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This is an experiment of a HUD head up display with collimating light. This simple setup of an iPad and Fresnel lens allows projections of any images or movies. We projected a wayfinding application to test the possibilities of implementing this technology at an airport.

When your excitement from looking on wayfinding arrows is wearing off, then you can also use this device to see into the future, actually. See movie...

//Viktor Sandqvist and Jessica Ho

This technology exploration is a part of the course Technology for Concept Design TfCD at TU Delft.

Step 1: Gather Materials

Material

  • Display: iPad (borrow one)
  • Collimator: we used a flexible PVC fresnel lens 400mm x 320mm with focal length: 670 mm (20 €)
  • Combiner: transparent reflective plastic sheet, we used 1mm Vivak clear PETG (7 €)
  • Frame: 2 x black foam board 5mm (2x 4,5€)

Total cost: 36€

NB!
The materials used are far from ideal (but easy to get hold of and kind of cheap).
Ideally you should try to get hold of:

  • Display: As bright as possible in order to get better contrast and visibility in light environments.
  • Collimator: Any set of lenses that transforms the light (rays) from the display from diverging to parallel. The more parallel the light is the further behind the screen the image will appear. The focal length (see step 3) determines the size of the contraption so keep is short if possible.
  • Combiner: The are specially coated combiner glass (partially silvered mirror does also work). The important factor is the transmission ratio. 50% transmission means half of the light goes through and hal is lost. To low transmission and you won’t see through the combiner screen, too low and you won’t see the screen image. Choose transmission rate depending on brightness of your display (or just grab the cheapest plastic sheet you can find as we did).

Tools

  • Cutting
  • Knife
  • Tape
  • Ruler

Step 2: Prepare Material

  • Frame for the fresnel lens (collimator)
  • Frame for plastic sheet (combiner)
  • Bottom box

Cut the foam board to create a bottom box for the ipad (to minimize reflections in the lens from ambient light).The height of the box should be the focal length of the fresnel lens, see following steps.

Step 3: Assemble Bottom Box

  1. Prepare iPad for the image you want to display, note that the image needs to be mirrored. We chose to test the wayfinding application HUDWAY.
  2. Assemble the box around the ipad

Step 4: Assemble Collimator

Attach the Fresnel lens to its frame and place on top of the box at the correct focal length. You can make slots at each corner to prevent taping on the lens directly.

Step 5: Attach Combiner

  1. Attach the plastic sheet to the foam board frame to create the combiner.
  2. Attach the combiner to the lens.
  3. Adjust the angle of the combiner to make sure that the entire projection is visible on the combiner.
  4. & 5. Secure the position of the combiner.

Step 6: Finished HUD!

The finished HUD, displaying the projection of the wayfinding image or any other images :)

Step 7: Some Theory

With collimation lens
Image appear further away, both image and background is in focus.

Without lens
Image appears close behind screen, camera can’t focus on background and image at the same time.

The optical collimator, in this case the Fresnel lens transforms the focal point of the virtual image to infinity. The collimation of the projected image appears to be focused far behind the transparent screen (combiner) that is reflecting the projection. Without the collimating lens, the projected image appears to be on the combiner screen.

<p>The collimator besides projecting at background, does it also magnify the image?</p>
<p>I imagine a really cool expansion of this would be using a camera mounted at about the same height and position as the HUD and doing some live processing in OpenCV for dynamic updates, creating something akin to the Microsoft Hololense </p>
<p>Awesome display. This could make a decent teleprompter. </p>

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