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30722Re: [midatlanticretro] Building a Better Tape Reader

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  • Mike Loewen
    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/
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