Advice on a "stretch" sensor

[Thot]

I am planning to make a breathing sensor (to check for breathing movements)
by strapping an elastic band around the chest and attaching a "stretch
sensor" to it that varies its characteruistics, such as resistence,
according to how much it is stretched and then recoils when the patient
exhales . I think somethig like that must exist as it should be something
like a modified potentiometer. But I don't know its name or where to find
one with the characteristics I need.

Can somebody point me in the right direction?

Thanks

Luca

 

[John Popelish]

I am planning to make a breathing sensor (to check for breathing movements)
by strapping an elastic band around the chest and attaching a "stretch
sensor" to it that varies its characteruistics, such as resistence,
according to how much it is stretched and then recoils when the patient
exhales . I think somethig like that must exist as it should be something
like a modified potentiometer. But I don't know its name or where to find
one with the characteristics I need.

Can somebody point me in the right direction?

Thanks

Luca

There is such a thing as a string potentiometer (a rotary
potentiometer, turned by an unwinding string, and the string under
tension from a rewind spring).

http://www.corsa-inst.com/sensorsez/sp10ez.html
http://www.spaceagecontrol.com/

But, in this case, the range is so small that I think you could use a
linear potentiometer with a spring preload. You might be able to
adapt a slide pot used in audio balance controls.
http://www.abra-electronics.com/catalog/potentiometers/p1k_sl_pc.html

The precision ones made for long term motion are kind of expensive:
http://www.etisystems.com/linearselect.asp

Maybe you can come up with something based on variable overlap of two
insulated plates to form a capacitor that varies as the wearer breaths.

 

[Roger Johansson]

Maybe you can come up with something based on variable overlap of two
insulated plates to form a capacitor that varies as the wearer
breaths.

Another idea:

Use black antistatic foam, the kind chips are pushed into to keep the
legs at the same potential.

Put a few such foam pads between two metal plates, the plates can be
unetched clean copper pcb material.

When this sensor is pressed together the resistance through the foam
will decrease.

Tie a rope around the chest of the person under test, put the sensor
between the rope and the chest.

When air is drawn in the chest is getting bigger, pressing the sensor
harder together, the resistance between the plates is decreasing.

Such foam can be used for many other sensor tasks, like put it under a
mat to indicate when people walk on it.

 

[John Smith]

I am planning to make a breathing sensor (to check for breathing movements)
by strapping an elastic band around the chest and attaching a "stretch
sensor" to it that varies its characteruistics, such as resistence,
according to how much it is stretched and then recoils when the patient
exhales . I think somethig like that must exist as it should be something
like a modified potentiometer. But I don't know its name or where to find
one with the characteristics I need.

Can somebody point me in the right direction?

Thanks

Luca

"Rope around their chest". I thought the Spanish Inquisition had ended?

Anyway... my idea is a strain guage.

 

[Z80]

Hi Luca
Stretch sensors are sold by this company - (It is in the UK)
http://merlinsystemscorp.com/live/518.0.html