Measuring stretch forces can be a real challenge, but not when you have this conductive rubber cord! The cord has a 2mm diameter and is 1 meter long. It's made of carbon - black impregnated rubber, typically used for EMF gasketing, but it's also super fun to experiment with. In its relaxed state, the resistance is about 350 ohms per inch. When you stretch it, the resistance goes up as the particles in the rubber move further apart. For example, a 6 - foot piece has a resistance of about 2.1 Kohms. Stretch it to 10 feet, and the resistance becomes 3.5 Kohms. You can stretch the rubber 50 - 70% longer than its resting length, so a 6 - foot piece shouldn't go beyond 10 feet. Once you release the force, the rubber will shrink back, though it's a bit slow and takes a couple of minutes to return to its original length. It's not a perfectly precise linear sensor, and the resistance can vary from batch to batch. But it's a great way to measure stretching motion. We'll give you a full meter of the cord, two alligator clips to connect to the cord, and a 10K resistor. With these, you can build a simple voltage divider. Then, use our Thermistor tutorial to measure the analog voltage and convert it back to resistance.
Using this conductive rubber cord stretch sensor is easy. First, take the alligator clips and connect them to the ends of the cord. Then, use the 10K resistor to build a simple voltage divider. You can find a detailed guide in our Thermistor tutorial to measure the analog voltage and figure out the resistance. When using the cord, don't stretch it more than 50 - 70% of its resting length. For example, if it's 6 feet long at rest, don't stretch it beyond 10 feet. After stretching, just let go and wait a couple of minutes for it to shrink back to its original length. As for maintenance, keep it in a dry place at normal room temperature. Since the resistance can vary from batch to batch, don't expect super - precise measurements every time. Have fun experimenting with it!
