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Friday, June 10, 2011

OBD-II USB adapter to Bluetooth adapter hack

Hi. Yes, I was pretty busy or lazy to write something. There was not interesting projects. The last one was a battery backup switcher, it switches power source to battery when mains go down. Based on relay and transistor.

Today project is not a big deal too :) I have a cheapo OBD-II USB adapter and serial bluetooth module. As bluetooth module was not used anywhere for a long time I decided to hack OBD-II USB adapter and make it Bluetooth instead of USB.
Yea I know I can buy a cheap Bluetooth OBD-II adapter, but I like DIY.

So I opened the box and found PIC18F4 mcu inside and FTDI232RL UART to USB serial converter.

Then I desoldered FTDI chip with usb crystal. My bluetooth serial module needs 3.3v supply, so I had to add 3.3v regulator with couple of capacitors (took 5v from 78M05 voltage regulator on pcb). OBD-II box has 5 leds indicating rx/tx from car and serial and power status, BT serial module can indicate it's status with led too, so I drilled a little hole in the box top right under sticker and glued the led with hot glue.

When I finally soldered this mess-o-wires to adapter pcb in place of FTDI chip I found that is does not work, not receiving or sending any data, but bluetooth pairing works and BT status led works as it should. Took a bit of time to solder FTDI chip and crystal back for debug. Find out that it works as USB ok but not bluetooth. Then I take a look where tx and rx connects to PIC mcu and you probably guess already, I connected BT module tx to PIC tx and that's wrong :) Changed wires and soldered them right to the PIC mcu legs, that works. Time run away and I leave FTDI chip on pcb.

That's it, works great with my Android phone even better than windows scanner apps under wine in Ubuntu :)