Strain Gauge Effect

[Phend]

Hello:
Could a strain gage be used in an effect.?  Imagine a flexible thin steel flat sheet supported on one end (cantilever) big enough for your foot to press.  It would act as a spring ie never permanently distorting. On said spring a strain gage would be attached. By pressing on it the strain gage will change electrically.  Would need to amplify the output and feed it into part of an existing effect for instance a simple fuzz.  What could it do ?? Thinking out loud....goggle strain gage if curious.

[Rob Strand]

The resistance changes are quite small on these things so you end-up dealing with small signals.   The impedance is quite low but the changes are even smaller.  You can get some to work at DC but often they are driven with AC and have synchronous demodulator to fend-off noise due to the small signals involved (forgot to mention it greatly helps reduce drift).   That type of system produces a DC output voltage proportional to the deflection.    An example is kitchen or bathroom scales, you bond a strain gauge to a metal bar.  The bar acts as a spring, the weight deflects the bar and the strain gauge measures the defection which is translated back to weight on the display.

To get it to work you would probably need to build a system like the above then feed the DC output into a voltage controlled audio circuit, for example a JFET, LDR or OTA etc.

[PRR]

You could get a bigger signal by putting pins in your eyebrow and squinting.

[Vivek]

Sounds like a great idea !!!

Then the pedal would sound nice and mellow when the guitarist is out drinking beer with friends

and go raging metal when the guitarist is having a troublesome divorce with a narcissistic wife.



PS : Where on the guitarist do you propose to attach the strain gauge ?

[Phend]

Ok, bag the strain , next girl I see at the market check out with metal attached to her face and eyebrows should make for a good experiment.

[GFR]

https://www.researchgate.net/publication/308900114_Towards_a_live-electronic_setup_with_a_sensor-reed_saxophone_and_Csound

http://lac.linuxaudio.org/2013/papers/41.pdf

[amptramp]

This would be an ideal pickup for a drum skin.  Imagine, no more microphone placement issues - the drum skin produces the output.  I do go along with Rob Strand's idea of a synchronous demodulator signal processing system set up to avoid local magnetic fields.  So you could have a strain gauge mounted off the drum skin sort of like a humbucking strain gauge pickup to cancel the hum output of the sound pickup.

Circular resonators like a drum skin have a frequency distribution that follows a Bessel Function of the zeroth order.  Since these are not harmonic multiples, some people call them partials rather than harmonics, so there would be edge strain gauge pickups and inward pickups corresponding to bridge and neck pickups.  I could see this getting complicated but you may be able to get sounds from a drum that are selectable and mixable.  Unless the drum is tall, like tams, the fundamental is missing.  The zeros of the Bessel function are:

1. 2.4048256
2. 5.5200781
3. 8.6537279
4. 11.7915344
5. 14.9309177
6. 18.0710840
7. 21.2116366
8. 24.3524715
9. 27.4934791
10. 30.6346065

and this is what you are looking at for drum frequencies.

[Phend]

Hum, sinking fast ie over my head. Original suggestion was to spark ideas....

[Rob Strand]

I was pondering how you could make use of one of those without without the usual problems and rubber-stamp solutions.   If you stick to AC signals it gets rid of one lot of headaches.    Next is low impedance, say the impedance of an emitter circuit.    Putting that together you get a strain-gauge as the emitter resistor of the a common emitter amplifier.

Next is the small change.   The gain of the CE amplifier should boost the signal and modulating the resistance will modulate the gain and the bias voltage on the collector.

Option 1 is DC (but AC out):   The changes modulate the bias point and you tap off the AC signal at the collector of the CE ampliifier.

Option 2 is AC:  You feed a reasonable amplitude sine or square-wave into the base, not enough to clip the amp though.  The frequency would need to be high, maybe 100kHz.   Then you rectify that like a AM receiver (crystal set) and extract the envelope of the gain.

It's all rough and ready but DIY friendly in terms of parts.   Linear technology actual make chips that let you do synchronous demodulation pretty easy though.

Anyway only a thought.

