Testbench setup?

[DV52]

I'm contemplating building a simple (meaning low-cost and easy to construct) set-up on a test-bench that will enable me to interrogate control modules using my VCDS cable. Before I launch into the project in earnest, can anyone provide guiding advice (as proof-of-concept) as to whether this is possible?

My preliminary thoughts are that I could (hopefully) use a J533 module and an OBDII connector in a stand-alone configuration as the interfacing arrangement to the VCDS cable. Then depending on which control module I want to test, power-up the test-module and hook-up the appropriate CAN high/low lines (whilst leaving the other CAN lines unattached) - see diagram below.

I suspect that this arrangement will cause all sorts of DTCs, but this aside - will it enable me to interrogate the control module for stuff like adaptation channel settings, coding, SA etc.?

Other questions are:
(1) Do I need terminating resistors on the CAN lines - if so which ones (used, or unused, or both)?
(2) Do I really need multiple pins connected for +12Volts and Earth on the ODBII connector - which pins does the VCDS cable need for power?
(3) Will I be able to register the test module to the CAN Gateway using the set-up?
(4) Is there a minimum length of twisted-pair wire needed for the CAN lines?

If my diagram below is "naively simplistic" (as I suspect that it is) can it be amended cheaply to provide a useable test-bench set-up

Any comments/thoughts welcomed

Don

 

[langers2k]

I'm contemplating building a simple (meaning low-cost and easy to construct) set-up on a test-bench that will enable me to interrogate control modules using my VCDS cable. Before I launch into the project in earnest, can anyone provide guiding advice (as proof-of-concept) as to whether this is possible?

It definitely is, I have got a few modules linked together on a bench for a bit of experimentation I'm planning:
- CAN gateway
- BCM
- Instrument cluster
- RNS310
- BT module
- Steering control module
- MFSW buttons

(1) Do I need terminating resistors on the CAN lines - if so which ones (used, or unused, or both)?

I haven't used any.

(2) Do I really need multiple pins connected for +12Volts and Earth on the ODBII connector - which pins does the VCDS cable need for power?

I'm sure I did for ground. You might want to have both a 12v and switched 12v too.

(3) Will I be able to register the test module to the CAN Gateway using the set-up?

Yup

(4) Is there a minimum length of twisted-pair wire needed for the CAN lines?

Probably, the shortest runs in my setup are 20-30cm.

I'd definitely recommend grabbing the wiring diagrams for a car which uses similar modules as that'll answer most questions. I haven't got the notes from my loom handy I'm afraid.

 

[Zenerdiode]

You've pretty much got it nailed there Don. In the 'olden days' of the VAG1551; the vehicle literally powered the test device from pin 16 and 4 for positive and negative respectively. You may also want to add a switch to simulate 'Terminal 15' and have a Terminal 15 to the DLC and another end to connect to the module, as some like to see 'ignition switched off' - as that is when they save stuff to EEPROM.

1) Not really. If you have to, a 120Ω should suffice
2) VCDS needs + on 16 and - on 4, but add 5 too
3) Yep, should be fine.
4) No, and I don't think you'll exceed the maximum either...

(You're going 'SA Mining' - aren't you? )

 

[DV52]

langers2K, Zenerdiode: Galvanised into action by your helpful suggestions (many thanks for these). I'll get down to the local wreckers and then fire-up the soldering iron!!
Don

 

[Sebastian]

Make sure to use a suitable power supply, we found that 5A or more may be needed in some cases to overcome the initial surge some of those module require. Also, personally I find it most efficient in the long run, not to solder onto modules directly but instead use the factory connectors. Many moons ago, one of our distrib and I sat down and looked at simple low-cost options to have a modular testbench setup. We decided to use DB25/LPT connectors, partly because they are dirt cheap and there are existing housings for DB25/LPT switches out there.

While the first versions still looked crude, they just worked...

...and some more professional ones came out of it.

The most important reason for using factory connectors for the control modules, you can easily swap to different modules if needed and the modules themselves stay physically untouched.

1) I never found a need to use any resistors on the CANs at all, since the modules themselves are already terminated and an open line will do no harm. If no module is connected at all it will just show as an open circuit in the gateway. If you have one module connected, that is plenty termination to overcome the open circuit detection.

2) You will likely need a J527 or a J519 to simulate the Ignition/Wake-Up messages, I strongly recommend to add a switch for Terminal 15 as well.

3) For gateways and possibly ECMs, it should work (except the lack of switched power) - some other modules may require Ignition/Wake-Up messages in order to start talking.

 

[DV52]

^^^^ Sebastian: Many thanks for the advice- very much appreciated indeed.

