B_Pin);
 		  }
+
+	  } else {
+		  LL_GPIO_SetOutputPin(LED_R_GPIO_Port, LED_R_Pin);
+		  LL_GPIO_SetOutputPin(LED_G_GPIO_Port, LED_G_Pin);
+		  LL_GPIO_SetOutputPin(LED_B_GPIO_Port, LED_B_Pin);
+	  }
     /* USER CODE END WHILE */
 
     /* USER CODE BEGIN 3 */
diff --git a/fw/iaq_wired_sensor Debug.launch b/fw/iaq_wired_sensor Debug.launch
index 647065f..e9df78e 100644
--- a/fw/iaq_wired_sensor Debug.launch	
+++ b/fw/iaq_wired_sensor Debug.launch	
@@ -68,6 +68,6 @@
     <listAttribute key="org.eclipse.debug.core.MAPPED_RESOURCE_TYPES">
         <listEntry value="4"/>
     </listAttribute>
-    <stringAttribute key="org.eclipse.dsf.launch.MEMORY_BLOCKS" value="&lt;?xml version=&quot;1.0&quot; encoding=&quot;UTF-8&quot; standalone=&quot;no&quot;?&gt;&#10;&lt;memoryBlockExpressionList context=&quot;reserved-for-future-use&quot;&gt;&#10;    &lt;gdbmemoryBlockExpression address=&quot;134742016&quot; label=&quot;0x08080000&quot;/&gt;&#10;    &lt;gdbmemoryBlockExpression address=&quot;134742020&quot; label=&quot;0x08080004&quot;/&gt;&#10;&lt;/memoryBlockExpressionList&gt;&#10;"/>
+    <stringAttribute key="org.eclipse.dsf.launch.MEMORY_BLOCKS" value="&lt;?xml version=&quot;1.0&quot; encoding=&quot;UTF-8&quot; standalone=&quot;no&quot;?&gt;&lt;memoryBlockExpressionList context=&quot;reserved-for-future-use&quot;&gt;&lt;gdbmemoryBlockExpression address=&quot;134742016&quot; label=&quot;0x08080000&quot;/&gt;&lt;gdbmemoryBlockExpression address=&quot;134742020&quot; label=&quot;0x08080004&quot;/&gt;&lt;gdbmemoryBlockExpression address=&quot;134742016&quot; label=&quot;0x08080000&quot;/&gt;&lt;/memoryBlockExpressionList&gt;"/>
     <stringAttribute key="process_factory_id" value="org.eclipse.cdt.dsf.gdb.GdbProcessFactory"/>
 </launchConfiguration>
diff --git a/tests/read_input_register_test.py b/tests/read_input_register_test.py
index e1067c5..ac5a2c5 100755
--- a/tests/read_input_register_test.py
+++ b/tests/read_input_register_test.py
@@ -5,7 +5,7 @@ import minimalmodbus
 import serial
 
 slave_address = 254
-instrument = minimalmodbus.Instrument('/dev/ttyUSB0', slave_address, close_port_after_each_call=True)  # port name, slave address (in decimal)
+instrument = minimalmodbus.Instrument('/dev/rs485', slave_address, close_port_after_each_call=True)  # port name, slave address (in decimal)
 
 instrument.serial.baudrate = 19200
 instrument.serial.bytesize = 8