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'[EE]: thin weight sensor'
2003\02\04@184923 by Patrik Husfloen

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I'm looking for some kind of sensor that will let me measure weight, the
problem is it can only be about 5mm thick. I don't need much resolution
5kg should do nicely, 10kg might also work.
The range would be something like 10kg to 100kg.


any help would be greatly apriciated,

Patrik

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2003\02\04@192002 by Des Bromilow

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HTH,
I don't know if it's premade, or if you'll have to make it yourself, but a piezo sensor MAY do the trick.
The FORCE on the faces of the piezo is directly related to the voltage across the other faces.
Perhaps you could scrap a piezo element out of a BBQ starter and reduce the supporting structures down to the 5mm thickness and move from there.
You MAY need to add some damping, or something to reduce high voltages from shock loads. (mechanical damping, or some sort of voltage clamping cct.

Does the thin peizo speaker (the one that looks like two pieces of metal concentrically stuck together) have a piezo element? Perhaps that would be easier to alter to suit?


other techniques....
capacitive methods (may need some mechanical advantage added
pressure methods (a closed bladder/ vessel? with a pipe coming out to a more accessable area - terminated with a ported pressure sensor (liquid or air depending upon fabrication method, spill risk etc) - interface the pressure sensor to an amplifier, ADC and "bob's your uncle")

Thanks,
Des

>>> .....pathu440KILLspamspam@spam@STUDENT.LIU.SE 5/02/03 9:47:55 am >>>
I'm looking for some kind of sensor that will let me measure weight, the
problem is it can only be about 5mm thick. I don't need much resolution
5kg should do nicely, 10kg might also work.
The range would be something like 10kg to 100kg.


any help would be greatly apriciated,

Patrik

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2003\02\04@192621 by PicDude

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Take a look at sensors for weighing race cars -- they are
usually pretty thin and use one sensor per wheel.  You'll
have to do some research to see who makes the actual sensor
element though.

Cheers,
-Neil.



> {Original Message removed}

2003\02\05@075119 by Olin Lathrop

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> The FORCE on the faces of the piezo is directly related
> to the voltage across the other faces.

Not exactly.  The voltage from a piezo sensor is directly related to the
rate of change deformation.  This means piezo sensors are useless for
measuring static or absolute forces.


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(978) 742-9014, http://www.embedinc.com

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2003\02\05@084223 by Dave Tweed

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Olin Lathrop <olin_piclistspamspam_OUTEMBEDINC.COM> wrote:
> > The FORCE on the faces of the piezo is directly related
> > to the voltage across the other faces.
>
> Not exactly.  The voltage from a piezo sensor is directly related to
> the rate of change deformation.  This means piezo sensors are useless
> for measuring static or absolute forces.

Not quite. The amount of charge movement is proportional to the force.
The amount of current is proprotional to the rate of change.

If you had a very high impedance input buffer, the voltage across
the piezo would be proportional to the force. However, if you run
the current through an external load resistance, the voltage you
see there is proportional to the rate of change.

Think about the reverse: If you apply a DC voltage, you get a
constant change in force/shape of the piezo.

Anyway, to answer the OP's question, there are many varieties of
strain gauge based load cells that meet his dimensional requirements.
A quick search should turn up several. They can't be too expensive if
they're used in kitchen and bathroom scales.

-- Dave Tweed

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2003\02\05@094050 by Olin Lathrop

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> Not quite. The amount of charge movement is proportional to the force.
> The amount of current is proprotional to the rate of change.

Right.  The charge only moves once as the load is changed.

> If you had a very high impedance input buffer, the voltage across
> the piezo would be proportional to the force.

Yes, because you are integrating the charge.

Looking back I was a little sloppy in my original statement, but I think
we are basically agreeing.  The end result is the same, a piezo sensor is
not useful for absolute static measurements because the integrator initial
value is unknown, and any real physical components will have leakage.
With any real circuit, there will be a frequency below which a piezo
sensor is not useful.


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(978) 742-9014, http://www.embedinc.com

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2003\02\05@142249 by M. Adam Davis

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If you'd like to roll your own, get stiff conductive foam (such as is
used to package semiconductors), place a thin aluminum or other
conductive plate on top and bottom, and measure the resistance between
the two plates.

