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'[PICLIST] [EE] Pressure/Mass sensor pad/mats'
2001\04\01@043852 by Jean-Michel Howland

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Hi all.

I need to to measure weight or to be more precise, measure if weight is
present or not in the rangeo of 0 to 100kgs.  I really need some sort of
flexible mat/pad that can be slipped under a cushion.

Does anything like this exist?

---
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(($h>>=8)+=$f+(~$g&$t))for@a[128..$#a]}print+x"C*",@a}';s/x/pack+/g;eval

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2001\04\01@081310 by Roman Black

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Jean-Michel Howland wrote:
>
> Hi all.
>
> I need to to measure weight or to be more precise, measure if weight is
> present or not in the rangeo of 0 to 100kgs.  I really need some sort of
> flexible mat/pad that can be slipped under a cushion.


With the intent of keeping it cheap and sensible I
suggest buying a digital bathroom scales, quite common
now, and they have all the hardware needed to measure
weight in that range. You could interface to the PIC
with little hassle.

"slipping under a cushion" sounds difficult as it is
hard to measure weight unless the person is stationary
and above the sensor. If they are on a lounge or chair
(you said cushion) they may have weight on their feet
or arms.

I'm sure if you explained more about the exact thing
you want to achieve there would be some helpful answers.
-Roman

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2001\04\01@111201 by mervin

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Do a search for a product/company called "Tape Switch" They sell mats and
ribbon tape that is used for that purpose (on/off not measuring amount).
{Original Message removed}

2001\04\01@114932 by Jean-Michel Howland

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>> I need to to measure weight or to be more precise, measure if weight is
>> present or not in the rangeo of 0 to 100kgs.  I really need some sort of
>> flexible mat/pad that can be slipped under a cushion.
>
>
>With the intent of keeping it cheap and sensible I
>suggest buying a digital bathroom scales, quite common
>now, and they have all the hardware needed to measure
>weight in that range. You could interface to the PIC
>with little hassle.
>
>"slipping under a cushion" sounds difficult as it is
>hard to measure weight unless the person is stationary
>and above the sensor. If they are on a lounge or chair
>(you said cushion) they may have weight on their feet
>or arms.
>
>I'm sure if you explained more about the exact thing
>you want to achieve there would be some helpful answers.
>-Roman

OK, good point about explaining more.

Last night I had an accident in my electric wheelchair, I was driving
around and ended up with my front in stuck in a drain hole, I fell forward,
barely able to breathe and was stuck like that for 40 minutes.  I never
want to go through that again so I need a solution.

I thought of of 2 possible solutions:

#1. Build some sort of pendant to wear around my neck that would contain a
tilt sensor, RF transmitter and a timer.  However this would be bulky to
wear because I couldn't build it small enough, battery life would be a
problem and the range would be very small.  In my opinion this is not workable.

#2. Slip a pressure transducer under my cushion and one behind my back,
hook them into a PIC.  If I'm sitting in the chair the unit is activated,
if I fall forward for more than a minute the PIC timesout and activates one
of those 110db alerts which will be heard by the people around my
house.  The advantage is everything can be mounted on and powered from the
chair.

The reason I want to find a mat/pad type of sensor is I'm reluctant to
drill/cut or modify an $8000 chair that I don't own.

Oh and before someone mentions the obvious, a seatbelt, well it's not an
option. :o)

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2001\04\01@122302 by S Bakaletz

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Try http://www.qprox.com

I suggest you try one of their E11x Eval boards (15.00 US).

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2001\04\01@122519 by mervin

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Jean-Michel
Tapeswitch is exactly what you need.
http://www.tapeswitch.com/
Go to their web site, and look at "ribbon switch"  or "safety mats" in their
products section.  I really think the ribbon switch would work best because
of the weight involved, mats are for heavier items I think.
I called them and they sent me a sample.

Malcolm


{Original Message removed}

2001\04\01@142815 by mmucker

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This might not even require a PIC.

Go to a department store and pick up one of those 'massage pillows.'  They
have some kind of pressure sensor in there to turn on the massage motor.
Should be easy enough to 'liberate' this sensor.  (And, as a bonus, you
could add a butt massage switch to your chair! <g>)

A simple 555 timer IC should be all you need to do the 1 minute timeout and
start the screamin' alert.

-Matt

> {Original Message removed}

2001\04\01@143446 by Dale Botkin

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On Sun, 1 Apr 2001, Jean-Michel Howland wrote:

> Hi all.
>
> I need to to measure weight or to be more precise, measure if weight is
> present or not in the rangeo of 0 to 100kgs.  I really need some sort of
> flexible mat/pad that can be slipped under a cushion.
>
> Does anything like this exist?

