Actually, like many have posted, the OBDii is fairly quick. The only problem becomes when you are trying to read multiple variables on the ECU side. Then it becomes a bottleneck.
With the software I'm working on, yes, it will span two 7" monitors, and I'll have a third monitor for my desktop space/frontend whatever, and I am using the multiple monitor stuff through windows, with 2 seperate video cards right now. My next option is buying a dual output card, along with onboard vga, to see if i can get three monitors going. My car is custom, so I'm able to do this behind the steering wheel. I agree that in most cars it would not be easy to be able to get this to work. More research should go into LCD's that span 3-4", and that could be coupled with some of the VGA boards out there (
www.earthlcd.com)
My software is also skinnable to 1 screen, or multiple screens. However many you have, you just have to write the skin correctly. I will release a slim version so you guys can do what you want with the graphic/skin side once I get the first skin coded in.
Yes, my hardware is extensive because of the uniqueness of this in an older model and VERY custom vehicle. An OBDii wrapper I could easily code to this once I get the skins finished up. I have the source to the more popular
http://www.obddiagnostics.com/ so it would probably be based around this.
The main things in the skin, that you have to remember to do, are the max/mins of the gauges, and the angle of the increment of whatever you're doing. So that the program knows the minimum and maximum angle of your numbers, and the increment to calculate the distance and locations of the rest. All of this is hardcoded to read in variables.
If you check out Dakota Digital (
www.dakotadigital.com), they sell an 8k pulse sending unit for tach/speedo. This basically says it does 8000 pulses per mile, depending on tire size etc. There are ways to configure it. This would be the easiest hardware solution to bypass the obdii port. 8k pulses is about the normal for most cars.
As for the coding of my app, I chose VB as I know it inside and out, I'm just having to learn DirectX 8, which is mostly Direct3D. This code can be ported to C, VB.NET and many others pretty easily.
Also another option to your 'smaller than 640x480' res problem, could be to switch back into old DOS, it has a Screen 13, or 13h which is 320x200 IIRC. I used to code this with sidescrolls and RPG type games back in the day. Though its only 256 colors, so you'd have to be picky with your graphics. I can get Windows to boot in about 15 seconds normally, but again, with a custom car, who cares? Its not a daily driver, but for you guys, faster = better.
I tell you something too, using something like MediaEngine, which can load over the default windows shell, makes booting a hella lot faster as well. If something like this could be incorperated, or even run at boot without loading the default windows kernal, it would boot a lot faster as well.