Would a piezo disk from a Motorola tweeter make a good strain guage? - diyAudio
Go Back   Home > Forums > General Interest > Everything Else

Everything Else Anything related to audio / video / electronics etc) BUT remember- we have many new forums where your thread may now fit! .... Parts, Equipment & Tools, Construction Tips, Software Tools......

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 5th April 2013, 03:46 AM   #1
Wizard of Kelts
diyAudio Moderator
 
Join Date: Sep 2001
Location: Connecticut, The Nutmeg State
Default Would a piezo disk from a Motorola tweeter make a good strain guage?

I have plantar fasciitis and a heel spur. My present day sneakers, bought at Xmas, are already running down but surprisingly, a memory foam insert bought at the Dollar Store is improving things immensely.

I still am going to buy new sneakers, (they call them running shoes these days), and still put in the memory foam insert because with my condition I want the absolute softest ride for the foot.

Adidas has just come out with a new material called Energy Boost that is both supposed to return more energy and be more comfortable than the traditional EVA foam used in sneakers. It's only a little more expensive than what I've been buying. https://www.youtube.com/watch?v=MZnAeK9l5oU

Before I make the switch from the Asics to the Adidas however, I thought it might be both a good idea and some fun to tape some kind of gauge to my heel and try on the sneakers in the store to see which gives the least shock.

I wonder if took apart a motorola horn tweeter, (does Radio Shack still have them?), soldered some wires and connected a multimeter to them if that would fill the bill.

The thing wouldn't have to be hugely accurate, just give some kind of proportional reading so I could tell which shoe transmitted the most shock to the heel.

I really don't care if I look peculiar in the shoe store, in fact I prefer it if the thing works.

If not, does anybody have any idea where I could get a strain gauge or other device which would work?
__________________
"A friend will help you move. A really good friend will help you move a body."
-Anonymous

Last edited by kelticwizard; 5th April 2013 at 04:08 AM.
  Reply With Quote
Old 5th April 2013, 05:05 AM   #2
diyAudio Member
 
sofaspud's Avatar
 
Join Date: Nov 2005
Location: San Antonio
I'd guess the answer is yes. I don't know details of a Motorola piezo; a cheap piezo disc may actually be better for this application.
Your general idea is reasonable, though. Just connecting the wires to a multimeter probably won't work very well. The signal will be just a transient spike that a digital meter will have difficulty locking in on. An op amp boost and some type of hold circuit would seem necessary. Does your meter have a peak hold function? If so, that still may or may not be enough - you'd have to check its specs.
__________________
It is error only, and not truth, that shrinks from enquiry. - Thomas Paine
  Reply With Quote
Old 5th April 2013, 05:19 AM   #3
Wizard of Kelts
diyAudio Moderator
 
Join Date: Sep 2001
Location: Connecticut, The Nutmeg State
Will check specs tomorrow, digital meter is downstairs now.

Not sure, think I have an old analog meter around. The reading doesn't have to be exact-I think I can judge approximately a sudden rise and fall on a dial. It would only be the comparison between brands that would be important, not exact data readings. Also, might find one of those inexpensive audio transformers useful in this application.
__________________
"A friend will help you move. A really good friend will help you move a body."
-Anonymous

Last edited by kelticwizard; 5th April 2013 at 05:22 AM.
  Reply With Quote
Old 5th April 2013, 05:34 AM   #4
diyAudio Member
 
sofaspud's Avatar
 
Join Date: Nov 2005
Location: San Antonio
The amplification may not be necessary, but a hold circuit would surely help. The outputs may not be different enough to differentiate via a rapidly moving meter pointer. A hold circuit might be as simple as a capacitor and some support components, but someone smarter than I would have to step in with practical details.
__________________
It is error only, and not truth, that shrinks from enquiry. - Thomas Paine
  Reply With Quote
Old 5th April 2013, 02:05 PM   #5
diyAudio Member
 
jneutron's Avatar
 
Join Date: Jan 2004
Location: away
Quote:
Originally Posted by kelticwizard View Post
I have plantar fasciitis and a heel spur.
I had the same issue. It was caused by falling arches. I inserted an arch support, I think the name was powersole..and a dr sholls foam insert about 1/4 inch thick.

No problem since.

I suspect plantar fascitis is overused as a diagnosis. Give the supports a try, 20-30 bucks.

Ah, forgot...It happened to my right foot about 10 years ago. I mucked around for almost a year with the intense pain until I figured it out. About 2 years ago, the left foot started hurting, I repeated the fix and it worked.

jn

Last edited by jneutron; 5th April 2013 at 02:08 PM.
  Reply With Quote
Old 5th April 2013, 02:28 PM   #6
diyAudio Member
 
Join Date: May 2002
Location: Switzerland
The piezo tweeter thingies might be too brittle. But there is flexible plastic foil available that is meant to be used for sensors, musical instrument pickups etc. Can't remember who made it.
And as display you might use something like that:

Testing DS0201 Mini Oscilloscope V1.5 - YouTube

It wouls also allow to see the shape of the pulse not only its amplitude.

