Ideas for electromechanical resonance?

[default]

I'm wondering if anyone has done this and how:

I want to resonate a high carbon steel bar at its fundamental
frequency to produce an audio tone. The bar is 1/8" thick, 6-1/2"
long and 1-1/2" wide and resonates at about 400 Hz when struck.

The bars are supported at their "nodes" and do resonate nicely.

What I'd like is a circuit to get it producing a continuous sine wave.
So far I haven't had much luck getting enough feedback to produce
oscillations using a simple circuit similar to a tuning fork
oscillator. (think Buliva "Acutron" watch circuit but with a high
current supply and a power transistor)

I want it to work with a plain steel bar - no magnets attached to the
bars nothing in contact with the bars and preferably a simple one
transistor low tech circuit -




--

 

[Tim Wescott]

On Mon, 24 Aug 2009 10:13:22 -0400, default wrote:

I'm wondering if anyone has done this and how:

I want to resonate a high carbon steel bar at its fundamental frequency
to produce an audio tone. The bar is 1/8" thick, 6-1/2" long and 1-1/2"
wide and resonates at about 400 Hz when struck.

The bars are supported at their "nodes" and do resonate nicely.

What I'd like is a circuit to get it producing a continuous sine wave.
So far I haven't had much luck getting enough feedback to produce
oscillations using a simple circuit similar to a tuning fork oscillator.
(think Buliva "Acutron" watch circuit but with a high current supply
and a power transistor)

I want it to work with a plain steel bar - no magnets attached to the
bars nothing in contact with the bars and preferably a simple one
transistor low tech circuit -

It would seem that a nice big coil at an antinode, with a DC current on
it or a permanent magnet providing a bias, will couple the bar's
mechanical energy nicely into electrical energy -- movement of the bar
through the magnetic field will generate a voltage in the coil, while
changing the coil's current will induce a changing force on the bar.

With one coil you'll see some distortion as the coil voltage will depend
more or less on the coil current times the bar velocity; depending on
what you want to do this may or may not make any difference.

--
www.wescottdesign.com

 

[John Larkin]

On Mon, 24 Aug 2009 10:13:22 -0400, default <default@defaulter.net>
wrote:

I'm wondering if anyone has done this and how:

I want to resonate a high carbon steel bar at its fundamental
frequency to produce an audio tone. The bar is 1/8" thick, 6-1/2"
long and 1-1/2" wide and resonates at about 400 Hz when struck.

The bars are supported at their "nodes" and do resonate nicely.

What I'd like is a circuit to get it producing a continuous sine wave.
So far I haven't had much luck getting enough feedback to produce
oscillations using a simple circuit similar to a tuning fork
oscillator. (think Buliva "Acutron" watch circuit but with a high
current supply and a power transistor)

I want it to work with a plain steel bar - no magnets attached to the
bars nothing in contact with the bars and preferably a simple one
transistor low tech circuit -

Two coils would be easiest:

A pickup coil operating in variable-reluctance mode. Wind the coil on
a ceramic magnet, lots of turns of fine wire, and put it close to the
bar.

Here's a fancy VR pickup:

http://img.directindustry.com/images_di/photo-p/variable-reluctance-speed-sensor-vrs-120292.jpg

ebay?

The other coil, the driver, can be fewer turns of fatter wire, on a
e-core maybe. Run it with DC bias, class A amp maybe.

You'll need a fair amount of voltage gain from pickup to driver, an
opamp driving an output transistor or power fet maybe, but I doubt
you'll need a lot of actual power to keep the bar singing. A single
transistor amp might work, if you get all the windings and impedances
just right.

Build the pickup coil first, whack the bar, and measure the signal.
Then work from there.

John

 

[default]

On Mon, 24 Aug 2009 21:10:13 -0700, John Larkin
<jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:

On Mon, 24 Aug 2009 10:13:22 -0400, default <default@defaulter.net
wrote:

I'm wondering if anyone has done this and how:

I want to resonate a high carbon steel bar at its fundamental
frequency to produce an audio tone. The bar is 1/8" thick, 6-1/2"
long and 1-1/2" wide and resonates at about 400 Hz when struck.

The bars are supported at their "nodes" and do resonate nicely.

What I'd like is a circuit to get it producing a continuous sine wave.
So far I haven't had much luck getting enough feedback to produce
oscillations using a simple circuit similar to a tuning fork
oscillator. (think Buliva "Acutron" watch circuit but with a high
current supply and a power transistor)

I want it to work with a plain steel bar - no magnets attached to the
bars nothing in contact with the bars and preferably a simple one
transistor low tech circuit -

Two coils would be easiest:

A pickup coil operating in variable-reluctance mode. Wind the coil on
a ceramic magnet, lots of turns of fine wire, and put it close to the
bar.

