Pressure sensor recommendation for amputee

Jonathan

HI All,

A friend of mine recently had the front third of his foot amputated due to diabetes and an infection. He will soon be allowed to bear some weight on his heel but not on the front of what is left of his foot. The trouble is that he has no feeling left and can't tell when he is putting weight where he shouldn't. His wife has asked me to make a device that will alert him when he does to help with retraining him to walk. Any suggestions for an appropriate sensor? I see the flexforce demo kit ( https://www.parallax.com/product/30056 ). Would this work and is it damaged if more than 25 pounds are applied to it?

Thanks!

Phil Pilgrim (PhiPi)

Google insole pressure sensor.

-Phil

Jonathan

Thanks Phil. When he gets back to being able to wear a shoe, that looks like an interesting option. For now though I need something that I can attach to his bandage/brace.

Beau Schwabe

In prosthetics, my experience with using TeckScan sensors is that the sensors delaminated very easily with sheer stress inside of the shoe. Also the slightest kink or fold in the sensor causes a false reading or caused the sensor to be inoperable.

While in prosthetics, we developed our own sensor that would last orders of magnitude longer which consisted of nothing more than a printed circuit coil on a flexible circuit board. The sensor was constructed using a metal foil separated from the coil with a neoprene foam barrier. At the time (1995) we contacted a company that makes flexible printer ribbon cable to make the flexible circuit board. Reading the coil was done in the same way a PI metal detector works. Pulse the coil, and then measure the energy response. This was done with a current mirror charging a cap, and then an ADC reading the cap before discharging the cap. This method is faster than allowing the coil to resonate and then measure/count then number of pulses withing a known amount of time. All of my links on the Parallax sight and the OBEX seem to be broken, but I had a Propeller version using the PI method in the OBEX. Perhaps someone can dig it up.

https://patents.google.com/patent/US6500210B1/en?inventor=Schwabe&oq=Schwabe

Publison

Beau,
This may be the file:

http://obex.parallax.com/object/780

All your files can be found in OBEX under the author "Parallax Inc".

Beau Schwabe

Publison,

Yes, I think that is the file... it uses the system clock to perform the ADC, but the original circuit used in the referenced patent above just read from a discrete ADC.

"All your files can be found in OBEX under the author "Parallax Inc"" - Perhaps, but the links to all of the web content are all broken. Thanks anyway.

Jonathan

Thanks Beau and Publison. I just spoke to his wife and at this point I don't think we need anything that fancy. When we get to him re-learning to walk I think we will. Right now the Doc says no weight at all. So a simple switch would even work for starters. I have been noodling around but can't seem to find the right search term for a simple pressure switch encapsulated in a little bubble or something like that.

Publison

Beau Schwabe wrote: »

Publison,

Perhaps, but the links to all of the web content are all broken. Thanks anyway.

I hate that I do not have permission to fix links. It bugs me also.

T Chap

I recently experimented with a load cell and HX711 breakout board. This was very easy to set up and measure pressure. You could have something running in a few hours. You can set a threshold for a certain pressure. A piezo switch is an alternative.

potatohead

https://goo.gl/images/fw4vBN

One of those may work. Just attach something to the lever that is big.

kwinn

Google metal dome switches. One or more switches in parallel should do what you need.