Would a piezo disk from a Motorola tweeter make a good strain guage? - Page 2 - diyAudio
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Old 6th April 2013, 03:01 AM   #11
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Default Try an accelerometer

You might want to try a one- (or three-) axis accelerometer chip, that is designed to measure G forces. If I recall Analog Devices makes a number of different versions, with various levels of sensitivity. Tie it in with a PIC controller and a memory chip, and you'll have a little item that will log your impacts (and number of steps) and download that info to a PC afterwards. I think there are non-DIYaudio threads on the internet that will guide you in the right direction. I had built (and programmed) one several years ago, to measure G-forces in a racecar I had designed. (Provided me with a lot of interesting data, regarding car suspension and chassis tuning). Good luck.
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Old 6th April 2013, 03:40 AM   #12
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Hi,
I think this will do what you want. Also they have the amplifier. Here it is the link:https://www.sparkfun.com/categories/143
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Old 6th April 2013, 04:46 AM   #13
Johno is offline Johno  Australia
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Remember the 80's when 'bio-feedback' was a fad?
Back then I was working in rehabilitation engineering for brain injured children - one idea was to train hemiplegic cerebral palsy individuals to walk efficiently on their affected side with some audible feedback representing the amount of weight they put into their heel as part of the desired heel-toe gait.

The transducer was simply some semi-closed cell foam about 5mm thick with thin copper (or aluminium) foil top and bottom in a shaped, sealed envelope. It was used as a variable capacitor. Capacitance increases with the inverse of the average distance between its plates.

The capacitor was part of a simple RC oscillator (LM555 or similar) feeding some bcd counters etc and set to beep in real time when a certain frequency (proportional to the weight applied) was reached. Within reasonable limits the calibration to weight applied was repeatable and stable.

The process actually worked and my results are published in the Archives of Physical Medicine and Rehabilitation, a peer review medical journal of NY, for what it is worth.
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Old 6th April 2013, 08:12 AM   #14
JMFahey is offline JMFahey  Argentina
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^^^^^^^ Wow !!!
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Old 6th April 2013, 09:18 AM   #15
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My initial reaction on reading this was to rip a piezo out of one of those greeting cards that records and plays back a message.

To capture the data accurately enough, I'd probably attempt recording the output as an audio stream into a decent DAW software on a laptop, so you can analyse the waveforms created (though there should be simple free analysis software available, the interesting thing to do would be balance a 'step' in each shoe so you the output wave effectively shows you a typical force/time distribution for equal magnitudes of energy transfer)

Johno's suggestion however is probably several leagues ahead of my own.

Alternatively, you could just trust your body to tell you which is more comfortable, ultimately, as an engineer that would be my final test and benchmark, the testing would just be done to achieve the desired result
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Old 6th April 2013, 09:33 AM   #16
Johno is offline Johno  Australia
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Thanks, (JMFahey) but that is not the point - a piezo device has a dynamic range of micro metres but on a human scale (or foot) is completely mismatched. A foot needs something soft and pliable not rigid and unyielding.

Some of the alternatives we also explored were pressure sensitive conductive polymers, but I am not sure if these still exist. (there was a US source looking for an application at the time and I think these ended up as tactile touch points in robotics). Another of our failed ideas was a fluid filled rubber sack with real strain gauges attached and these were just too soft and would not calibrate.
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Old 6th April 2013, 07:53 PM   #17
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Piezoelectricity from rain water
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Old 6th April 2013, 11:51 PM   #18
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I think that can meet your needs if you get a Film Pressure Sensor like this.Click the image to open in full size.
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Old 7th April 2013, 02:04 AM   #19
DUG is offline DUG  Canada
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A strain gauge will measure how much you bend it.

You really need an accelerometer to measure shock.

Something like these:

Sensors, Transducers | Accelerometers | DigiKey

Interesting project.
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Old 7th April 2013, 02:30 AM   #20
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Hi,
I think this is what your are looking. It will work up to 7000lb with just some modification like adding an op amp. Just follow their instructions and a voltmeter. I hoped you do not weight 7000lb.
here it is the link: http://www.tekscan.com/pdf/A401-force-sensor.pdf
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