It's crude, and has to be calibrated infrequently, but it'll work for a
quick-n-dirty prototype.

-Adam

Patrik Husfloen wrote:

{Quote hidden}

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2003\02\05@200654 by Peter L. Peres

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On Wed, 5 Feb 2003, Patrik Husfloen wrote:

*>I'm looking for some kind of sensor that will let me measure weight, the
*>problem is it can only be about 5mm thick. I don't need much resolution
*>5kg should do nicely, 10kg might also work.
*>The range would be something like 10kg to 100kg.

What size ? A flat balloon with a MPX pressure sensor sandwiched between
two rigid boards with pin guides is one of the things I'd try. There are
strain gages thinner than that but making the mount will be interesting.

Peter

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2003\02\05@205723 by Patrik Husfloen

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Instead of going down this one track that I decided was the right way,
probably wrongly so. I will state my goal as I should've done from the
beginning, I apologize for not doing so.

This is purely a for-fun project and is not to be taken too seriously.
The idea is that you somehow can detect the presence of someone in a bed
(specifically, me, in my bed, at 6 am in the morning) and use this as an
input to an alarmclock, which would not stop ringing until the subject
crawled out of bed, and stayed out.

I have a _very_ hard time getting out of bed in the morning and I
somehow manage to turn off my alarm (which is in another room) and go
back to bed without waking up.

The idea I was going for was one where you would weigh the bed, or one
of it's legs,  but it might not be the optimal solution.


/Patrik



Peter L. Peres wrote:
{Quote hidden}

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2003\02\05@212924 by Jonathan Johnson

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In that case why don't you use a piezo sensor as a microphone input, it will
detect your breathing and movements on the bed. either that or use some sort
of vibration sensor to pick up your movements. there are baby monitors that
work on this principle.....sleep angel I think one is called, its used to
pick up when a child stops breathing to prevent cot death, there would be
some thing similar around for sleep apnoea, I knew someone years ago that
had it, from memory he had something like this.

cheers

JJ
{Original Message removed}

2003\02\05@213122 by Josh Koffman

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How about an infrared beam that shoots across the top of your bed?

Josh
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Patrik Husfloen wrote:
> The idea I was going for was one where you would weigh the bed, or one
> of it's legs,  but it might not be the optimal solution.

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2003\02\05@213549 by Jonathan Johnson

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or ultrasonic looking down from your ceiling onto you and checking your
motion to detect you.....sort of like a radar set-up

JJ
{Original Message removed}

2003\02\05@213747 by Tom Messenger

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At 02:56 AM 2/6/03 +0100, you wrote:
>
>I have a _very_ hard time getting out of bed in the morning and I
>somehow manage to turn off my alarm (which is in another room) and go
>back to bed without waking up.
>
>The idea I was going for was one where you would weigh the bed, or one
>of it's legs,  but it might not be the optimal solution.
>
>/Patrik

Patrik,

When <much> younger, I had a similar problem.  I set my alarm clock radio
to turn on an AC outlet. My stereo was plugged into this outlet. The stereo
was set to a rock-n-roll FM station at nearly full volume.

In the morning, sound asleep, I would become aware of the tiny *click* of
the clock mechanism switching on. In about 150 milliseconds, I would throw
back the sheets and blankets, leap out and down the length of the bed, take
one giant leap across the floor and whip the volume control on the stereo
down to nearly zero JUST as the power supply in the stereo was comming up
sufficiently high enough to start pumping horrible rock-n-roll noise into
the room.

At that point, it took about another 150 milliseconds to jump back into
bed, pull the covers over my head and NOT EVEN BE AWARE I HAD DONE SO.
Later my parents would come in and say "Didn't your alarm go off this
morning?"

My solution: Move out from home, pay my own way in life, get a life. It
actually worked for me.

Laughing all the way,
Tom M.

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2003\02\05@224729 by PicDude

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Okay, I admittedly have this problem occassionally as
I'm a deep sleeper.  My thought was to have a remote
alarm-off switch mounted on the other side of the
room, etc.

Cheers,
-Neil.



