I was looking around the internet and I found this pdf that talks about OBD-II. 
http://fett.tu-sofia.bg/et/2006/ET2006%20BOOK%204/Electronic%20Systems%20in%20Measurement%20and%20Control/105%20Paper-P_Dzhelekarski.pdf

Good find. The schematic and description are very helpful.

I wonder what the details of the block marked "J1850 VPW & PWM transceiver" are?

Deduced from the credits:
Ozen elektronik OE90C2600
http://www.ozenelektronik.com/downs/pdf/oe90c2600.pdf

A ELM-327 chip would support more protocols though.

Also, I don't know whether a EUSART is mandatory (for the elm chip) but it might be a
design constraint when choosing a obdii interface.

That almost seems like cheating. I'd prefer to do it with discrete components and
firmware.

How about this: 
http://www.obddiag.net/allpro.html

It looks like a USB PIC, MCP2512, MCP2551, and some other parts. I'm not sure how
many protocols it covers. Which are most important to you? OBD2?

I agree, going discrete would be preferable.

Here's another site with schematics:
(probably older info than the link above)
http://www.planetfall.com/cms/content/opendiag-obd-ii-schematics-pcb-layout

It says in the paper; http://ecad.tu-sofia.bg/et/2006/ET2006%20BOOK%204/Electronic%
20Systems%20in%20Measurement%20and%20Control/105%20Paper-P_Dzhelekarski.pdf... that 
at the time of publishing, that the J1850 transceiver is not implemented. Thats ok 
for me.  I want it for, ISO15765 CAN-4. I think it should provide access using BMW 
Ediabas software to all control units in ~>2007 BMW's.

I have tried to reproduce the schematic in Eagle Cad soft (my first one) based on 
the Fig 2 schematic. I would really appreciate gentle criticism from those of you 
who visit this forum.

I chose through hole components over surface mounts. A move, I new I might regret.

I have many questions, but I am enthusiastic to learn.

Sorry for posting a broken link and attaching an unreadable file. 
It was my first post.
Here is the academic paper with schematic on page 3

http://fett.tu-sofia.bg/et/2006/ET2006%20BOOK%204/Electronic%20Systems%20in%
20Measurement%20and%20Control/105%20Paper-P_Dzhelekarski.pdf

Is there anyone monitoring these posts anymore?

D-Can IF.pdf 24.2 KB   Download

Yup, I think a couple people are watching here. I'd love to implement this protocol,
but I don't have access to a car or other OBD-II test case. 

I am still watching.  I just bought a used 2008 Chevy Coblat and I would like my own
obd reader.  I think that I can be lazy with my car because from 2008 on everyone is
supposed to be using CAN.  If anyone has access to the ISO 15765 standard I would
like a copy.

Hello, I would like to test my BPv3 with OBDII protocols ISO 9141-2 and ISO 14230-4,
if someone first implements them. I have access to Renault Laguna 2000 model, but I'm
not 100% sure if it's OBDII enabled at all. At least it has the connections.