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PICList Thread
'[EE] Magnetic driveway monitor'
2007\10\15@141433 by Brad Stockdale

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face
Hello all,

  I am working on a little project to help secure my home... I have a long
driveway and would like to know when someone is approaching my house. I used
to use a driveway monitor that had an IR motion detection sensor. This
worked, but produced more false alarms than true alarms. Not that it was
malfunctioning, but since I live in a rural area, it would detect every deer,
groundhog, dog, whatever...

  I would like to design something similar to:

       http://www.smarthome.com/790908.html

  It uses magnetic probes to detect vehicles approaching.

  Unfortunately, I know nothing about metal detection. I've never even used a
metal detector, let alone know how one works well enough to design one.

  Can anyone give me some pointers on how to go about making magnetic probes
such as the ones used in the above system? Maybe a website explaining the
basics of ferrous material detection and some simple schematics for a basic
metal detection probe? Basically I just want to find a circuit that upon
detection of the metal, it sends out a digital pulse. From there I'll use
that to activate the alarm be it over wireless, wired, whatever...

  I'd appreciate any advice.

Thanks,
Brad

2007\10\15@142948 by Marcel Birthelmer

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Brad,
have you thought about those drive-over detectors that they use to
count traffic sometimes? It seems to be just a cable that reacts to
being compressed by the weight of a car. It's not as "magicky" as what
you're proposing, but seems much simpler.
Also, an acquaintance of mine once had a radar setup in his office,
pointed out the window, and he could get a decent tracking of what
cars were driving by.
Just some thoughts.
- Marcel

On 10/15/07, Brad Stockdale <spam_OUTbrad_listsTakeThisOuTspamgreenepa.net> wrote:
{Quote hidden}

> -

2007\10\15@145813 by M. Adam Davis

face picon face
The theory is pretty simple.  You form a simple oscillator with a
coil, only the coil in this case is very large.
http://www.electronics-tutorials.com/oscillators/oscillator-basics.htm

The frequency of the oscillator will change quickly as a car drives
over the coil.

Alternately, measure the inductance of the coil with a PIC and if it
changes suddenly, you've got a lot of metal on top of it.

You simple need to detect the frequency shift.  In our world (PICs)
this can be done fairly simply.  Of course, the devil is in the
details.  Signal strength, shift magnitude, etc can be hard to deal
with correctly, but for a one-off project that can be tuned, these
shouldn't be overwhelming.

This might get you started, or at least help you to know what
questions to ask depending on how you want to proceed.

-Adam

On 10/15/07, Brad Stockdale <.....brad_listsKILLspamspam@spam@greenepa.net> wrote:
{Quote hidden}

> -

2007\10\15@152238 by Dr Skip

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If I remember, it is not weight that triggers, it's a large coil and ferrous
metal interacts with it, changing some frequency in the controller. Probably
the same with the system in the link shown.

You could probably find a cheap metal detector and mount the coil at the edge
of the drive. I've found cheap ones that do detect ferrous stuff at gross
sensitivities for less than $10. Get one with a light as well and you'll have a
binary interface already set to go. ;)

Even if the side of the driveway isn't good enough, you could bury it just
under the surface and that would guarantee detection...


Marcel Birthelmer wrote:
{Quote hidden}

2007\10\15@152806 by Richard Seriani, Sr.

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----- Original Message -----
From: "Brad Stockdale" <.....brad_listsKILLspamspam.....greenepa.net>
To: "Microcontroller discussion list - Public." <EraseMEpiclistspam_OUTspamTakeThisOuTmit.edu>
Sent: Monday, October 15, 2007 1:38 PM
Subject: Re: [EE] Magnetic driveway monitor


{Quote hidden}

Brad,

A search for magnetic vehicle detector produced many results. Maybe
something like these?

www.sensourceinc.com/PDF/SS-MS30%20Vehicle%20Sensor.pdf
http://www.ssec.honeywell.com/magnetic/mark_det.html

Good luck,
Richard


2007\10\15@153112 by Andy Tuthill

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Hi Brad,

I'm doing something similar for my Dad who has had similar problems with the X10 infrared system he uses.