> {Original Message removed}

2003\02\05@225801 by cdb

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What really seems to be required here is a PIC controlled contraption as featured in Wallace and Gromit 'The Wrong Trousers'

Why not a variation of the water probe technique? Two electrodes that conduct from either the presence of dampness or from being shorted together make a circuit that is detected by some electronics.

Or those capacitive sensors that someone mentioned recently, they work as a proximity sensor through material as thick as glass.

Colin
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2003\02\05@231011 by Jinx

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> What really seems to be required here is a PIC controlled
> contraption as featured in Wallace and Gromit 'The Wrong
> Trousers'
>
> Why not a variation of the water probe technique? Two electrodes
> that conduct from either the presence of dampness or from being
> shorted together make a circuit that is detected by some electronics.

> Colin

I just KNEW you'd have soggy strides Colin ;-)

=============================

How about a temperature sensor ? Use two to compensate
for ambient

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2003\02\05@235606 by Peter L. Peres

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Well, the alarm clock is useless, try a fog horn (the kind with compressed
air). For your application you can easily assume that weighing one leg of
the bed is enough and use a simple spring and microswitch. A deflated auto
inner tyre folded several times could act as spring I think. To make sure
of success I would use a device that tosses you out of bed by lifting one
side until it's at 45 degrees angle although there is no guarantee that
this will work either ...

Peter

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2003\02\06@010510 by Jake Anderson

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look up "aura interactor" jaycar in Australia sells the drivers for them for
about $10 or so
(they are like backpack sized sub-sub-sub woofers with weights instead of
speakers so that when your computer game/movie makes the explosion/thwack
sound the speaker thing "rumbles" "just like you are there" if you believe
their literature.)
stick a couple of dozen of those on your bed it'll either wake you up by
being violently shaken or alternately give you a nice relaxing massage type
vibration. Either way you win. Hmmm now you got me thinking ;->

the other cheaper option is go to bed earlier and just get the amount of
sleep your body tells you it needs.
(a good 14 to 16 hours seems to work for some mammals)

hmmm spell check has the word "thwack" in it. Does the fact I find that
exciting mean my life is dull?
{Original Message removed}

2003\02\06@010525 by Jonathan Johnson

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and don't forget the flyback transformer tazer across your big toes ;-/ THAT
should wake you up!

JJ
{Original Message removed}

2003\02\06@010534 by Roman Black

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Peter L. Peres wrote:
> To make sure
> of success I would use a device that tosses you out of bed by lifting one
> side until it's at 45 degrees angle although there is no guarantee that
> this will work either ...


I second that, maybe a 12v car winch mounted up on
the wall, lifting the bed to a tilt of 60' or more.
And maybe a car ignition coil attached to the metal
bedsprings for that extra "good morning" jolt. ;o)
-Roman

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2003\02\06@011544 by Jonathan Johnson

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----- Original Message -----
From: "Jake Anderson" <grooveeeSTOPspamspamspam_OUTOPTUSHOME.COM.AU>
To: <spamBeGonePICLISTSTOPspamspamEraseMEMITVMA.MIT.EDU>
Sent: Thursday, February 06, 2003 3:25 PM
Subject: Re: [EE]: thin weight sensor


>
> hmmm spell check has the word "thwack" in it. Does the fact I find that
> exciting mean my life is dull?



LOL
well.......my mobile phone's built in dictionary now knows how to use many
'colourful metaphors' :-) after being in my company for some time. :-)

JJ

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2003\02\06@022504 by William Chops Westfield

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> I have a _very_ hard time getting out of bed in the morning and I
> somehow manage to turn off my alarm (which is in another room) and go
> back to bed without waking up.

Heh.  Been there, done that.  except that I noticably woke up.  One or
more times back in college, I managed to wake up every 10 minutes, walk
across the room, hit the snooze alarm on the clock, decide that I really
wanted to go back to bed, and went back to sleep.  For three hours...

One thing I've done that has helped, as an adult, is to get one of those
timer-controlled thermostats.  Now, the heat goes on (up) rather before
it's time to wake up, and there is less motivation to crawl back under
the covers.

