diff --git a/ros_arduino_msgs/CMakeLists.txt b/ros_arduino_msgs/CMakeLists.txt
index bd6cfb3..44a57fa 100644
--- a/ros_arduino_msgs/CMakeLists.txt
+++ b/ros_arduino_msgs/CMakeLists.txt
@@ -6,6 +6,7 @@ find_package(catkin REQUIRED COMPONENTS std_msgs message_generation)
 add_message_files(FILES
                   AnalogFloat.msg
                   Analog.msg
+                  ArduinoConstants.msg
                   Digital.msg
                   SensorState.msg
                  )
diff --git a/ros_arduino_msgs/msg/ArduinoConstants.msg b/ros_arduino_msgs/msg/ArduinoConstants.msg
new file mode 100644
index 0000000..0fe70f4
--- /dev/null
+++ b/ros_arduino_msgs/msg/ArduinoConstants.msg
@@ -0,0 +1,5 @@
+# Arduino-style constants
+uint8 LOW=0
+uint8 HIGH=1
+uint8 INPUT=0
+uint8 OUTPUT=1