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AR Glasses

low power laser projector for AR glasses to display vector graphics

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I am currently working on a small laser projector that can be mounted to the frame of glasses that projects vector graphics onto one lens of the glasses. The goal is to make AR more power efficient and cheap while increasing the image quality. In the end I hope to achieve a package that is smaller than regular AR displays and their required optics. More details will follow.

The Idea

I was always fascinated by AR glasses and wanted to make my own, but most DIY glasses feature small low resolution screens or require bulky screens. I want to find a way to reduce the size of the display technology while increasing the output quality.

My idea is inspired by oscilloscope music. Oscilloscope music encodes a video in the music, and the video can be decoded by hooking up the left and right audio channel to a X-Y oscilloscope. The oscilloscope only outputs a single dot, that is moved to the position that matches the analog voltage of the audio signal. Through persistence of vision (and the screen but that's not important here) the point traces lines, which are used to display vector graphics. Now the beauty of vector graphics is that the resolution mainly depends on your analog signal, and it is possible to encode nearly all types of form outlines into analog signals. The beauty of this system is that you only need a single ray that is steered to where it is needed, which means it could possibly be shrunken down beyond the size of a display.

Now the question is how I can use this technology in a pair of glasses. Instead of electrons, I want to use a laser. The only problem is that light can't be bent in the same way an electron beam can. So I looked at showlasers, that use this exact principle. But they rely on high power high precision motors that align mirrors in the right way. This is not suitable for wearables and also way too slow to display text or complicated graphics. So my idea was to use piezo ceramics to adjust the mirror. The beauty of piezo crystals is that they use low power and operate at high frequencies all while being tiny compared to any electromagnetic system.

Working principle

This idea is not new, however existing systems (like this) are still bulky and require large drivers. This is because they are made for ultra high precision applications, and provide feedback for accurate positioning. I hope to get around all that by making my own small system from cheap piezo ceramics I found on eBay (I am still awaiting the package from China).

Difficulties

While piezos are amazing they are also very difficult to drive. They require high voltages (in my case up to 100V) and high frequencies. And even at that voltage they only extend in the micrometer range so I need to work very accurately to get a clear image. Also I may need to use optics to scale the output range to match my glasses.

While I had hoped to project the laser image directly onto the retina, I don't have the resources for complicated optics. That's why I will try to use cheap HUD foil, that is used to project a smartphone screen onto the windshield and it should reflect the image into your eye. I will place the foil on one lens of my glasses and project the laser onto it. That means, the image will probably be visible from the outside, but for now this is a drawback I am willing to accept.

Another difficulty will be to reduce the laser diode's output so it won't damage the eye.

Goal of this project

I hope this project enables hardware hackers and tinkerers to play with high resolution monochrome (color of the laser) AR glasses that they can build themselves for less than 100€. Should this project succeed, it will probably not be world breaking technology, considering it uses moving parts, and can't be used to display color images, but on the other hand it could provide an eye catching aesthetic and a new challenge to design user interfaces optimized for analog vector output.

Vector based UI

  • 1 × sun glasses
  • 1 × laser diode + driver 0.5 W red laser
  • 1 × HUD foil
  • 1 × mirror
  • 4 × piezoelectric ceramic actuator

View all 9 components

  • Piezo actuators

    Joel7 days ago 2 comments

    The piezo ceramic actuators finally arrived. They are miniscule. For my first tests, I glued them to an aluminium plate and glued a mirror on top. I hope they work as intended, because I only have a few. The mirror I am using is a regular glass mirror, and has to be replaced with a dedicated laser mirror in the future, but it will be enough for testing purposes. I haven't made any calculations so it's very much possible that this design will not work at all. All I have to do now is to find a high voltage source.

    piezo array
    piezo array with mirror

  • HUD foil

    Joel06/10/2021 at 16:14 0 comments

    Glasses with HUD foil on the right lens
    Glasses with HUD foil on the right lens

    For reflecting the laser from the glasses into the eye I  am using a cheap HUD foil. It is used to project your phone screen onto the windshield and reflect it into you eye.

    HUD foil

    I cut a circular piece from the foil and stuck it onto the glasses. The view is still more or less clear. However, I may need to come up with a solution because the reflection is not at the right angle to fill the entire lens. I have some ideas how to fix this issue though. For now I am still awaiting the laser diodes and most importantly the piezo elements.

    To assess whether the foil is actually useful, I used a strong laser, to see how much light would get reflected. While the effect is not as strong as I had hoped, you can still see, that the reflected laser is much brighter, which means the projector requires less power and less of the image will be visible from the outside.

  • Electronics

    Joel05/31/2021 at 13:11 0 comments

    The brain

    For now I will be using an ESP32-WROOM-32 board as a brain for the glasses. It comes with built-in wireless capabilities, but can also be used in low-power applications. I will be using the Arduino Framework because I am most familiar with it. The plan is to generate vector data on my phone and extract coordinates into an analog signal. I will probably use an audio protocoll like I2S to transfer the data to the ESP.

    HV-Amplifier

    I am planning to design a custom pcb that has a 100V DC-DC booster which I will try to turn into an analog voltage with a high voltage op-amp IC.

    Battery

    Depending on the required voltage I will use one or more small Li-Po batteries. I will also try to include a charging circuit and BMS, depending on the available space. I worry that the HV converter will require big capacitors and inductors, so the space will be tight.

  • The glasses

    Joel05/28/2021 at 18:07 0 comments

    As a basis for my AR glasses I have decided to use these old sunglasses I had laying around. The frame is wide enough to mount components onto and the aesthetic fits the cyberpunk style I am aiming for. I got these from Amazon for cheap a while ago, they used to have a second set of lenses with diffraction filters for nice effects, but I took them of to use for other projects. 

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Discussions

nagup wrote 06/10/2021 at 21:00 point

There is an esp32 module by the name of "micro 32" by TTGO if you want to use something a lot smaller

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Joel wrote 06/11/2021 at 17:20 point

Thanks for the remark. For my first prototype, size isn't too important, and I have a bunch of WROOM modules laying around. I'll come back to it when I need something smaller.

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nagup wrote 06/11/2021 at 17:35 point

understandable, wish you all the best

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Mike Szczys wrote 06/10/2021 at 16:57 point

You should enter this into the Hackaday Prize. The "Reinvent Displays" challenge closes Monday but finals aren't until the end of October, so if you make the first cut you'd have a long time to work on the final design. Good luck!

  Are you sure? yes | no

Joel wrote 06/11/2021 at 17:18 point

that was my intention. Do I have to do anything besides the tag, I added to the project?

  Are you sure? yes | no

Joel wrote 06/11/2021 at 17:36 point

nvm i got it. Thanks for the reminder, I almost missed the deadline!

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