VAGCOM: Motorcomputer antwortete nicht | Posts 32+

hi,

I also used HC14 because I didn't have HC04 available. However, this shouldn't be seen as an advantage or disadvantage; the 74HCxx receives a digital 0V/5V signal from the 'Sens' transistor.
I would reconsider the 300 ohms, since Maik has a 1K and a 10K potentiometer as a pull-up on the K-line. If the potentiometer is at 0 ohms or a very small resistance, then a significant voltage drop will occur across the 300 ohms.
I think a Z-diode for protection is already better, since there is a roughly 30 Ohm resistor in the ECU. Maybe you could also connect a small C (1-10nF) capacitor, which shouldn't interfere when the adapter or ECU is operating at low levels (low-ohm drivers), but should work with the 1-11K resistors when operating at high levels.
In the K-Line specification, I believe a 510 Ohm resistor is required (as a pull-up). However, I don't recall the exact details.

What might be a good alternative to the 'Sens' transistor is to use a Schmitt trigger, but this would then require a 74HCXX component to be powered by V_Batt.
This would probably be the cleanest solution.

The transistor that is now installed also performs a Schmitt-like function, but without a hysteresis window. If we simply raise the threshold value a bit, then a low level should be detected more readily when the K-line has a slow transition.
What do you think?
hello

Greetings

Hi,

The images of the adapter are now also online.

http://www.alexweiss.gmxhome.de

Unfortunately, they aren't very good. My camera isn't very good either.
I will try to improve things on Monday.

Greetings

Hi Nick

You have connected the Optos in such a way that only the photodiode and the BE (base-emitter) part of the output transistor's circuit lies between +5V and GND - meaning without any ohmic current limiting

Can this Opto really be used like this?
I would, as a precaution, always connect approximately 470 Ohms between the photodiode and the +5V terminal.

By the way, the picture is quite blurry, making it very difficult to recognize the circuit
Do you still manage to phrase it better?

Hi,
Here is the Eagle schematic for download.
I can make the schematic 'sharper,' but it will be larger. Anyone who wants to see it more clearly can download it now.
Regarding the Opto: it should be fine without a pre-resistor. In the datasheet:
http://www.farnell.com/datasheets/15121.pdf even suggests a 100nF capacitor in parallel with pins 8 and 5 on page 15.
The symbol in the schematic is only shown schematically.
One could also provide a base voltage to the OK pin via a resistor on pin 7, in order to achieve a better CTR.
But it also works without being 'super,' as it's only a low-speed application compared to what the OK can do. It becomes interesting when it needs to be a bit faster. We are currently integrating optocouplers into USB, and at USB 1.1 full speed, this results in 12MBaud (which, of course, is not compatible with the 6N136). It's not always easy to get there, but in the end, somehow it always works out *gg*

Greetings

Hi Nick,
Regarding the schematic: take a look at FreePDF. With the PS Output of the Eagle CAM module, you can easily create readable, legal, and small PDF files of the schematics.
Regarding Optos: Take a look at the HCPL 7710/0710. This allows even a 1MBit CAN to be disconnected without the sender stumbling over its own dominant signal
http://literature.agilent.com/litweb/pdf/5968-7458E.pdf


Best regards, Rudi

hi,

The HCPL 0710 is also quite good, I also use the HCPL 0721.
However, for CAN, I prefer the 6N136 because it is cheaper. I then usually use 2 pieces before the physical layer driver, 82C250 Philips or Infineon 6250G, which saves me the problem of overwriting the dominant bits (arbitration).

Ich kenne FreePDF nicht, ich habe völlig vergessen, dass Eagle PDF drucken kann. Ich kann auch mit Acrobat ein PDF erstellen. Is it possible to view a PDF file without downloading it in the browser?

Greetings

Hi Nick,
Most browsers (assuming the Acrobat plugin is installed; however, the plugin is usually installed together with the Reader) can display PDFs by clicking on them (but it's also essentially a download).
I always use the 251 as the physical layer driver because it is significantly more robust than the 250. In my case, the specification required potential separation on the TTL side of the driver. Therefore, the 0710.

Best regards, Rudi

Hi Nick

I have downloaded the Eagle Schematic, and now I can see everything

A few questions still:

1. What type of DC-DC converter are you using (I can't find the model number in the .sch file)?

2. What are the values of R7 and R8?

2. What should the adapter be able to do more/better than, for example, my 2.4?
If it's only about eliminating the trimmer in the context of universal COM-port compatibility - this could also be achieved with the relatively simple concept of 2.4 GHz with an additional DC-DC converter

Hi,

Okay, so I'm using the NME0505TM (SMD) for DC/DC conversion.
R7 = 100k / R8 = 33k is only for testing, I wanted to see what I should do with the Z-diode. Maybe it will work out.
I have never said that the adapter is better or worse than your 2.4 version. I just think that a serial interface should have a MAX or something comparable, or that, as a DCDC, it makes either 2/-12V and then perhaps uses transistors to control the serial interface. This ensures that the adapter works with all PCs, especially laptops, without damaging the interface with the LED power indicator.
I bought my DC-DC converters on eBay. I bought 50 of them for a very low price. Each one should cost around 11 Euros at the manufacturer.
It would also be possible to build one yourself, a simple DCDC, but it shouldn't be too difficult, but I still have 49 *gg*

Greetings

Nicklas wrote:

I think that a serial interface requires a MAX or something similar, or that it uses a DC-DC converter to generate 2/-12V, and then uses transistors to control the serial interface. +1This ensures that the adapter works with all PCs, especially laptops, without overloading the interface with the LED power indicator.

Hi Nick

OK, I can understand that from a "perfectionist" perspective.

That the OK-current requirement "compromises" the interface should only be conceivable if the CTR (--> type selection) is far too low without sufficient subsequent current amplification.
My laptop is providing approximately + / - 5.5 volts at the COM port, which is more than enough to operate the PC 817 (even with optimal adjustment, no trimmer is touching its limit).

I still find it the safest (and also somewhat elegant) way to generate the RXD signal from the "own" high and low levels of the interface