BillW

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2003\02\06@035619 by Ian McLean

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I was going to post the idea of putting an ignition coil across your toes -
but didn't because I thought it a bit silly - maybe I should have gotten in
first with the idea after all !

{Original Message removed}

2003\02\06@084729 by Patrik Husfloen

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It didn't work for me, I guess working from 1pm-9pm doesn't exactly
promote a good sleeping schedule either :/
Someone mentioned that going to bed earlier might help, it might, but it
doesn't, I've tried.

Lots of interesting ideas on the list though :)

Thanks,
Patrik

Tom Messenger wrote:
> My solution: Move out from home, pay my own way in life, get a life. It
> actually worked for me.

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2003\02\06@094606 by llile

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At one time I had an alarm clock which was named "Gabriel", for its
legendary horn announcing the end of the world.  It was hacked out of an
alarm panel from a hazardous waste tank farm.  Built inside a Nema 12
raintight box, it sported a 150 watt light bulb on top, and a honker that
could be heard across a 40 acre tank farm.  I kept it across the room. The
light bulb would come on first, then a few seconds later the honker would
begin its earsplitting cacophony.  The idea was that the sleeper would so
abhor the honking, as to be willing to get out of bed to disable the thing
once the light went on.  Worked most of the time.  Nobody slept through
it, at least.

-- Lawrence Lile





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02/05/2003 08:31 PM
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       Subject:        Re: [EE]: thin weight sensor


Well, the alarm clock is useless, try a fog horn (the kind with compressed
air). For your application you can easily assume that weighing one leg of
the bed is enough and use a simple spring and microswitch. A deflated auto
inner tyre folded several times could act as spring I think. To make sure
of success I would use a device that tosses you out of bed by lifting one
side until it's at 45 degrees angle although there is no guarantee that
this will work either ...

Peter

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2003\02\06@113920 by William Chops Westfield

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>    At one time I had an alarm clock which was named "Gabriel", for its
>    legendary horn announcing the end of the world.

I've got a 4-y old daughter named Gabrielle.  Works about the same way...

"louder alarms" only work if in fact the person is not waking up.  Since
in fact the circumstances involve going into another room to turn off the
alarm, and then returning to bed, the problem is slightly different, and I
claim that arbitrarilly loud alarms will simply be adapted to.  (Hmm.  In
fact, it might be that a clock radio, modified to start SOFTLY and
gradually increase in volume, might be more effective.  The idea is to
engage the brain before it gets sufficiently annoyed to elminate the
stimulus.)

"people" tend to think the difference beween "morning people" and "night
people" is just a matter of when you wake up and go to sleep, and ought
to be easy to switch just by changing hours.  *I* think it has a lot more
to do with whether you have an easy time making the transitions.  It can
take me hours to get to sleep at night, and hours to wake up in the
morning.  Much better to stay awake till I'm very tired, and get up when
I wake up naturally...  Unfortunately, reality tends to interfere.

BillW

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2003\02\06@135935 by Ian McLean

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I for one write my best code between the hours of 1 and 3 in the morning,
and I know I am not alone here ...
I think it is something to do with lack of distractions.


{Original Message removed}

2003\02\06@145151 by PicDude

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Ian McLean mumbled:
>
> I for one write my best code between the hours of 1 and 3 in the morning,
> and I know I am not alone here ...
> I think it is something to do with lack of distractions.
>

Bingo -- between 11-ish pm and 3-ish am, I get more thinking-type
work done than I can in the other 12 hours of the day.

Cheers,
-Neil.

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2003\02\18@061359 by Jinx

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> When <much> younger, I had a similar problem.  I set my alarm
> clock radio to turn on an AC outlet. My stereo was plugged into
> this outlet. The stereo was set to a rock-n-roll FM station at nearly
> full volume

I think this is [EE} - there are motors and electronics involved

http://www.betrisey.ch/ereveil.htm

But the real pages are here. Absolute horological mechanical
marvels made by a craftsman

http://www.betrisey.ch/eindex.htm

A lot of photos, videos and technical descriptions. At least check out
the Malevoz, Foucaults and Chronolith light-powered clock

Timing graphs on some pages made with Microset, made by (still
current ?) list member Bryan Mumford

http://www.bmumford.com/

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