Hi All,
Geat forums Cool board!
Hope I can finally give back something useful to the DIY community.
I have developed a piece of software that reads the SAE-J1850 VPW signal directly into a PC com port - no hardware needed.
Maybe some voltage regulation and filtering but no "intelligent" hardware is required.
I have pulled trouble codes using the software - it works but it needs to be made more stable.
I anyone is interested - the source code is 100% free and available here:
http://www.blacky.co.nz/free (called VPW)
Or use the batauto mirror if geocities spits the dummy.
The software will not run under WinNT or Win2k due to not being able to access the serial port hardware.
It is very unstable under Win95/98 due to Window's interrupts.
It is a little unstable under DOS due to DOS interrupts.
If anyone wants to work with me to clean up the timer routines and in preventing the interrupts - then this could be turned into a 100% free solution for pulling OBD-II trouble codes on a DOS PC. No need for expensive hardware.
I'll make the code available and if the members of this board can get it to work properly then I will add the code to pull the trouble codes. I would like to see any software that uses this software driver be made freely available.
Even if can be made stable I would not recommend using it for anything other than pulling trouble codes (with engine off) because it does not implement bit arbitration and therfore it screws up other messages on the BUS.
Any DOS programmers want to try and get it working properly?
Any electronics experts know if plugging the classII data line into your PC serial port can cause electrical problems?
If so what's the bets way to match the voltage levels required?
(I've plugged them together a number of times and not suffered any problems but maybe I was just lucky)
The VPW spec says classII data line:
Input: Low voltage is -1.0 to 2.2V, High voltage is 2.8 to 6.25V
Output: Low voltage is 0 to 1.2V, High voltage is 3.8 to 5.25V
Regards
Paul