Here's a fancy VR pickup:

http://img.directindustry.com/images_di/photo-p/variable-reluctance-speed-sensor-vrs-120292.jpg

ebay?

The other coil, the driver, can be fewer turns of fatter wire, on a
e-core maybe. Run it with DC bias, class A amp maybe.

You'll need a fair amount of voltage gain from pickup to driver, an
opamp driving an output transistor or power fet maybe, but I doubt
you'll need a lot of actual power to keep the bar singing. A single
transistor amp might work, if you get all the windings and impedances
just right.

Build the pickup coil first, whack the bar, and measure the signal.
Then work from there.

John

Good idea. There might be some homebrew guitar pickups around.

Surely a steel string would be harder to amplify than a heavy metal
bar?

--

 

[whit3rd]

On Aug 24, 7:13 am, default <defa...@defaulter.net> wrote:

I want to resonate a high carbon steel bar at its fundamental
frequency to produce an audio tone.  The bar is 1/8" thick, 6-1/2"
long and 1-1/2" wide and resonates at about 400 Hz when struck.

The bars are supported at their "nodes" and do resonate nicely.

What I'd like is a circuit to get it producing a continuous sine wave.

There will be longitudinal P wave modes, flex modes, and torsion
modes; probably your apparatus is in flex mode (lower frequency).
It is possible to use a pull-on-the-middle motor to maintain the
oscillation,
probably what you want to do is to shift one of the supports to
slightly
off a node and use it as a microphone/motor to maintain the
oscillation.
Push-pull drivers of the right kind are the core of pulse-width-
modulation
switching power supplies, so you can drive the linear motor with
a (for instance) TL494 and control the amplitude of the oscillation
by the pulse-width.

 

[gearhead]

On Aug 25, 6:01 pm, default <defa...@defaulter.net> wrote:

On Mon, 24 Aug 2009 21:10:13 -0700, John Larkin



jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
On Mon, 24 Aug 2009 10:13:22 -0400, default <defa...@defaulter.net
wrote:

I'm wondering if anyone has done this and how:

I want to resonate a high carbon steel bar at its fundamental
frequency to produce an audio tone.  The bar is 1/8" thick, 6-1/2"
long and 1-1/2" wide and resonates at about 400 Hz when struck.

The bars are supported at their "nodes" and do resonate nicely.

What I'd like is a circuit to get it producing a continuous sine wave.
So far I haven't had much luck getting enough feedback to produce
oscillations using a simple circuit similar to a tuning fork
oscillator.  (think Buliva "Acutron" watch circuit but with a high
current supply and a power transistor)

I want it to work with a plain steel bar - no magnets attached to the
bars nothing in contact with the bars and preferably a simple one
transistor low tech circuit -  

Two coils would be easiest:

A pickup coil operating in variable-reluctance mode. Wind the coil on
a ceramic magnet, lots of turns of fine wire, and put it close to the
bar.

Here's a fancy VR pickup:

http://img.directindustry.com/images_di/photo-p/variable-reluctance-s...

ebay?

The other coil, the driver, can be fewer turns of fatter wire, on a
e-core maybe. Run it with DC bias, class A amp maybe.

You'll need a fair amount of voltage gain from pickup to driver, an
opamp driving an output transistor or power fet maybe, but I doubt
you'll need a lot of actual power to keep the bar singing. A single
transistor amp might work, if you get all the windings and impedances
just right.

Build the pickup coil first, whack the bar, and measure the signal.
Then work from there.

John

Good idea.  There might be some homebrew guitar pickups around.
Surely a steel string would be harder to amplify than a heavy metal
bar?

--

I foresee a significant challenge in that the heavy metal bar exhibits
mere microscopic movement when it vibrates.
A guitar string swings through what, several millimeters over the
pickup (reluctor) when you pluck it.
How much will your bar move, a few microns? Try picking that up with
an ordinary surplus reluctor like a guitar pickup or a crankshaft
position sensor. If you roll your own like JL says, and do some
serious work on the circuitry, might could do it. The sensor would
have to be just about touching the bar.
I hate to be a party pooper, but I think you might have to induce a
magnetic field in your hunkasteel to get anywhere.

