This is just an idea I explored today – I have not done this.
The idea is to attach a pico projector to the side of your head, and hack its optics to provide a small heads-up display for you.
Available commercial models for the pico projector:
- Samsung EAD-R10, 20 ANSI Lumen, ca. 300 USD (see English intro, German intro)
- Aiptek MobileCinema A50P, 40 ANSI Lumen, ca. 300 USD (see German intro). This one is a bit larger, but has a higher resolution.
- maybe more in the list of awesome projectors
For hacking the optics, I would look into something from old VHS cameras. Or from normal digital cameras.
The trick is that these pico projectors have HDMI input, and many Android smartphones have MHL output [list], which can be converted to HDMI with an adapter. Some have even HDMI output directly.
For example, this is possible with the HTC Sensation and HTC Sensation XE, even with custom ROMs [instructions].
However when thinking a bit more about this all, it appears to me that hacking a HUD device for a smartphone is not really a good idea:
The biggest need they would solve is having a bigger screen on the smartphone. However, while the display will appear larger, it will have a lower resolution (640 x 480 px with the Aiptek A50P). Other problems are the added need for power, plus that you need a different input device instead of "touch". The resolution problem can be ignored, or you can go for the Zeiss Cinemizer video goggles, providing 870 x 500 px but costing however 700 USD. But you will not wear such video goggles in public or all day while working, and taking them on and off will also be a nuisance. Likewise, a HUD will be a strange sight and you will not want to wear it in many situations.
So what we want is just: a bigger screen and faster access to the phone. This would give it the main functions of a HUD / wearable computing. And for that, I propose to use loupe goggles (tip: ESCHENBACH Maxdetail) and mounting your phone to your left wrist (if you are right-handed). The ESCHENBACH Maxdetail glasses will give a 2.0x magnification, with sharp sight at 40-60 cm distance, and a viewing field of 15×15 cm at 40 cm distance. That's just decent for example for a 4.3" smartphone, which will appear visually the same size as a 12" notebook display then.
For HUD / augmented reality, I really can wait until Google Glass is selling and I can get one for cheap enough …