Try using the NXP (formerly Phillips) KMZ10B or KMZ51 detectors.  These are what the traffic systems usually use.  They have a bridge resistor inside that changes when a change in the surrounding magnetic field is detected.  You can check out the web page at http://www.nxp.com.

You will need an op amp on the output but it all works on 5 volts so that helps.  I'm running the output of the op amp into a PIC which just watches for significant rises over the normal level.  From there the world is your oyster for what you do with the signaling from there.

Regards,
Andy


{Quote hidden}

> -

2007\10\15@160949 by Eoin Ross

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The units I have used have been pre-built. The coil specs are for about two-three turns, and then doing a twisted pair back to the sensor.

They use an LC circuit, and a frequency counter - when a vehicle enters there is a delta Hz due to the change in L, above a certain threshold and fiddle with an output.

Search for vehicle loop detector...

http://emxinc.com/vehicle-loop-detector-d-tek.html
http://www.neverfail.com/NewFiles/Products.html
http://renoae.com/traffic/files/AX/Model%20AX%20Operating%20Instructions%20%2003-30-04%20(551-0106-01).pdf




>>> KILLspambrad_listsKILLspamspamgreenepa.net 15 Oct 07 13:38:50 >>>
Hello all,

  I am working on a little project to help secure my home... I have a long
driveway and would like to know when someone is approaching my house. I used
to use a driveway monitor that had an IR motion detection sensor. This
worked, but produced more false alarms than true alarms. Not that it was
malfunctioning, but since I live in a rural area, it would detect every deer,
groundhog, dog, whatever...

  I would like to design something similar to:

       http://www.smarthome.com/790908.html

  It uses magnetic probes to detect vehicles approaching.

  Unfortunately, I know nothing about metal detection. I've never even used a
metal detector, let alone know how one works well enough to design one.

  Can anyone give me some pointers on how to go about making magnetic probes
such as the ones used in the above system? Maybe a website explaining the
basics of ferrous material detection and some simple schematics for a basic
metal detection probe? Basically I just want to find a circuit that upon
detection of the metal, it sends out a digital pulse. From there I'll use
that to activate the alarm be it over wireless, wired, whatever...

  I'd appreciate any advice.

Thanks,
Brad

2007\10\15@164317 by Mike Hord

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>    Unfortunately, I know nothing about metal detection. I've never even used a
> metal detector, let alone know how one works well enough to design one.

If I were doing it, I'd buy an NVE giantmagnetoresistive sensor, a PIC10F, and
200 feet of 3-conductor wire.  Those GMR sensors are sensitive enough
that I've been able to detect a regular sized screwdriver from 8+ inches away.
A car should be NO problem.

Read it with an ADC and send a hi-lo signal across the third conductor.  A
one-afternoon job, if that.

Mike H.

2007\10\15@173310 by Jinx

face picon face
Hi Brad, there was a PIClist thread exactly a year ago called

[EE] Vehicle detection - magnetic sensors?

which you could look up

> I have a long driveway and would like to know when someone
> is approaching my house. I used to use a driveway monitor that
> had an IR motion detection sensor

> http://www.smarthome.com/790908.html

I suggested

http://www.siliconchip.com.au/cms/A_102998/article.html

Was available as kit KC5402 from http://www.jaycar.com.au , way less
than the $500 smarthome unit. They have sales reps in the US

or a broken-beam system using a laser pointer

2007\10\15@173955 by Peter Todd

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On Tue, Oct 16, 2007 at 10:32:54AM +1300, Jinx wrote:
{Quote hidden}

How much current did the device consume? I have an project where that'd
be useful, but it has to be fairly low power so I can run it off
batteries.

- --
http://petertodd.org
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2007\10\15@194006 by David VanHorn

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You don't even have to do that..

