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optical punch card reader

Discussion in 'General Electronics Discussion' started by mattsains, Jun 8, 2012.

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  1. mattsains

    mattsains

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    Jun 8, 2012
    Hello

    I'm thinking of making a punch card reader as an arduino project. I'll have an LED for each punched row, and some sort of light sensor on the other side.

    Would an LDR be reactive enough to pick up a chads (holes) if I'm going to be swiping this card through the reader?

    Is there something better I should be using? I've only worked with LDRs before; I'm not sure what is what when it comes to photo semiconductors, so some buying advice would be nice if LDRs aren't sufficient

    Thanks

    PS: A Youtube video of what I'm wanting to achieve, except using metal brushes instead of optics:
     
    Last edited: Jun 8, 2012
  2. GreenGiant

    GreenGiant

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    Feb 9, 2012
    I personally would use phototransistors, this will give you a clean either on or off if it senses anything, rather than a small shift in the readings.

    There are some questions though...

    What are the cards made out of?
    What will the placement and number of possible holes be?
    What is the output going to be?
    Does it need to swipe or can you insert, wait and then remove?

    Green
     
  3. Harald Kapp

    Harald Kapp Moderator Moderator

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    Nov 17, 2011
    As far as I remember the holes in a punchcard are spaced rather close compared to the size of a typical LDR (there may be very small ones out there, but the ones I know are rather big). So you would have to stagger the LDRs and use the µC to correct the displacement of the signals caused by the staggered LDRs.

    Anothe rsolution would use photodiodes. These come in very small packages (even SMD) and it should be possible to space them as close as required for the punch card raster.

    See here: http://sales.hamamatsu.com/assets/applications/SSD/si_pd_circuit_examples.pdf for photodiode applications.

    Harald
     
  4. mattsains

    mattsains

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    Jun 8, 2012
    Thanks for the replies!
    I'm thinking of rolling my own punch cards as in the video, so space isn't an issue (read: I can't solder SMD :p )

    Cards will be made out of something opaque enough, probably card of considerable thickness. This is more a data reading experiment than a perfect replica of legacy. I'm thinking of, say, five rows which I'll service with five LEDs and sensors. (might need to be hooded to stop light leaking into other sensors)

    I do want to swipe... I'll probably have a clock row (again, as in the video) so I know when the bits are passing through.

    Could you explain a bit about how phototransistors work? What exactly do they do in the presence of light?

    Harold, thanks for the link to the photodiodes, I'll study it a bit.
     
  5. mattsains

    mattsains

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    Jun 8, 2012
    I suppose, in essence, I'm asking whether an LDR will pick up the rapid pulsing of light from swiping this punch card (from the perspective of a sensor) or is it going to be too sluggish to respond to this change
     
  6. GreenGiant

    GreenGiant

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    Feb 9, 2012
    Phototransistors act like switches, when light is present it will either open or close (depending on the type) like a switch, see here

    you should be able to line up the LED's (probably better off using an IR LED and transistor) so that when you slide the card the Arduino can read multiple lines though that would be pretty complicated, unless you go from parallel to a serial stream of numbers (1's and 0's) which the Arduino could read
     
  7. mattsains

    mattsains

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    Jun 8, 2012
    cools! Thanks for the link to the photo trannies.
    I think you're probably right about doing serial. I'll go with that. Thanks for the advice!
     
  8. GreenGiant

    GreenGiant

    842
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    Feb 9, 2012
    Like I was saying, LDR's is just going to give you a small change in readings, where a photdiode, or a phototransistor will give you a more clean on and off

    so basically a sine waveform vs a square
     
  9. mattsains

    mattsains

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    Jun 8, 2012
  10. GreenGiant

    GreenGiant

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    Feb 9, 2012
    Yes, those are correct, they take the light in and use it, therefor they must be mostly clear, some of the different colored ones usually have different filters (ex. IR) so be careful with that
     
  11. gorgon

    gorgon

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    Jun 6, 2011
    It will be both too sluggish and too big to implement easy. For a swipe reader the electronics and optics must be significant faster than the fastest person using it. If you just want to experiment, it's ok to be inside the user envelope, but only a while.

    You should use an optotransistor, one for each bit/position.

    You should also be aware of ambient electric light, where you'll get 50/60Hz optical noise/overload.

    You may reduce this with a filter and IR-LEDs as light sources.

    TOK ;)
     
  12. mattsains

    mattsains

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    Jun 8, 2012
    they seem to leave off the base. do you recommend getting one with a base?
     
