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'[EE] Vehicle detection - magnetic sensors?'
2006\10\11@190357 by Debbie

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PICers,
I have  a possible(?) project coming up that involves vehicle
detection/counting. Pessure mats, wire loops etc not an option. The gizmo needs
to be small, & portable - the requirement is to count cars as they enter/leave
a large outdoors *BIG* temporary car park. The cars will come down a narrow
track marked out with poles/flags, so the sensor can be positioned pretty close
as they pass buy. digging up the grass for cables etc - No No.

I was thinking maybe of Honeywell's detectors. To wit, one of these --->

http://www.ssec.honeywell.com/magnetic/mark_det.html

Has anyone used them? Are they OK? Are there better/cheaper devices around?

Thanks for advice - Debbie



               
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2006\10\11@191600 by Mauricio Jancic

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I would suggest to use a desktop computer and a camera, it would be chip and
you will avoid developing it, if it's a one time project. I have a software
to do the task, it can use, for example a cheap ip camera. It's intended for
other purposes, but can be modified to identify moving cars and count them.

Regards,

Mauricio Jancic
Janso Desarrollos
http://www.janso.com.ar
spam_OUTinfoTakeThisOuTspamjanso.com.ar
(54) 11-4542-3519


> {Original Message removed}

2006\10\11@191946 by Shawn Wilton

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How narrow is the track?  You could potentially use laser or IR if you can
position the vehicles such that only one goes through at a time (laser or
IR) and/or the track is narrow enough to get the sensor (IR) close to the
vehicle)





On 10/11/06, Debbie <.....cyberia429-piclistKILLspamspam@spam@yahoo.com.au> wrote:
{Quote hidden}

> -

2006\10\11@192801 by Shawn Wilton

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Well, if you're going to do that then you could write a small filtering
program in Matlab.  We wrote an application to count the amount of change in
a picture taken with one of those small Agilent CMOS cameras you see in all
of the phones now.  Fun project, and not terribly difficult either.

But I still think some sort of laser sight would work the best.  Every time
the line is broken, you have a vehicle in the "trap".


On 10/11/06, Mauricio Jancic <infospamKILLspamjanso.com.ar> wrote:
{Quote hidden}

> > {Original Message removed}

2006\10\11@193936 by peter green

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> PICers,
> I have  a possible(?) project coming up that involves vehicle
> detection/counting. Pessure mats, wire loops etc not an option.
> The gizmo needs
> to be small, & portable - the requirement is to count cars as
> they enter/leave
> a large outdoors *BIG* temporary car park. The cars will come
> down a narrow
> track marked out with poles/flags, so the sensor can be
> positioned pretty close
> as they pass buy. digging up the grass for cables etc - No No.
what are you using theese counts for?

do in cars and out cars take different routes?

what accuracy do you need (e.g. what proportion of counts can you afford to
gain/lose before the data becomes useless to you)


2006\10\11@195012 by Jinx

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Get a laser pointer and bounce it back off a mirror. Into a
parabolic collector if necessary. BTDT

2006\10\11@195444 by Jinx

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> digging up the grass for cables etc - No No

If you do decide to use a wired solution, not really necessary
to make a mess (although presumably vehicles are going to
do that anyway - is that why you don't want to lay a wire that
will get trashed ?). You need only make a slit in the turf with a
spade and lay the wire down in that

2006\10\11@210400 by Debbie

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--- peter green <EraseMEplugwashspam_OUTspamTakeThisOuTP10Link.net> wrote:

> what are you using theese counts for?

Sounds like they want to check up on ticket sales vs cars in/cars out.

> do in cars and out cars take different routes?

Yep.

>
> what accuracy do you need (e.g. what proportion of counts can you afford to
> gain/lose before the data becomes useless to you)

Basically, want to log all cars. The vehicles will be pretty close to the
sensor and slow moving (<15 k/h) so should give big magnetic sig? Path width
should be, say, <5metres. It's a sports event - as the car park fills up, they
move the poles, path and traffic wardens someplace else. Ditto car counter. So
you probly don't want a gizmo that needs turf dug up or dangles loops or is
fiddly to align. I'm thinking magnetic would be the way to go? Those Honeywell
sensors have analogue o/p but that wouldn't be a big drama.
Thanks -Debbie


               
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2006\10\11@212220 by Richard Prosser

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Do they need to detect motorbikes / bicycles / golfcarts  etc..