A car driving by a coil, distorts the earth's field by a surprising amount.
With a simple differential amplifier (three op-amps and some 1%
resistors) you can see traffic going by on the third floor of an
apartment building, 10-20 feet from the street below, using a
"telephone pickup" coil.  Been there, done that.

With a larger coil, especially one with a large area, and closer in,
the signal is much larger.

A loop of wire in the road is good too, but you don't need to go to
that extreme.

The "metal detector" approach works, but you'll be better off, if you
must go that route, to use the balanced field type, that won't be
sensitive to heat, cold, rain etc.
A pair of coils are used, with the larger one in a shape that's hard
to describe in text, but basically such that the smaller coil can be
placed right over it in a spot where it gets no, or almost no signal
when the large coil is driven with a fairly large signal. External
metal, ferrous or not, distorts that field, and imbalances the system
resulting in a larger signal in the small coil.  Boxcar integrator or
other synchronus detection can be done, to reject noise, and the
amplitude and phase of the signal will tell you something about the
target.

2007\10\16@063645 by cdb

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face
Have you thought about using piezo cable? This is the same type of cable that in road traffic light sensors and roadside speed recorders use.  This stuff can be quite sensitive.

Colin

::   I am working on a little project to help secure my home... I
:: have a long
:::: driveway and would like to know when someone is approaching my
:::: house. I
:::: used
:::: to use a driveway monitor that had an IR motion detection
:::: sensor. This
:::: worked, but produced more false alarms than true alarms. Not
:::: that it was
:::: malfunctioning, but since I live in a rural area, it would
:::: detect every
:::: deer,
:::: groundhog, dog, whatever...
--
cdb, RemoveMEcolinTakeThisOuTspambtech-online.co.uk on 16/10/2007

Web presence: http://www.btech-online.co.uk  

Hosted by:  http://www.1and1.co.uk/?k_id=7988359

Even if faith is lacking, and hope is non existent, you always have charity and compassion to offer.





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Checked by AVG.
Version: 7.5.488 / Virus Database: 269.14.12/1073 - Release Date: 10/16/2007 8:22 AM


2007\10\16@114240 by Vasile Surducan

face picon face
On 10/15/07, Brad Stockdale <spamBeGonebrad_listsspamBeGonespamgreenepa.net> wrote:
> Hello all,
>
>   I am working on a little project to help secure my home... I have a long
> driveway and would like to know when someone is approaching my house. I used
> to use a driveway monitor that had an IR motion detection sensor. This
> worked, but produced more false alarms than true alarms. Not that it was
> malfunctioning, but since I live in a rural area, it would detect every deer,
> groundhog, dog, whatever...
>
>   I would like to design something similar to:
>
>        http://www.smarthome.com/790908.html
>
>   It uses magnetic probes to detect vehicles approaching.

And you're supposing they will approach using a car and never by foot, right ?
It seems your burglars have leak of imagination...


{Quote hidden}

> -

2007\10\16@124134 by M. Adam Davis

face picon face
On 10/16/07, Vasile Surducan <TakeThisOuTpiclist9EraseMEspamspam_OUTgmail.com> wrote:
> And you're supposing they will approach using a car and never by foot, right ?
> It seems your burglars have leak of imagination...

Engineering is just another form of applied economics - the allocation
of scarce resources.  One method to manage decision making is to
simplify the problem.

1.  Assume the burglar is a spheroid...

:-)

-Adam

--
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
- - - - - - - - - - - - - - - - - - - - - - - - -
Moving in southeast Michigan? Buy my house: http://ubasics.com/house/

Interested in electronics? Check out the projects at http://ubasics.com

Building your own house? Check out http://ubasics.com/home/

2007\10\16@203144 by Peter P.

picon face

> And you're supposing they will approach using a car and never by foot, right ?
> It seems your burglars have leak of imagination...

They are *rich* burglars, Vasile ...

Peter P.


