Diffuser IR Leds (how)


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  1. #1
    Fanatical Contributor Tim's Avatar
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    Default Diffuser IR Leds (how)

    Hi....

    My task (still! ) is to measure the water level in a tube to high accuracy. One system I know works is to use a slot opto sensor. But they are expensive and way to big. My resolution needs to be 1-1.5mm.

    So I'm looking at placing the 80 or so ir detectors on a PCB at the desired pitch. This can be done as they are only 0.8mm wide. But now I need the other side. I do not want to mount 80+ ir emitters opposite them. So looking is I can place say 20 on a strip and diffuse them to get an even spread. I can see a diffuser over a visible led works but have no idea on what will happen to IR light. Do I need a special type of plastic. Can I print a semi opaque ink on vinyl?

    Really I have no idea.

    Any thoughts appreciated.
    Tim

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    Prolific Poster normnet's Avatar
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    Default Re: Diffuser IR Leds (how)

    See Dexter a open-source, 3D printed, high precision robotic arm with trainability.

    These don't have encoders and are prone to slipping, so we build our own optical encoders mounted on the axes themselves. We use 2 sensors with one of them 90 degrees out of phase so we get a quadrature encoder out of the system. Our software interpolates these values as sin and cos and allows us to measure each axis.


    Their code disks get about 8,000 points per slit which results in over a million points per revolution on the critical axis. The project uses an FPGA to process 5 million position updates per second however Tims application may be fine with less.

    Norm

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    Member craig's Avatar
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    Default Re: Diffuser IR Leds (how)

    Hi Tim

    Just a thought, Years ago I built a IR beam system into poles for a client to conceal them in an ornamental garden light, What I used was Clear Perspex tubes
    and then I covered it with a dark green Adhesive Vinyl. I had to do a lot of testing to find one that would let the IR penetrate but, after some testing I found one.
    You would probably need to cut out the UV light on the outside but let it penetrate on the inside to get the readings.
    Have a look at Maizey Plastics too see what is available In Perspex tubes and on the Vinyl front and then you can source them in the UK as most of these products are manufactured in Europe www.maizey.co.za. I know you get Black Perspex Tubes which Will let IR Through and others which will block it. The Clear does let it through as I have said. What we also did was to cut down the IR beam on the TX side by letting it look through a very narrow tube but, in your case this will be tiny but, possible. I am not sure but you could look at maybe passing the TX through a Fiber Optic Strand to get it very precise, I think you can get very small diameters in them, I hope this helps.
    Kind regards
    Craig

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  7. #4
    Fanatical Contributor Tim's Avatar
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    Default Re: Diffuser IR Leds (how)

    Hi,

    Just to address a few important points. I need it to be solid state, mechanical movement is not a good idea as it will add cost and reduce reliability and be bulky.

    Cameras will not work due to parallax.

    IR through slots works as I have used that with slot optos through acrylic tubes in the past (8mm dia)

    Fiber optics
    Please remember that there are at least 80 sensors. Drilling 80 holes and inserting 80 fibers is not manufacturing viable for me.

    Daylight susceptibility
    The whole unit is inside a box and can be shielded from external light.

    I do not have a choice of tube material. Acrylic is just about the only viable option. Yes it will reduce the transmission of IR at the freq I will be working in. EG 940nm. That is not an issue as the signal from the sensor will be fairly consistent and will change when the ir passes through water. So can be detected.

    Now my issue is as I said in my post I do not want to mount 80 ir leds. I want only say 12 and the light diffused so its spread over the entire length more or less evenly. Like you get with visible light through an opaque printed membrane like on a keyboard. I us that system already for visible light.

    I am looking to know if it will that work like that with ir through a vinyl sticker and opaque printing?

    Thanks

    Tim
    Tim

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    Prolific Poster See_Mos's Avatar
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    Default Re: Diffuser IR Leds (how)

    I don't know if it will help, Most LCD screens only have a CCFL tube at the top and at the bottom but the light is diffused very evenly.

    Recently I have been converting industrial monitors to LED back lighting. There is one thick piece of plastic and four or five layers of thinner plastic. The thick piece has a pattern on the one side but does not appear to have a Fresnel lens effect or much refraction. The CCFL line up with the edge of the thick piece. The layers have to be in the correct order and correctly aligned.
    Last edited by See_Mos; 4th February 2019 at 12:08.
    My RAM is failing

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    Prolific Poster See_Mos's Avatar
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    Default Re: Diffuser IR Leds (how)

    I had a scrap one in the garage. It was already in pieces and I see one of the thin plastic sheets has a metallic appearance and acts like a very effective Fresnel lens.
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    Prolific Poster rcurl's Avatar
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    Default Re: Diffuser IR Leds (how)

    Hi Tim-
    does the sensor only work in the IR range? I wonder if it may have sensitivity in the visible range. If it does, then you have a lot more options, like CCFL tubes, or the LED arrays used in fax machines.

