Question about Maik's VAGCOM interface

Hello diesel mechanics,

'I recreated Maik's OBD interface some time ago, and I have a question: What is the exact purpose of the 10k and 100k potentiometers (trimmers)?' While the thing is now working after a long period of calibration, I would still have been interested in understanding its true purpose and ideal settings.
And: Which of V1 and V3 shows TxD, and which shows RxD?

My experiences/tips regarding this matter:

-In my Golf, manufactured in 2000, the mass is only connected to ODB pin 5. Pin 4 is not connected (there is no contact insert). In the Audi A4, it ranks 4th.

- Occasionally, I receive 'Too many communication errors' messages. Alignment issue?

- To reduce noise (e.g., from the vehicle's power supply), you can connect a 100nF ceramic capacitor and a 10-100µF electrolytic capacitor between the in-GND and out-GND terminals of the voltage regulator. Use the larger electrolytic capacitor on the input side. It also works without it.

- Traffic LEDs can be added for the serial side (mainly useful for debugging on the adapter PC). Connect LEDs with a 470 Ohm resistor from serial pin 2 to pin 5, and from pin 3 to pin 5. The cathode of each LED should be connected to pin 5. To indicate a low level, simply reverse the polarity of the LEDs (low = -12V).

- Very thin, flat connectors are suitable for the ODB socket. Can you also adjust or refine something by filing?


'Are there any really cheap sources for ODB connectors? I haven't found anything below 12 euros, and that's too expensive for me.'

Have a nice weekend.
andi

andi wrote:

I recreated Maik's OBD interface some time ago, and I have a question: What is the exact purpose of the 10k and 100k potentiometers (trimmers)? The thing works now, after a long period of calibration, but I would still have been interested in the real meaning and the ideal settings.

Hi Andi,

She took that from my earlier (unrefined) opto proposals, as far as I know.
This allows you to adjust the H-L detection threshold of the adapter for the K-line, as well as the K-pullup (which is roughly the impedance of the K-line).

and which of the two is for what purpose? do the designations 1 and 2 correspond to each other?

andi wrote:

and which of the two is for what? do the designations 1 and 2 match?

Hi.

The trimmer, which is located between K-Line and 2 volts, controls the K-impedance.
The other one is for the detection threshold.

Some time ago, I replicated Maik's OBD interface. First, a question: What is the exact purpose of the 10k and 100k trimmer potentiometers? The thing works now, after a long period of calibration, but I would still have been interested in the real meaning and the ideal settings.

Hi Andi,

She took that from my earlier (unrefined) opto proposals, as far as I know.
This allows you to modify the H-L detection threshold of the adapter for the K-line, as well as the K-pullup (which is roughly the impedance of the K-line).



Hello,
That's exactly right. When I have a little more time again, I will revise the circuit and also develop a new PCB .

Regards,
Maik.