2007\10\17@020912 by Robert Rolf
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Peter P. wrote:
>>And you're supposing they will approach using a car and never by foot, right ?
>>It seems your burglars have leak of imagination...
>
>
> They are *rich* burglars, Vasile ...

Or they are using a stolen vehicle, probably my wife's van :-{

Apparently vans are a very popular theft target so they can haul
their break in booty away, and then ditch it.
I know of three people now, where that was the case (leftovers in the
van that weren't the owners).
R

2007\10\17@041651 by Peter P.

picon face
Robert Rolf <Robert.Rolf <at> ualberta.ca> writes:
> Apparently vans are a very popular theft target so they can haul
> their break in booty away, and then ditch it.

Perhaps this is a STRONG hint towards the need to install immobilizer type
alarms buried deep in the engine and transmission ? I have no idea how I'd go
about fitting such a thing to a car that is not prepared for it but I'm sure it
is no impossible at all. It could even involve a pic or ten.

Peter P.



2007\10\17@081736 by M. Adam Davis

face picon face
It wouldn't be too hard to intercept and modify the throttle signal.
When the immobilizer is activated, it simply starts reporting lower
and lower values for the throttle position.  The engine will slowly
get starved of gas, slowly lose power, and no damage will occur to the
vehicle or the occupants.  It could be hard to remove or modify
depending on placement, but without modifying the ECU itself it can
always be jumpered.

-Adam

On 10/17/07, Peter P. <RemoveMEplpeter2006spamTakeThisOuTyahoo.com> wrote:
{Quote hidden}

> -

2007\10\17@083131 by Carl Denk

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How are you going to jumper the signals to 6 fuel injectors or time the
ignition. The key is coded, and the computer is looking for that code,
where when you get an extra key, the dealer needs to know you are the
owner, and if I know Ford's IT systems, the coding for the new key comes
from a server, and isn't local generated.

M. Adam Davis wrote:
{Quote hidden}

>> --

2007\10\17@101616 by M. Adam Davis

face picon face
I was responding to the question, "How hard is it to make/install an
immobilizer".  One could make an immobilizer by making the engine
controller think that there's no throttle/air, therefore causing the
engine to slow down to idle power and essentially immobilizing the
car.

It seems you believe I was suggesting a way to get around existing immobilizers.

The key coding in my 1998 ford is locally generated.  As long as you
have two keys that the controller accepts, then programming an
additional key is straightforward.  When you have one key, then it has
to be a "primary" key, and then you can program another key.  If
you've lost all your keys you have to go to the dealer to have it
reset.  They have undoubtedly strengthened this over the years.

You are correct that attempting to bypass this type of system is
difficult.  So much so that insurance companies apparently are turning
down some claims of stolen cars because they believe the system is
foolproof.

It is, however, not impossible.  Some cars even have relatively simple
override procedures for the system, or so I've read...

-Adam

On 10/17/07, Carl Denk <EraseMEcdenkspamalltel.net> wrote:
{Quote hidden}

2007\10\17@104506 by Alan B. Pearce

face picon face
>You are correct that attempting to bypass this type of system
>is difficult.  So much so that insurance companies apparently
>are turning down some claims of stolen cars because they
>believe the system is foolproof.
>
>It is, however, not impossible.  Some cars even have relatively
>simple override procedures for the system, or so I've read...

As was reported here within the last 2-3 months IIRC ...

2007\10\17@114038 by Bob Blick

face picon face
--- Carl Denk <RemoveMEcdenkspam_OUTspamKILLspamalltel.net> wrote:

> How are you going to jumper the signals to 6 fuel
> injectors or time the
> ignition. The key is coded, and the computer is
> looking for that code,
> where when you get an extra key, the dealer needs to
> know you are the
> owner, and if I know Ford's IT systems, the coding
> for the new key comes
> from a server, and isn't local generated.

You are giving them way too much credit. The car has
eeprom space for up to 16 trusted keys. When the
dealer wants to add another key, they plug their
Rotunda analyzer into the car and tell the car to add
the next key put in the ignition. The security is by
obscurity and nothing more.

