DIY Diagnostic Adapter: Build Your Own!

Hello,
To get it out of the way, I have already used the search function.

I built the adapter according to the minimal circuit diagram.

http://www.dieselschrauber.de/Adapter%20Standard.png

I used the ILD74 as an optocoupler; the transistors are 2N3904.
(I ordered and assembled everything according to the instructions from: hal9000.vc-graz.ac.at...)

I've already checked the circuit, and it seems correct. The problem is that the adapter isn't recognized by either VAG-COM 311.2 or 409.0. I've also already replaced R7 with a 10kOhm resistor, but the problem persists.

Please provide the text you would like me to translate from German to English.
Does the VAG-COM adapter test require any specific baud rates, KW2 delays, etc. to be configured in order for the adapter to be recognized?
Does the OBD cable need to be connected to the vehicle (due to battery voltage)?

2.
Is it really advisable to build such a simple adapter? I've also read the technical article on this page, which states that this adapter is not ideal. Are the optocouplers I used "good," or are other types more recommended?

Are there any other tricks or things to keep in mind when setting up the circuit?

4.
I want to solder in an LED that indicates whether there is voltage coming from the car. Do I need to solder the LED to pin 16 and pin 4 on the OBD connector, or to pin 16 and pin 5?
I'm asking because I read about pin 4, but isn't pin 5 actually the vehicle's ground? Pin 4 is just a signal ground...


And one more thing.
I also intended to build the "Worst-Case Design" version 4.0. Has anyone had experience with this adapter? What optocouplers and transistors did you use?

5. How can I determine if a car uses 2K-Lines or K-Lines? Is it simply a matter of trying both switch positions with the adapter?


Thank you in advance .

Best regards,

Hi,

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

1:
The detection test works regardless of the settings. Could the COM port be occupied by something else, or is it disabled in the BIOS? Have you checked to see if it's actually outputting anything?

2:
You haven't mentioned anything about your vehicle. It will likely be difficult with sensitive vehicles (especially older ones). With the others, you have a good chance of success, but you will probably encounter problems from time to time. It might also not work with some laptops. Everyone has to decide for themselves whether they can live with that.

3:
It should already be properly structured .

4:
Check where the ground connection is in your vehicle. To do this, measure the voltage between pins 4 and 16, and also between pins 5 and 16, to see where you have power. Both the LED and the ground connection of your circuit need to be connected to the same point; otherwise, it won't work.

to 5:
No assistance will be provided without vehicle details.

Basically:
Rainer understandably doesn't like seeing such problems discussed in his forum, as he makes his living by selling quality adapters. On the other hand, such posts also confirm why it's worth buying from him. --> See the "Common Mistakes" article, located at the top of every page...

Regards,
Guste.

Hi.

tuner01 wrote:

Hello, To get it out of the way, I have already used the search function. I built the adapter according to the minimal switching scheme. http://www.dieselschrauber.de/Adapter%20Standard.png I used the ILD74 as an optocoupler; the transistors are 2N3904. (I ordered and assembled everything according to the instructions from: hal9000.vc-graz.ac.at...) I've already checked the wiring, and it seems correct. The problem is that the adapter isn't recognized by either VAG-COM 311.2 or 409.0. I've also already replaced the R7 resistor with a 10kOhm resistor, but the problem persists. Please provide the text you would like me to translate from German to English. Does the VAG-COM adapter test require any specific baud rates, KW2 delays, etc. to be configured in order for the adapter to be recognized? Does the OBD cable need to be connected to the vehicle (due to battery voltage)?

No, but the adapter should receive +12V.

Quote:

2. Is it even advisable to build such a simple adapter? I have also read the technical article here on this page, which states that this adapter is not very optimal. Are the optocouplers I used "good," or are other types more recommended?

It's a mixed bag. The problem with most optocoupler circuits is the limited signal edge steepness.
VAG-COM version 404.0 and later checks the 'speed' of the adapter. Therefore, almost all optocoupler circuits only work up to version 311.2. However, I have to admit that I have never tested Ulf's version .
The kit from the shop works perfectly with the current 409.1 version.
http://shop.dieselschrauber.de/diagnose-schule.php

To prevent uncontrolled proliferation, most of the new features we develop as VAG-COM plugins/utilities will only be usable with diagnostic adapters that have a dongle function (or, depending on the plugin, with a more convenient setup).

Quote:

3. Are there any other tricks or things to keep in mind when setting up the circuit?

Please double-check everything carefully, including whether the correct connection cables (pins) have been selected.

Quote:

4. I want to solder in an LED that indicates whether there is voltage coming from the car. Do I need to solder the LED to pin 16 and pin 4 on the OBD connector, or to pin 16 and pin 5? I'm asking because I read about Pin 4, but Pin 5 is actually the vehicle's ground. Pin 4 is just a signal ground...

Pins 4 and 5 are like cat food... all the same (unfortunately).

Quote:

And one more thing. I also intended to build the "Worst-Case Design" version 4.0. Has anyone had experience with this adapter? What optocouplers and transistors did you use? 5. How can I determine if a car uses 2K-Lines or K-Lines? Is it simply a matter of trying both switch positions with the adapter?

If you have an Audi A4 manufactured between 2002 and 2004, there's a good chance it will work.

Best regards, Rainer.

Hi,

To be honest, I've actually considered buying one of those kits... However, for the price, it wouldn't be worth it for me (and I don't mean to say that it's overpriced!), because it's really just meant to be a "fun hobby."


The vehicles are a Volkswagen Golf IV Cabrio and an Audi A4 manufactured in 2002, with a 1.9 TDI engine and 96 kW of power.

The COM port is working. Also, there's something strange. If you plug in the null modem cable and bridge pins 2 and 3, VAG-COM 311.2 detects an adapter, even though nothing is connected... that's why I'm sure it works!

Okay, so if the optocouplers are "bad," would that affect the circuit?

"Circuit for a diagnostic adapter without galvanic isolation and without MAX232."

"better" performance and also compatibility with the new VAG versions?


Pins 4 and 5 are supposed to be the same?? I measured something different yesterday. 16 versus 4 initially gave 6 volts (ignition off), later 2 volts .

16 minus 5 always resulted in 12.1 volts!
It doesn't matter... I'll solder the LED in place, and I'll figure it out if it doesn't work.


@ Rainer: Is it true that you don't like seeing questions like this in your forum? I'm not sure where else I should turn.

Okay, I built a 12-volt power supply, but the adapter still isn't being recognized!

Do I need to have continuity between pin 2 and pin 3 of the RS232 side when the power source is disconnected, when using a continuity tester?

Hi.

tuner01 wrote:

@ Rainer: Is it true that you don't like seeing questions like this in your forum? I don't know where else I should turn...

Well, I already answered, right? Ulf's circuit is working, but something must have been assembled incorrectly.

Quote:

G4 Cabrio & 2002 A4

, but no money for a tank of gas (which is the price of the kit), well I won't say anything more about that.