OBD2 - RS232 adapter cable (ISO 9141-2) project

• Solder all the components directly to the DSUB like the picture below
  
• The cable I used is a USB 1.1 cable which I cut off the USB connectors from.
  This cable suits the adapter cable perfectly because it is shielded and contains four wires.
  I used Red for +12V, Green for L line, White for the K line, the sield ad Gnd and the Black wire is not connected
  
• The next step is to make the OBD2 connector (I havn't found a affordable connector anywhere).
  The pin spacing in the OBD2 connector is 4 mm so I bought a 4 mm pinheader from Elfa (43-848-63) but these pins where round
  so I hit it with a hammer to make them flat. Next I soldered them to a piece of Vero board. The connector then looked like this:
  

• I have tested the cable on my Audi A4 -99 and on a Audi A3 -97 using VAG-COM 409.1
  
• But the cable should work on any car using the ISO 9141-2 protocol and a software compatible with "Dumb" interfaces.
  Check your car at: www.obd-2.de
  
• The cable contains a minimal amount of components (it is therfore possible to build it inside the DSUB housing).
  R1, R7 and R10 is only for protection. Escpecially R7 is needed for the "After market radio problem"
  where you might burn your equipment if using non original Audi/VW car radio
  
• Total component price under 7 Euro!
  
• This cable works much more reliable then the opto coupler ones. It gives correct signal levels for both the car and the RS232 port
  
• The cable don't work very well with USB-RS232 dongles (probably due to timing and incorrect baudrate problems)
  I have found two types of dongles on the market. One has a maximum baudrate 128kbps and the other one has a maximum
  baudrate of 921kbps (based on a FTDI chip). The 129kbps version works with some control modules in the car including the
  instrumentation module and the 921kbps works with all the control modules except the instrumentation module :-(
  This is a big problem today since most laptops don't have a RS232 port (serial port)
  I bought my adapters at Clas Ohlsson (The 128kbps type, Product #32-4038) and Kjell & Company (The 921kbps type, Product #38885)
  
  If you have any question or feedback please send me an e-mail att: mail

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