Does such a stretch sensor exist?

Hey,
I'm currently prototyping for a device I'm trying to make, and it requires relatively precise and accurate readings of stretch.
My question is: is there such a thing on the market right now? I know there are stretch sensors available but some vary in resistance per batch and have either low accuracy, precision or both.

I need a stretch sensor that is reliable, consistent, and most importantly- one that won't tear and lose functionality with continued use.

There is currently a product called stretch sense available right now, but it is very expensive and way beyond my budget (the initial kit is $700 for 2 stretch sensors).

If anyone knows of a stretch sensor that fits some or even any of these specifications (durability and affordability would be the most important!), I would appreciate any recommendations!!

Thanks!
John

Define "stretch", and give us an idea of your required parameters. You mention accuracy, precision, and cost, but they are all relative to your needs and budget.

I mean a stretch sensor as in a sensor that changes in resistance depending upon how much it is stretched.
An example product would be this one:

I am essentially looking for a sensor that is decently stretchy (kinda) like lycra and able to be incorporated into fabric. These sensors should be sensitive enough to be able to detect at least a 10% stretch in the fabric. I am not to familiarized on the specific resistances and such, because I am sure it depends upon the material used. As long as it is sensitive enough to be measured at 10% stretch, then it is good enough for my purposes.

Regarding cost, Each of the units that I plan to construct will require approximately 4 ~4" stretches of the sensor, so ideally each sensor shouldn't cost more than $15.

If there is no such thing, references to construct my own sensors would also be very helpful!!

Thanks pantaz,
John

Still not very defined.

These sensors should be sensitive enough to be able to detect at least a 10% stretch in the fabric.

So is the minimum stretch you want to measure 10%, that is to measure the stretch in units of 10%?
Or do you want a total stretch of 10% and be able to measure that in say 1024 unit resolution.

What is wrong with that conductive rubber you linked to?

Hi,
I know it is an Instructable, but it has surprisingly so interesting information.

Tom… :slight_smile:
google stretch sensor fabric

@Grumpy_Mike

I mean 10% stretch as in I want to be able to detect a notable change in resistance after the material is stretched only 10% of its length.
And regarding the conductive rubber, it states in the product description that its set of resistances often changes per batch, while I am looking for consistency. Although, I have already bought a sample to test it out so I'll let you know if it works out in the end!

although something that could be knit into fabric like lycra would also be much more convenient.

@tomgeorge
thanks for the link, I'll definitely check it out!

John

If the sensor does everything you want except it needs to be calibrated once in its lifetime, is that bad? The beauty of using a programmable microcontroller like the Arduino is you can write a program to do the calibration for you.

If it is just the zero that needs calibration, then have the Arduino look for a long period of inactivity. Then the thing is probably not in use and that is the zero reading.

If you want a factory calibration, have it store the calibration in EEPROM. The first time it is powered up in your factory the EEPROM is empty. It can assume it is on the first test point and then you stretch it over another test unit and it can calibrate the second point.

jyams77:
@tomgeorge thanks for the link, I'll definitely check it out!

John

And, don't forget to check out the 391,000 hits from the google search he suggested. I suspect the answer(s) to your question(s) can be found there.... :wink:

TomGeorge:
Hi,
I know it is an Instructable, but it has surprisingly so interesting information.

Thank Tom, ( +1 ) yes that was a surprise. I have some of the conducting thread but it does roughen and make sore your hands when you are trying to stitch with it but putting it with an other thread might solve this.

@MorganS - Yes I quite agree with the calibration stuff. The only thing I found with the conductive rubber is the change in resistance was not so great when stretching it over the range I felt if could cope with. If I were to use that then I suspect you would have to have an op-amp in the circuit as well.