Need help creating interactive light sensitive grid

Hello,

I want to create a sensor grid that the user can interact with. In talking with people who are knowledgeable on these type of matters two suggestions have stood out: narrow beam infrared LEDs and lasers.

Apparently LEDs are much cheaper and have a smaller footprint (more easily concealed) but they have a wide beam.

The surface are is 50" x 30" and am thinking of having the sensor spaced 6" apart. Is there way to narrow the beam so that it doesn’t strike the neighboring sensors?

For example, would recessing the receiver be effective in shielding it from spillage from the neighboring emitters? Or would it be better to just go with a laser?

In researching LEDs the sites don’t say what the emitting angle is so much as what the receiver is capable of so I’m a bit in the dark on what to buy.

Thanks for any help you can offer.

It will help to understand:

  • In what way will the user interact with the grid?
  • What does the interaction with the user do?
  • Will the user interact at only one place in the grid or multiple places at a time?
  • How is the grid positioned relative to the user?
  • On what and how will the sensors be mounted?
  • Is there a cost goal?
  • Is there a reliability goal [# of activations]?
  • What kind of environement will the sensors be in?

Ideas that come to mind:

  • PCB membrane or mechanical switches (simple & cheap)
  • Touch (captive) switches (more electronics)
  • IR beam interruption schemes (simple, may have ambient light noise problems)
  • X and Y laser diodes with receivers were fingers breaks the beam [lots of challenges with this approach]

Depending on the type and mounting sensors that are spaced 6" apart should not have a crosstalk problem…

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Hi Don,

  • In what way will the user interact with the grid?
  • What does the interaction with the user do?

The goal of the project is to make an interactive table that has a back-lit pattern across the top. We plan on using a laser cutter to create a stencil in the tabletop and then have a layer of addressable LEDs underneath it so that we can control the display based on the inputs from the grid.

The idea is that as people place dishes, glasses etc. on the surface of the table they will intersect with the grid. Since we will have mapped the grid locations to the LEDs we can create interesting effects and patterns.

It is essentially an interactive art piece for a Burningman theme camp that I am part of.

  • Will the user interact at only one place in the grid or multiple places at a time?
    I’d like to be able to program it to receive multiple inputs to increase the interactive nature of the piece. Since we are programming the LEDs we have a large degree of control over how to handle the inputs.

  • How is the grid positioned relative to the user?
    lower by 45 degrees roughly

  • On what and how will the sensors be mounted?
    The would be hidden within the design of the table in some manner. The small footprint of LEDs makes them an attractive option.

  • Is there a cost goal?
    All in, about $1,500 but that includes time on the lasercutter, table materials, possible charges for programming expertise etc. We can raise more if need be but the last art project raised almost this much without too much effort.

  • Is there a reliability goal [# of activations]?
    Not sure. Haven’t considered this yet. We can set a limit if need be.

  • What kind of environement will the sensors be in?
    Outdoors, unheated tent at music / art festival. Needs to operate in cool to hot temperature ranges (10C to 40C).

Capacative Switch might be a good way to go but it could be limited if it only reacts to human touch.

I am what you would call the producer of the piece. We have some volunteers who are good with electronics, programming and graphic design. That said, this is beyond what we have for existing knowledge. Hence the reason I’m reaching out to the greater maker community for guidance.

It is definitely a stretch-goal project.

You could try a technology called frustrated total internal reflection. This was used by Microsoft to make a Surface table, renamed to Pixelsense when they used ‘Surface’ for their line of capacitative-touch tablets, which are an unrelated technology.

It’s based on the idea that you can ‘fill’ a glass slab with light and it will escape at a point where an external object touches it, providing an interface where TIR can’t operate. The light leaks and is picked up by a camera. Typically, IR light is used and a visible-light projector puts an image on the table but the IR-sensitive cameras see only the light leaking at touch points.

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Hi Artag,

Very cool. I can see that being used for other types of projects. For this one tho we need a pretty durable surface which from the looks of things the silicon rubber layer may not be able to take the wear and tear.

Great interactive tool tho.

Essentially you have to sense multiple human and inanimate objects sitting anywhere on a 50"x30" surface.
This clever technique looks promising:
http://jtgonz.com/led-sensing-matrix.html

This technique uses a phototransistor to sense if each LED is visible during a scan. Put a photosensor above an array of LED"s.
https://blog.arduino.cc/2019/05/01/use-an-led-matrix-as-a-scanner/

Hi Don,

after looking at all the suggestions and talking to friends who have technical backgrounds I’m leaning towards paying for some engineering help. There is a company in Victoria BC that does this type of work and it turns out that I know someone who works there and is part of the burner community to boot.

I’ll have lots on my plate with fundraising and assembly etc. so no shortage of things to keep me busy.

I do like the capacitative touch option tho. It would be cool to work that in somehow.

Here is a very crude mock-up of what what the piece would look like.

This is a generic top without colour or pattern. Open to lots of ideas.
whiteTop

This one has a wood pattern but it’s too intense so still thinking on it.
woodTextureTabletop

This one is an attempt to replicate a frosted acrylic top to soften the large sections of LED
frostedTopTable

Generally speaking, I think the large silhouettes create too much open space. I like the more intricate gears better but this will be up to the graphic designer to work with.