Regards

Charles
  Reply With Quote
Old 5th April 2013, 10:44 PM   #7
diyAudio Member
 
sofaspud's Avatar
 
Join Date: Nov 2005
Location: San Antonio
A small disc for under the heel should have force distributed evenly enough to avoid breakage. I'd try just a diode followed by any low-leakage capacitor of about 0.1μF or less. Add a 100Ω resistor and momentary pushbutton as a reset, and see if a DMM provides a reading. Since you're just looking at comparison and not accuracy something simple like this might work.
__________________
It is error only, and not truth, that shrinks from enquiry. - Thomas Paine
  Reply With Quote
Old 6th April 2013, 12:22 AM   #8
JMFahey is offline JMFahey  Argentina
diyAudio Member
 
JMFahey's Avatar
 
Join Date: Mar 2009
Location: Buenos Aires - Argentina
2 answers:

1) I also had an incredibly long heel spur, very painful.
Took 6 months to be bearable and 1 year to dissappear, involving a process of de-calcification.
I made my own custom inserts , X-Rays in hand, and glueing many EVA spongy rubber sheet cutouts where oval holes of progressive diameter were cut, so final shape was an inverted cone which applied even pressure *around* the spike.
It worked very well.
Made it bearable and lack of localized pressure (due to my excessive overweight) signaled to my body that it didn't need to keep reinforcing the "house foundations". Oh well.

2) I have done something similar, but one proper way is:
a) Piezo disk : I used "brass" clock alarm disks, you can use Tweeter disks (which are "pure ceramic= brittle) if you sandwich them between 2 aluminum disks or similar, previously applying a drop of silicone caulking material on each side, so there is not *air* anywhere between layers.
You connect it to:

b) a 10M impedance preamp or buffer.
Maybe a FET or a TL072 with a 10M input resistor.
which drives:

c) some kind of rectifier and crude sample and hold , as 100K series resistor, 1uF capacitor, a 470K to 1 M discharge resistor.
Why "crude is better"?
Because it's not a Lab instrument to measure Piezo characteristics or whatever, no need to get a peak voltage and hold it steady for future measurement, I connected it to a squarewave oscillator which got modulated by the detected voltage, so I want detected voltage to be able to go up and down.
If you want to call it a "long time constant average rectifier", fine with me.

What did I build it for?
For fun, of course
I glued the transducer under a wooden staircase as a "people detector", it was fun to hear the "scuiiic scuiiic scuiiic" made by anybody going up and down.
By the way, up and down can be easily distinguished and after sometime we could even relate noise signature to different people.

And *nobody* could go up or down undetected.

In a nutshell, rather than a multimeter, which will show little if anything at all, something like what I described, installed inside a shoe can give you a believable aural clue as to how it dampens your walking.

Just imagine the shop attendant's faces
  Reply With Quote
Old 6th April 2013, 02:24 AM   #9
diyAudio Member
 
Join Date: Nov 2005
The piezo disk in this application would take a bit of fiddling to work. You'd likely not have great luck with a large diameter part like that used in tweeter drivers. However, the 10 or 12mm parts from PUI Audio, in stock at Digikey, might be workable at making some usable electric output from the direct distortion forces presented to it with some added brass shim material, maybe <=.5mm or so epoxied directly to the original brass disk. Not enough strength in the disk will inevitably lead to fractured piezo material and some level of failure. If you really want to do this, you'd probably be far better off to just get a real accelerometer and go from there.

Sensors, Transducers | Accelerometers | DigiKey
  Reply With Quote
Old 6th April 2013, 02:32 AM   #10
Ron E is offline Ron E  United States
diyAudio Member
 
Ron E's Avatar
 
Join Date: Jun 2002
Location: USA, MN
I have had foot pain in the past. I found out that arch support is a cure. My favorite shoes nowadays are these:
Amazon.com: Hi-Tec Men's Altitude IV Hiking Boot: Shoes
Amazon.com: timberland hiking: Shoes

...although I think the older versions had better arch support:
__________________
Our species needs, and deserves, a citizenry with minds wide awake and a basic understanding of how the world works. --Carl Sagan
Armaments, universal debt, and planned obsolescence--those are the three pillars of Western prosperity. Aldous Huxley
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
How to make a good transformer for ribbon tweeter? pecamuzicar Planars & Exotics 146 14th September 2014 05:48 PM
Would a piezo disk from a Motorola tweeter make a good strain guage? kelticwizard Everything Else 4 7th April 2013 02:33 AM
Output transformer in reverse to drive a piezo disk haakok Analog Line Level 0 6th May 2011 11:51 AM
Motorola Piezo HF any good? rotaspec Multi-Way 5 13th December 2009 10:17 PM
4" Seas long throw woofs, Motorola piezo compression drives, TangBand 2" widebands mr_ro_co Swap Meet 4 15th April 2008 01:16 AM


New To Site? Need Help?

All times are GMT. The time now is 01:45 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2