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Author Topic: Connecting K-Line (OBD) adapter to Arduino Mega  (Read 2407 times)
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I have K-Line OBD-2 to COM port adapter (VAG/COM 409.1) and need to connect it to my Arduino Mega board as serial device.

The matter I don't use standard ELM327 is that I have Honda CR-V (2000) with 3-pin diagnostic connector that uses proprietary Honda serial port protocol. I successfully connect to my car and see real-time data from PC with K-Line OBD-2 - COM port adapter.

But how to connect this COM port (as slave device) to my Mega? Please suggest. As long as I know 9-pin com ports use higher voltage signals than TTL signals used by Mega? What interface I need and what should be the wiring?
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You need a MAX232 or similar chip to do the level conversion. As soon as you have TTL level you can go with it to any of the 4 hardware serial interfaces of the Mega.
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My OBD2 K-Line diagnostic cable is OBD2 16 pin at one side and DB9 female (RS-232) at the other side (for connecting to PC COM port).
I have just ordered MAX232 based RS232 (COM) to TTL converter designed for Arduino (from ebay). This converter is also female COM.

Will I manage to connect to my OBD if I connect diagnostic cable to MAX232 TTL converter via DB9 male to DB9 male cable? Is it proper to use such connections? Regular COM cables have female at one side and male at the other.
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It's not important, if the connector is male or female, you have to take care for the electrical parameters. You have to take care that the RX/TX wires are crossed exactly once.

BTW: ELM327 (and compatibles) are able to access the K line protocols too (if that connector really is a K line).
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It's not important, if the connector is male or female, you have to take care for the electrical parameters. You have to take care that the RX/TX wires are crossed exactly once.

BTW: ELM327 (and compatibles) are able to access the K line protocols too (if that connector really is a K line).

Thanks a lot for help.

So, as long as I understood I must cross RX to TX ans TX to RX wires within the cable between TTL/RS232 converter and my existing K-Line/RS232 interface . Am I correct? Is it called null-modem if I am not mistaken?

My car interface is not K-Line (ISO9141) compatible, it is Honda proprietary protocol (which I am more or less familiar with at byte level) that just uses K-Line serial wiring. So ELM327 can't be used since it only supports 4 standard OBD2 protocols.
« Last Edit: November 14, 2012, 04:11:08 am by micbox » Logged

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Quote
So, as long as I understood I must cross RX to TX ans TX to RX wires within the cable between TTL/RS232 converter and my existing K-Line/RS232 interface . Am I correct? Is it called null-modem if I am not mistaken?

Usually this is true. I've seen boards where the crossing of the RX and TX lines where already done onboard, so it depends a bit from device to device. But in most cases you need to cross them.
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hi micbox,

how bout this one:

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