opendiag-obd-ii-schematic

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Opendiag OBD-II Schematics & PCB Layout

This page contains plans to build a device to

interface RS-232 (a laptop computer) to the

ISO9141-2 / ISO14230 / SAE J1962 (OBD-II)

diagnostic connector on many Volkswagen, Audi,

Seat, Skoda, and Subaru 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 was a goal of the Freediag

project. Commercial software is also available which works with this interface.

Please don't email me questions about this project.

This document is viewed by hundreds of people a day. It has helped thousands build the

interface described here. The information presented here is as complete and accurate as

necessary for a person of sufficient skill to build their own interface. If you require help,

please seek it from a discussion group or your local electronics guru. I lack the time (and

often, the ability) to answer questions. Thanks for your understanding.

Here is a parts list for Digi-Key:

Item Qty Part Number Description Application

1 3 PS2501-1-ND1 CHANNEL OPTO COUPLER TRANS

DIP

COMBINED MAKES A 2501-

3

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

Page 1 of 8Opendiag OBD-II Schematics & PCB Layout | Planetfall

12/25/2010http://www.planetfall.com/cms/content/opendiag-obd-ii-schematics-pcb-layout

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 was US$8.33, plus a $5 handling fee and shipping charges.

You can get other parts, such as perf board, etc., at Fry's or maybe Radio Shack. I do not sell any

parts. You need to get them from an electronics distributor such as Digi-Key.

Frequently Asked Questions & Answers:

Question Answer

Will this device work with my

car?

If your car supports VAG, ISO9141-2 or ISO14230, it should

work. That includes cars sold by Volkswagen, Audi, Seat,

Skoda, and Subaru (1996+). Most vehicles sold by Ford,

GM, or Chrysler are not electrically compatible with this

interface.

More information on OBD-II and ISO standards can be found

here.

Many newer cars (model year 2001+) utilize two K-lines and

this device only supports one. If you'd like to contribute a

schematic or other information on how to support dual K-

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 2501-3.

What should I use?

There is no such thing as a 2501-3. I've simply stuck three

2501-1's together and called it a 2501-3.

In North America, you can easily find the NTE NTE-3098

(Compatibility confirmed by Dale Kirstein). Fry's Electronics



carries NTE parts.

You can also try the Infineon SFH615-A2 (Compatibility

confirmed by Nigel Middleton)

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.

My OBD-II connector has a

contact for 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?

Yes, but it hasn't been updated since 2003. Check out

Freediag for more information.

The Opendiag discussion group at Yahoo Groups is another

resource.

Ross-Tech seems to have discontinued their free version of

VAG-COM.

How do I make a circuit

board?

I have written a basic guide that explains how built the

board in the photos. These days I use cheap PCB

manufacturers in Malaysia and China. A few can even accept

EAGLE files directly.

I'm interested in writing

software. Where can I find

technical documentation on

OBD-II online?

You probably want a copy of HS-3000 from the Society of

Automotive Engineers. The cost is around US$240 (in 2009).

My computer doesn't have a

serial port.

The Keyspan USA-19HS is an excellent USB to Serial (RS-

232) adapter for this application. Be aware that most other

USB to Serial adapters will give you lots of trouble with this

circuit. You have been warned.

I have another question that

you haven't answered here.

Please look elsewhere on the internet, or ask your friendly

local electronics guru.

Thanks for sharing. How can

I express my gratitude?

Please consider sending a donation to help cover hosting

costs, or a postcard:



Jeff Noxon

1139 Rutland St

Houston, TX 77008 USA

Pictures

Here are some pictures of my first assembled prototype.

This is an early prototype. The jumper wires on the bottom are not necessary with the current

board layout.



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.



This picture shows component values and placement. Note that the 2501-3 is actually three NEC

2501-1 optoisolators. The Digi-Key part number is PS2501-1-ND.

Part Substitutions

The following parts are suitable replacements:

NEC 2501 Optoisolator: Infineon SFH615-A2 (Thanks: Nigel Middleton) or NTE NTE-3098

(Thanks: Dale Kirstein)

2N3904 Transistor: NTE NTE-123AP (Thanks: Dale Kirstein)

These substitutions have been used by others who have built this device.

LICENSING / COPYRIGHT NOTICE

The files linked below and the images on this page (also referred to as "software") are Copyright © 2000 Jeff Noxon, and are distributed under the terms of the GNU Public License. By downloading these files you agree to the terms of the license.

The GPL license has been chosen for two reasons. First, the documentation necessary to make

this project possible was released to the public under open terms. Second, I have spent a

great deal of time on this project. Any commercial vendor who sells this device (or one

derived from these files) is obligated under the license to provide the schematics and/or board

layout to their customers.

Files / Downloads

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)

Sponsored Links

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.

Document Revision History

Latest Update on 1-13-2009

The location of this document has moved.

Formatting has been vastly changed

Various edits have been made to improve accuracy, clarity, and brevity.

Attempted to improve the accuracy and relevance of the links.

Update on 8-13-2003

Re-iterated the desire to not be e-mailed about this page.

Update on 8-19-2002

I am no longer answering questions related to this page via e-mail.

Update on 5-21-2002

Added parts list table.

Mil Spec Wire Connectors Many Different Mil Specs In Stock & Ready To Ship Same Day. Call Today! www.WireMasters.net/Connectors

$79 for 3 prototype Turnkey service for PCB&PCBA Good price for small or mid order www.ourpcb.com

Original auto scanners Piwis KTS520 scanner diagnostic Latest software free! express ship www.autoscanit.com

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Update on 1-11-2001

PCB artwork now available in PCL format

Update on 7-24-2000

Added Digi-Key part number for 2501 Optoisolator

Added information on Multiplex Engineering's OBDII cable

Added link to Ross-Tech's VAG-COM software

Added section on part substitutions



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opendiag-obd-ii-schematic