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30696Re: [midatlanticretro] Building a Better Tape Reader

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  • DuaneCraps
    May 15 5:04 AM
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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.

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