VAGCOM Adapter, die Prinzipfrage

[Translating...]

Hallo zusammen

Nachdem JörgS nun auch mit Opto-Adaptern Verbindung zu seinem Problem-1Z bekommt

(Posting vom 28.2. in https://community.dieselschrauber.org/en/viewtopic.php?p=12622

bestätigt sich (in diesem Fall) meine Vermutung über VAGCOM und die erforderlichen Adapterqualitäten:
Vereinfacht ausgedrückt liegen die Übertragungs-Anforderungen von VAGCOM IMO sozusagen auf Trabi-Niveau, was schon mit „lahmen“ Optokopplern sicher erreichbar ist.

Der Einsatz von Adaptern ohne Optokoppler (wie den neueren Kauf-Adaptern) für VAGCOM ist dann ungefähr so, als würde man einem Trabi die Sicherheitsgurte ausbauen und ZR-Reifen aufziehen.
Verkauft wird diese Trabi-Version dann mit dem Hinweis „mit diesen Reifen können Sie über 240 km/h fahren, zudem können wir Ihnen den Wagen ohne Sicherheitsgurte trotz VR-Reifen sogar etwas billiger anbieten. Und weil man Sicherheitsgurte eigentlich nie braucht, werden sie künftig auch nicht mehr eingebaut.“


@Maik: nix für ungut. Ich weiß, daß Du Deinen Adapter als zuverlässiger funzende Alternative entworfen hast, als meine Opto-Bauvorschläge teilweise nicht einmal Trabi-Niveau erreichten

Ich will auch nicht völlig ausschließen, daß es (exotische) Einzelfälle unglücklicher Kombinationen von Diagnose-PC, Hintergrund-Software und Autos geben kann, wo auch gute Opto-Schaltungen versagen und nur Adapter wie Deiner gerade noch eine sichere Kommunikation ermöglichen.

Und ich weiß auch, daß z.B. mit dem Opto-Adapter 2.4 bei stark schwankender Bordspannung (z.B. beim Anlassen) der Dialog kurzzeitig abreißen kann. Das ließe sich auf entsprechenden Wunsch mit einem Festspannungsregler beheben, der natürlich entsprechend höheren Bau-Aufwand bedeutet.

Übrigens kann man auch Opto-Adaptern noch mehr Speed als beim 2.4 beibringen – Jörg hatte ja meinen „internen“ etwa 3 fach schnelleren 2.5 gebaut, der aber in seinem Fall auch keine besseren Ergebnisse brachte.
Bei ihm waren also sozusagen schon HR-Reifen auf dem Trabi umsonst

@ulf

You're basically right! The 2.5 adapter doesn't offer any significant advantage compared to the 2.4 adapter, or only a very minor one.
Furthermore, it is undeniable that adapter operating times and signal distortions likely have a significant impact on communication! What made me suspicious was the fact that even the original minimal adapter works quite well with modified VAG-COM settings! I say 'quite well' because occasional communication interruptions are still observed/were observed during driving.

However, the adapter is only one cause. The main problem lies in the differences in bit lengths of the control unit! As I mentioned yesterday, there should be a way to either use a microcontroller within the adapter to shape the signals so that VAG-COM can understand them, or to use a synchronization clock to make the control unit/or the RS232 synchronize with the other device. Alternatively, access the communication through software adaptation!

It's a shame that I won't be able to work on my Golf as much starting at the end of March! Most likely, a Passat with an AWX engine will be here soon!

by the way: does a Passat from 2000 (already the new model) actually have 2 K-lines, or just one?

@maik:
How can we potentially enlarge the holes in your adapter to fit two K-line connections?

joergs wrote:

Furthermore, it is undeniable that the adapter runtimes and signal distortions likely have a huge impact on communication!

Hi Jörg,

If the errors reach extreme proportions, then you are probably right.
A previous opto-adapter I designed (which didn't yet have trimmers on the opto inputs) had problems because it shortened the bit lengths from the car to the PC by approximately 30 microseconds.
That seems to be the approximate threshold for the problem (at least in my tractor).

Below these deviations, I can freely adjust my adapter, and VAGCOM continues to run without interruption.

Quote:

@maik: How can we possibly enlarge the hole in your adapter to fit two K-line connectors?

Although I am not Maik, but in my opinion, the rectifier concept from my proposal for 2 K-Lines should also be applicable to Maik's adapter .

Sure, here is the translation of the text from German to English:

"Addendum:"

Quote:

What made me suspicious is the fact that the original minimal adapter also works quite well with modified VAG-COM settings! It works "quite well" because, during driving, communication interruptions are sometimes observed/were observed.

Probably, the bit length errors of the minimal adapter , in conjunction with your PC and car , are usually just below the error threshold, and in combination with fluctuations in the on-board voltage, the critical limit is sometimes exceeded .

Hello,

I once created a circuit diagram using a MAX232 and an optocoupler.
Maik's circuit diagram has been slightly expanded.
Could you all take a look at this?

http://www.alexweiss.gmxhome.de

The DC/DC converter is still in progress, I'm working on it at the moment, but it should be finished by the end of this week.
I wanted to use a 6N136 optocoupler instead of the 6N135 shown in the circuit diagram.