    -Rick

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    Member ricardourio's Avatar
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    Default Re: Diffuser IR Leds (how)

    Hi Tim,

    I have the same challenge here. Need to measure oil in a 35 cm height glass tube, with same resolution than you. I tried with laser sensor VL53L0X, but it isn't stable enough. I used this one : https://www.aliexpress.com/item/VL53...2-46b2e4e284dd

    Ricardo Urio

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    Member craig's Avatar
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    Default Re: Diffuser IR Leds (how)

    Hi Tim

    you could look at Reflecting the IR once it has passed through the Tube @ 45 Degrees by using a small triangular Mirror and then pass this through a diffuse plate this will give you more room to work if it is available and also Widen the IR signal. Your RX's can sit behind the plate to do the measurements or straight in the path of the Reflected image.
    A lot of the Top Intrusion detectors use Mirror Optics to accurately project the Infra Red Signal in a very specific Pattern. A lot of them have the patterning built onto the Mirror instead of the lens and then reflect that through the lens. Google the PARADOX NV75MW or the HONEYWELL DT900 to see the Idea!
    There are many Holographic and Mirror Tapes with all kinds of patterns available on the market especially used on Art Lures in the Fishing industry which could be used. You could try testing and see what pattern you could project out and how accurate it is.

    Regards
    Craig

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    Prolific Poster pic-ignorant's Avatar
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    Default Re: Diffuser IR Leds (how)

    What is the distance between the IR emitter & receiver Tim? If the receivers are close to each other, would the IR beam not spread across several receivers anyway?

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    Fanatical Contributor Tim's Avatar
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    Default Re: Diffuser IR Leds (how)

    Hi, Lots of good tips.

    Some more info before I look through them some info perhaps missed.

    The RD work is to produce a product I need to sell. So I have to source parts that I can get easily.
    I cannot sell a product that is temperamental and needs kid gloves to use. I ship around the world, so if it breaks not only does it do my reputation no good it costs me a fortune getting it sent back. I know as I have had to do it already. It was a dodgy crimp that came loose. Lost the profit on the job.
    So that rules out lashed together motors etc. I also have to make a profit so inexpensive is important eg if I can build a part for 25 i'm going to do that over a 100 part.

    One more thing in relation to the vinyl question. I find that you can buy frosted vinyl in various opacities, in fact I have used them. So will look at getting some and trying it with an IR remote.

    Ricardo, I have that part but never bothered to even test it as after ordering I found it was not up to the job. (web search) For your application I recommend a float with a magnet in it. Then use hall effect sensors about 5-10mm apart. The code converting the signwaves to a position will not be fun but is doable.
    I cannot use floats due to patent clashes. Ir would work for you as well. I will keep you informed of my progress. You can buy IR sensors for 0.06 each!

    Craig, very interesting but I think the diffuser is my first best option.

    Rick Ir detectors are better priced but not much cheaper. The issue is that unless I use the magnifying effect of the light through the water and view it at the side with a contrast background, the light level does not seem to increase or decrease. At least when I looked through a small dia tube at the light levels.
    With IR the water absorbs it and you do notice a change in signal.

    See_Mos
    One issue I see is that I need IR and have not seen ir emitting strips. So will have to make my own.

    pic-ignorant
    The sensors will be in contact almost with the side of the tube.
    Yes ir spread is an issue from the emitter but hope that as the detectors will be viewing through the slots in the vinyl that should not be an issue as those sensors below the water line will be affected by the water those above will get light from those above the water and that will flood out that from below.




    Thanks
    Tim

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    Fanatical Contributor top204's Avatar
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    Default Re: Diffuser IR Leds (how)

    Tim, are you sure you cannot use a simple B\W VGA camera, that I mentioned a year ago, or so?

    They are very inexpensive, quite easy to interface with and by removing the IR filter, will operate in low light. They could easily detect the movement of water in a good resolution, and a simple program would only scan a few lines of the VGA and see if these have changed. i.e. the lines of VGA that match the water mark area.

    Or... Something I haven't interfaced with, but a detector chip from an optical mouse is, essentially, a low res camera that detects movement. This could be matched up to the position in the container holding the water and detect differences etc...

    Taking a few hundred scans or samples, then filtering, will give a good resolution as to where the water actually is in the container.

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    Prolific Poster See_Mos's Avatar
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    Default Re: Diffuser IR Leds (how)

    Tim, what is the wall thickness, internal and external diameter and length of measurement area for the tube.

    Is the water clean, distilled or other?

    I have an idea that might work but might need a full size piece of tube to do some tests.
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    Fanatical Contributor Tim's Avatar
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    Default Re: Diffuser IR Leds (how)

    Hi Les

    The issue is that you cannot see the whole column properly up close. If you can stand back enough and have perfect lighting and resolution it might work.

    But get up close and you need a wide angle lens. Then add in that the camera will need to to see the top move not in 1 mm like need but in 0.1mm increments due to perspective.

    Have a parallel 1-1 system like I propose with the ir sensors needs no high speed cpu, no custom lenses, no cameras that need to keep in focus from 25mm to 75mm at the same time while only 30mm away.
    One pic with a few CD74HC4067M 16:1 Analog Multiplexer/Demultiplexer IC's and your done.
    It's just the IR backlighting I need to sort.
    Tim

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    Fanatical Contributor top204's Avatar
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    Default Re: Diffuser IR Leds (how)

    If I am following correctly...

    A diffused backlight can be done with edge lit acrylic, who's face has been scuffed to a high resolution finish. All the light will scatter on the scuffing and come out the front of the acrylic plate. The edges of the acrylic can have tape around so the light is reflected back, if silver tape used, or dampened if black tape is used.
    Last edited by top204; 6th February 2019 at 12:26.

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