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Film for IR light sensor — Parallax Forums

Film for IR light sensor

T ChapT Chap Posts: 4,223
edited 2015-01-05 10:48 in General Discussion
I got in these sensors from Sparkfun

https://www.sparkfun.com/products/12787

I want to drill a small hole in a face plate and put this behind it out of site, and want to cover the rear of the hole with some black film that will hide the sensor but still allow the IR to pass with the least reduction. Is there something off the shelf that will work, like at a photography store? I am sure there are products for this purpose but not sure what the name of it is.

Comments

  • Duane DegnDuane Degn Posts: 10,588
    edited 2015-01-04 23:58
    A 87C filter is used with infrared photography to block visible light.

    Here's a link to a polyester film filter. 87C filters are also available in glass and gelatin (I have some of this stuff from my infrared photography days).

    I think there's also some plastics which are opaque to visible light but transparent to near IR.
  • RDL2004RDL2004 Posts: 2,554
    edited 2015-01-05 04:29
    At one time, many years ago, I was heavily into photography and had a Kodak IR filter. It might have been an 87C. I remember it being a kind of dull dark brown color. Since the sensor already has UV and Infrared blocking filters, I'm guessing you're probably just looking for something to darken the recess behind the face plate for aesthetic purposes.

    I'd try Googling for "infrared transparency", "infrared transparent plastic" or something along those lines. Assuming the space behind the hole opening is dark, I'd bet there are a lot of cheap things that would work.

    Forrest Mims often recommended exposed color film in his books and articles, but that may not be easy to find these days.

    In case you actually do want to block everything else, here's the first hit for infrared transparent plastic:

    http://www.eplastics.com/Plexiglass_Acrylic_Sheet_Infrared_Transmitting
  • twm47099twm47099 Posts: 867
    edited 2015-01-05 07:10
    Back in the film era, when I wanted to block visible light from a flash while passing IR, I would use the exposed (and developed) leader from a roll of color negative film. Since I had a large number of packs of prints and negatives, I could always (and can still) find some. If you have some old packs of developed color film, you can probably find enough for your application. If using E6 color slide film, you would need to use developed UNexposed film which might be harder to find.

    Tom
  • ercoerco Posts: 20,256
    edited 2015-01-05 07:51
    It might not be that simple if this sensor is projecting an IR beam outward and looking for a reflection, as the Sharp sensors do. If that's the case, then any film you put there will reflect some IR and likely give an erroneous reading.

    If not, then Tom's photo film suggestion has merit. It's common practice to put passive IR receivers behind materials that are visibly opaque but transparent to IR.
  • PublisonPublison Posts: 12,366
    edited 2015-01-05 08:38
    The Sensor has an IR LED on board to provide the IR illumination, therefore it must go out and come back in.

    May be too much attenuation as erco suggests.

    I know the Parallax Gesture Sensor works though glass, but have not tried any colored glass.
  • PublisonPublison Posts: 12,366
    edited 2015-01-05 08:40
    The Data Sheet states:
    The RGB and ambient light sensing feature detects light intensity under various lighting conditions and through various attentuation materials including darkened glass.

    http://www.avagotech.com/pages/en/optical_sensors/integrated_ambient_light_and_proximity_sensors/apds-9960/

    It doesn't mention the IR component.
  • T ChapT Chap Posts: 4,223
    edited 2015-01-05 10:37
    Thanks for the info guys. Yes the reflections from any film would be a question to consider. I also thought about putting the film direct to the surface of the emitter and detector sections of the device so that there are no reflection at all. I am not reading ambient light, only IR so it does not matter about muting ambient light. The sensor does allow you to set high and low thresholds for proximity, so I think it is built in to filter out reflections below a certain distance and above a certain distance, so the reflections from material may be able to be handled in the settings. I have spent a lot of time on studying the registers, the device is pretty nice. I don't have an "object", but have a lot of messy Spin code someone could at least see the device work with if interested. My main goal is to hide the PCB and components from view, so even if I used a laser on some film to allow the light to pass through the two main areas, that will work.
  • ercoerco Posts: 20,256
    edited 2015-01-05 10:38
    Jim wastes no time making a monkey out of me! :)

    This sensor is starting to sound interesting. I might have to get one to stack on top of my very tall "to play with" pile of cool stuff.
  • PublisonPublison Posts: 12,366
    edited 2015-01-05 10:48
    erco wrote: »
    Jim wastes no time making a monkey out of me! :)

    Of course you know that was not my intention. :)

    When I got my Parallax Gesture Sensor, I did a lot of investigations an these devices. I guess that's why I don't post much code, because I'm always researching. :)
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