I would appreciate it if someone could offer some feedback on what's good and what's not.
I hope I can get the first working prototype board completed this weekend.


Best regards,

Nicklas wrote:

Hello, I once created a circuit diagram using a MAX232 and an optocoupler. Maik's circuit diagram has been slightly expanded. Could you all take a look at this? http://www.alexweiss.gmxhome.de

Hi Nick,

The image in the direct link is too blurry, and the Eagle schematic is essentially just Maik's plan?

You can omit the trimmer resistors on the K-line. Use a pull-up resistor of 2.2k or 3.3k ohms, and for the 1-0 detection of the K-line, use a voltage divider with 100k and 33k ohms (with the diode placed before the transistor base).

I would also use this opportunity to configure the LEDs in such a way that each only displays the bits sent by the car.
Based on Maik's circuit, it is possible to achieve this by simply rearranging some of the connections.
But I don't want to take away all of your work .

Hello,

I've uploaded the wrong Eagle file; I'll correct it later tonight when I'm home.
I can probably remove the trimmer; it shouldn't be a problem, and it will free up more space on the PCB.
I've been thinking about the LED thing, and it should work, but I'll also need a PNP transistor.
I'll update the circuit diagram again and upload it tonight.

Best regards,

[Translating...]

[quote="ulf"]Hallo zusammen

Nachdem JörgS nun auch mit Opto-Adaptern Verbindung zu seinem Problem-1Z bekommt

(Posting vom 28.2. in https://community.dieselschrauber.org/en/viewtopic.php?p=12622

bestätigt sich (in diesem Fall) meine Vermutung über VAGCOM und die erforderlichen Adapterqualitäten:
Vereinfacht ausgedrückt liegen die Übertragungs-Anforderungen von VAGCOM IMO sozusagen auf Trabi-Niveau, was schon mit „lahmen“ Optokopplern sicher erreichbar ist.

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Ich habe 1998 auch den simplen Interface nach Jeff´s homepage nachgebaut mit optos SFH 615 von Siemens. Es lief auf anhieb. Mein Wagen ist ein Galaxy tdi mit 1Z Motor und noch MSA12 !!!! Steuereinheit. Ich komme an alle Steuergeräte ran. Ich habe vielleicht an 20, 25 Fahrzeugen den Interface dran gehabt - nur ein Seat Ibiza Bj 1999 wollte nicht mitmachen.
Ich könnte ein anderes Problem beobachten können: sobald recht kalt wird, Arbeitspunkt der Transistoren drifftet so weit ab, dass keine verbindung zu stande kommt (auch mit Ladegerät am Akku).
Gruß Lukas

Hello,

I can't imagine that the operating point of the transistors is to blame. The transistors are only being used as digital switches.

Hello.

Nicklas wrote:

I can't imagine that the operating point of the transistors is to blame. The transistors are only used as digital switches.

Hi Nick,

Take a look at the biasing of the "sensor transistor" for the K-line: 150k from K to the base, and that's it.
That means the on-board electronics must draw less than 0.6 volts to recognize a bit.
I can certainly imagine that this delicate balance is temperature-dependent.

Hello everyone.
To anyone currently struggling with an OBD2 interface for VAG.COM, I recommend searching on eBay under 'OBD2'.
You can get those things complete with plugs and cables for €55 or €60.
I think it's almost not worth building it yourself anymore.

I ordered it two weeks ago. This part works perfectly with my 1999 Sharan (AFN) using VAG.COM version 208.2.

(No! I'm not the seller and I won't receive any commission, nor do I want to promote anything. Just a tip.)

Regards,

Reinhard.

Hi,

'The transistor already has a pull-down resistor at its base, so it only needs to be pulled up. Of course, this isn't for reading a bit, but rather for static operation, which is what the 4.7kΩ resistor does. In the control unit, there's only a high-impedance pull-up resistor and a series resistor (30-80 ohms) to protect against short circuits. Older control units often have a simple open collector circuit (an NPN transistor), while newer ones use an ASIC (e.g., ATM46), which can easily pull the level down relative to the 4.7kΩ resistor. The open collector in the car might cause more problems, but that should generally be easy to fix. I've also had ECUs at -40°C in a climate chamber, and never had any issues with the K-line.'
The value of the base resistor, whether it's high or low impedance, doesn't matter because the BC337 has an hfe (current gain) of 600, and it only needs to pull down a 10k resistor and two TTL inputs, which draws approximately 0.5mA. Additionally, the transistor itself contributes 8.3 * 10^-7 A.

I've updated the circuit diagram and corrected the download link.
For those who want to take another look.

http://www.alexweiss.gmxhome.de

Regards,

P.S. Building your own adapters is more fun than buying them.

Nicklas wrote:

Hi, The transistor already has a pull-down resistor at the base, so it only needs to be pulled up, of course not to read a bit, but just statically, which is what the 4.7kΩ resistor does (in the control unit, there's only a high-impedance pull-up and a long resistance [30-80 ohms] to protect against short circuits). . .

Hi Nick,

Um... are we talking about the same circuit?

I'm referring to adapters like the one from Noxon, which Lukas essentially recreated, and which served as a reference for the "minimally designed circuit" described in the adapter technical article.
And in there, for example, there isn't a single 4.7k resistor...