RP

On 12/10/06, Debbie <cyberia429-piclistspamspam_OUTyahoo.com.au> wrote:
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> -

2006\10\11@213647 by Bob Axtell

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Debbie wrote:
{Quote hidden}

The system I was familiar with used a loop buried in the concrete. The
loop (plus the concrete) formed a tuned
circuit. When a car drove over it, it detuned it because of the metal of
the car. It was rugged and durable. Very
easy to design, too, and insensitive to people and small objects  over
it. About 2m in diameter, buried about 4"
deep. About 100 turns of #24 magnet wire.

Very similar to the familiar "metal detector" design, where a loop of
wire, covered with a lead foil shield, was embedded
into a plastic wheel.  You have to have the shield to stop capacitive
(leaving only  the inductive) effects.

These are used in airport parking lots to dispense a ticket when a car
drives up, as well as to verify that the car has left
the dispenser.

--Bob

2006\10\11@215758 by Jinx

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> Very similar to the familiar "metal detector" design

The detector doesn't have to go in the ground. It can sit on
top, perhaps under a plank, which would also be the spacing
for the poles, so the whole thing could be moved intact from
point to point

Silicon Chip had this as a project a couple of years ago

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

Available as kit KC5402 from http://www.jaycar.com.au

2006\10\11@220524 by Jinx

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> So you probly don't want a gizmo that needs turf dug up or
> dangles loops or is fiddly to align

IMHonestO, a laser is the least problematic solution. It won't
get dirty, is cheap, reliable, and not really that much of a chore
to set up. The beam is quite plainly visible on the target so it's
easily aligned. The detection process is very simple. Although
people will be sensed, their passage across the beam is of much
shorter duration than a vehicle and can be ignored / filtered out

If the beam can also be modulated, that makes it (almost) totally
immune to ambient perturbations, especially with a specific colour
filter over the target sensor

2006\10\11@234023 by Debbie

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--- Jinx <RemoveMEjoecolquittTakeThisOuTspamclear.net.nz> wrote:
> Silicon Chip had this as a project a couple of years ago
>
> www.siliconchip.com.au/cms/A_102998/article.html
>
> Available as kit KC5402 from http://www.jaycar.com.au

Hey, goodonya Jinx!!!! That article sounds //very// much like what I was
thinking of.

RP asks: golf carts, m'bikes?

No, don't think they're of concern.

Thanks guys. Ideas .....

Debbie :)




               
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2006\10\12@000504 by Sergey Dryga

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Jinx <joecolquitt <at> clear.net.nz> writes:

>
> > So you probly don't want a gizmo that needs turf dug up or
> > dangles loops or is fiddly to align
>
> IMHonestO, a laser is the least problematic solution. It won't
> get dirty, is cheap, reliable, and not really that much of a chore
> to set up. The beam is quite plainly visible on the target so it's
> easily aligned. The detection process is very simple. Although
> people will be sensed, their passage across the beam is of much
> shorter duration than a vehicle and can be ignored / filtered out
>
> If the beam can also be modulated, that makes it (almost) totally
> immune to ambient perturbations, especially with a specific colour
> filter over the target sensor
>
Are there any health/legal problems with lasers for such application as
parking?  Suppose somebody gets drunk at the sporting event and decides to look
into the laser?  Even 5 mW laser pointer can be bad for eyes. Legal liabilities
could be very high.

Sergey Dryga



2006\10\12@005646 by Stephen D. Barnes

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Why not use a standard industrial retro-reflective (IR) sensor with the
appropriate reflector?
See http://www.banner.com for more info. There are many other manufacturers of
these but the Banner mini-beam
sensors are great.

