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'[EE]:Tilt sensor'
2002\05\17@065727 by Pang

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Hi all,

Can anyone give me some recommendations on sensors for detecting tilting? I
hope to have a sensor that can detect when a car is being jack up, or towed.

Thanks.

Rgds,
pang

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2002\05\17@072104 by Alan B. Pearce

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Check out the Analog Devices accelerometer series, specifically the ADXL202
devices and their application notes. They will do this for you.

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2002\05\17@074953 by Olin Lathrop

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> Can anyone give me some recommendations on sensors for detecting tilting?
I
> hope to have a sensor that can detect when a car is being jack up, or
towed.

You could use a single accellerometer looking at the down component of
gravit.  However, that will be rather innaccurate at small tilt angles.  A
more sensitive system would use two or a dual axis accellerometer looking at
the horizontal components of gravity.


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

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2002\05\17@081138 by Peter L. Peres

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On Fri, 17 May 2002, Olin Lathrop wrote:

>> Can anyone give me some recommendations on sensors for detecting tilting?
>I
>> hope to have a sensor that can detect when a car is being jack up, or
>towed.
>
>You could use a single accellerometer looking at the down component of
>gravit.  However, that will be rather innaccurate at small tilt angles.  A
>more sensitive system would use two or a dual axis accellerometer looking at
>the horizontal components of gravity.

Automotive applications use electrolytic tilt sensors. See my previous
posting on this.

Peter

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2002\05\17@085658 by Peter L. Peres
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On Fri, 17 May 2002, Pang wrote:

>Hi all,
>
>Can anyone give me some recommendations on sensors for detecting tilting? I
>hope to have a sensor that can detect when a car is being jack up, or towed.

Look at electrolytic (liquid) tilt sensors.

Peter

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2002\05\17@115413 by Pic Dude

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How about a pair of simple mercury tilt-switches?
-Neil.



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[spam_OUTPICLISTTakeThisOuTspamMITVMA.MIT.EDU]On Behalf Of Alan B. Pearce
Sent: Friday, May 17, 2002 6:17 AM
To: .....PICLISTKILLspamspam@spam@MITVMA.MIT.EDU
Subject: Re: [EE]:Tilt sensor


Check out the Analog Devices accelerometer series, specifically the ADXL202
devices and their application notes. They will do this for you.

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2002\05\17@120449 by Alan B. Pearce

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>How about a pair of simple mercury tilt-switches?

>Check out the Analog Devices accelerometer series,
>specifically the ADXL202 devices and their
>application notes. They will do this for you.

Well the ADXL devices have the advantage that when you turn the car off they
can remember the current angle of the car (well your software would be doing
this) and then if that changed before the car was started again then the
alarm goes off. An allowance would need to be made for the car rocking in
the wind or any other activities .... no lets not go there .... and it then
means that it does not need manual calibrating if parked on a hill.

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2002\05\17@121122 by Pic Dude

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Ack, hang on.  Just realized that the car could be parked
on an incline when being towed, and the tilt switches
would not do well in that case.  Ignore this option 8-O.

-Neil.



{Original Message removed}

2002\05\17@130613 by Herbert Graf

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Mercury sensors are about as simple as you can get, you can also get one of
those sensors with a ball bearing in it. TTYL

> {Original Message removed}

2002\05\17@135826 by Peter L. Peres

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On Fri, 17 May 2002, Alan B. Pearce wrote:

>>How about a pair of simple mercury tilt-switches?
>
>>Check out the Analog Devices accelerometer series,
>>specifically the ADXL202 devices and their
>>application notes. They will do this for you.
>
>Well the ADXL devices have the advantage that when you turn the car off they
>can remember the current angle of the car (well your software would be doing
>this) and then if that changed before the car was started again then the
>alarm goes off. An allowance would need to be made for the car rocking in
>the wind or any other activities .... no lets not go there .... and it then
>means that it does not need manual calibrating if parked on a hill.

As a general rule alarms operate when the car is not operating. Why would
you store the 'previous' 'horizontal' level ?!

There is a 'slight' price difference between the ADXL devices and
electrolytic tilt sensors, also, the ADXL is more sensitive to impacts,
shaking from wind, etc.

Peter

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2002\05\17@141738 by Bob Ammerman

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> How about a pair of simple mercury tilt-switches?
> -Neil.

