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Can you please help me to identify Rx / Tx pins of this OBD adapter in order to connect to it using an Arduino?

I did that once with other adapter that looks the same on outside but different in inside :)

Thanks in advance

enter image description here

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  • \$\begingroup\$ What have your oscilloscope/logic analyzer probing revealed so far? \$\endgroup\$ – winny Apr 3 '19 at 8:33
  • \$\begingroup\$ I don t have an oscilloscope unfortunately \$\endgroup\$ – lucian_v Apr 4 '19 at 7:30
  • \$\begingroup\$ You can measure continuity/resistance of a trace by using multi-meter, therefore you can figure out where a pin or lead is connected to. \$\endgroup\$ – Unknown123 Apr 4 '19 at 8:31
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This is the schematic provided by ELM Electronics for their ELM327 demo board. You can see that serial communication is done through pins 17 and 18.

Since your board is different (and I assume is a proprietary adapter) your best course of action is:

  • Find the ELM chip on the board
  • Find the pinout of the chip (most likely available in the manufacturer's datasheet)
  • Find pins 17 and 18 and check where they lead to (double-check the datasheet, it should mention the pins used as well!)
  • Connect to the outputs of the pins (this may not be the pins themselves, for example on the demo board they feed into an RS232 interface circuit which then is broken out)
  • Test!

Hope that helps. Don't be afraid to test it, if you start by just trying to read data out there is little chance you'll fry it.

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!antenna connection]1The tx/rx pin is probably the same pin or two very close by. The antenna is that squiggly thing at the lower left of the picture. Most like the two pins adjacent to the antenna.

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  • \$\begingroup\$ I am not sure I understand on which you reffer..can you mark them please somehow? Thanks \$\endgroup\$ – lucian_v Apr 4 '19 at 6:20
  • \$\begingroup\$ @lucian_v Close up image attached. Click on antenna connection. That should be clear enough. \$\endgroup\$ – Old_Fossil Apr 4 '19 at 7:03
  • \$\begingroup\$ You means the 2 ones i marked with red arrow? [IMG]i68.tinypic.com/8x697p.png[/IMG] \$\endgroup\$ – lucian_v Apr 4 '19 at 7:27

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