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Reed switches with shutters

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  • Reed switches with shutters

    We're converting the tubular pneumatic action on the pedal of a small Harrison organ to electric action. We'll install 30 reed switches and scan them with an Arduino which in turn will switch the drivers. In the past, I've always operated the reed switch using the "moving magnet" approach. This takes some fiddling adjusting the strength of the magnets so that adjacent switches don't interfere with each other. The hysteresis is also greater than I would like.
    As a result, I've been experimenting with mounting the magnets on a small bracket in a fixed position over the reed switch, leaving about a one cm. gap. The reed switch is then permanently on until I insert a "shutter" of tin plate or any ferromagnetic material in the gap which "short circuits" the magnetic field and turns the reed switch off.
    The "shutter" is of course then screwed to the pedal. This system seems much less prone to interference, and to my delight, it reduces the hysteresis to a few millimetres.
    I recall seeing this type of arrangement on a Viscount organ once, and I was wondering if anyone else has tried this approach and what the pitfalls might be.
    John

  • #2
    Coenraads, Not too many replies coming your way! I haven't tried the shutter approach, although it sounds very promising. In the 1980's I made a number of analogue electronic organs for Sydney churches. Instead of mounting the magnet above its reed switch, I glued it to the front end of the pedal, and its moving action was almost to almost swipe the reed switch rather than approach it vertically. This was an attempt to reduce hysteresis effects. I also alternated the north/south polarity of adjacent magnets. (Don't know whether that made any difference.) Still a bit fiddly to get each one right. Also, in one installation I recall that after some years of use, one or two pedals tended to go beyond the correct position because the felt had bedded down, causing the note to sound and then to go off. They needed to be readjusted eventually.

    John Reimer

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    • #3
      Finished hooking up the pedal board today and everything worked flawlessly the first time. There were no tricky adjustments or any interference between switches to deal with. The hysteresis was reduced to about two millimetres, and unlike with the moving magnet approach, there is no chance of the magnet overshooting the reed switch.
      I liked this enough that from now on I will use this approach, with a fixed magnet and a tin plate shutter, on all future pedal board conversions.
      John

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      • myorgan
        myorgan commented
        Editing a comment
        Hurry up and patent your approach! It might be worth it. Thanks for sharing your success story.

        Michael

    • #4
      Interesting approach. Glad you found a solution to your problem. I have mounted reed switches staggered so that the magnets were also staggered and did not interfere with the adjacent reeds. Thanks for sharing your idea.

      Michael

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      • #5
        On my website I've posted more detailed instructions plus a picture.

        https://sites.google.com/site/casava...00/reed-switch

        John

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