Concept Design

We started out by trying to answer a basic question-

   Could a strain gage be senstive enough to detect motion from breathing alone?  In order to test this original concept, we attached a strain gage to a air mattress that Colby happened to have.  After some careful application with super glue, we tested the connectivity on a Digital Multimeter

The team doing some "heavy breathing" simulation

Overall, the device did seem to function, but it wasn't quite as sensitive as we would have liked to see.  However, this did help set the tone for the remainder of the project.  We began to realize that perhaps a matress pad wasn't necessarily the best Idea.

 Moving Forward

After we tested this device, the team agreeded that we'd need more exact measurements as to how much force downard we would expect to see.  This lead to the development of the model that attached a water collumn to the same air mattress.  We once again found this functional, however the percentage change of the total range was insignificant, and hard to change.

So, to put the design to rest, so to speak, we borrowed the scales at the local recycling center.  We found that we'd notice about a 1/10th of a pound change during breathing of an adult human - a significant amount.

Another Design - Inductive Elastic

At the sleep center at Gritman Hospital in Moscow, ID, we found that they used piezoelectic crystals in straps in order to detect the length of someone's chest.  However, we found that these devices were rather expensive.  So, a cheap alternative was found - weaving an inductor into elastic.

This rather simplistic design involves measuring a changing inductance due to a changing length strap.  More detail on this can be found in following pages.