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'[EE] shake, rattle and roll'
2005\09\23@155456 by alan smith

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I have an application that I was thinking of using an accelrometer for, but now I wonder if there is a less expensive and easier method.  Essentially I want to wake up the circuit if the box is picked up.  So I guess more of a movement sensor....its known by another name, as googling hasn't been all that helpful so far.  

               
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2005\09\23@162433 by Howard Winter

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Alan,

On Fri, 23 Sep 2005 12:54:55 -0700 (PDT), alan smith wrote:

> I have an application that I was thinking of using an accelrometer for, but now I wonder if there is a less
expensive and easier method.  Essentially I want to wake up the circuit if the box is picked up.  So I guess
more of a movement sensor....its known by another name, as googling hasn't been all that helpful so far.  

Do you mean a tilt switch?  At one time made by using a blob of mercury that shorted a pair of contacts, or
didn't, according to its angle to the ground.  Nowadays they are mercury-free, so much less fun!  :-)


Cheers,


Howard Winter
St.Albans, England


2005\09\23@174036 by alan smith

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probably thats what I mean, I just haven't found exactly what...so would a tilt switch operate if the unit was simply picked up or does it need to actually tilt

Howard Winter <spam_OUTHDRWTakeThisOuTspamh2org.demon.co.uk> wrote:Alan,

On Fri, 23 Sep 2005 12:54:55 -0700 (PDT), alan smith wrote:

> I have an application that I was thinking of using an accelrometer for, but now I wonder if there is a less
expensive and easier method. Essentially I want to wake up the circuit if the box is picked up. So I guess
more of a movement sensor....its known by another name, as googling hasn't been all that helpful so far.

Do you mean a tilt switch? At one time made by using a blob of mercury that shorted a pair of contacts, or
didn't, according to its angle to the ground. Nowadays they are mercury-free, so much less fun! :-)


Cheers,


Howard Winter
St.Albans, England


2005\09\23@190112 by Howard Winter

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Alan,

Tilt switch...

On Fri, 23 Sep 2005 14:40:33 -0700 (PDT), alan smith wrote:

> probably thats what I mean, I just haven't found exactly what...so would a tilt switch operate if the unit
was simply picked up or does it need to actually tilt

Well it needs to experience a change in gravity that feels like tilting - either actual tilting or
accelerating horizontally in the right direction would do it - but I can't think of anything (even an
accelerometer) that would reliably indicate being picked up.  But If you do it slowly enough, you could defeat
almost any non-contact sensor.  Have you considered just having a switch underneath, bearing on the surface
it's resting on, so that it operates when lifted off it?

Cheers,


Howard Winter
St.Albans, England


2005\09\23@191215 by William Chops Westfield

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On Sep 23, 2005, at 12:54 PM, alan smith wrote:

> Essentially I want to wake up the circuit if the box is picked up.
> So I guess more of a movement sensor.

The standard in toys is a spring, fixed at one end, as one contact,
an a central rigid conductor as the other contact, but you'd be
very challenged to make such a thing respond to being "picked up"
(as opposed to shaken, or thrown against the floor.)  Tilt sensors
using mercury or balls likewise require tilting.

BillW

2005\09\23@192017 by Jinx

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> probably thats what I mean, I just haven't found exactly
> what...so would a tilt switch operate if the unit was simply
> picked up or does it need to actually tilt

Alan, they'd be called pick-up switches otherwise ;-))

Mercury tilt switches aren't particularly sensitive, although you
can get them in a variety of degrees. The simplest for you might
be a pendulum. It's the type of sensor used as a "TILT" switch in
pinball machines and motorbike alarms. Basically a wire hangs freely
in the middle of a wire ring. If the two touch, the circuit is completed.
Something you could make yourself. The smaller the ring or greater
its distance from the wire pivot, the more sensitive the alarm. The
best wire to use is gold-plated, because it doesn't get a non-
conducting oxide layer as other metals would over time, and you
can get that free (or very cheap) as scrap from anyone who electro-
plates for jewellers or maybe even a manufacturing jeweller

2005\09\23@210057 by Jinx

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> Have you considered just having a switch underneath, bearing on
> the surface it's resting on, so that it operates when lifted off it ?

eg a mouse microswitch - very low operation force


2005\09\24@052350 by Tim ODriscoll

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On Fri, 2005-09-23 at 12:54 -0700, alan smith wrote:
> I have an application that I was thinking of using an accelrometer
> for, but now I wonder if there is a less expensive and easier method.
> Essentially I want to wake up the circuit if the box is picked up.  So
> I guess more of a movement sensor....its known by another name, as
> googling hasn't been all that helpful so far.  
Vibration sensor? They're used in car alarms and the like.. About UK£1
from RS..

