OBD2: Is it true? How do they do it?

While browsing the website of a manufacturer of OBD2 diagnostic cables, I came across the following:
'Optical isolation using optocouplers was deliberately omitted because, in rare cases, their effective benefit is not proportional to the disadvantage of slower data communication or significantly higher manufacturing costs that result from their use.'

Is there any truth to that?
What is the importance of faster data transfer?
And how do they do it, if not with optocouplers?

Best regards,
Karsten.

Hello,

Just type "optoisolator" into the search function; that should largely answer your questions.

However, just to add a brief note:

Without CAN bus communication, there is no galvanic isolation, and adapters don't even attempt to provide it. They don't actually become faster with it, but they become more PREDICTABLE, which in turn makes the tuning (you'll find a lot of information on this topic with the suggested search) much easier and makes the adapter more compatible with a wider range of cars.

Adapters with OK certification are safer because they prevent both ground loops and voltage fluctuations (from whatever source) from damaging the computer or car, but they are more complex and expensive.

If you want to compare them directly, take a look at the circuit diagrams offered on this site, specifically those by Ulf (with OK) and Maik (without OK).

Best regards,

Jan.

kfh wrote:

"Optical isolation using optocouplers was deliberately omitted because, in rare cases, their effective benefit is not proportional to the disadvantage of slower data communication or significantly higher manufacturing costs that result from their use." Is there any truth to that? What is the importance of faster data transfer? And how do they do that, if not with optocouplers?

Hi Karsten,

I was able to adjust "my" 2.4 GHz adapter in the Dialog system, connected to my tractor, almost to the maximum limits of the trimmers, before communication problems started to occur.
The data communication always ran at the same speed, even though the adapter becomes significantly "slower" (simplified) when the trimmers are adjusted.

That means even a very poorly calibrated opto-adapter is still faster than what's required for VAGCOM - at least for cars manufactured in 1997.

IMO, the faster data transfer rate is just an empty marketing argument used to counter the security advantages of Opto-adapters, so that customers don't complain about the "cheaply produced" adapters of the newer generation.

Yeah, the advertising...

You have 3 chances to guess how my post will be transmitted to you.
Okay, about optocouplers...

The OBD interface typically operates at 10.4 kbaud. My modem runs at 56k, and the LAN operates at 100M.

The couplers used here can actually handle frequencies well above 100 kHz without any problems.

At 10k, an optocoupler would get incredibly bored... hmm... maybe that's the problem?

CU Gremlin.

ok, thanks for the information!
Sure, here's the translation:

'So, just a 'fluffy' argument.'
I already thought so.

Something completely different:
VAG Com is known to only work with...
with cars from the Volkswagen Group (VW, Audi, Skoda, Seat).
Is there a program that works with Mitsubishi?
I once read something about the 'Check Engine' light.
can provide information by varying its blinking pattern.
Does anyone know how this works?

Best regards,
Karsten.