So, to confirm my understanding and in summary:
-

1. make sure that I use a low impedance power supply -inrush current can be high on switch-on for some modules. (Why is that - are these modules intrinsically inductive?)
2. avoid soldered connections - use connectors where possible to allow-for ease of turn-around of modules (DB25/LPT connectors - what an inspired choice! But why so many pins? Even if the test module was networked across all CAN bus-es, that's only 10 wires? Do these modules use hand-shaking lines in addition to CAN high and CAN low?)
3. CAN bus termination resistors not needed - good, one less thing to worry-about. (I notice that on your set-up you don't bother to use twisted pairs - does your laboratory environment and the short wire lengths mean that noise cancelling is not a problem for the CAN speeds?)
4. Install Terminal 15 switch - got it (not sure that I understand your advice about needing a BCM - is this required for bench-testing all/most modules? If so, is there any other way of generating the ignition/wake-up message)?

Cheers
Don
PS: Special thanks for the pictures - adds an extra dimension and it's good to see how the professionals do it! I particularly like the termination box with the OBDII connector and the DB25 sockets at the rear (I assume that the CAN Gateway lives inside the box). Real neat idea -I may borrow the design - if you will allow!

 

[Sebastian]

1) I never put much effort into looking why some modules required a decent power supply, had a proper one from the beginning and never had the time on my hand to bother. I tend to have 5+ modules on my bench setups at most times, the cool thing about the DB25 setup - you can easily extend it by adding just another box. The maximum amount of modules I had connected were 16 at some point for a training course.

2) CAN-High/Low for Powertrain, Infotainment, Comfort, Extended, Running Gear makes up for 10 pins - that leaves CAN-Diagnostics and CAN-Instruments which brings us up to 16 pins already. Add Terminal 15, 30, 31 and K1, K2/L and W - 22 pins in use now. On some vehicles, there's a dedicated wake-up line, also there is a special diagnostic line for MOST related components. That's 24 so far. Reality is, our DB25 approach is OK for most of our purposes but for a true remaining bus simulation and additional in- and outputs it won't suffice. Looking at my/our scenario, in those rare occasions we simply ran those additional connections separately. For example if you need to hook up dual ECUs, there are some extra lines between those... It also helps to have one DB25 with open lines/pins to it for testing purposes before one ends up making the actual connectors for a specific module.

4) Some modules will simply not talk via diagnostics, unless you get them to wake up. Many Audi instrument clusters are like that for example. Other modules only have Terminal 30/31 while 15 is purely virtual (i.e. CAN message), meaning without that message they just won't do you any good. If you got some decent CAN tools and know what to send you can probable generate/send the wakeup/ignition messages yourself without hooking up a J527/J519. I found that in most cases it's most convenient to use what's around, meaning the specific modules that generate the messages anyway - besides it's cheaper to buy and hook up a module than to buy and setup said CAN-equipment...

P.S.: No, the J533 is never in the box. We need to play with different gateways, therefor having the ability to replace them easily is mandatory. The box itself is pretty much full with parallel wiring for the DB25 connectors.

 

[Jef]

I'll just leave that here... used one of the Ross-Tech OBDII extension.
http://store.ross-tech.com/shop/OBDEXT-1A.html

Soldiered up everything and secured under the cap for the ECM connector, then everything is neatly tapped up and supported. Even touched the zip ties on bench grinder so there are no sharp edges from where they were cut. Not shown are the alligator clips on the power and ground lead.

For my power supply, I'm using an old computer desktop power supply unit with banana plug post sticking out of it. Something like this:
https://www.youtube.com/watch?v=b9NhsdiX0mc

I use this step up for pulling PINs on Immob2 and Immob3 ECMs and instrument clusters.

I like Seb's suggestion of using the LPT connectors if you want to make something more modular.

 

[DV52]

Jeff: I never cease to be amazed at the ingenuity of the folk at Ross-Tech - how does Uwe find all these clever people? I envisage a detector in the front foyer of the RT's Lansdale Office, but instead of detecting weapons, it detects IQ - anyone with a number less than 125 doesn't get admission into the office!

Thanks for the insight into your way of doing-it. My head is spinning with new ideas - all I have to do now is to find some used control modules that need a good home (at the local wreckers).
Just a question: Do Component Protection issues arise with test-bench polling and if so, do you have any tips for a rank-amateur?
Don

 

[NZDubNurd]

Does it's prove my "DubNurd" status, that I REALLY want to do this, but don't really have any use for it currently?

I like this thread.

I have pretty much the whole car loom from the A3 donor, so have all the OEM connectors. It'll be YEARS before I get a round tuit though

 

[Uwe]

how does Uwe find all these clever people?

I've rarely gone looking for people. Most of them found us...

-Uwe-

 

[Jef]

Just a question: Do Component Protection issues arise with test-bench polling and if so, do you have any tips for a rank-amateur?
Don

In my case, not a concern since I'm working with Immob2 and Immob3 generation modules. But I'd say Component Protection would become an issue on a bench top pretty quickly on the newer generation of modules that have that feature.