We called 'em whoopie cushions...  they gave an audible indication  8-)

Sorry, couldn't resist!  Seriously, check out suppliers of security
equipment, they make pressure sensors for carpets, mats etc.

Dale
---
The most exciting phrase to hear in science, the one that heralds new
discoveries, is not "Eureka!" (I found it!) but "That's funny ..."
               -- Isaac Asimov

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2001\04\02@095945 by Roman Black

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Jean-Michel Howland wrote:

> OK, good point about explaining more.
>
> Last night I had an accident in my electric wheelchair, I was driving
> around and ended up with my front in stuck in a drain hole, I fell forward,
> barely able to breathe and was stuck like that for 40 minutes.  I never
> want to go through that again so I need a solution.


Ouch! Sorry to hear about your bad experience.
There have been some good suggestions about pressure
mats like used in alarm systems etc, but maybe you
should also look at getting a pendant button as
well. You can buy these commercially with base
station, popular with the elderly who might fall
down and break a hip etc. I think some have dialers
in the base station so you can ring someone for help
too if needed. :o)
-Roman

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2001\04\02@152127 by Chris Carr

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Jean-Michel Howland wrote:

>I thought of 2 possible solutions:

>#1. Build some sort of pendant to wear around my neck that would contain a
>tilt sensor, RF transmitter and a timer.  However this would be bulky to
>wear because I couldn't build it small enough, battery life would be a
>problem and the range would be very small.  In my opinion this is not
>workable.

Snip

I have been thinking about this and believe I may have a solution by
adapting an existing design of mine.
The pendant or badge can be easily built and would be small, un-powered and
could contain a tilt sensor and/or a switch to trigger off an alarm.
The second part of the design, a separate unit mounted on the wheelchair
could be powered by its battery, this could either set an audible
alarm off or trigger a radio transmitter.

If you are interested, Jean-Michel, contact me off list and we will see if
the idea can be refined into a workable solution.

Regards

Chris

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2001\04\02@170613 by Peter L. Peres

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I don't think that the cushion can be made to work reliably. I think that
you should investigate a non-intrusive addition to the $8000 wheelchair,
like a pair of strain gages (the glue-on kind) attached on some convenient
structural elements in the chair, near the wheel bearings. This will
indicate strain (i.e. weight) on each rear wheel. The analog circuitry
required to read the gages can be built for $20 to $50 in parts (Burr
Brown, Linear Tech, Analog Devices etc all have gage amplifiers). You
could trigger on low weight or imbalance (chair tilted at a serious angle
with you in it, or you hanging out of chair sideways while inconscious
or hurt), and high weight (front wheel(s) not touching ground).

hope this helps,

Peter

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2001\04\02@210046 by mervin

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The reason I am learning to program PICs was originally to make a car anti
theft device.  For that device I needed a switch that could be placed under
the carpet (and even the padding) of the car.  I found a product called Tape
switch that was perfect http://www.tapeswitch.com/ .
You purchase the switch part in rolls and cut to the length needed then
(with PVC glue) glue on the wire lead end and the terminating end.   They
also sell premade lengths.  Pressure upon any portion of the tape makes a
connection (normally open contact switch).  The tape is flexible and
available with sticky back so it can be used on most any surface without
affixing geminately.  And no I don't work for them, I just thought it to be
the perfect solution for the project. If placed on the seat and maybe also
on the back (giving 2 sensing sources) if the person fell or was removed
from the seat the switch would break and start whatever program .  I am a
mechanical engineer and usually have the problem of over designing a
project, but this would make this project ultra simple.  Dare I say it, it
may not even need a PIC.  Maybe just a 555 to wait X time then turn on
something.
{Original Message removed}

2001\04\06@113528 by Shawn Yates

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A company called Curbel already makes a wheel chair monitor.   There are two
basic kinds.  One is just what you describe, a pad you sit on and if you get
up it sets off an alarm (or triggers an output if you hack it right).  The
second is a clip you clip to the back of you clothing and if you get up or
fall forward the clip has a string that pulls a pin out of a device which
triggers an alarm.

If you want more on these let me know I can get you a phone number and part
number from Curbel.

Shawn

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2001\04\06@113942 by Shawn Yates

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> >#1. Build some sort of pendant to wear around my neck that would contain
a
> >tilt sensor, RF transmitter and a timer.  However this would be bulky to
> >wear because I couldn't build it small enough, battery life would be a
> >problem and the range would be very small.  In my opinion this is not
> >workable.


We sell a product that does exactly this.  Its marketed as a duress call for
the elderly, but all it does is trigger a relay on a receiver.  You have to
be withing about 70 feet of the receiver so you could not mount the receiver
in you house, but you could mount it on the chair and then trigger something
else (a cellular phone?)