Regards,
Stephen D. Barnes

Debbie wrote:
{Quote hidden}

2006\10\12@005806 by Jinx

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> Are there any health/legal problems with lasers for such application
> as parking?  Suppose somebody gets drunk at the sporting event
> and decides to look into the laser?  Even 5 mW laser pointer can
> be bad for eyes. Legal liabilities could be very high

I think you'd have to be *** extremely *** drunk for the blink
response not to be working. And I'm sure even someone
completely sodden with booze would turn away, if only out of
irritation, and stagger off muttering. Anything's possible of
course, and there have been some silly PC liability issues in
Australia recently

2006\10\12@010927 by Shawn Wilton

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You could go purchase the a garage door opener and use the child detection
sensors out of that.  If you can't find the sensors elsewhere.

On 10/11/06, Stephen D. Barnes <spamBeGonestephendbarnesspamBeGonespamcox.net> wrote:
{Quote hidden}

> -

2006\10\12@024158 by Tony Smith

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> You could go purchase the a garage door opener and use the child detection
> sensors out of that.  If you can't find the sensors elsewhere.


Personally, I'd use the child AS the detection method.  One of those metal
clicky counter thingys, and a block of chocolate as a bribe.

Reliability varies, of course.

Tony

(Cheap too, until WorkCover or Child Services finds out)

2006\10\12@082517 by Mark Scoville

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How about something air operated - like the old gas station drive over the
hose ding-ding. Maybe you could use a small aquarium pump to generate air
pressure and pump the pressure into an open-ended hose stretched across the
road. If someone drives over the hose the pressure builds up and trips an
air switch - then count the pulses - 1 pulse per axle.

Something like this...
http://www.metrocount.com/products/roadsideunit/index.html

Maybe this is not an option because it's too much like a pressure mat
though.

-- Mark

> {Original Message removed}

2006\10\12@113131 by Aaron

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Stephen D. Barnes wrote:

>Why not use a standard industrial retro-reflective (IR) sensor with the
>appropriate reflector?
>See http://www.banner.com for more info. There are many other manufacturers of
>these but the Banner mini-beam
>sensors are great.
>

This is exactly what I was going to suggest, but OP should note that
these will detect anything that breaks the light beam.  People, etc.  
You will also have to align the reflector and sensor every time it is moved.

BTW, that link should be http://www.bannerengineering.com.

(I am partial to the Mini-Beam SM312.)

Aaron

2006\10\12@153456 by Debbie

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--- Aaron <TakeThisOuTaaron.piclistEraseMEspamspam_OUTgmail.com> wrote:
> Stephen D. Barnes wrote:
> >Why not use a standard industrial retro-reflective (IR) sensor with the
>
> This is exactly what I was going to suggest, but OP should note that
> these will detect anything that breaks the light beam.  People, etc.  
> You will also have to align the reflector and sensor every time it is moved.

Hey, that's a good point! There'll be lots of people walking about, going
to/from cars, there'll be children, couple of kiosks/vendors selling balloons,
sausages etc. But it's only cars they want to count.

-- Mark Scoville <RemoveMEmscovillespamTakeThisOuTunicontrolinc.com> wrote:
> How about something air operated - like the old gas station drive over the

Yeah, I thought about those pressure hoses. The police(?) put them across roads
to monitor traffic. There are two snags with the hose idea, as I see it -->
1/ The ground in the car park (temporary venue) is soft in places. ie grass,
sandy soil etc. The wardens will move the flags + detectors etc about and you
don't know where, exactly.
2/ You don't want the tube getting snagged in cars' wheels or passersby
tripping over it.

So @ the mo' .... I'd say I'm leaning very much towards magnetic sensors. I
located a copy of that Silicon chip article in a local library, Jinx. Will go
dig it out today.
Debbie



               
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2006\10\12@162242 by Andre Abelian

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check this web site.
http://www.magneticsensors.com/datasheets/amr.pdf#search=%22honeywell%20car%20detection%22


Andre



{Original Message removed}

2006\10\14@071004 by Raphael Wimmer

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On Thu, 12 Oct 2006 01:03:55 +0200, Debbie  
<cyberia429-piclistEraseMEspam.....yahoo.com.au> wrote:

> PICers,
> I have  a possible(?) project coming up that involves vehicle
> detection/counting. [...]

