Hi, I am looking for a similar Project, using an Arduino Uno, one, HC05 Serial BT, an a OBD2 BT device. The fact is if you can use an automated procedure to connect serial BT HC05 and OBD2 BT every time you put power to HC05 serial BT ( or the Arduino in which it is connected). The procedure is simple, first ger the MAC addres of the OBD2 BT, simply connecting to it with a BT device and pairing it, an android phone or a PC, are suitable to do, then in properties of the OBD2 BT device you can find the MAC. When you get it, then you must to insert this MAC as a pairable ítem in the Serial BT HC05, al so a simple fact. First take a RS232 USB module (in DX.com you can find a cheap one), and connect it to de serial BT HC05, put the HC05 in AT command mode shorting pin 34 (pio11) with VCC using a resistance about 470Ohms or so, when short VCC-Pin34 at boot, the module enters in AT command mode, so you can program it, then the short must be opened. With a few googling you can find USB RS232 driver (CP210x Windows XP/2003/Vista(32/64)/7(32/64)/8(32/64) Driver v6.6.1 , file is CP210x_VCP_Windows.zip) that is mandatory to use usb serial. In a Hyperterm sesión, open the COM port that is created, the module BT enters in AT mode, and you can create a Hyperterm sesion with 32800,1,0,None. The AT commands are defined in a tutorial or datasheet of HC05 (see this versión, nor HC06/04) like this (google) HC-0305_serail_module_AT_commamd_set_201104_revised.pdf. The commands AT can be entered in lower case, and after you send it hitting Return. Activate Echo in Hyperterminal sesión to see the commans in screen. Fisrt command to put is AT, an OK is the response. Then put the module in Master mode (slave is the default): AT+ROLE=1, then AT+CMODE=0 to allow the BT module to connect to any BT specified, then AT+BIND=bind MAC, this bind MAC is the one you take of the OBD2 BT, but with a special format. The special format is, i.e. if the MAC is: 00:01:02:03:04:05, then AT+BIND=0001,02,030405. Then if you powers off the BT Serial, and put power again, the module seeks for OBD2 BT and pairs with it without doing nothing more.
My tries to make work a LCD1604 using program that displays OBD2 parameters but using an RS232 cable instead a BT serial module don´t Works using BT serial, but with Kostas code and a little time, sure I finally make it works. if someone wants to make a working group with me, feel free to contact me at email@example.com.