 

[gearhead]

On Aug 29, 12:04 pm, gearhead <nos...@billburg.com> wrote:

On Aug 25, 6:01 pm, default <defa...@defaulter.net> wrote:



On Mon, 24 Aug 2009 21:10:13 -0700, John Larkin

jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
On Mon, 24 Aug 2009 10:13:22 -0400, default <defa...@defaulter.net
wrote:

I'm wondering if anyone has done this and how:

I want to resonate a high carbon steel bar at its fundamental
frequency to produce an audio tone.  The bar is 1/8" thick, 6-1/2"
long and 1-1/2" wide and resonates at about 400 Hz when struck.

The bars are supported at their "nodes" and do resonate nicely.

What I'd like is a circuit to get it producing a continuous sine wave..
So far I haven't had much luck getting enough feedback to produce
oscillations using a simple circuit similar to a tuning fork
oscillator.  (think Buliva "Acutron" watch circuit but with a high
current supply and a power transistor)

I want it to work with a plain steel bar - no magnets attached to the
bars nothing in contact with the bars and preferably a simple one
transistor low tech circuit -  

Two coils would be easiest:

A pickup coil operating in variable-reluctance mode. Wind the coil on
a ceramic magnet, lots of turns of fine wire, and put it close to the
bar.

Here's a fancy VR pickup:

http://img.directindustry.com/images_di/photo-p/variable-reluctance-s....

ebay?

The other coil, the driver, can be fewer turns of fatter wire, on a
e-core maybe. Run it with DC bias, class A amp maybe.

You'll need a fair amount of voltage gain from pickup to driver, an
opamp driving an output transistor or power fet maybe, but I doubt
you'll need a lot of actual power to keep the bar singing. A single
transistor amp might work, if you get all the windings and impedances
just right.

Build the pickup coil first, whack the bar, and measure the signal.
Then work from there.

John

Good idea.  There might be some homebrew guitar pickups around.
Surely a steel string would be harder to amplify than a heavy metal
bar?

--

I foresee a significant challenge in that the heavy metal bar exhibits
mere microscopic movement when it vibrates.
A guitar string swings through what, several millimeters over the
pickup (reluctor) when you pluck it.
How much will your bar move, a few microns?  Try picking that up with
an ordinary surplus reluctor like a guitar pickup or a crankshaft
position sensor.  If you roll your own like JL says, and do some
serious work on the circuitry, might could do it.  The sensor would
have to be just about touching the bar.
I hate to be a party pooper, but I think you might have to induce a
magnetic field in your hunkasteel to get anywhere.

Hey -- don't bother with a sensor. Just drive it near the resonant
frequency.
Put a big solenoid under an antinode and adjust the drive frequency
until it sings.
Done.

 

[John Larkin]

On Sat, 29 Aug 2009 09:04:09 -0700 (PDT), gearhead
<nospam@billburg.com> wrote:

On Aug 25, 6:01 pm, default <defa...@defaulter.net> wrote:
On Mon, 24 Aug 2009 21:10:13 -0700, John Larkin



jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
On Mon, 24 Aug 2009 10:13:22 -0400, default <defa...@defaulter.net
wrote:

I'm wondering if anyone has done this and how:

I want to resonate a high carbon steel bar at its fundamental
frequency to produce an audio tone.  The bar is 1/8" thick, 6-1/2"
long and 1-1/2" wide and resonates at about 400 Hz when struck.

The bars are supported at their "nodes" and do resonate nicely.

What I'd like is a circuit to get it producing a continuous sine wave.
So far I haven't had much luck getting enough feedback to produce
oscillations using a simple circuit similar to a tuning fork
oscillator.  (think Buliva "Acutron" watch circuit but with a high
current supply and a power transistor)

I want it to work with a plain steel bar - no magnets attached to the
bars nothing in contact with the bars and preferably a simple one
transistor low tech circuit -  

Two coils would be easiest:

A pickup coil operating in variable-reluctance mode. Wind the coil on
a ceramic magnet, lots of turns of fine wire, and put it close to the
bar.

Here's a fancy VR pickup:

http://img.directindustry.com/images_di/photo-p/variable-reluctance-s...

ebay?

The other coil, the driver, can be fewer turns of fatter wire, on a
e-core maybe. Run it with DC bias, class A amp maybe.

You'll need a fair amount of voltage gain from pickup to driver, an
opamp driving an output transistor or power fet maybe, but I doubt
you'll need a lot of actual power to keep the bar singing. A single
transistor amp might work, if you get all the windings and impedances
just right.

Build the pickup coil first, whack the bar, and measure the signal.
Then work from there.

