diff --git a/due_obd2/due_obd2.ino b/due_obd2/due_obd2.ino
index ed09a96..0831f01 100644
--- a/due_obd2/due_obd2.ino
+++ b/due_obd2/due_obd2.ino
@@ -59,13 +59,6 @@ enum DeviceLabel
     DEV_DONE = 3
 };
 
-enum BluetoothState
-{
-    BT_INITIALISING = 0,
-    BT_CONNECTING = 1,
-    BT_CONNECTED = 2
-};
-
 /* extern fonts */
 extern uint8_t BigFont[];
 extern uint8_t SmallFont[];
diff --git a/due_obd2/obd2_bt.c b/due_obd2/obd2_bt.c
new file mode 100644
index 0000000..a4d58da
--- /dev/null
+++ b/due_obd2/obd2_bt.c
@@ -0,0 +1,21 @@
+#include "wiring_digital.h"
+#include "obd2_bt.h"
+
+void obd2_bt_init(obd2_bt_t *bt)
+{
+    bt->state = BT_INITIALISING;
+}
+
+void obd2_bt_process(obd2_bt_t *bt)
+{
+    __UINT32_TYPE__ bt_state = digitalRead(BT_STATE_PIN);
+    if (bt_state)
+    {
+        bt->state = BT_CONNECTED;
+    }
+    else
+    {
+        bt->state = BT_INITIALISING;
+    }
+    bt->on_state_change();
+}
\ No newline at end of file
diff --git a/due_obd2/obd2_bt.h b/due_obd2/obd2_bt.h
index 53e4069..2d91162 100644
--- a/due_obd2/obd2_bt.h
+++ b/due_obd2/obd2_bt.h
@@ -21,4 +21,23 @@ Be sure to disconnect the TX and RX pins from the BT module when programming the
 #ifndef OBD2_BT_H
 #define OBD2_BT_H
 
+#define BT_STATE_PIN 3 /* state connection pin from bluetooth module -> level high on connected */
+
+enum BluetoothState
+{
+    BT_INITIALISING = 0,
+    BT_CONNECTING = 1,
+    BT_CONNECTED = 2
+};
+
+typedef struct obt2_bt_tag
+{
+    enum BluetoothState state;
+    void (*on_state_change)();
+} obd2_bt_t;
+
+void obd2_bt_init(obd2_bt_t *bt);
+void obd2_bt_process(obd2_bt_t *bt);
+
+
 #endif // OBD2_BT_H
\ No newline at end of file
diff --git a/readme.md b/readme.md
index c272151..658b1c5 100644
--- a/readme.md
+++ b/readme.md
@@ -21,6 +21,7 @@
 - [FSC-DB0004 schematic and assembly](https://www.feasycom.com/wp-content/uploads/2022/04/1649387973-FSC_DB004_V1_1_Sch_and_Assembly.pdf)
 
 ### HC-05
+- [Datasheet](https://components101.com/sites/default/files/component_datasheet/HC-05%20Datasheet.pdf)
 - [How to configure](https://lastminuteengineers.com/hc05-at-commands-tutorial/)
 
 ### 3.5 inch TFT display