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Re: [midatlanticretro] Building a Better Tape Reader

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  • Mike Hatch
    ... Interesting idea. I have seen leds used successfully on on solar trackers and having used leds for sensing in component counters before you might find you
    Message 1 of 11 , May 15, 2013
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      On 14/05/2013 21:19, DuaneCraps wrote:
      > When I was playing with my Arduino micro controller I read articles
      > about using led’s as light detectors.
      > It got me thinking .....
      > led bar graphs displays have .1 inch spacing to fit in DIP sockets .
      > My idea is to use 2 bar graphs one as a light source and one one as the
      > sensor.

      Interesting idea.
      I have seen leds used successfully on on solar trackers and having used
      leds for sensing in component counters before you might find you need a
      mask over the sensor array, with a line of holes at 0.1" spacing to stop
      bleed (laterally) from one track to its neighbour. Also to stop bleed
      from one row (longitudinally) to the next as individual segments in led
      bar-graph displays are usually quite longer than they are wide.

      > I did bread board one segment feeding an OP Amp with a 10K feedback
      > resistor and got a
      > 0 to 3.7 volt change with my LED flashlight through a sprocket hole
      > sized hole.

      The emitter array may need some tweaking on the current as well to get
      usable signals.

      Food for thought though, might just try it, I have some old PDP-7 tapes
      I want to read.

      > If anyone wants to run with this, go ahead, you can have the glory
      > Duane

      Regards.
      Mike.
    • DuaneCraps
      Mike, Thanks for the input The only gotcha that I remember is that the LED’s have a memory effect due to the capacitance across the P-N junction causing it
      Message 2 of 11 , May 15, 2013
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        Mike,
         
        Thanks for the input
        The only gotcha that I remember is that the LED’s have a memory effect due to the capacitance across the P-N junction causing it to tend to hold a charge. Some people have used gates to clamp the LED to ground between readings.  
         
        Sent: Wednesday, May 15, 2013 4:29 AM
        Subject: Re: [midatlanticretro] Building a Better Tape Reader
         
         

        On 14/05/2013 21:19, DuaneCraps wrote:
        > When I was playing with my Arduino micro controller I read articles
        > about using led’s as light detectors.
        > It got me thinking .....
        > led bar graphs displays have .1 inch spacing to fit in DIP sockets .
        > My idea is to use 2 bar graphs one as a light source and one one as the
        > sensor.

        Interesting idea.
        I have seen leds used successfully on on solar trackers and having used
        leds for sensing in component counters before you might find you need a
        mask over the sensor array, with a line of holes at 0.1" spacing to stop
        bleed (laterally) from one track to its neighbour. Also to stop bleed
        from one row (longitudinally) to the next as individual segments in led
        bar-graph displays are usually quite longer than they are wide.

        > I did bread board one segment feeding an OP Amp with a 10K feedback
        > resistor and got a
        > 0 to 3.7 volt change with my LED flashlight through a sprocket hole
        > sized hole.

        The emitter array may need some tweaking on the current as well to get
        usable signals.

        Food for thought though, might just try it, I have some old PDP-7 tapes
        I want to read.

        > If anyone wants to run with this, go ahead, you can have the glory
        > Duane

        Regards.
        Mike.

      • Mike Hatch
        Hi, This article I think you may have seen - http://www.thebox.myzen.co.uk/Workshop/LED_Sensing.html Another - http://www.robotroom.com/ReversedLED.html This
        Message 3 of 11 , May 15, 2013
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          Hi,

          This article I think you may have seen -
          http://www.thebox.myzen.co.uk/Workshop/LED_Sensing.html

          Another -
          http://www.robotroom.com/ReversedLED.html

          This article actually gives a few values, looks like a HE Green array
          might work the best -
          http://www.instructables.com/id/LEDs-as-light-sensors/

