By Scott A. Keen (Scottkeen) on Saturday, August 25, 2001 - 04:31 pm: Edit

Just found out about this OBD-II scanner on another car forum.
http://www.ghg.net/dharrison/obdscan.html

Has anyone used this one? Like it?

One nice thing is he has a version that works with a Palm handheld PDA computer.

By Scott A. Keen (Scottkeen) on Saturday, August 25, 2001 - 05:23 pm: Edit

Hey, I was just thinking -- there should be a way to build an OBD-II interface at home, cheaply. It's a data converter from MUX to RS-232 data, plus software to display the data and lookup/translate the codes.

Anyone know how to build an interface to convert the MUX data to RS-232 data which the serial port of a computer can accept? I'm not an electronics engineer.

Somewhere I read that there's a Radio Shack chip that does it.

I'm a software programmer and if I can get RS-232 codes coming into the serial port of a computer, I could write a program to read/write the OBD-II data (pretty sure).

Wouldn't this be a cool public domain project.

By TucsonSean on Saturday, August 25, 2001 - 06:46 pm: Edit

Scott,

The chip that you are thinking about is an RS232 to TTL converter. The number for the chip is MAX232 and was originally made by Maxim. I believe that you can pick one up at Radio Shack.

As far accomplishing what you want to do, you need more than just the MAX232 chip. I believe that the ODBII data is inverted logic, so you would need a simple converter to accomplish this. A transistor works nicely and they're cheap. Also, the data is not in a typical RS232 format, meaning 1 start/ 1 stop bit with 8 data bits and the baud rate does not sync up to standard RS232 as well. You would be better off interfacing to a microcontroller first and then sending the data out to a PC with a standard baud rate.

If I get a chance, I will dig out the schematics that I have and all related info and post it.
I was thinking along the same lines as you, but I was looking to do a little more than just read and clear codes. Reprogramming the ECU was on my agenda. Time is my only set-back right now.

Sorry for the long post. BTW, I do know a little about electronics.

By Chris Merritt (Smokinbro) on Sunday, August 26, 2001 - 05:18 am: Edit

I like the palm option - !!!