I used one in a car alarm project.. It was a tad too sensitive though
and tended to resonate with lorries and loud bass-boxes..and people
kicking the bumper :)

The action of picking a vibration sensor up will almost certainly set it
off. I think they consist of a tiny ball mounted vertically on a spring,
in a gold-plated dome. When one touches the other the circuit is made.
Or that's what it sounds like when you shake 'em...

Cheers,

Tim.

2005\09\24@121823 by Peter van Hoof

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>> Have you considered just having a switch underneath, bearing on
>> the surface it's resting on, so that it operates when lifted off it ?
>
> eg a mouse microswitch - very low operation force

I have just seen another good idea (does not work in dark) a cds photocel
mounted in the bottom

Peter van Hoof


2005\09\24@135340 by PicDude

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How about a shock/vibration sensor from a car-alarm?  Some of these I've seen
have adjustable sensitivity.  There are also shock/vibration sensors for
house/building windows.

Cheers,
-Neil.


On Friday 23 September 2005 02:54 pm, alan smith scribbled:
{Quote hidden}

2005\09\24@143934 by Roland

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You can make your own with a piezo disk, a ball bearing and small capsule, like a plastic cover that fits over a tubular table leg, or even a cooldrink cap. The ball rests on the smooth side of the piezo, and when someone picks the device up, the ball bearing rolls to the side and,.. smack, generates a good many volts. Needs some filtering because it's very sensitive(but narrowband) to general floor noise.

Regards
Roland


{Quote hidden}

Regards
Roland Jollivet

2005\09\24@181839 by Jinx

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> I have just seen another good idea (does not work in dark)
> a cds photocel mounted in the bottom

Commonly found as a drawer alarm, can be used in a very
low power configuration. If quiescent is an issue, a metallic
contact type can be the trigger for a self-latching PSU switch,
so no power at all is consumed until there's a contact

2005\09\25@143841 by Gus Salavatore Calabrese

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reed switch and magnet that falls away
( could be hinged )

AGSC

2005\09\26@124227 by alan smith

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Thanks for all the interesting suggestions.  The photocell idea wont work because it may be dark, the the primary reason to have this is to backlight a display if the unit is picked up.  The other ideas of homebuilt won't work because this is going to be a high volume (he hopes) product, so it needs to be simple.  A switch on the bottom wont work because there is no guarantee it will always sit flat on a surface.  Even if the unit needs to be jostled a bit to turn on the backlight is fine, the user will just know if they do that enough the backlight will turn on.  

OK...someone is going to suggest a button for the backlight.  Only issue with that is if the person has impaired vision, they wont be able to find a button.

I might be able to solve this by other means....this just seemed to be a good way to momentarily backlight a display.

Gus Salavatore Calabrese <.....gscKILLspamspam@spam@omegadogs.com> wrote:
reed switch and magnet that falls away
( could be hinged )

AGSC

2005\09\26@125548 by William Chops Westfield

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On Sep 26, 2005, at 9:42 AM, alan smith wrote:

> Even if the unit needs to be jostled a bit to turn on the backlight is
> fine

In that case, one of the spring or rolling ball based switches ought
to work fine.  I was worried you wanted to detect motion that the
"user" was trying to keep undetectable.

The other interesting idea is some sort of capacitive or noise-pickup
"touch switch", so the backlight would go on whenever you touched it.

BillW

2005\09\26@131213 by alan smith

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true....both good ideas....but needs to be cheap...or almost free.  I've got a couple of other ideas as well...just need some 'thinkin' time to figure them out.

Thinkin time is where you are sitting feet up..staring out in the abyss and the boss walks by and says....wake up...get to work....

William Chops Westfield <westfwspamKILLspammac.com> wrote:
On Sep 26, 2005, at 9:42 AM, alan smith wrote:

> Even if the unit needs to be jostled a bit to turn on the backlight is
> fine

In that case, one of the spring or rolling ball based switches ought
to work fine. I was worried you wanted to detect motion that the
"user" was trying to keep undetectable.

The other interesting idea is some sort of capacitive or noise-pickup
"touch switch", so the backlight would go on whenever you touched it.

BillW

2005\09\27@195054 by Gus Salavatore Calabrese

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More ideas

piezo strip parallel to table, inside box with small weight
on end.  Acceleration causes voltage which is detected.
Also detects earthquakes.

resistive flex strip set up the same way.  Acceleration causes
resistive change.

AGSC






2005\09\29@053801 by Vasile Surducan

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On 9/28/05, Gus Salavatore Calabrese <.....gscKILLspamspam.....omegadogs.com> wrote:
>
> More ideas
>
> piezo strip parallel to table, inside box with small weight
> on end.  Acceleration causes voltage which is detected.
> Also detects earthquakes.

Yeep. But everything is piezo is also more or less pyro. So avoiding
heat variation which is increasing the error or it must be
compensated. And will be a voltage variation for an acceleration
variation. Not easy for an accurate measurement.
And good only for great earthquakes where anyway does not care, you'll
don't be allive to monitorise the signal...

cheers,
Vasile

{Quote hidden}

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