Opendiag OBD-2 plans
Last Updated on July 22, 2024 by Mutiara
This article 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 a 1998 VW GTI 8v and a 1998 VW Passat GLS. Most vehicles sold by Ford, GM, or Chrysler are not electrically compatible with this interface. This article was written and all images and files created by Jeff Noxon at planetfall.com
Components list
The cost of these parts is around $ 10 from most electronic parts distributors. The components including per board can be purchased from Frys, Radio Shack, Digi Key, Mouser Electronics, and others.
| Item | Qty | Part Number | Description | Application |
|---|---|---|---|---|
| 1 | 3 | PS2501-1-ND | 1 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 |
| 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 |
Notes
- The type of capacitor used is not critical, however if it is going to be a polarized capacitor then make sure the polarity is correct.
- For best results, the 140k resistor should be replaced with a 150k resistor.
- The NEC 2501-3 does not exist. In this instance three 2501-1’s were stuck together and called 2501-3.
- In North America, the NTE NTE-3098 can easily be found (Compatibility confirmed by Dale Kirstein). Fry’s Electronics carries NTE parts.
- An Infineon SFH615-A2 can also be used (Compatibility confirmed by Nigel Middleton).
- If the OBD-2 (J1962) connector only has electrical contacts in pin positions 4, 5, 7 and 16, and pin 15 (L-line) is missing, this is because not every car has an L-line connection. However, in this case the circuit will still work.
- If the OBD-2 connector has a contact for pin 4 (or pin 5) but not both, then the two ground pins need to be connected together on the circuit board. Some vehicles only have one of the ground connections.
- Free software is available however it has not been updated since 2003. The software can be found at freediag.sourceforge.net
- Ross-Tech seems to have discontinued their free version of VAG-COM.
- Directions on how to make a circuit board.
- It’s possible to use cheap PCB in Malaysia and China. A few can even accept EAGLE files directly.
- If you are interested in writing software, it is recommended to get a copy of HS-3000 from the Society of Automotive Engineers. The cost is around US$240 (in 2009).
- If the computer doesn’t contain a serial port then one solution is the Keyspan USA-19HS, which is an excellent USB to Serial (RS-232) adapter for this application. Most other USB to Serial adapters will give you lots of trouble with this circuit.
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).
Schematics
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.
Assembled example
This is an early prototype. The jumper wires on the bottom are not necessary with the current board layout.
Files
- 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).
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