Conductive Rubber Cord Stretch Sensor + extras!SEN-CRUB
Measuring stretch forces isn't easy - unless you have some conductive rubber cord! This cord is 2mm diameter andmade of carbon-black impregnated rubber. Usually this material is used for EMF gasketing, but its also very fun to play with.
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 linearly. 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.
Please note: The length of the rubber band varies a lot in the batch we have on sale. Depending on your luck, you will get a piece between 85 cm to 115 cm.
You will also get two alligator clips (to connect to the cord) and a 10K resistor. Together, you can use these to make a simple voltage divider.
Some notes on the use of this sensor:
- Please see the graph pictures above to see how the sensor reacts
- There is a quite large spike in the values when the tension released, and a long decay time when the rubber band settles to its original state
- The initial values from the sensor might seem very jumpy and random. Therefore, it is recommended to condition the sensor before use to get more reliable readings. You can do it like this:
- Connect the sensor to your circuit (a simple voltage divider will work)
- Stretch the sensor back and forth with varying speeds. Stretch it to about 50-70% longer than the resting length.
- The readings should be quite stable after a few minutes
- Some smoothing in the values is recommended
- With the Arduino's 10bit ADC and a simple voltage divider, you will get a usable resolution of about 50 steps. (tested with a 10 cm piece of the rubber band)