Survey: Diagnose adapter with MAX232

Hello,
As I have already sent out several sets of my diagnostic adapter and I am sure that more have also been assembled, I would like to ask about your experiences with them. Which vehicles work without problems, and which ones have problems? Perhaps we can derive some improvements from this. For example, I have a VW Golf 3 TDI, manufactured in 1994, engine code 1Z. I can easily read out the engine control unit, the ABS control unit, and the airbag control unit on it. My car doesn't have more than control units.

Then let's get started

Greetings
Maik

hi maik

passat variant, year 1994, 1Z engine. Runs quite well. However, lately, I've been getting 'too many communication errors' infrequently. But, there's a problem with the engine control unit (motor-stg) with the flashing pre-ignition indicator and the engine briefly revving up when using the original control unit (028 906 021 B).
see also: /viewtopic.php?t=1907
But it is very likely not an adapter problem!

with a different engine control unit (028 906 021 FB) - absolutely no problems!

'So far, it's been the only adapter that has worked on my vehicle!'


Hi Jörg

Hello

Maik's adapter is definitely easier to handle and more reliable in communication than adapters with optocouplers that are not properly configured.

But surely, the developers of the Opto-adapters had some thoughts about it??

I have also designed a circuit on paper without an optocoupler – in the simplest form with 3 transistors, including. L-Line-Treiber, hergestellt aus Bauteilen, die man sogar noch in jedem schlecht sortierten Elektronikladen finden sollte.

However, it becomes problematic, IMO, if such adapters are not the only connection between the car and the PC, especially if, for example, a laptop is powered from the car's network.

For example, if the ground contact in the cigarette lighter socket is not functioning properly, significant voltage differences can arise between the laptop and the car, which then attempt to compensate for this - not to mention the fact that the signal voltages are shifted, which can lead to communication errors, completely leaving adapters with optocouplers unaffected.

In the Maiks adapter, there is also a current brake (R1 = 100 Ohm) that limits the current through pin 5 of the COM port to approximately 120 mA in the extreme case.

However, if an adapter represents a near-zero-ohm connection between pin 5 of the COM port and pin 4 of the OBD connector, then the operating current of a laptop's onboard power supply may potentially run through the COM port if the power cable's ground connection is poor - and I suspect that very few laptops, with their delicate circuit boards, can handle 3 amps or more.
Then the COM port is probably mostly broken

I believe that such or similar considerations were the basis for the development of galvanically isolated adapters.

However, someone who exclusively powers their laptop in the car using a battery, can actually do nothing wrong with adapters without galvanic isolation, IMO.

I will also be assembling and testing my Primitiv adapter soon, of course, including the mass current brake for emergency situations.

If it works - is there interest in another plan for an adapter "from the junk drawer"?

Hello Maik,

I painstakingly assembled the kit from you. The double-sided PCB is very small (but nice), and you also have to solder from the component side. After borrowing a tiny 12V soldering iron, it actually went better... then I had soldered the LEDs the wrong way around, and the output transistors probably got damaged during testing (+12V on the K and L lines). I set the potentiometers to the middle position and then tested it in the car: I immediately got it working: into the engine control unit, navigation system (MCD), central locking, climate control, I didn't try the others. Then I immediately went for a test drive and logged the data. +1Two groups were able to log a total of 8 measurements, but with 3 groups and 12 measurements, there were synchronization errors and the connection suddenly disappeared, and I could hardly work with a second application even when data was being transmitted (Win98)). Don't think it's the adapter, then!?
The car is a Golf IV 90PS ALH, 07/00, with 98500km, and the entire car is in perfect condition (at least, none that I can attribute to the car).
But it seems that the air mass limit is not quite reached at maximum power.

I have been running it with an IBM Thinkpad 600E + 220V original power supply and a 12/220V/150W voltage converter in the car. The power supply is 100% galvanically isolated (between input/output), only the ground conductor is galvanically connected to the output circuit, but is not connected, so I don't have to worry about large leakage currents.
I'll leave the AC component to the 100Ohm resistor; it won't be much.

So, ich finde Maiks Adapter gut gelungen. Er hat eine einfache Schaltung und durch den MAX232 ist er funktionssicher. But building it yourself isn't quite as simple; it's better to buy a pre-made module from him.

Best regards, Gerd

Hello Maik,

'I had already answered before, but perhaps some interested people will read this: The adapter worked immediately, and I had a properly connected PCB (thanks to EAGLE). The assembly was fiddly due to the ground surfaces.' Test drive with Ford Galaxy (AFN) - two groups logged and dirty LMM located.

