Stretch sensor

Before we start the development of Home Apnea Monitor using stretch sensor, there are some study with previous work and present work. Then also do the analysis about the stretch sensor, vibration motor, microcontroller (PIC), and also study about the hardware to known their characteristic, function, and all circuit with related.

1. Stretch sensor 

This is a stretch sensor. As you can see in the picture, when the rubber is stretched, the light becomes brighter. It can also be made to work in reverse, as the rubber stretches the bulb can dim.

Imagine pulling a rubber cord and causing the lights in your room to dim. That is an example of how this material can be applied. Or imagine weaving this onto fabrics to sense if the material is stretching. This sensor allows you to measure how stretched something is,it even works bent around corners.

The material itself is a synthetic rubber. It conducts electricity because of integrated conductive carbon particles. When stretched, the spacing between these particles increases, causing the conductivity to decrease. The decrease in conductivity can be measured or observed visually with some simple electronics, like a light bulb.

Measuring stretch forces isn't easy - unless you have some conductive rubber cord! This cord is 2mm diameter, and 1 meter long, made of carbon-black impregnated rubber. Usually this material is used for EMF gasketing, but it’s also very fun to play with. ^[5]

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 it’s not very 'fast' and it takes a minute or two to revert to its original length. ^[6]

Some ideas for applications:
• Virtual-reality body suits
• Monitor your breathing by wrapping a strap of this material around your chest
• Monitor contractions during childbirth
• Interactive art displays
• Security systems