          Regards,
          Mike.
          www.soemtron.org

          On 15/05/2013 13:04, DuaneCraps wrote:
          > Mike,
          > Thanks for the input
          > The only gotcha that I remember is that the LED’s have a memory effect
          > due to the capacitance across the P-N junction causing it to tend to
          > hold a charge. Some people have used gates to clamp the LED to ground
          > between readings.
          > *From:* Mike Hatch <mailto:mike@...>
          > *Sent:* Wednesday, May 15, 2013 4:29 AM
          > *To:* midatlanticretro@yahoogroups.com
          > <mailto:midatlanticretro@yahoogroups.com>
          > *Subject:* Re: [midatlanticretro] Building a Better Tape Reader
          >
          > On 14/05/2013 21:19, DuaneCraps wrote:
          > > When I was playing with my Arduino micro controller I read articles
          > > about using led’s as light detectors.
          > > It got me thinking .....
          > > led bar graphs displays have .1 inch spacing to fit in DIP sockets .
          > > My idea is to use 2 bar graphs one as a light source and one one as the
          > > sensor.
          >
          > Interesting idea.
          > I have seen leds used successfully on on solar trackers and having used
          > leds for sensing in component counters before you might find you need a
          > mask over the sensor array, with a line of holes at 0.1" spacing to stop
          > bleed (laterally) from one track to its neighbour. Also to stop bleed
          > from one row (longitudinally) to the next as individual segments in led
          > bar-graph displays are usually quite longer than they are wide.
          >
          > > I did bread board one segment feeding an OP Amp with a 10K feedback
          > > resistor and got a
          > > 0 to 3.7 volt change with my LED flashlight through a sprocket hole
          > > sized hole.
          >
          > The emitter array may need some tweaking on the current as well to get
          > usable signals.
          >
          > Food for thought though, might just try it, I have some old PDP-7 tapes
          > I want to read.
          >
          > > If anyone wants to run with this, go ahead, you can have the glory
          > > Duane
          >
          > Regards.
          > Mike.
          >
          >
        • Dave McGuire
          ... Forrest Mims popularized the use of LEDs in photodiode mode in the early 1970s, and has done quite a bit with them. But...with real photodiodes and
          Message 4 of 11 , May 15, 2013
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            On 05/15/2013 04:29 AM, Mike Hatch wrote:
            >> When I was playing with my Arduino micro controller I read articles
            >> about using led’s as light detectors.
            >> It got me thinking .....
            >> led bar graphs displays have .1 inch spacing to fit in DIP sockets .
            >> My idea is to use 2 bar graphs one as a light source and one one as the
            >> sensor.
            >
            > Interesting idea.
            > I have seen leds used successfully on on solar trackers and having used
            > leds for sensing in component counters before you might find you need a
            > mask over the sensor array, with a line of holes at 0.1" spacing to stop
            > bleed (laterally) from one track to its neighbour. Also to stop bleed
            > from one row (longitudinally) to the next as individual segments in led
            > bar-graph displays are usually quite longer than they are wide.
            >
            >> I did bread board one segment feeding an OP Amp with a 10K feedback
            >> resistor and got a
            >> 0 to 3.7 volt change with my LED flashlight through a sprocket hole
            >> sized hole.
            >
            > The emitter array may need some tweaking on the current as well to get
            > usable signals.
            >
            > Food for thought though, might just try it, I have some old PDP-7 tapes
            > I want to read.

            Forrest Mims popularized the use of LEDs in photodiode mode in the early
            1970s, and has done quite a bit with them.

            But...with real photodiodes and phototransistors available for pennies, I'm
            note sure of what the point would be, other than for hack value.

            -Dave

            --
            Dave McGuire, AK4HZ
            New Kensington, PA
          • Dave McGuire
            ... The capacitance is a direct function of the junction area; smaller LEDs will work better here. -Dave -- Dave McGuire, AK4HZ New Kensington, PA
            Message 5 of 11 , May 15, 2013
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              On 05/15/2013 08:04 AM, DuaneCraps wrote:
              > The only gotcha that I remember is that the LED’s have a memory effect due to
              > the capacitance across the P-N junction causing it to tend to hold a charge.
              > Some people have used gates to clamp the LED to ground between readings.

              The capacitance is a direct function of the junction area; smaller LEDs
              will work better here.

              -Dave

              --
              Dave McGuire, AK4HZ
              New Kensington, PA
            • Mike Loewen
              ... How about using optical fiber to position the output from the emitters, and on the other side to the phototransistors? You should be able able to get the
              Message 6 of 11 , May 15, 2013
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                On Wed, 15 May 2013, Dave McGuire wrote:

                > On 05/15/2013 04:29 AM, Mike Hatch wrote:
                >>> When I was playing with my Arduino micro controller I read articles
                >>> about using led?s as light detectors.
                >>> It got me thinking .....
                >>> led bar graphs displays have .1 inch spacing to fit in DIP sockets .
                >>> My idea is to use 2 bar graphs one as a light source and one one as the
                >>> sensor.
                >>
                >> Interesting idea.
                >> I have seen leds used successfully on on solar trackers and having used
                >> leds for sensing in component counters before you might find you need a
                >> mask over the sensor array, with a line of holes at 0.1" spacing to stop
                >> bleed (laterally) from one track to its neighbour. Also to stop bleed
                >> from one row (longitudinally) to the next as individual segments in led
                >> bar-graph displays are usually quite longer than they are wide.
                >>
                >>> I did bread board one segment feeding an OP Amp with a 10K feedback
                >>> resistor and got a
                >>> 0 to 3.7 volt change with my LED flashlight through a sprocket hole
                >>> sized hole.
                >>
                >> The emitter array may need some tweaking on the current as well to get
                >> usable signals.
                >>
                >> Food for thought though, might just try it, I have some old PDP-7 tapes
                >> I want to read.
                >
                > Forrest Mims popularized the use of LEDs in photodiode mode in the early
                > 1970s, and has done quite a bit with them.
                >
                > But...with real photodiodes and phototransistors available for pennies, I'm
                > note sure of what the point would be, other than for hack value.