Mercury tilt switches are frowned upon nowadays -- all that nasty toxic
mercury you know.

Bob Ammerman
RAm Systems

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2002\05\20@044000 by Alan B. Pearce

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>As a general rule alarms operate when the car is not
>operating. Why would you store the 'previous'
>'horizontal' level ?!

You do not want to store the previous 'horizontal' level, you want to store
the current level when you park, so if you do park on a hill you do not need
to go and tweak some control to level the sensor.

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2002\05\20@131933 by Jinx

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There's the original pinball machine tilt sensor - a pendulum
(contact 1) in a wire hoop (contact 2)

Mercury or mercury-alternative tilt switches, that might not
be sensitive enough if the car is lifted only slightly to get
in on a towing platform under the back wheels

The problem you'll have is that you may not be parked on
a horizontal surface. Whatever sensor you use has to take
its reference from whatever the orientation the car is in and
that you want it to stay in.

A self-levelling gimbal housing the sensor that locks in
place when the ignition goes off ?

Perhaps an accelerometer on the whole body or IR sensors
that measure the distance between the top of the tyre and
the mudguard, or something like that which detects changes
to the wheel heights as the suspension moves

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2002\05\20@150209 by Peter L. Peres

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On Mon, 20 May 2002, Alan B. Pearce wrote:

>>As a general rule alarms operate when the car is not
>>operating. Why would you store the 'previous'
>>'horizontal' level ?!
>
>You do not want to store the previous 'horizontal' level, you want to store
>the current level when you park, so if you do park on a hill you do not need
>to go and tweak some control to level the sensor.

Yes but why in eeprom ? Or did I misread your posting ?

Peter

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2002\05\20@185142 by Michael Rigby-Jones

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> -----Original Message-----
> From: Alan B. Pearce [SMTP:A.B.Pearcespamspam_OUTRL.AC.UK]
> Sent: Monday, May 20, 2002 9:39 AM
> To:   @spam@PICLISTKILLspamspamMITVMA.MIT.EDU
> Subject:      Re: [EE]:Tilt sensor
>
> >As a general rule alarms operate when the car is not
> >operating. Why would you store the 'previous'
> >'horizontal' level ?!
>
> You do not want to store the previous 'horizontal' level, you want to
> store
> the current level when you park, so if you do park on a hill you do not
> need
> to go and tweak some control to level the sensor.
>
I guess a potentiometer with a weighted arm hung off the end would do the
trick?

Regards

Mike

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2002\05\20@204534 by Dwayne Reid

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At 09:43 AM 5/20/02 +0100, Michael Rigby-Jones wrote:
> >
>I guess a potentiometer with a weighted arm hung off the end would do the
>trick?

Even better: one of those fairly inexpensive quadrature encoders from
Bourns: 256 pulses per rev with ball bearing shaft.  Reset an up-down
counter to 0 when the ignition is turned off and sound the alarm when the
count exceeds some pre-set value.  Using a quadrature encoder and up-down
counter helps ensure that swaying and wind gusts don't cause the counter to
just climb to the trigger value.

I'm not sure if the sensor from a mouse has enough resolution but that may
also be worth a try.

dwayne


Dwayne Reid   <RemoveMEdwaynerTakeThisOuTspamplanet.eon.net>
Trinity Electronics Systems Ltd    Edmonton, AB, CANADA
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2002\05\20@215430 by Pang

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Hi all,

I have look at the Electrolytic sensors and also the ADXL202E accelerometer.
The electrolytic sensors seems to be what I need. The only problem is, in my
opinion, one need to invest some time to produce a tilt sensor module from
it. The electrolytic sensors need to be powered by an ac and that means you
need to have some sort of dc to ac converter ( not sure if it need a sine
wave or a square wave). In addition you also need a controller to interpret
the data from the sensor and perform calibration to the module (so does the
accelerometer). And if I am not wrong, the electrolytic sensor is slower
than the accelerometer.

My intention is to get hold of a ADXL202E and try to construct a dependable
tilt sensor module. Dependable here means that there should not be any false
alarms from winds, thunder, kids sitting on top of the car and immune to
automotive noise and must be rugged. The datasheet states that the ADXL202
should not be subjected to shock more than 1000g, and it continues saying -
" Drops onto hard surfaces can cause shocks of greater than 1000 g and
exceed the absolute maximum rating of the device. Care should be exercised
in handling to avoid damage."

