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In the past, I have had considerable success using reed switches on pedal boards. But when I last ditched the switch box on a Casavant organ pedal and decided to use reed switches instead, all the flaws inherent in reed switches seemed to coalesce at the same time. Reed switches:
1. are fragile and I seemed to have hit a bad batch where switches would fail just by looking at them.
2. are subject to "push through," i.e., if the pedal stroke is too deep, the reed will just turn off again near the end of the stroke.
3. are sensitive to neighbouring magnets causing them to fire when an adjacent pedal is pushed.
4. have considerable hysteresis (the difference between the ON point and the OFF point)
5. are finicky and tricky to adjust.
After several tries I thought I had nailed it but when I started getting calls from the organist complaining of non-working pedal notes, I ripped it all out in frustration and decided to try something I had never used before: Hall switches.
The first thing one needs to understand is that the principle of operation of a reed switch and that of a Hall switch is quite different. Whereas a reed switch depends on setting up a magnetic circuit along the length of the switch, the Hall switch is sensitive simply to the presence of a magnetic field. It's like the difference between sensing current and sensing voltage.
Hall switches have several advantages. They:
1. are rugged, much like a transistor which they resemble.
2. are not susceptible to "push through" since one can simply extend the presence of the magnetic field by using a second magnet in tandem.
3. have little sensitivity to the field from adjacent magnets even though the magnets used are much stronger than those normally used with reed switches.
4. have very little hysteresis
So is there a down side? Unfortunately, yes. Hall switches generate only a tiny signal that needs to be amplified before being put to use. Casting around for something that would give me a large gain, I settled on the ever versatile 555 timer chip, the most popular chip in all of electronics. It easily generated the 16V output the organ switching system expected to "see." B.t.w, a 555 timer is happy working over a large voltage range.
Here is the circuit diagram:
For each pedal note I mounted the components on a little circuit board which when mounted on the pedal board was clamped down under a thin strip of wood (I use bamboo skewers) with a screw on each side that could be loosened to allow the position of the sensor to be adjusted. The sensor is the three lead transistor lookalike.
Although one magnet would probably have sufficed, I mounted two magnets in tandem to ensure there would be no "push through." Note how the diagram shows both magnets having their polarity in the same direction! I used 12 mm x 3mm magnets with countersunk holes that could be screwed to the aluminum bracket.
https://www.amazon.ca/gp/product/B07...?ie=UTF8&psc=1
These are the Hall switches I used:
https://www.amazon.ca/gp/product/B07...?ie=UTF8&psc=1
Everything has worked reliably with no call backs, as befits one of the largest organs in Victoria. And the hours spent building 32 little circuit boards was time well spent. Of course I left several extra circuit boards with the organ should one fail in the future.
1. are fragile and I seemed to have hit a bad batch where switches would fail just by looking at them.
2. are subject to "push through," i.e., if the pedal stroke is too deep, the reed will just turn off again near the end of the stroke.
3. are sensitive to neighbouring magnets causing them to fire when an adjacent pedal is pushed.
4. have considerable hysteresis (the difference between the ON point and the OFF point)
5. are finicky and tricky to adjust.
After several tries I thought I had nailed it but when I started getting calls from the organist complaining of non-working pedal notes, I ripped it all out in frustration and decided to try something I had never used before: Hall switches.
The first thing one needs to understand is that the principle of operation of a reed switch and that of a Hall switch is quite different. Whereas a reed switch depends on setting up a magnetic circuit along the length of the switch, the Hall switch is sensitive simply to the presence of a magnetic field. It's like the difference between sensing current and sensing voltage.
Hall switches have several advantages. They:
1. are rugged, much like a transistor which they resemble.
2. are not susceptible to "push through" since one can simply extend the presence of the magnetic field by using a second magnet in tandem.
3. have little sensitivity to the field from adjacent magnets even though the magnets used are much stronger than those normally used with reed switches.
4. have very little hysteresis
So is there a down side? Unfortunately, yes. Hall switches generate only a tiny signal that needs to be amplified before being put to use. Casting around for something that would give me a large gain, I settled on the ever versatile 555 timer chip, the most popular chip in all of electronics. It easily generated the 16V output the organ switching system expected to "see." B.t.w, a 555 timer is happy working over a large voltage range.
Here is the circuit diagram:
For each pedal note I mounted the components on a little circuit board which when mounted on the pedal board was clamped down under a thin strip of wood (I use bamboo skewers) with a screw on each side that could be loosened to allow the position of the sensor to be adjusted. The sensor is the three lead transistor lookalike.
Although one magnet would probably have sufficed, I mounted two magnets in tandem to ensure there would be no "push through." Note how the diagram shows both magnets having their polarity in the same direction! I used 12 mm x 3mm magnets with countersunk holes that could be screwed to the aluminum bracket.
https://www.amazon.ca/gp/product/B07...?ie=UTF8&psc=1
These are the Hall switches I used:
https://www.amazon.ca/gp/product/B07...?ie=UTF8&psc=1
Everything has worked reliably with no call backs, as befits one of the largest organs in Victoria. And the hours spent building 32 little circuit boards was time well spent. Of course I left several extra circuit boards with the organ should one fail in the future.
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