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Conductive Rubber Cord Resistance clues
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Conductive Rubber Cord Resistance clues

by ale_bellaz on Mon Sep 16, 2019 5:29 am

Good morning,

can you please give me some clues about the characteristics between resistance variation and lenght variation of the conductive rubber cord? As I saw from some measurements not only it is not linear but also presents histeresis.

Thank you

ale_bellaz
 
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Re: Conductive Rubber Cord Resistance clues

by adafruit_support_bill on Sun Sep 22, 2019 6:43 am

The cord is not specifically designed to be a stretch sensor, so the resistance characteristics of do vary from batch to batch.

The product description gives describes 'typical' response. But for best results, you should calibrate it in place on your project.

https://www.adafruit.com/product/519
In a 'relaxed' state, the resistance is about 350 ohms per inch. As you pull on it, the resistance increases (the particles get further apart). As you stretch it out, the resistance increases. So lets say you have a 6" piece - thats about 2.1 Kohms. Stretch it to 10" long and now it is 10"/6"*2.1K = 3.5 Kohms. You can stretch the rubber about 50-70% longer than the resting length, so a 6" piece shouldn't be stretched more than 10". Once the force is released, the rubber will shrink back, although its not very 'fast' and it takes a minute or two to revert to its original length. It's not a true linear sensor, and the resistance may vary from batch to batch, so we consider it a way to measure stretching motion but isn't really precise.

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