Mechanical Virtual Theremin

[Stumpy]

I built Arthur Harrison's minimum theremin last night, and it was easy to
put together and worked "right out of the box".

Was trying to think of a way to make a virtual theremin, found that it
already exists.

http://www.simple-media.co.uk/music/vsti/fvspook keys.htm

So I now want to use sensors to drive oscillators similar to a Theremin or a
Tannerin. What type of magnetometer would be sensitive to a permanent
magnet being brought into proximity to it? I want a cheap sensor that can
be driven by OpAmp.

 

[Paul Hovnanian P.E.]

I built Arthur Harrison's minimum theremin last night, and it was easy to
put together and worked "right out of the box".

Was trying to think of a way to make a virtual theremin, found that it
already exists.

http://www.simple-media.co.uk/music/vsti/fvspook keys.htm

So I now want to use sensors to drive oscillators similar to a Theremin or a
Tannerin. What type of magnetometer would be sensitive to a permanent
magnet being brought into proximity to it? I want a cheap sensor that can
be driven by OpAmp.

A Hall Effect sensor can detect PM fields. But for typical permanent
magnets, I don't know if their range will be as great as that of an
actual theremin (maybe a few inches). But why not use a capacitive
effect (like an actual Theremin uses)? You could use that as an input to
the 'virtual Theremin' if you wanted to. If you don't want to duplicate
the non contact feature of a Theremin, just use a joystick.

BTW, isn't a "Mechanical Theremin" just a trombone?

 

[Stumpy]

A Hall Effect sensor can detect PM fields. But for typical permanent
magnets, I don't know if their range will be as great as that of an
actual theremin (maybe a few inches). But why not use a capacitive
effect (like an actual Theremin uses)? You could use that as an input to
the 'virtual Theremin' if you wanted to. If you don't want to duplicate
the non contact feature of a Theremin, just use a joystick.

BTW, isn't a "Mechanical Theremin" just a trombone?

Ha! My nomenclature is weak. If I described it as an analog GUI for
audio, I'd be even less accurate.

My goal is to use 2 sensors perpendicularly mounted so that an object will
be sensed by both simultaneously. This would enable it to be played "one
handed".

 

[Joerg]

Hello Stumpy,

Ha! My nomenclature is weak. If I described it as an analog GUI for
audio, I'd be even less accurate.

My goal is to use 2 sensors perpendicularly mounted so that an object will
be sensed by both simultaneously. This would enable it to be played "one
handed".

Capacitive sensors as Paul mentioned can do that. Mount one below and
one on the side.

Regards, Joerg

 

[Tim Williams]

BTW, isn't a "Mechanical Theremin" just a trombone?

Nah, that's an acoustic Theremin.

Or whistling (which a Theremin is often compared to).

Tim

 

[[email protected]]

My goal is to use 2 sensors perpendicularly mounted so that an object will
be sensed by both simultaneously. This would enable it to be played "one
handed".

I did this with two LDRs for a toy application.

 

[Stumpy]

Capacitive sensors as Paul mentioned can do that. Mount one below and one
on the side.

The original Theremin had to have the two capacitive sensors separated by
some distance so they didn't interfere with each other. That's why I
thought a sensor that responds to a discrete object would be preferable.

 

[Stumpy]

I did this with two LDRs for a toy application.

Using a light source or shadows?

 

[Paul Hovnanian P.E.]

This might be overkill: http://www.polhemus.com/fastrak.htm

 

[Stumpy]

This might be overkill: http://www.polhemus.com/fastrak.htm

Looks expensive. I don't even know what I'd do with the 3rd dimension. Z
axis = tremolo?

 

[Stumpy]

http://www.cy-sensors.com/Hall-IC.htm

I'm in over my head, but will check out which of these might work.

 

[Rich Grise]

I did this with two LDRs for a toy application.

Anybody remember the "Lumemin"?
http://antiqueradio.org/pe0455.htm

The page shows a schematic of a toob-type Theremin, but the article was
about using LDRs or something, which is where the "lume" comes from.

I'd think that the two antennas might not interact very much if
they're at different frequencies that aren't harmonically related.

Good Luck!
Rich

 

[Mike]

http://www.cy-sensors.com/Hall-IC.htm

I'm in over my head, but will check out which of these might work.

As someone posted earlier, It will be very difficult to sense distance
more than just a few inches with any magnetic sensor. You could very
well get into a situation where stray magnetic fields will dominate
your signals. IMHO you would be much better off trying 2 modulated
RF,light, or ultrasonic sources tuned to 2 different frequencies.
It would seem that the major problem with one handed operation will be
involve overcoming the problem of sensing the hand broadside and
edgewise, since edgewise presents a much smaller profile to sense.
This seems to be especially true when trying to minimize interaction
between the 2 axes of motion. As usual, I could be wrong.

Mike

 

[Stumpy]

As someone posted earlier, It will be very difficult to sense distance
more than just a few inches with any magnetic sensor. You could very
well get into a situation where stray magnetic fields will dominate
your signals. IMHO you would be much better off trying 2 modulated
RF,light, or ultrasonic sources tuned to 2 different frequencies.
It would seem that the major problem with one handed operation will be
involve overcoming the problem of sensing the hand broadside and
edgewise, since edgewise presents a much smaller profile to sense.
This seems to be especially true when trying to minimize interaction
between the 2 axes of motion. As usual, I could be wrong.

Mike

Earlier I had indicated that a permanent magnet would be the object sensed.
I could hold it or mount it on a stick and wave it about like a mad
conductor. I'm still presuming that a Hall Effect sensor would work with a
strong enough magnet. I suppose a battery powered electromagnet is not out
of the question. Don't want it to look like a cattle prod and scare the
audience.

 

[Paul Hovnanian P.E.]

Looks expensive. I don't even know what I'd do with the 3rd dimension. Z
axis = tremolo?

There's 6 degrees of freedom if you count the angular measurements. Like
I said, overkill.

On the other hand, add a couple of VR gloves and you can make an air
guitar. ;-)

 

[Mike]

Earlier I had indicated that a permanent magnet would be the object sensed.
I could hold it or mount it on a stick and wave it about like a mad
conductor. I'm still presuming that a Hall Effect sensor would work with a
strong enough magnet. I suppose a battery powered electromagnet is not out
of the question. Don't want it to look like a cattle prod and scare the
audience.

I hate to sound like a pesimist, but another problem with using a
permenant magnet will be the orientation of the magnet relative to the
sensors. The analog hall sensors that I have worked with are
ratiometric with the output sitting at VCC/2 with no field present and
goes up or down depending on field polarity, I.E. north or south pole
facing the sensor. How far it moves up or down is determined by the
field strength. I don't think you realize just how small the signal
will be with even a very strong magnet. I'm sure these problems can be
overcome, but I sure wouldn't want to tackle it.

Mike

 

[Stumpy]

I hate to sound like a pesimist, but another problem with using a
permenant magnet will be the orientation of the magnet relative to the
sensors. The analog hall sensors that I have worked with are
ratiometric with the output sitting at VCC/2 with no field present and
goes up or down depending on field polarity, I.E. north or south pole
facing the sensor. How far it moves up or down is determined by the
field strength. I don't think you realize just how small the signal
will be with even a very strong magnet. I'm sure these problems can be
overcome, but I sure wouldn't want to tackle it.

Mike

I hear what you're saying. Time for me to stop talking and go away and get
some work done. The polarity issue would mean that rotating the magnet in
place would vary tone and volume .:. reproducibility would be challenging.