By the way, you don't have to go to the dealership to
add a new trusted key. If you already have two trusted
keys, start the car with both of them and then the new
key, which will automatically be added to the list of
trusted keys. Of course, you have to plan ahead to
make it work, which most people don't do. But when I
got my car I bought 2 spare keys ($38 each if you know
where to look) and ran through the add-a-key process
using the 2 keys that the car came with.

Cheerful regards,

Bob

2007\10\17@142853 by Herbert Graf

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face
On Wed, 2007-10-17 at 08:16 +0000, Peter P. wrote:
> Robert Rolf <Robert.Rolf <at> ualberta.ca> writes:
> > Apparently vans are a very popular theft target so they can haul
> > their break in booty away, and then ditch it.
>
> Perhaps this is a STRONG hint towards the need to install immobilizer type
> alarms buried deep in the engine and transmission ? I have no idea how I'd go
> about fitting such a thing to a car that is not prepared for it but I'm sure it
> is no impossible at all. It could even involve a pic or ten.

No need to go "deep in the engine and transmission". I installed an
immobilizer in my 87 Olds, simply a relay turning off the power to the
ignition module. Instant dead engine with no damage. In my case I simply
used an extra output from an aftermarket keyless entry module I
installed when I got the car.

TTYL

2007\10\17@143026 by Vasile Surducan

face picon face
On 10/16/07, Peter P. <RemoveMEplpeter2006TakeThisOuTspamspamyahoo.com> wrote:
>
> > And you're supposing they will approach using a car and never by foot, right ?
> > It seems your burglars have leak of imagination...
>
> They are *rich* burglars, Vasile ...

If they are rich from burglary,  they are not stupids.
Meaning they know to fools an infrared pyroelectric detector, go
inside the house and deactivated the car monitor system, go back end
enter with the van, and empty your house.

Which is a good point, because sometime you need to redecorate and
starting from an empty room is always easiest. Think positive.

2007\10\17@144516 by Brooke Clarke

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face
Hi Brad:

I'd like to learn what you end up using and how it works.

I've spent some time studying what I call outdoor intrusion detectors, see:
http://www.prc68.com/I/ID.shtml

I live in the forest where there are a lot of deer and other animals amongst
the trees so seismic type sensors are of no value.

There are a great number of ways that magnetic distrubances can be detected.
The more sensitive ones will detect the metal eyelets in a pair of tennis shoes
 a few feet away.  More on my sensors page:
http://www.prc68.com/I/Sensors.shtml#Magnetic

--
Have Fun,

Brooke Clarke
http://www.PRC68.com
http://www.precisionclock.com
http://www.prc68.com/I/WebCam2.shtml 24/7 Sky-Weather-Astronomy Cam

2007\10\17@160508 by Richard Prosser

picon face
I used to use a switch in series withn the electric fuel pump. (I used
the switch normally used to turn the instrument lights off). Without a
fuel pump the car would only go for a few hundred metres. Seemed to
work OK but was never actually required. (Fitted to a mini van - rough
value ~$NZ250 in 1976).

RP

On 18/10/2007, M. Adam Davis <EraseMEstienmanspamspamspamBeGonegmail.com> wrote:
{Quote hidden}

2007\10\18@044504 by Alan B. Pearce

face picon face
>More on my sensors page:
> http://www.prc68.com/I/Sensors.shtml#Magnetic

Gee, how do you get the time to put all this together ... ;))

That is a powerful list of sensors and stuff.

but
I couldn't get to the Honeywell Turbidity sensor page (came back saying
couldn't resolve IP address).

And you spelt Agilent wrong in the IRDA sensor notes.

Under the turbidity sensor you might like to put a link to the page that
someone posted here some time back.

http://instruct1.cit.cornell.edu/courses/ee476/FinalProjects/s2005/jsa25_jyh25/TurbidityMeter.htm

Found it eventually in the archives, I thought I had saved a link, but the
archives saved me again.

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