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OT CDS cell filter — Parallax Forums

OT CDS cell filter

ArchiverArchiver Posts: 46,084
edited 2002-01-31 03:22 in General Discussion
While this specific question is off-topic, the project does include a
stamp...

Can anybody recommend a way to filter a photodiode or CDS cell to respond
only to a specific wavelength of light? I am specifically interested in
the infared (650nm?) wavelengths. Kinda like a band-pass filter, but
with light.

Regards,
Aaron Garber

Comments

  • ArchiverArchiver Posts: 46,084
    edited 2002-01-30 03:52
    Aaron asked:

    >While this specific question is off-topic, the project does include a
    >stamp...
    >
    >Can anybody recommend a way to filter a photodiode or CDS cell to respond
    >only to a specific wavelength of light? I am specifically interested in
    >the infared (650nm?) wavelengths. Kinda like a band-pass filter, but
    >with light.

    In general, you do this the same way as any other filtering job:
    combine a low-pass filter that blocks wavelengths shorter than, say,
    640 nm with a high-pass filter that blocks wavelengths longer than,
    say, 660 nm. Make sure to evaluate what the shape of the receptor's
    spectral response is in the region of interest, too, since if it is
    steeply changing in that region it will influence the overall shape
    of the passband. "Photodiodes" vary enormously in this respect. If we
    know more about what you're trying to do we might be able to
    recommend something more specific...

    Reg Neale
  • ArchiverArchiver Posts: 46,084
    edited 2002-01-30 09:44
    Aaron,

    This is solved by using photography lens filters. You can also get gel film
    which is much cheaper and used for darklights and stuff. There is also high
    temperature plate glass filters used for floodlights.

    Support your local photography shop if it still exists, by asking there.
    Failing there, a search on google will probably do the trick.

    Regards,

    Tony Wells
    Original Message
    From: "Reginald Neale" <rneale@m...>
    To: <basicstamps@yahoogroups.com>
    Sent: Wednesday, January 30, 2002 3:52 AM
    Subject: Re: [noparse][[/noparse]basicstamps] OT CDS cell filter


    > Aaron asked:
    >
    > >While this specific question is off-topic, the project does include a
    > >stamp...
    > >
    > >Can anybody recommend a way to filter a photodiode or CDS cell to respond
    > >only to a specific wavelength of light? I am specifically interested in
    > >the infared (650nm?) wavelengths. Kinda like a band-pass filter, but
    > >with light.
    >
    > In general, you do this the same way as any other filtering job:
    > combine a low-pass filter that blocks wavelengths shorter than, say,
    > 640 nm with a high-pass filter that blocks wavelengths longer than,
    > say, 660 nm. Make sure to evaluate what the shape of the receptor's
    > spectral response is in the region of interest, too, since if it is
    > steeply changing in that region it will influence the overall shape
    > of the passband. "Photodiodes" vary enormously in this respect. If we
    > know more about what you're trying to do we might be able to
    > recommend something more specific...
    >
    > Reg Neale
    >
    >
    > To UNSUBSCRIBE, just send mail to:
    > basicstamps-unsubscribe@yahoogroups.com
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    Body of the message will be ignored.
    >
    >
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    >
    >
    >
  • ArchiverArchiver Posts: 46,084
    edited 2002-01-30 13:10
    There were two responses to this post. The one recommending optical filters is
    your best bet.
    Clark

    agarb@j... wrote:

    > While this specific question is off-topic, the project does include a
    > stamp...
    >
    > Can anybody recommend a way to filter a photodiode or CDS cell to respond
    > only to a specific wavelength of light? I am specifically interested in
    > the infared (650nm?) wavelengths. Kinda like a band-pass filter, but
    > with light.
    >
    > Regards,
    > Aaron Garber
    >
    > To UNSUBSCRIBE, just send mail to:
    > basicstamps-unsubscribe@yahoogroups.com
    > from the same email address that you subscribed. Text in the Subject and Body
    of the message will be ignored.
    >
    >
    > Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
  • ArchiverArchiver Posts: 46,084
    edited 2002-01-30 13:34
    There are several ways. Easiest is to get some gel color filters from
    Edmund or a photo supply house. I wouldnt do it with the CDS cell though.
    Its sensistivity is a lot like the eye and has little rleative response in
    the deep red. stick to a photo diode.
  • ArchiverArchiver Posts: 46,084
    edited 2002-01-30 16:16
    Are you looking for intensity of IR or just looking for IR you
    can by phototransistors and other types of sensors made for the
    wave length you are looking for.
    Original Message
    From: "Phillip W Mann" <pwmann@w...>
    To: <basicstamps@yahoogroups.com>
    Sent: January 30, 2002 5:34 AM
    Subject: Re: [noparse][[/noparse]basicstamps] OT CDS cell filter



    There are several ways. Easiest is to get some gel color filters
    from
    Edmund or a photo supply house. I wouldnt do it with the CDS cell
    though.
    Its sensistivity is a lot like the eye and has little rleative
    response in
    the deep red. stick to a photo diode.


    To UNSUBSCRIBE, just send mail to:
    basicstamps-unsubscribe@yahoogroups.com
    from the same email address that you subscribed. Text in the
    Subject and Body of the message will be ignored.


    Your use of Yahoo! Groups is subject to
    http://docs.yahoo.com/info/terms/
  • ArchiverArchiver Posts: 46,084
    edited 2002-01-31 03:22
    Intensity.

    On Wed, 30 Jan 2002 08:16:02 -0800 "Larry Gaminde" <lgaminde@t...>
    writes:
    > Are you looking for intensity of IR or just looking for IR you
    > can by phototransistors and other types of sensors made for the
    > wave length you are looking for.
    >
    Original Message
    > From: "Phillip W Mann" <pwmann@w...>
    > To: <basicstamps@yahoogroups.com>
    > Sent: January 30, 2002 5:34 AM
    > Subject: Re: [noparse][[/noparse]basicstamps] OT CDS cell filter
    >
    >
    >
    > There are several ways. Easiest is to get some gel color filters
    > from
    > Edmund or a photo supply house. I wouldnt do it with the CDS cell
    > though.
    > Its sensistivity is a lot like the eye and has little rleative
    > response in
    > the deep red. stick to a photo diode.
    >
    >
    > To UNSUBSCRIBE, just send mail to:
    > basicstamps-unsubscribe@yahoogroups.com
    > from the same email address that you subscribed. Text in the
    > Subject and Body of the message will be ignored.
    >
    >
    > Your use of Yahoo! Groups is subject to
    > http://docs.yahoo.com/info/terms/
    >
    >
    >
    >
    > To UNSUBSCRIBE, just send mail to:
    > basicstamps-unsubscribe@yahoogroups.com
    > from the same email address that you subscribed. Text in the
    > Subject and Body of the message will be ignored.
    >
    >
    > Your use of Yahoo! Groups is subject to
    > http://docs.yahoo.com/info/terms/
    >
    >
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