HTH

Shawn
http://www.caretechnologies.com
(770) 261-7844

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'[PICLIST] [EE] Pressure/Mass sensor pad/mats'
2001\05\07@120607 by John Waters
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Hi mervin/others,

I have interest to use a sensor to detect if a seat is occupied, the "Tape
Switch" seems to be a promising solution, however, I don't want to do any
damage to my chair, so I can only stick the sensor on its surface which may
be a soft cushion. Since the cushion doesn't provide a hard, solid support,
when somebody sits on it, the "Tape Switch" may be bending in irregular
shape, will this be any problem? If the "Tape Switch" is not applicable, is
there any sensor or solution you can think of?

Thanks in advance!

John

{Quote hidden}

>{Original Message removed}

2001\05\07@122013 by Michael C. Reid

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the coolest sensor on the market is manufactured by Sure Action
(800)648-4301  Ask for Austin Stack .  I work for a home automation lighting
control manufacturer and many of our installers use the Sure Action Stress
Sensors.  These are a strain relief type sensors that are epoxied on the
side of, or under a floor or joist. They sense microscopic flexing and
trigger a low voltage relay contact.  They have 2 or 3 sensitivity levels
available for different applications.  I have had clients place them under
steel trusses with 2 inches of concrete on top and they have worked.  You
might have to be creative to get it to work under a chair, but it would work
under the floor where the chair is located.  I have even seen clients put
them on the floor under a toilet to turn the fan on in the bathroom..  Maybe
they could mate the sensor with a "methane detector" to vary the speed of
the fan :)

These sensors have been around for many years and are ultra reliable.  They
were originally developed for the marine industry to protect boats from
intuders.  They will not trigger from wave action moving a dock, but from
weight applied by a person walking on the dock.  One client put them under
the window sills in his teenagers bedrooms to monitor if they were sneaking
in or out of the room via the window!

{Original Message removed}

2001\05\07@164923 by Alexandre Domingos F. Souza

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>I have interest to use a sensor to detect if a seat is occupied, the "Tape
>Switch" seems to be a promising solution, however, I don't want to do any
>damage to my chair, so I can only stick the sensor on its surface which may
>be a soft cushion. Since the cushion doesn't provide a hard, solid support,
>when somebody sits on it, the "Tape Switch" may be bending in irregular
>shape, will this be any problem? If the "Tape Switch" is not applicable, is
>there any sensor or solution you can think of?

       carbonated spounge!!! That spounge that comes with integrated circuits. That one is resistive, when you press it, you see a BIG decrease in it's resistence. If you put it in the A/D of the pic, you can even measure weight!!! I've used it a number of times for car alarms, hehehe :o)

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2001\05\07@180550 by John Waters

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Where to buy? Thanks!

>         carbonated spounge!!! That spounge that comes with integrated
> >circuits. That one is resistive, when you press it, you see a BIG
> >decrease in it's resistence. If you put it in the A/D of the pic, you
> >can even measure weight!!! I've used it a number of times for car
> >alarms, hehehe :o)

_________________________________________________________________________
Get Your Private, Free E-mail from MSN Hotmail at http://www.hotmail.com.

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2001\05\07@191428 by Jinx

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> >  carbonated spounge!!! That spounge that comes with
> integrated circuits. That one is resistive, when you press
> it, you see a BIG

It works, but the problem is that it eventually deforms to the
shape that is pressurising it. I've tried it to make soft switches
and it's OK for a while, but sooner or later it won't bounce
back to the original shape. The polyurethane foam base
breaks down. The conductive black plastic used for IC bags
is better but only in two dimensions (ie like a pot rather than
sqeezed like the foam). You need to cut a strip of it to make
a resistor, a sheet is just a huge array of parallel/series
resistors. A 5mm strip 100mm long is around 100k, but the
closer the two contacts get together the less accurate it is
because of the contact distance v area ratio

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2001\05\09@201239 by miked

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I don't know when or if they wiill be generally available, but CTS got a
contract to make sensors to measure the weight of people in GM vehicle
seats.
> Hi mervin/others,
>
> I have interest to use a sensor to detect if a seat is occupied, the "Tape
> Switch" seems to be a promising solution, however, I don't want to do any
> damage to my chair, so I can only stick the sensor on its surface which may be
> a soft cushion. Since the cushion doesn't provide a hard, solid support, when
> somebody sits on it, the "Tape Switch" may be bending in irregular shape, will
> this be any problem? If the "Tape Switch" is not applicable, is there any
> sensor or solution you can think of?
>
> Thanks in advance!
>
> John

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