                How about using optical fiber to position the output from the emitters,
                and on the other side to the phototransistors? You should be able able to
                get the desired spacing that way.


                Mike Loewen mloewen@...
                Old Technology http://sturgeon.css.psu.edu/~mloewen/Oldtech/
              • Dave McGuire
                ... I think that s an excellent idea. One could mold them into a little tub of epoxy or similar, to make an optical read head. -Dave -- Dave McGuire, AK4HZ
                Message 7 of 11 , May 15, 2013
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                  On 05/15/2013 03:15 PM, Mike Loewen wrote:
                  >>>> When I was playing with my Arduino micro controller I read articles
                  >>>> about using led?s as light detectors.
                  >>>> It got me thinking .....
                  >>>> led bar graphs displays have .1 inch spacing to fit in DIP sockets .
                  >>>> My idea is to use 2 bar graphs one as a light source and one one as the
                  >>>> sensor.
                  >>>
                  >>> Interesting idea.
                  >>> I have seen leds used successfully on on solar trackers and having used
                  >>> leds for sensing in component counters before you might find you need a
                  >>> mask over the sensor array, with a line of holes at 0.1" spacing to stop
                  >>> bleed (laterally) from one track to its neighbour. Also to stop bleed
                  >>> from one row (longitudinally) to the next as individual segments in led
                  >>> bar-graph displays are usually quite longer than they are wide.
                  >>>
                  >>>> I did bread board one segment feeding an OP Amp with a 10K feedback
                  >>>> resistor and got a
                  >>>> 0 to 3.7 volt change with my LED flashlight through a sprocket hole
                  >>>> sized hole.
                  >>>
                  >>> The emitter array may need some tweaking on the current as well to get
                  >>> usable signals.
                  >>>
                  >>> Food for thought though, might just try it, I have some old PDP-7 tapes
                  >>> I want to read.
                  >>
                  >> Forrest Mims popularized the use of LEDs in photodiode mode in the early
                  >> 1970s, and has done quite a bit with them.
                  >>
                  >> But...with real photodiodes and phototransistors available for pennies, I'm
                  >> note sure of what the point would be, other than for hack value.
                  >
                  > How about using optical fiber to position the output from the emitters,
                  > and on the other side to the phototransistors? You should be able able to
                  > get the desired spacing that way.

                  I think that's an excellent idea. One could mold them into a little
                  "tub" of epoxy or similar, to make an optical read head.

                  -Dave

                  --
                  Dave McGuire, AK4HZ
                  New Kensington, PA
                • Mike Hatch
                  On 15/05/2013 19:47, Dave McGuire wrote: I think the main idea Duane had was the readily available array form of a led bar graph module on a pitch
                  Message 8 of 11 , May 16, 2013
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                    On 15/05/2013 19:47, Dave McGuire wrote:
                    <..snipped>

                    I think the main idea Duane had was the readily available array form of
                    a led bar graph module on a pitch to suit the paper tape, rather than
                    having to arrange individual components. I might give it a try just for
                    the fun of it.

                    Mike.

                    >
                    > Forrest Mims popularized the use of LEDs in photodiode mode in the early
                    > 1970s, and has done quite a bit with them.
                    >
                    > But...with real photodiodes and phototransistors available for pennies, I'm
                    > note sure of what the point would be, other than for hack value.
                    >
                    > -Dave
                    >
                    > --
                    > Dave McGuire, AK4HZ
                    > New Kensington, PA
                    >
                    >
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                  • Mike Hatch
                    Hi, ... Simplicity, if it works, readily available modules on the right pitch. No fiddling with light guides, optical fibre. But I would want to know if there
                    Message 9 of 11 , May 16, 2013
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                      Hi,

                      On 15/05/2013 20:15, Mike Loewen wrote:
                      > On Wed, 15 May 2013, Dave McGuire wrote:
                      > > But...with real photodiodes and phototransistors available for
                      > pennies, I'm
                      > > note sure of what the point would be, other than for hack value.
                      >
                      > How about using optical fiber to position the output from the emitters,
                      > and on the other side to the phototransistors? You should be able able to
                      > get the desired spacing that way.

                      Simplicity, if it works, readily available modules on the right pitch.
                      No fiddling with light guides, optical fibre. But I would want to know
                      if there was any "bleed" from adjacent channels within the packages.

                      Mike.

                      > Mike Loewen mloewen@...
                      > <mailto:mloewen%40cpumagic.scol.pa.us>
                      > Old Technology http://sturgeon.css.psu.edu/~mloewen/Oldtech/
                      >
                      >
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