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Reed Switches with Shutters

Building organ consoles for use with Hauptwerk, adding MIDI to existing consoles, obtaining parts, ...

Reed Switches with Shutters

Postby Coenraads » Wed Aug 28, 2019 6:01 pm

In the past, when installing reed switches, I've always installed the magnets at the ends of the pedals but found adjustments to be tricky. And although I know this idea is not new, I recently decided to try a different approach where the magnet is mounted on a bracket in a fixed position over the reed. Inserting and removing a strip of tin plate attached to the pedal then turns the reed switch on or off. After minor adjustments to the depth of touch, the pedal worked flawlessly to the extent that I think I will use this approach from now on. The firing point can be precisely adjusted and the hysteresis was reduced to a couple of millimetres. Also, there is no chance of the magnet "overshooting" the reed.

I used half inch reed switches because of their small "magnetic foot print" which I further reduced by soldering the switch to a small square of prototyping board and cutting the leads as short as possible since they also contribute to the "magnetic foot print." On the same piece of board, I mounted an isolating diode and then fastened the little boards at the front of the pedal board so that the axes of the reed switches were parallel to the floor.

Next, on small brackets extending over each reed switch, I mounted a pair of my favourite 12 mm dollar store craft magnets with their central axes parallel to that of the switches. For each switch, I alternated the polarity so that the magnets did not "suck" magnetic flux from their neighbours.

The gap I left between switch and magnet was about one centimetre and into this gap I introduced a rectangle of tin plate (bottom of a cookie tin) which was then screwed to the pedal.

As the pedal is pushed down, the edge of the tin plate, which is now parallel to the reed switch, uncovers the complete reed switch with only a few millimetres of travel giving that very precise firing point and reduced hysteresis.

I feel more confident in the reliability of this "moving shutter" approach than I've ever felt using the conventional "moving magnet" approach.
John
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Re: Reed Switches with Shutters

Postby engrssc » Wed Aug 28, 2019 8:52 pm

Sounds like a neat idea. Any chance of a picture?

Rgds,
Ed
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Re: Reed Switches with Shutters

Postby Coenraads » Wed Aug 28, 2019 10:58 pm

For a photograph, visit my website:

https://sites.google.com/site/casavanto ... eed-switch

John
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Re: Reed Switches with Shutters

Postby engrssc » Thu Aug 29, 2019 4:21 am

Was curious as to your source for the tinplate.

Rgds,
Ed
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Re: Reed Switches with Shutters

Postby itsabird » Thu Aug 29, 2019 2:29 pm

Coenraads wrote:... The gap I left between switch and magnet was about one centimetre and into this gap I introduced a rectangle of tin plate (bottom of a cookie tin) which was then screwed to the pedal.

You must have eaten a lot of cookies I suppose :D
bert
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