This project would be great for use with a teleprompter, where any app could be displayed instead of just the normal (white text on black background) teleprompter apps. I'm very interested in this. 

Whats the app you're using?

Also I see some double-reflection on the acrylic, have you found a way around this problem? I heard there are some films for that but I'm not sure

First navigation app is Navier HUD which supports screen mirroring. 

The second one in the video is google maps (After tweaking android source to mirror the screen).

And yes., check this comment for the reason of double-reflection. https://hackaday.io/project/168005-hud-display-for-cars/discussion-134292

Have already added a film as you suggested, can reduce it further by adding a thicker layer of that film. We can also reduce the double-reflection by reducing the thickness of the glass. Haven't tried anything though.

Interesting, I seen some people using polarized film to increase the visibility in daylight but I dont know if it would reduce double-reflection

Also have you considered using one of those tiny DLP projectors? wouldnt be brighter than a phone screen?

BTW is there a repo for that moded gmaps apk?

polarized film. sounds interesting. should check it out.

Will have my phone in the max brightness. it is bright enough for me.

I dint modify the gmaps app, i modded the android and built a custom rom which flips the entire screen's display. will create a repo for that once i find some time.

A HUD display? So it's a "heads up display display"? 

This is cool!

However, could you have reflected the phone screen onto a mirror that then reflected the screen onto the wind screen? Would that have solved the issue of the reflection being flipped?

Thanks @Jacob MacLeod . The idea you suggested can work., but with a mirror in the middle, i think it adds another layer of complexity to the design making it look bulkier. And it can also take some efforts to get the angles right.

Yes, that makes sense

That's pretty cool - I always imagined building a HUD for my car during those long commutes.

Question: Does it look more in-focus in person? Seems like every photo I see of a HUD, even on fighter jets, looks a bit fuzzy.

thanks @Dan Maloney . Not sure about fighter jets. But here it is not actually projecting in an angle, so focus is not an issue in these types. But as the glass surface has some thickness, the front surface of the glass reflects some light, and so does the rear surface. This can cause us to see some double images. hopefully reducing the glass thickness should reduce the distance between the two overlays and make it less fuzzy.

The HUDs on fighter jets set the focal distance to infinity, this is impossible to do with just a flat mirror. You need some lenses and some distance between the projection screen and the lens.

Car manufacturers who put this stuff into the dash hides the optics since they can manufacture it right into the car. None of the cheap HUDs you can buy on Amazon has the optics required. They do not project to infinity and thus your eyes need to shift focus to see the HUD.

The 3rd party HUDs you can buy that actually does have some optics will likely be a very small image. They exist! They are impressive! They are expensive! But they look small.