Heads up Display?
 

For a HUD, I think you would want to use a bright LCD that inverts the image (i.e. green numbers on black background). And a bit of concave mirror will correct the image and allow you to scale it up.

http://img526.imageshack.us/img526/5...micshudlk0.jpg

Never tried it myself however.

Cool, I guess it is more appropriate to have my own thread than continuously hijack the OBDuino thread. I was thinking the exact same thing about using a reverse polarized LCD with a bright backlight. Either that or a Vacuum Fluorescent Display but those are much more expensive so I'm hoping a reversed LCD will work (I can reverse the polarizer myself, have been doing it with cheap calculators to make sure it works). Right now I have just been using my cell phone to "prototype" the set up. I have experimented a bit with a cheap fresnel lense and can "project" the image on a plane that is perfectly vertical instead of reflected on the slanted windshield. Due to the small width of the screen, distortion due to the curved windshield doesn't seem to be a big issue, however ghosting is. Have gotten some ideas from a thread on mp3car.com. Not sure I will be able to get the image projected out in front of the car though.
Zac

I thought that was a really cool idea when I read it in the other thread. I encourage you to try it and post pics!

I encourage you to try it as well! Also, separate threads are good, since I'd stopped following the obduino thread, and wanted to see this, ;)

I had to do a quick experiment with a makeup mirror too, and a short extender cable :) It is promising, it is brighter in real life and the lcd is currently limited to half brightness (and might be pulse overdriven to a brighter appearance). A LED array might not be a bad idea either, but complicated.

http://opengauge.org/diympggauge/hud1.JPG

http://opengauge.org/diympggauge/hud2.JPG

So you reflected the upside down lcd onto a mirror and from the mirror to the windshield? Not a bad idea but I'm hoping to use the software to reverse the LCD, reflecting the image only once (onto the windshield) should maintain a higher brightness than multiple reflections. I just read a little about OLED displays (as they are available with the proper driver) and they are supposed to have significantly greater brightness and contrast than an LCD with a cost much cheaper than a VFD. The cheapest I have found a 16x2 VFD is $65, found a 16x2 OLED for $25 on ebay. I am certain that even a backlit LCD will work at night but I think it will take something brighter with higher contrast during the day. Right now the only backlit LCD i have is my cellphone and its difficult to read in bright daylight driving conditions anyway.

From my experience with OLED backlights, they are not that bright and don't last very long. Normal LED backlights or even CCFL backlights are a better bet.
BTW, the OLED-backlit display I have cost only $8 from a local electronics parts store and it's a 2x24. I would not recommend it, of course, as the OLED backlight became unusably dim after just 4 years while the normal LEDs had no noticeable aging in the same time period.

yup

One thing I haven't mentioned about trying to do it in software is that the lcd character generator is all fixed (except for 8 customizable ones). There is no reasonable way to reverse/flip the bit patters for the standard character set so "TANK MPG" will be upside down in the big display, as will all standard characters. But if you are doing all big block numbers then you have control of the arrangement of the "blocks" there and can generate an upside down image. Maybe with a flash of the screen abbreviation when you press a button (up to 4 chunky letters).

Also, regarding brightness, a single mirror isn't losing much, especially compared to the windshield. Though it does add some bulk, cost.

I loved the heads up display in some of the GM cars. I wonder if you could use one of their assemblies and adapt it to this. Might give you a few more ideas on what works in practice to look at too.
http://www.ranrich.com/gp97hud.jpg

What a great idea - nice pics, dcb!