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  1. #1
    Mustafa Umut Sarac's Avatar
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    One rotating photodiode and slit, what does it see per rotation? Curiosity.

    There are hundreds of photodiodes available at the market. If we get one and connect to electronics , put a slit in front of it and if we rotate it , what does it see ? Does it see one pixel high image or more ?

    Umut

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    polyglot's Avatar
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    Depends on what you put in front of it and what axis you're rotating around, and how you're sampling the signal from the photodiode.

    If you have a slit and no other optics, the diode will see a whole slice of the scene summed. If you then scan the slit across, the slice will of course change. Say you take a vertical slit and scan it horizontally, the image recorded by the diode would be the same as if you'd made a pinhole image and averaged everything vertically, i.e. you have an Nx1 pixel image. There is only 1 diode, so there can be only 1 pixel, multiplied by how many samples (in time) you took horizontally.

    There are IR imaging sensors that work a little like this, though they have lenses for good focus, a single (cooled) extremely sensitive photosensor (looking at one very small point in the scene at a time) and then scan that in a circular pattern that slowly slides to one side. It's very slow and requires a static subject, but it removes all inter-pixel calibration issues; assuming you have a well-calibrated sensor then the result is of extremely high precision.

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    The web is full of references relating to photodiode rotational sensors. See for example: http://www.ti.com/lit/an/slaa289/slaa289.pdf

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    By definition with only a slit and photo diode each each revolution will provide one pixel. The rotation and slit are in control.

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    I certainly wouldn't call the electronic pulse a 'pixel'.

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    Hexavalent's Avatar
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    This has what to do with analog photography?
    - Ian

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    Quote Originally Posted by Hexavalent View Post
    This has what to do with analog photography?
    Actually, the pulse created by such a system is definitely analog.

  8. #8
    Mustafa Umut Sarac's Avatar
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    Is there a thin long photodiode which made from two solid semiconductor -pn- and would be able to scan a horizontal rotation with recording more than one tiny photodiode and is there a way to get reliable message from this complex signal with timing - more distance the semiconductor to cable , it would take more time to reach signal to the cable- ?

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    Hexavalent's Avatar
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    Well I suppose it is analog... just like the signal coming from a CCD.

    Still don't see how it belongs on APUG.
    - Ian

  10. #10

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    Quote Originally Posted by Mustafa Umut Sarac View Post
    Is there a thin long photodiode .....?
    Yes, there are linear sensors; but a discussion of such technology doesn't belong on APUG.

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