John

Good idea.  There might be some homebrew guitar pickups around.
Surely a steel string would be harder to amplify than a heavy metal
bar?

--

I foresee a significant challenge in that the heavy metal bar exhibits
mere microscopic movement when it vibrates.
A guitar string swings through what, several millimeters over the
pickup (reluctor) when you pluck it.
How much will your bar move, a few microns? Try picking that up with
an ordinary surplus reluctor like a guitar pickup or a crankshaft
position sensor. If you roll your own like JL says, and do some
serious work on the circuitry, might could do it. The sensor would
have to be just about touching the bar.
I hate to be a party pooper, but I think you might have to induce a
magnetic field in your hunkasteel to get anywhere.

It would be easy to get an old guitar pickup and try it. Output
voltage will be - very roughly - proportional to frequency and inverse
on magnetic gap. But gain is cheap, essentially free, so a guitar
pickup can probably be made to work.

Hey, bounce a laser off it! Atomic force microscopes detect really
tiny deflections with a pointer-quality laser bounced off a flexing
cantelever into a photodiode.

Or use a microphone, one of those cheap electret cartriges.

John

 

[gearhead]

On Aug 29, 3:03 pm, John Larkin
<jjlar...@highNOTlandTHIStechnologyPART.com> wrote:

On Sat, 29 Aug 2009 09:04:09 -0700 (PDT), gearhead



nos...@billburg.com> wrote:
On Aug 25, 6:01 pm, default <defa...@defaulter.net> wrote:
On Mon, 24 Aug 2009 21:10:13 -0700, John Larkin

jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
On Mon, 24 Aug 2009 10:13:22 -0400, default <defa...@defaulter.net
wrote:

I'm wondering if anyone has done this and how:

I want to resonate a high carbon steel bar at its fundamental
frequency to produce an audio tone.  The bar is 1/8" thick, 6-1/2"
long and 1-1/2" wide and resonates at about 400 Hz when struck.

The bars are supported at their "nodes" and do resonate nicely.

What I'd like is a circuit to get it producing a continuous sine wave.
So far I haven't had much luck getting enough feedback to produce
oscillations using a simple circuit similar to a tuning fork
oscillator.  (think Buliva "Acutron" watch circuit but with a high
current supply and a power transistor)

I want it to work with a plain steel bar - no magnets attached to the
bars nothing in contact with the bars and preferably a simple one
transistor low tech circuit -  

Two coils would be easiest:

A pickup coil operating in variable-reluctance mode. Wind the coil on
a ceramic magnet, lots of turns of fine wire, and put it close to the
bar.

Here's a fancy VR pickup:

http://img.directindustry.com/images_di/photo-p/variable-reluctance-s....

ebay?

The other coil, the driver, can be fewer turns of fatter wire, on a
e-core maybe. Run it with DC bias, class A amp maybe.

You'll need a fair amount of voltage gain from pickup to driver, an
opamp driving an output transistor or power fet maybe, but I doubt
you'll need a lot of actual power to keep the bar singing. A single
transistor amp might work, if you get all the windings and impedances
just right.

Build the pickup coil first, whack the bar, and measure the signal.
Then work from there.

John

Good idea.  There might be some homebrew guitar pickups around.
Surely a steel string would be harder to amplify than a heavy metal
bar?

--

I foresee a significant challenge in that the heavy metal bar exhibits
mere microscopic movement when it vibrates.
A guitar string swings through what, several millimeters over the
pickup (reluctor) when you pluck it.
How much will your bar move, a few microns?  Try picking that up with
an ordinary surplus reluctor like a guitar pickup or a crankshaft
position sensor.  If you roll your own like JL says, and do some
serious work on the circuitry, might could do it.  The sensor would
have to be just about touching the bar.
I hate to be a party pooper, but I think you might have to induce a
magnetic field in your hunkasteel to get anywhere.

It would be easy to get an old guitar pickup and try it. Output
voltage will be - very roughly - proportional to frequency and inverse
on magnetic gap. But gain is cheap, essentially free, so a guitar
pickup can probably be made to work.

Hey, bounce a laser off it! Atomic force microscopes detect really
tiny deflections with a pointer-quality laser bounced off a flexing
cantelever into a photodiode.

Or use a microphone, one of those cheap electret cartriges.

John

I didn't even think of a mic, but that would be the way to go.
If this was a git-r-done job, I still think it would be simpler to do
a manual adjustment when you set it up and let it then work
forevermore. But let me not be the one to deny an experimenter his
experimenting.