Reed switches vs optical switches

Hi

I am not familiar with any contacts. May I ask what is a difference between them two?
I wonder which type of switches are used in Hoffrichter's keyboards?

Tom

Hi Tom,

Reed switches are a type of mechanical switch with the contacts sealed in a glass envelope. The switch (if 'normally open' - the only kind relevant in this context) is closed by bringing a small magnet sufficiently close to the envelope. The main advantage of reed switches is their very great reliability. The main disadvantages are their fragility (especially during installation) and the distinctive 'tick' they make when opening or closing. Also, like other mechanical switches, there is always a period where the contacts open and close rapidly for a short period ('bounce') but this is predictable for reed switches and easily accommodated by the hardware used to convert switching signals to MIDI messages.

Because of the 'ticking' I personally wouldn't use reed switches for manuals. On the other hand I would always use them for MIDIfying a pedal board.

Optical switches vary greatly in their construction and appearance, but all use the same priciple. There is an emitter, usually a LED producing Infra-red radiation, and a detector, usually a photo-transistor.

Sometimes the emitter and detector are contained in the same package and may be configured side by side so they respond to a reflective surface in front of them, or facing each other in which case they respond to an obstruction placed between them. Alternatively, the emitter and detector can be bought in separate packages in which case they should be 'spectrally matched' which means that the emitter produces radiation of the same wavelength that the detector is most sensitive to.

Optical switches are also reliable, but need some extra circuitry to make them work. They are silent and easier to set up (in my experience) than reed switches. Overall I'd say the costs are about the same. I always use optical methods for MIDIfying manuals.

I'm afraid I don't know what kind of sensing Hoffrichter uses.

Nick

Morning Tom,

Just midified my Rogers pedalboard using the standard reed switches it was made with in the 70's.... yes, they make a little "click" when activated by a magnet, but nothing you can hear when you're playing music. But of course...... I like my music like I like my woman - LOUD . Just kidding.... even at low volume I can't hear them clicking. You really have stick your ear really close to hear the click; during my rebuild and final checkout before dragging to the music room the pedals were on my workshop table - I had DIRECT access to the switches..... the little click is very soft and very faint.... I would say quieter than a mouse passing gas.

Hoping this helps..... hoping you don't have to LISTEN to mice passing gas!!...,
Mark

"I am marching right along with Nick",

Except that I am using "2 spaced, Optical interrupters" under each of my keys,
providing, both first and second touch, "or if needed, touch control",
for the past three years, as well as,
Two op switches under each of my 32 Pedals.

The second set of 32 pedal contacts, are connected in parallel, and
I use them to operate the "Piano sustain pedal" on my sampled Steinway Piano
"a very effective trick" !

These provide "absolutely positive keying",
that is very noticeable when playing !

The only Reed-Switches in my system, are in my "Syndyne Sam's", and they also work perfectly !
Mel

Now I know much more about those switches.
Thank you!

Tom

Hi Tom,
Optical-switches like those that I utilized, are presently used by many modern organ builders,
because they are so positive, and reliable.

If one should choose to use "Magnetic Reed switches" they must be of very tiny size,
as this allows for much easier placement of them upon the key-bed's,
and better placement their associated tiny magnets !

Biggest problem with them is that the magnet for one note, can easily play the adjacent notes reeds !
Careful placement of the small reed's and magnets will eliminate this fault,
but the tiny "reed-switches" may be hard to find !

There are also "Hall effect switches" that can be used reliably with
carefully placed placed magnets on the keys.
These devices resemble a "small transistor", but they are switched on, by a magnetic field.
The same care must be utilized, to prevent adjacent notes from being played by the magnets

If you carefully search the internet, using the names of the devices above,
or organ keying systems as I did years ago,
I am sure that you will
find Photos of devices as well as sketches of the devices used,
and find specifications of all the devices on electronic parts supply houses,
such as "Digi Key" !
Best wishes, Mel

...the magnet for one note, can easily play the adjacent notes reeds !

Thanks Mel, I had forgotten to mention this problem.

The very first time I MIDIfied a (reed organ) keyboard I used reed switches and found it was much more difficult to set up reliably than I anticipated. I remember that eventually it was possible to set up each note to switch reliably, without actually triggering an adjacent note, but there were still interactions between notes in the sense that the depth of touch (ie where in the key travel the reed switched on/off) of one key could vary according to the position of the next note.

Another problem is that with reed switches the hysteresis (the difference in switching positions whether the key is rising / falling) can be rather large.

In principle, these issues would also arise with Hall effect sensors but I haven't as yet made a systematic investigation of this. There's so much else to do!

None of these problems, in my experience, arise with pedal boards where the spacing of the notes is considerable compared to manuals.

Nick

...the magnet for one note, can easily play the adjacent notes reeds !

Thanks Mel, I had forgotten to mention this problem.

The very first time I MIDIfied a (reed organ) keyboard I used reed switches and found it was much more difficult to set up reliably than I anticipated. I remember that eventually it was possible to set up each note to switch reliably, without actually triggering an adjacent note, but there were still interactions between notes in the sense that the depth of touch (ie where in the key travel the reed switched on/off) of one key could vary according to the position of the next note.

Another problem is that with reed switches the hysteresis (the difference in switching positions whether the key is rising / falling) can be rather large.

In principle, these issues would also arise with Hall effect sensors but I haven't as yet made a systematic investigation of this. There's so much else to do!

None of these problems, in my experience, arise with pedal boards where the spacing of the notes is considerable compared to manuals.

Nick

Unfortunately it can Had to tear one pedal board apart and start over because of this problem.

Thomas

My Allen pedalboard had been set to activate the reeds a bit too low. That combined with felts that were wearing out allowed some pedals to raise high enough that they initiated a Note On possibly from the magnetic lobe from the bottom of the magnet (?). This created stuck notes off course. So while the pedal reed switches can be very reliable once set correctly, they can be a real hassle when slightly out of adjustment. Moving a console on an uneven floor or to a new spot on the carpet where the console settles in deeper and faster than the pedalboard can be enough to create difficulties.