Heads up Display?

[bobski]

Originally Posted by miket

A screen [...] thats reflective to the exact narrow wavelength of the display but transparent to others?

In theory, sure. Unfortunately, most people don't have a means of measuring the exact wavelength of light emitted by their display. Even if that issue were solved (using display spec numbers or whatever), where would one find such a narrow-band reflective material at a reasonable price?

[miket]

They sell them to work with the real HUD's. If your using an led display or led backlight then id think you buy one of the same spec'd wavelength.

[bobski]

Originally Posted by miket

They sell them to work with the real HUD's.

Who is "they"?

[dcb]

you could make a mostly see-through array of LEDs that you thwack onto the windshield. Some SMDs and magnet wire and some silicone or ??

[miket]

Originally Posted by dcb

you could make a mostly see-through array of LEDs that you thwack onto the windshield. Some SMDs and magnet wire and some silicone or ??

They would have to make it more complicated then that if you want the image to appear in the distance. Theres something in the wikipedia article on HUDs about optical waveguides.

[miket]

Originally Posted by bobski

Who is "they"?

Idk, i read the Wikipedia article on HUD and thats how they said it was done.

Now its not clear to me if they do reflect indvidual wavelengths like that in car windshields or not. I dont know if they need to do that because they're not covering the whole screen like a fighter jet just a small part of it above the dash.

Some of the aftermarket HUDS include a square of partially reflective tint to stick on the glass. That area of glass looks somewhat darker but the reflected image on inside of the glass is much much brighter so you dont need as much power and the ghost image on the outside is dimmer in comparison. You should probably try that. I've heard that the original GM car windshields had a darker spot where the HUD would be but the newer ones don't the whole window looks like the same tint level. Im not sure if the area above the hud and dash is more reflective and less absorptive tint or if its wavelength specific or if theres no difference there.

Lookup Dupont wedge. Apparently they can vary the thickness of the glass and plastic layer between the layers of windshield glass so it forms a wedge shape above the HUD that aligns the two reflections from the inside and outside surfaces of the glass so the driver sees only one image and no ghosting ! Wonder if a wedge could be stuck to the inside surface?

I found an interesting article where GM created a whole screen HUD that had layers of different color phosphors that illuminate when hit by lasers. Neat research.

Edit:searching this thread now i see you've mentioned tint. After reading the Wikipedia i searched for combiner here and didn't see it mentioned. this thread is 8 pages long but heres one that is 47. http://www.mp3car.com/vbulletin/hard...rputer-47.html

edit2: That is how they do it on the new GM cars. http://www2.dupont.com/Automotive/en...e20050606.html

[miket]

What focal length lens or mirror do you need to get the image to appear floating in the distance??
Say around the front bumper like the oem versions.

I wouldnt want to remove my focus from the road to read the hud, thats kind of the whole point of a hud.

[bobski]

Originally Posted by miket

I wouldnt want to remove my focus from the road to read the hud, thats kind of the whole point of a hud.

Even the nose of the car would require some re-focusing, but putting the focal point at traffic-like distances would be a mistake. If you do that, the numbers will appear to be part of traffic which could make you misinterpret or completely blind you to some key event. Keeping the display at dashboard or at least attached-to-the-car distances avoids that problem by providing some focal separation... Some kind of information the brain can use to sort visible objects.
Really, the practical point of changing the HUD's focal point is to reduce eye strain. Frequently switching between near and far focus tires the eyes. The not-so-practical point is visual impact... It looks cool to have numbers that appear to float in mid air.

Going back to the value of a HUD, I think the main point is to keep your field of view on or very near the road. That way you aren't completely oblivious to the car in front of you that jabbed on its brakes just as you looked down at your mpguino. Your vision doesn't have to be perfectly focused on traffic to see brake lights flip on, but those brake lights do have to be in your field of vision.

[miket]

If that's the case then put the mpguino in the bottom of the window glass so you dont have to look down or bother with HUD... I think changing focus to a foot in font of your bumper is many times easier than the winshield so close to your face.

[dcb]

so do it, there's a diagram in post 1 to give you the general idea of what goes where.