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| Home | OBD-II | Litterbox Central | Today is Thursday, August 28, 2008 |
This page contains plans to build a device to interface RS-232 (a laptop computer) to the ISO9141-2 / SAE J1962 (OBD-II) diagnostic connector on many Volkswagen, Audi, Seat, and Skoda automobiles. It should also work on many pre-OBD-II models. It has been tested on my two vehicles, a 1998 VW GTI 8v and a 1998 VW Passat GLS.
Please note that this page does not contain software. Free software is the goal of the OpenDiag project. Please do not write me to ask for copies of software. If you are interested in the OpenDiag development effort, I suggest you join their mailing list.
News: This page updated 8-13-2003!
Do not e-mail questions about this project. Over the past year, I received hundreds of support questions in e-mail.I will delete questions without responding to them. If you email a question, it's either because:
If you have a question, I will try to answer it if you mail it to me on the back of a post card. If that's too inconvenient, well -- it's meant to be. You've already received more than you paid for. |
Previous Update on 8-19-2002
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Previous Updates on 5-21-2002
By popular request, here is a parts list from Digi-Key:
| Item | Qty | Part Number | Description | Application |
|---|---|---|---|---|
| 1 | 3 | PS2501-1-ND | 1 CHANNEL OPTO COUPLER TRANS DIP | 2501-3 IS 3 OF THESE |
| 2 | 2 | 2N3904-ND | NPN SML SIG G.P. AMP&SWITCH TO92 | T1 & T2 |
| 3 | 2 | 1N4004DICT-ND | RECTIFIER GPP 1A 400V DO-41 DIODES | D1 & D2 |
| 4 | 10 | 1.0KQBK-ND | 1.0K OHM 1/4W 5% CARBON FILM RES | R1,R2,R5,R6,R7,R9 |
| 5 | 5 | 1.5KQBK-ND | 1.5K OHM 1/4W 5% CARBON FILM RES | R3 |
| 6 | 5 | 10KQBK-ND | 10K OHM 1/4W 5% CARBON FILM RES | R4 |
| 7 | 5 | 150KQBK-ND | 150K OHM 1/4W 5% CARBON FILM RES | R8 |
| 8 | 1 | P10312-ND | CAP 1UF 50V ELECT FC RADIAL | C1 |
| 9 | 1 | A23279-ND | 09 MSFL PLUG RA 318 (SL,FM,BL) | DB9 MALE |
| 10 | 1 | A23305-ND | 09 MSFL RCPT RA 318 (SL,FM,BL) | DB9 FEMALE |
On 5/21/2002, the cost of these parts is US$8.33, plus a $5 handling fee and shipping charges. You can get other parts, such as perf board, etc., at Radio Shack. I do not sell these parts. You need to get them from an electronics distributor such as Digi-Key.
Here are the answers to some frequently asked questions:
| Question | Answer |
| Will this device work with my car? |
If your car is made by Volkswagen, Audi, Seat, or Skoda, then the answer is probably yes. If your vehicle is compliant with ISO9141-2, but not made by Volkswagen, Audi, Seat, or Skoda, then the device will work, but to my knowledge no software has been written to support it in this way -- so you're probably out of luck. If you have a Ford, GM, or Chrysler vehicle, the answer is absolutely not! Some (all?) newer cars (model year 2001+?) utilize "dual L-lines" and this device only supports one. If you'd like to contribute a schematic or other information on how to support dual L-lines, please contact me. But don't ask me -- if you don't see the information here, I don't have it. Thanks! |
| Do you sell these things? | No. You can buy a complete hardware and software package from Ross-Tech at a very reasonable price. |
| What kind of capacitor should I use? | It isn't critical. If you use a polarized capacitor, make sure you get the polarity correct. (You should be able to figure that out yourself.) |
| Does it really work? | Yes, hundreds of people have built this thing, and it works. I suggest you replace the 140k resistor with a 150k resistor for the best results, however. |
| I can't find the NEC 2501. What should I use? | The NTE part should be easy to locate. Look for other substitutions below. |
| My OBD-II (J1962) connector only has electrical contacts in pin positions 4, 5, 7 and 16. Why is pin 15 (L-line) missing? | Not every car has an L-line connection. If yours doesn't, don't worry. This circuit will still work. |
| I have pin 4 (or pin 5) but not both. | I suggest you connect the two ground pins together on the circuit board. Some cars only provide one of the ground connections. |
| Is free software available? | A few people are working on it. Join the Opendiag mailing list at Yahoo Groups if you're interested. So far, there has not been much progress. If you're a shade-tree mechanic and you're looking for a tool, try the freeware version of VAG-COM. |
| How do I make a circuit board? | I have written a basic guide that explains how I did it. |
| I'm interested in writing software. Where can I find technical documentation on OBD-II online? | You can't. You need to buy a copy of HS-3000 from the Society of Automotive Engineers. The cost is around US$140. |
| I have another question that you haven't answered here. | I get a lot of questions via e-mail, and most of them can be answered by reading this page. I am no longer answering questions via e-mail. If you send your question on the back of a postcard, I'll try to answer it for you. Please be sure to include your e-mail address. |
| It works! You have saved me thousands of dollars. How can I thank you? | Please send me a postcard via snail mail: Jeff Noxon |
Previous Updates on 1-11-2001
Previous Updates on 7-24-2000
PICTURES
Here are some pictures of my first assembled prototype.
ASSEMBLY
This is the artwork used in the latest revision of the board. It is a single-layer design. If you plan to etch your own board, use the Postscript or PDF files in the files section for greater accuracy.
PART SUBSTITUTIONS
The following parts may be suitable replacements:
These substitutions have been used by others who have built this device.
LICENSING / COPYRIGHT NOTICE
FILES
COPYING.TXT - License agreement for all files - IMPORTANT
ISO_B1.PS - Board layout, revision B1, Postscript
ISO_B1_LJET.PCL - Board layout, revision B1, PCL, 300dpi, HP LaserJet
ISO_B1_LJET4.PCL - Board layout, revision B1, PCL, 600dpi, HP LaserJet 4+
ISO_B1.PDF - Board layout, revision B1, PDF (for Adobe Acrobat Reader)
SCHEMATIC_B1.PDF - Schematic (PDF Format)
ISO_B1.SCH - Schematic (EAGLE Format)
ISO_B1.BRD - Board Layout (EAGLE Format)
EAGLE parts libraries are available upon request.
Helpful Links
OpenDiag - Aims to develop GPL'd software to use with this device. OpenDiag also provided the basis for this schematic.
B&B Electronics - Sells a rather expensive, but nice, SAE J1962 to DB9F cable compatible with this project.
Multiplex Engineering - Sells an alternative, much cheaper SAE J1962 to DB9F cable. See this e-mail for more information. I have not tried this cable. If you buy one and it works, please let me know!
Ross-Tech - Sells VAG-COM diagnostic software, which is compatible with this interface.
Cadsoft - Sells the Windows & Linux CAD software (EAGLE) used to develop the board.
| Last modified: Unknown |
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Jeff Noxon<jeff@planetfall.com> |