The only way I'd know to get around it... take the rig to the dealer and use drunk ODIS and fake it. I used my first bench top rat's nest rig to with drunk ODIS and got the PIN out of a Immob3 ECM.

http://forums.ross-tech.com/showthread.php?3631-Immob-3-ECM-swapping-getting-the-PIN-the-hard-way-)

I suspect the same concept would work with Component Protection as long as the needed modules were talking.

 

[DV52]

^^ Jeff: thanks again for the response:. Although I'm not surprised by your answer, I was hoping that somehow there was a way (on a test-bench set-up) to "trick" the CAN gateway into believing that the test module had been previously registered with it. My immediate interest is MQB platform modules and as you know, the CP "constellation" for this platform is not insubstantial (plus-for MQB, it appears that all the interesting modules are captured by CP-damn!). The thought of having to "get down on bended knee and beg" (this is the appropriate phrase down here because many VW dealers simply refuse do these tasks unless they fit the modules as well) and to pay a dealer for this task is deeply distressing! Hmmm............... don't tell Uwe, but I might need to investigate the CP capabilities of the "other cable"!

Don

 

[Sebastian]

CP is IMO not a big deal when it comes to a bench setup. If you truly need matched control modules, that can be overcome by putting them in a suitable car or even by hooking the bench setup to SVM/GeKo but really, CP doesn't block any diagnostic functionality in the first place and so doesn't the immobilizer in most cases.

 

[Jack@European_Parts]

Personally to keep things flexible, and simple for immediate fast expansion on a daily .........
I use an OBD2 break out box with lit LED com identifiers, and switchable pull up resistors.

All with serial and banana plugs ........switchable, ground 15 and 30 or even wake. ( comes in handy depending on what sate of probing you are actually doing )
Sometimes to add fast expansion I plug two or more break out boxes.

The lit LED breakout is the shit, because it lets you know what you have com on K or CAN and sometimes I add a tail end logger.

CP can be initiated/adapted on the bench with or without GeKo/ODIS online connections......further, termination resistors are a handy thing, especially when looking to meet a simulated criteria in the car...... on the bench.

 

[DV52]

Personally to keep things flexible, and simple for immediate fast expansion on a daily .........
I use an OBD2 break out box with lit LED com identifiers, and switchable pull up resistors.

All with serial and banana plugs ........switchable, ground 15 and 30 or even wake. ( comes in handy depending on what sate of probing you are actually doing )
Sometimes to add fast expansion I plug two or more break out boxes.

The lit LED breakout is the shit, because it lets you know what you have com on K or CAN and sometimes I add a tail end logger.

CP can be initiated/adapted on the bench with or without GeKo/ODIS online connections......further, termination resistors are a handy thing, especially when looking to meet a simulated criteria in the car...... on the bench.

JacK : Even more good ideas - thanks for the suggestions!

Is the LED box a commercial product? Sounds like it's something that I could build, but I would need to understand more about the loading limits for a CAN bus. As a preliminary solution (if I need to "see" if there is comms happening), I was hoping that I could use my trusty oscilloscope. I fully expect that my CRO won't be able to see the actual high/low states of individual pulses , but I'm hopeful that I can make-out the general activity on the comms lines in sufficient clarity to confirm that the test module is in discussion with the CAN gateway. Do you think that I'm being too naive?
Don

 

[DV52]

Does it's prove my "DubNurd" status, that I REALLY want to do this, but don't really have any use for it currently?

I like this thread.

I have pretty much the whole car loom from the A3 donor, so have all the OEM connectors. It'll be YEARS before I get a round to it though

NZDubNurd: I'm reminded of the title to the old skyhooks song (I'm sure that you guys across the ditch have heard of skyhooks) - "Nurd" is not a dirty word!

Don

PS: remember - carp diem. My philosophy: it's important to feed and to nourish the inner nurd (the nurd and the opposable thumb is what separates us from the apes!- heaven help us all if the simian race ever learns how a CAN bus works!)

 

[NZDubNurd]

My philosophy: it's important to feed and to nourish the inner nurd

I do that every day at work - We all hassle each other about it, because we're all the same.

I need to drag out "Revenge Of The Nerds" and watch it ;-) again ;-)

 

[mattylondon]

Hi everyone,

New member and first proper post.

I kind of stumbled upon using an OBD breakout box linked to VCDS out of curiosity. I have been investigating CAN messages from various control modules within the A8 D3 platform and next on my list was to capture live messages on the CAN BUS between the J533 Gateway and J285 Instrument Cluster. Studying the current flow I noticed the CAN wires had a spur to the OBD connector (pins 3 & 11), which makes it easy to connect to my CAN analysing hardware via a breakout box.

Anyhow, since I had the breakout box I wondered if VCDS could communicate with the Gateway and whatever various other modules I had connected via CAN to the gateway on the bench, and yes VCDS works perfectly on the bench.

 

[DV52]

Matty: OOOOH .... where did you get the OBD break-out box? And how much did it cost?
Don