  13. BobK

    BobK

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    Jan 5, 2010
    The base is connected to the light coming in!

    Bob
     
  14. mattsains

    mattsains

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    Jun 8, 2012
    Figured! ;) but I have read that some have a base leg so that you can bias the light coming in (in my murky knowledge of electronics that means you can make the transistor more or less sensitive)
     
  15. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    For this purpose you won't need one with a base connection.

    There are other ways to control sensitivity in any case.
     
  16. mattsains

    mattsains

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    Jun 8, 2012
    ok, thanks. (goes on shopping spree)
     
  17. eptheta

    eptheta

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    Dec 20, 2009
    hahaha ! "photo trannies"
    This should be a fun project for you. T̶h̶e̶ ̶o̶n̶l̶y̶ ̶t̶r̶o̶u̶b̶l̶e̶ ̶I̶ ̶t̶h̶i̶n̶k̶ ̶y̶o̶u̶'̶l̶l̶ ̶h̶a̶v̶e̶ ̶i̶s̶ ̶d̶e̶f̶i̶n̶i̶n̶g̶ ̶t̶h̶e̶ ̶d̶e̶l̶a̶y̶ ̶f̶o̶r̶ ̶t̶h̶e̶ ̶'̶0̶'̶ ̶s̶t̶a̶t̶e̶ ̶w̶h̶i̶l̶e̶ ̶s̶w̶i̶p̶i̶n̶g̶.̶ ̶Y̶o̶u̶ ̶s̶h̶o̶u̶l̶d̶ ̶t̶r̶y̶ ̶a̶n̶d̶ ̶m̶a̶k̶e̶ ̶y̶o̶u̶r̶ ̶p̶r̶o̶j̶e̶c̶t̶ ̶s̶w̶i̶p̶e̶-̶s̶p̶e̶e̶d̶ ̶i̶n̶d̶e̶p̶e̶n̶d̶e̶n̶t̶.̶ ̶
    I̶ ̶n̶o̶t̶i̶c̶e̶d̶ ̶i̶n̶ ̶t̶h̶e̶ ̶v̶i̶d̶e̶o̶ ̶t̶h̶a̶t̶ ̶t̶h̶e̶r̶e̶ ̶a̶r̶e̶ ̶t̶w̶o̶ ̶l̶i̶n̶e̶s̶ ̶o̶f̶ ̶h̶o̶l̶e̶s̶ ̶i̶n̶ ̶t̶h̶e̶ ̶p̶u̶n̶c̶h̶ ̶c̶a̶r̶d̶.̶ ̶T̶h̶a̶t̶ ̶w̶o̶u̶l̶d̶ ̶e̶l̶i̶m̶i̶n̶a̶t̶e̶ ̶d̶e̶p̶e̶n̶d̶e̶n̶c̶e̶ ̶o̶n̶ ̶s̶w̶i̶p̶e̶-̶s̶p̶e̶e̶d̶.̶ ̶I̶s̶ ̶y̶o̶u̶r̶ ̶c̶a̶r̶d̶ ̶d̶e̶s̶i̶g̶n̶ ̶g̶o̶i̶n̶g̶ ̶
    t̶o̶ ̶b̶e̶ ̶s̶i̶m̶i̶l̶a̶r̶,̶ ̶o̶r̶ ̶a̶r̶e̶ ̶y̶o̶u̶ ̶g̶o̶i̶n̶g̶ ̶t̶o̶ ̶t̶r̶y̶ ̶a̶n̶d̶ ̶g̶e̶t̶ ̶i̶t̶ ̶d̶o̶n̶e̶ ̶w̶i̶t̶h̶ ̶j̶u̶s̶t̶ ̶o̶n̶e̶ ̶r̶o̶w̶ ̶o̶f̶ ̶h̶o̶l̶e̶s̶ ̶?̶

    EDIT: Sorry, I just read your post about the clock row.
    I guess this is now just a 'good luck' post.
     
    Last edited: Jun 9, 2012
  18. mattsains

    mattsains

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    0
    Jun 8, 2012
    will definitely have a "clock row" which will be all punched. Then I will read the state of the other rows when I get a signal from the clock row
     
  19. mattsains

    mattsains

    35
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    Jun 8, 2012
    there's nothing wrong with being nice :) thanks for the encouragement
     
  20. mattsains

    mattsains

    35
    0
    Jun 8, 2012
    It might be a bad idea, but I want to get this to work in the visible spectrum. I hate buying invisible lights, and I'd also like to use these components for other things later
     
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