K-Line: Setup Help & FAQs

I have the following problem:

I built the interface according to Noxon's design, but I used PC817 optocouplers.
http://hal9000.vc-graz.ac.at/3rdfloor/projects/diagnose/Diagnose-Interface-Dateien/image002.jpg

Only I am unable to establish a connection to the interface, even though the LEDs are lit during the LED test, indicating that the optocouplers are being activated.

I used a null modem cable for testing, assuming it was a proper one, but it had crossed wires on pins 2.3, 7.8, and 1.4. However, this doesn't seem to matter during the LED test, as only the DTR line being unreachable is the issue.

I was definitely unable to achieve a positive result with the VCDS interface test, nor could I access my control unit.

My measured values are as follows:
The adapter voltage is 12.56 volts.
The voltage between GND and the K-line is approximately the same value.
The voltage at the optocoupler, which is driven by the K-line, is 1.95V.

The real question is: Can the functionality of the interface even be tested through the VAG-COM software with the K-line disabled? Because I don't have a laptop, and setting up a PC in the parking lot is a bit too much trouble.
I had actually tried this before, but as described above, I was using the wrong cable.

I plan to replicate the interface based on guideline 2.1 and then measure the corresponding values again.


Questions about K-Line:

What kind of leveling techniques does K-Line use, and how do they work?
As I see it from the circuit diagram, the K-line is only pulled to ground to transmit a single bit to the control unit.
And the adapter also recognizes the reverse signal in the same way (if the K-line doesn't provide a signal, it's a bit that has been sent back).

Can someone explain this to me? I have absolutely no idea what bidirectional transmission is.

Breakdown:
While checking the wiring in the car, I caused a short circuit between the K-line and ground using the probes of my multimeter.

The car is running normally. However, I haven't had a diagnosis performed on a professional diagnostic device in a workshop at a friend's place, just for testing. Based on my assumption regarding the K-Line (see above), nothing should have happened, right?

qubeck wrote:

I have the following problem: I built the interface according to Noxon's design, but I used PC817 optocouplers. http://hal9000.vc-graz.ac.at/3rdfloor/projects/diagnose/Diagnose-Interface-Dateien/image002.jpg Only I am unable to establish a connection to the interface, even though the LEDs are lit during the LED test, indicating that the optocouplers are being activated. Bitte gib mir den deutschen Text, den du übersetzt haben möchtest. I was definitely unable to achieve a positive result with the VCDS interface test, nor could I access my control unit. The real question is: Can the functionality of the interface even be tested through the VAG-COM software with the K-line disabled? Because I don't have a laptop, and setting up a PC in the parking lot is a bit too much trouble. I had actually tried this before, but as described above, I was using the wrong cable. I plan to replicate the interface based on guideline 2.1 and then measure the corresponding values again. Questions about K-Line: What kind of leveling techniques does K-Line use, and how do they work? As I see it from the circuit diagram, the K-line is only pulled to ground to transmit a single bit to the control unit. And the adapter also recognizes the reverse signal in the same way (if the K-line doesn't provide a signal, it's a bit that's being sent back). Can someone explain this to me? I have absolutely no idea what bidirectional transmission is. Breakdown: While checking the wiring in the car, I caused a short circuit between the K-line and ground using the probes of my multimeter. The car is running normally. However, I haven't had a diagnosis performed on a professional diagnostic device in a workshop at a friend's place, just for testing. Based on my assumption regarding the K-Line (see above), nothing should have happened, right? [url][/url][url][/url][url][/url][url][/url]

Hi.

First, I'd like to know what resistance values you used.
Because of the link you sent, I can't see any details; the resolution is too low on my end.

Otherwise, you can refer to the circuit diagrams in the diagnostic technical article for information about null modems, etc.

In order for the adapter to be recognized as functional, it also requires the vehicle's operating voltage, meaning you must apply at least 12 volts between the positive and ground terminals. If it works, the "Test" menu option will display an "OK" result.

The K-line is pulled high by a pull-up resistor when the system is in a resting state.
In the dialogue, the PC and the on-board electronics are each referenced to ground.
Both sides are aware of whether the current low level is caused by themselves.
If this is not the case, the low levels will be interpreted as a message from the other side and evaluated accordingly.

A short circuit between the K terminal and ground won't damage anything because it's essentially a normal operating condition (in this context).

Sorry, I posted the wrong link.

http://hal9000.vc-graz.ac.at/3rdfloor/projects/diagnose/Diagnose-Interface-Dateien/image001.png

Where can I find the diagnostic article?


The voltage levels at the optos are causing me concern, as the datasheets indicate that the PC817 requires 1.2V to 1.4V, which is not the case in my setup.
Should I perhaps replace the current-limiting resistors before the optocouplers with potentiometers and then start with an adjustment?
and should I also replace the input transistor's input resistance of 150K with a potentiometer?

qubeck wrote:

Where can I find the diagnostic article

?


Hi.

On Rainer's website (on the left-hand side).

Take a look at the plans for version 2.x of the laptop.