Any advice, please?

In addition, are there any accompanying notes that aids one in understanding
those terms in the ADXL202E datasheet ? I am totally lost in those terms and
metrics used. Appreciate if anyone can point me to any of these links of
information describing these terms.

Some terms here -

Measurement Range  1 2g
Cross-Axis Sensitivity    12 %
Noise Density
Acceleration (Any Axis, Unpowered for 0.5 ms) . . . . . . 1000 g
Acceleration (Any Axis, Powered for 0.5 ms) . . . . . . . . . . 500 g

Thanks and have a nice day.

Rgds,
Pang

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2002\05\21@040958 by Alan B. Pearce

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>Yes but why in eeprom ? Or did I misread your posting ?

I never mentioned storing in eeprom. Perhaps it could have been read that
way, but what I was meaning was an algorithm along the following lines.

1. remember current tilt angle when engine switched off (in suitable ram
location)

2. allow settling time for tilt to change as occupants leave vehicle. This
can probably be denoted by vehicle being locked.

3. allow a small rapid change in tilt value for short time to allow wind or
draught from passing vehicles to rock car. This can probably be recognised
readily by knowing the natural resonant frequency of the suspension system.

4. Sound alarm if long term slow rate of change in tilt (car being
jacked/lifted for towing) or large amplitude natural resonance oscillation
(car being attacked by joyriders/rioters etc).

An accelerometer of the type made by Analog Devices would be ideal for doing
something like this.

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2002\05\21@041826 by Alan B. Pearce

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>> You do not want to store the previous 'horizontal' level, you want to
>> store
>> the current level when you park, so if you do park on a hill you do not
>> need
>> to go and tweak some control to level the sensor.
>>
>I guess a potentiometer with a weighted arm hung off the end
>would do the trick?

Well it could do for a simple system I guess. See my previous posting on
what I envisaged one could do with an accelerometer. Got a couple of these
things, must give it a go :)

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2002\05\21@043615 by Ken Evans

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Also check out Memsic MXD2020, can take 50,000g.

http://www.memsic.com

ADXL202 can be easily broken.

see below for more

Ken
{Original Message removed}

2002\05\21@143131 by Peter L. Peres

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On Tue, 21 May 2002, Pang wrote:

>Hi all,
>
>I have look at the Electrolytic sensors and also the ADXL202E accelerometer.
>The electrolytic sensors seems to be what I need. The only problem is, in my
>opinion, one need to invest some time to produce a tilt sensor module from
>it. The electrolytic sensors need to be powered by an ac and that means you

It is not so hard. You can use a square wave, f.ex. a PIC output pin, and
read using two opamps per axis connected as precision rectifiers. Then you
use four PIC A/D inputs to interpret the data. You can request application
notes and recommended schematics etc from the makers.

The questions about the ADXL sensor data sheet will be answered by others,
I just want to add that the ADXL requires significant lowpass filtering
for your application afaik. Car body noise and fast passing vehicles
could do strange things to your system. The electrolytic sensors can be
ordered with different time constants as needed.

Peter

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2002\05\22@034248 by Roman Black

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I've repaired some commercial car alarms etc,
the standard system is very cheap and simple.
Usually using a fine spring about 3cm long
with a weight at the end. The other end is
soldered on a piezo or in some systems the spring
goes through a metal loop, so when it vibrates it
touches the loop and provides a closed circuit.
These work very good and are cheap and easy to
make, you really can't bang the car, or jack it
up at all (even horizontal jacking) without the
alarm being triggered.
-Roman


Alan B. Pearce wrote:
{Quote hidden}

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2002\05\22@144056 by Peter L. Peres

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However you can drive by it real close and failry fast with a van or bus
and have alarms. If the bus runs on shedule all hight there will be a
crowd of fans looking for you (the designer of the alarm) fairly soon.
About 5% of the installed car alarms are too sensitive and go off for no
reason (thunder, bus, fat cat jumping on hood etc).

Peter

On Wed, 22 May 2002, Roman Black wrote:

{Quote hidden}

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2002\05\23@113237 by Joe McCauley

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Any idea of how much these cost?

