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Old 12-04-2010, 01:27 PM   #87 (permalink)
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My I suggest something I worked on many many years ago.

To display MPG, it really is just a single number, and a single number can be represented as a bar graph. So instead of doing a HUD with digits, just create an LED bargraph that runs along the base of the windshield. With a bargraph that is 3-feet long, you can easily see the differences of a single digit.

My very first electronics project was creating a bargraph for the RPM display on my racecar. It ganged up 80 10-segment led bargraphs together (using LM3914), and displayed an 0-12v analog voltage signal as the bargraph. It was placed at the base of the windshield, and ran from right to left. This placed the spot where you shift right in front of the driver.
It also doubled as the speedometer when not racing, since RPM shows speed at a fixed gear ratio (always in 1:1 3rd gear on highway in my car).
This had never been done before, and still hasn't been done AFAIK. Totally cool seeing the "RMMMM, RMMMM" with the LED jumping to the left along with it.

The bargraphs were too dim in daylight (and too bright at night) so I created a shade for the display, but with todays LEDs this isn't a problem.

You could also use two or three different colors, and display three variables together.
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