I have a noname laptop with 500 MHz and Win98 running on battery power.

In a 1997 Golf III with 90 hp, even the indicator lights for power don't light up. I would like to have the airbag control unit read out because the warning light is constantly on.

Question - this probably has nothing to do with your adapter: Is this normal - do I need to supply 12V externally?

Best regards

Helmut

Hello Helmut,
The red LED should actually light up as soon as the ODB2 connector is plugged into the car. Perhaps the fuse for the ODB2 power supply has blown. As far as I know, it's the same fuse as for the cigarette lighter.

Greetings
Maik

Hello,

When I re-measured, I noticed that the voltage at pins 6 and 7 of the MAX232 IC is not being reached. The desired voltage is (-)10V DC at pin 2 and (-)10V for logic 1 and +10V for logic 0. However, I could only measure approximately 0.6V for the negative level.

It was due to the 4 capacitors C5, C10, C12, C13 (10000nF):
should be according to Data Sheet:
MAX232 = 1000nF
MAX232A = 100nF
ST232 (compatible with MAX232A) = 100nF

After I had replaced the existing KOS, the tensions were correct.
The adapter also worked with the oversized Kos. However, according to the V24 specification, the levels for logic 0 should be +3 to +12V, and for logic 1, they should be -3 to -12V.
By the way, these are voltage levels, and therefore, directly controlling optocouplers that draw current at this point is also a form of

Hello HGK,
Ashes to ashes. I must have missed something in the datasheet. Thanks for pointing that out.

Hello
Maik

Hello Maik,

Congratulations on your adapter - it's working perfectly!
Since I have no through-hole connections on my PCB, I had to solder on both sides. Looks terrible, but it works.
I used an ST232 instead of the Max232, using the C's you suggested. I set the two trimmer R's to the middle position and then tried to plug it in. The connector I ordered from OBD-2.de (which only took 2 days) was unsuitable for my vehicle. On the Passat 3b, the connector can only be plugged into the OBD-2 port with 'force'. The housing of the connector is much too thick and therefore only fits very tightly through the plastic frame above the port. I then simply pulled the pins out of the connector housing and plugged them directly into the port. Furthermore, this plug does not have a strain relief.

Hardware: Laptop 500 MHz with XP, Passat 3b TDI 85kW PD
Software: vag-com 2.082

Greetings,

fred.labosch

Hello,
I have received more PCBs. If you are interested, please send an email to me.

Greetings
Maik

Hello Maik!

Can only add -- Your adapter works with VAG-COM at my place

So far, absolutely no problems!

There were no corrections or adjustments needed, it was just "plug'n play"...

Passat, 1Z, VIN 08/95 Notebook: 120MHz, 48MB RAM, Battery-powered

Greetings

JRoth

Yep, I can only agree. Works perfectly on my Golf 4 ALH, built in 1998.

Hi Maik,
The adapter worked on the OBD interface on the first try.
The connection was immediately established after connecting to my Golf 4 MJ01.
I just read out all the error codes from all available control units as a test (everything is okay).

For the pots, I left the middle setting, as you unfortunately don't provide an optimal setting.

Plating was not easy to solder due to the very small pads.
However, the through-hole connections under the SUB-D interface are the most problematic. From a component-side perspective, it is not possible to solder, as the connector body is located above the through-hole. But I also found through-hole rivets (0.8mm outer diameter) that were perfectly suitable.

If you could also provide some information on the optimal setting of the potentiometers, I would be completely satisfied (measurement values)?

Harry

Hi Harry,
You can leave the potentiometers in the middle position if the communication functions without errors. If you experience communication problems, you can try to improve the connection quality by adjusting the potentiometers. I will soon release a new version without Potis.

Greetings
Maik

Hello Maik,

I also have the adapter (and have built it several times) according to your plan, and so far I haven't had any problems. It's really a useful piece. Tested so far on: Golf 4, Golf 3 and Audi A4s.

I have created a one-sided layout for your schematic, which is approximately 4x6cm in size (SubD components are not 'onboard', they are connected with cables). There are about 4 cables per side. Fits perfectly into a Conrad enclosure, 100x50x25.
If you are interested in having the layouts for the adapter instructions available for download, please let me know.

Where can I get a double-sided PCB made? Is it really expensive, though?

Greetings
andi

Hi Andi,
I'm glad everything is working so well.

The PCBs are self-made and also not through-plated. You basically have to solder on both sides.

Greetings
Maik