Joe

-----Original Message-----
From: pic microcontroller discussion list
[RemoveMEPICLISTEraseMEspamEraseMEMITVMA.MIT.EDU]On Behalf Of Ken Evans
Sent: 21 May 2002 09:29
To: RemoveMEPICLISTspam_OUTspamKILLspamMITVMA.MIT.EDU
Subject: Re: [EE]:Tilt sensor


Also check out Memsic MXD2020, can take 50,000g.

http://www.memsic.com

ADXL202 can be easily broken.

see below for more

Ken
----- Original Message -----
From: "Pang" <RemoveMEklpangTakeThisOuTspamspamAICM.COM.MY>
To: <EraseMEPICLISTspamspamspamBeGoneMITVMA.MIT.EDU>

>I am totally lost in those terms and
> metrics used. Appreciate if anyone can point me to any of these links of
> information describing these terms.
>
> Some terms here -
>
> Measurement Range  1 2g

1g is the gravitational acceleration. If you point the accelerometer
sensitive axis (see data sheet) down or up, you will get + and - 1g. Useful
for calibration.

> Cross-Axis Sensitivity    12 %

The device in question is a dual accelerometer. Its 2 accelerometers
measures acceleration in 2 axes nominally at right angles to each other.
However each has a small reponse to acceleration along the direction (axis)
at right angles to its own axis - cross axis sensitivity.

> Noise Density
residual noise expressed in spectral terms. Can be reduced by suitable low
pass filter.

> Acceleration (Any Axis, Unpowered for 0.5 ms) . . . . . . 1000 g

beyond this the device will be permanently damaged. ie the silicon breaks !

> Acceleration (Any Axis, Powered for 0.5 ms) . . . . . . . . . . 500 g

as above.
{Quote hidden}

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'[EE]:Tilt sensor'
2002\06\03@205638 by Pang
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I remember seing somewhere on the ADXL202 costing some USD12. As for memsic,
ahem.......
MXD2020A/B, MXR2500AL, MXA2500AL all cost  USD14.50. Minimum quantity order
is 85 pieces and then there is the minimum order value at USD500. (
quotation from local supplier )

Even if I managed to get some samples from them, this product will be
difficult to sell due to the price. Ideas from earlier posting suggest using
encoders and also ball bearing potentiometer. But having difficulty getting
local supplier for these parts.

have a nice day.

Rgds,
pang



----- Original Message -----
From: "Joe McCauley" <spamBeGonejoe.mccauleySTOPspamspamEraseMETCD.IE>
To: <KILLspamPICLISTspamBeGonespamMITVMA.MIT.EDU>
Sent: Thursday, May 23, 2002 11:31 PM
Subject: Re: [EE]:Tilt sensor


> Any idea of how much these cost?
>
> Joe
>
> {Original Message removed}

2002\06\05@024853 by Peter L. Peres

picon face
On Tue, 4 Jun 2002, Pang wrote:

>I remember seing somewhere on the ADXL202 costing some USD12. As for memsic,
>ahem.......
>MXD2020A/B, MXR2500AL, MXA2500AL all cost  USD14.50. Minimum quantity order
>is 85 pieces and then there is the minimum order value at USD500. (
>quotation from local supplier )
>
>Even if I managed to get some samples from them, this product will be
>difficult to sell due to the price. Ideas from earlier posting suggest using
>encoders and also ball bearing potentiometer. But having difficulty getting
>local supplier for these parts.

If you still haven't found what you are looking for I'd look into building
the items locally. Surely you have inexpensive subcontractors.
Electrolytic tilt sensors are relatively simple to design and build if the
required precision is low. The only trick is the electrolyte and here a
chemist will help. You get what yuo pay for ...

Peter

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2002\06\05@072956 by Brent Brown

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> >I remember seing somewhere on the ADXL202 costing some USD12. As for
> >memsic, ahem....... MXD2020A/B, MXR2500AL, MXA2500AL all cost
> >USD14.50. Minimum quantity order is 85 pieces and then there is the
> >minimum order value at USD500. ( quotation from local supplier )
> >
> >Even if I managed to get some samples from them, this product will be
> >difficult to sell due to the price. Ideas from earlier posting
> >suggest using encoders and also ball bearing potentiometer. But
> >having difficulty getting local supplier for these parts.

ST have released a device called the LIS2L01, dual axis 1g, 30Hz.
Find it from http://eu.st.com/stonline/index.shtml
Looks like it might be cheaper but I don't know the price.
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