[Jdansti]

If you're looking for something that hasn't been done yet, how about using a pressure transducer to modulate an effect such as a wah?  This would be particularly useful for handicapped guitarists who can't work a pedal with their feet. They put a tube in their mouth and change the air pressure in the tube to control the effect. A device like this would probably do the job: https://www.analog-micro.com/en/products/pressure-sensors/board-mount-pressure-sensors/ams6916/. It has an analog output of 0.5 VDC to 4.5 VDC.

[Gus]

good link
https://strainblog.micro-measurements.com/
https://micro-measurements.com/stress-analysis-strain-gages

[Mark Hammer]

If you're looking for something that hasn't been done yet, how about using a pressure transducer to modulate an effect such as a wah?  This would be particularly useful for handicapped guitarists who can't work a pedal with their feet. They put a tube in their mouth and change the air pressure in the tube to control the effect. A device like this would probably do the job: https://www.analog-micro.com/en/products/pressure-sensors/board-mount-pressure-sensors/ams6916/. It has an analog output of 0.5 VDC to 4.5 VDC.

Breath controllers have been around for a while.  I have an old Yamaha CS-01 synth that has a jack for breath controller.  I'm not sure what the actual pressure transducer at the heart of it is, but they exist.

We need to see more ideas here for use of force-sensing resistors.

[Rob Strand]

Pressure sensors have been around quite some time.   Readily available and reasonably priced back in the early 90's.
They are basically a strain gauge put down on silicon!  Exactly the same circuits.

[Phend]

Getting back to the cantilever beam pressed with your foot,  and incorporating it into an existing effect, question.  Maybe use it to change a bias .

[Vivek]

All this appears similar to connecting a wah to a weighing machine.

[Mark Hammer]

And let us not forget Hall sensors.  In correspondence with Tore Mogeson, while he was at TC, I learned that the MASH switch incorporated into some TC pedals used a Hall effect sensor as a sort of onboard expression controller.  Like I said to Tore, I don't know whether to be more impressed by how clever they were in incorporating it, or by the sensitivity of the sensor and how little distance the magnet had to travel to result in usable changes.

Of course, whether we are dealing with strain gauges, force-sensing resistors, breath controllers, or Hall sensors, ultimately they all rely on the users ability to translate bodily motion into musically expressive control.  Imagine if you had to operate a wah or volume pedal as if it was one of those big yoga/exercise balls, and sweeping the control depended on how hard you sat.  Aside from looking rather foolish and "unrock", just how fast can you sit down and get up, and how well could you achieve variations between the extremes?

I set up a photocell as the expression controller on my Line 6 M5, mounted it on the top of my guitar, and worked it by covering and uncovering it with my pinky.  VERY different feel to the effect, compared to working a pedal with my foot.  Every form of expression control will be somewhat different, depending on the responsiveness of the control element AND the controllability and articulation of what part of the body we use to control it.  That such body parts and devices can be put to use is not in question.  Rather, the question is whether such control allows us to say what we want to say, tonally, musically, with the speed and precision we are aiming for.

That is not to say there are NO productive uses of these various alternatives to potentiometers.  The mission is to match them up with the sorts of tonal and expressive changes that suit the musical material.

[EBK]

We need to see more ideas here for use of force-sensing resistors.

I have done some dabbling with FSRs.  I even have made a decent foot pressure actuator for one. It's a rather fun way to control an effect, like a wah pedal that doesn't move but gives you a similar control experience.

[amptramp]

There are air pressure modulated strain and hall-effect devices on most cars to sense evaporative emissions leaks (gives you a P0455 OBDII code if there is a failure) and manifold absolute pressure gauges that feed a 0 to 5 volt signal to the engine control computer.  Most have 12 volt, ground and output, so the processing is already done.

[Mark Hammer]

We need to see more ideas here for use of force-sensing resistors.

I have done some dabbling with FSRs.  I even have made a decent foot pressure actuator for one. It's a rather fun way to control an effect, like a wah pedal that doesn't move but gives you a similar control experience.

It's what David Rainger uses for the Igor foot controller on his Rainger pedals.

[Phend]

Phono cartridge ? Very small motion, but mounted in the right place on a cantilever of calculated (or measured) deflection might have a usable output ?