Would a capacitive sensor do the job? There should be a sufficient  
difference in capacitance between people and cars. Using a LMC555 or  
similar for converting capacitance to frequency, and then counting this  
frequency with a PIC should be cheap and straightforward. I'm using the  
same technique for tracking gestures, and it works quite well even with a  
small human hand. Look at  
http://thereminvision.com/version-2/TV-II-index.html for a useable circuit  
design.
Using two 20x20 cm electrode plates should provide sufficient range and  
redundancy. Place one plate on each side of the track - if both show a  
capacitance change at the same time it's probably a car and not someone  
standing in front of it.

Raphael

--
Raphael Wimmer
LFE Media Informatics              E-Mail: EraseMEraphaelspamhcilab.org
University of Munich               WWW: http://hcilab.org
Amalienstr. 17                     Tel: +49 89 2180-4659
80333 München                      Fax: +49 89 2180-99-4659
Germany

2006\10\14@122858 by Anand Dhuru

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How about a 38  khz signal, being sent as 1 ms pulses; a 3 pin IR detector
would easily detect the pulses at the distance you want. Keep polling the
pulses; if they are interrupted, you increment the counter.

This would also work the other way (the vehicle reflects the signal) if you
need the trasnmitter and the detector on the same side. In this case, you'll
need to shield them from each other to prevent direct crossover, though.

Regards,

Anand

{Original Message removed}

2006\10\15@214451 by Debbie

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--- Anand Dhuru <RemoveMEardhuruEraseMEspamEraseMEvsnl.com> wrote:

> How about a 38  khz signal, being sent as 1 ms pulses; a 3 pin IR detector
>
> Anand

> From: "Richard Prosser" <RemoveMErhprosserspam_OUTspamKILLspamgmail.com>
>
> > Do they need to detect motorbikes / bicycles / golfcarts  etc..
>
Hmmm. Looks like it's either an IR sig, modulated @ 38-40kHz, to a reflector
and back or a magnetic sensor, Honeywell probly.
The reflector set up would work, I'd say, but needs to be aligned + I'm
thinking about battery capacity if you're flashing the light non stop all day.
The battery wouldn't have to be particularly small, however.

The gizmo described in that Si-chip article used a hand wound sensor coil, so
not really practical. Basically, it was a metal detector cct like you go after
nuggets with.

So, OK, I have a few 3-pin IR rx/demodulators ... will do some expts, see how
it looks. Thanks for all the tips, guys.
Debbie

PS: It's mainly cars they want to count. Bikes etc don't pay so not of
interest. I think motorbikes do but I'm guessing a big bike like a Harley or
top end BMW would probably have a (magnetic) signature like a car anyway.


               
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2006\10\15@231417 by Jinx

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> The gizmo described in that Si-chip article used a hand-
> wound sensor coil, so not really practical. Basically, it was
> a metal detector cct like you go after nuggets with

As they say in the article, the coil is thousands of fine turns
on a soft iron core and impractical to wind youself, so it's
supplied ready-made with the kit. The difference between
what SC did and a metal detector is that their coil is passive,
and relies on the disturbance of the Earth's magnetic field
to cause voltage in the coil. They call it a low-power system
(70mA, though I can see room for improvement in the circuit)
but I've no idea how that compares with a typical metal
detector

2006\10\15@234810 by Debbie

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--- Jinx <RemoveMEjoecolquittTakeThisOuTspamspamclear.net.nz> wrote:
>
> As they say in the article, the coil is thousands of fine turns
> on a soft iron core and impractical to wind youself, so it's
> supplied ready-made with the kit. The difference between
> what SC did and a metal detector is that their coil is passive,
> and relies on the disturbance of the Earth's magnetic field
> to cause voltage in the coil. They call it a low-power system
> (70mA, though I can see room for improvement in the circuit)
> but I've no idea how that compares with a typical metal
> detector

Yep, you're right Jinx. :) A metal detector has an oscillator to excite one
coil, usually. I built one a ways back. Turned out ants in central Victoria
have this habit of piling up tiny iron pellets all over their nests .... :(
Debbie



               
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2006\10\16@005035 by Jinx

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> Turned out ants in central Victoria have this habit of piling
> up tiny iron pellets all over their nests .... :(

I'd ask why, but can't think of a single reason why I'd want to ;-)

Ants haven't developed cannon warfare yet have they ? Cool
if they had

2006\10\16@033700 by Howard Winter

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Debbie,

On Mon, 16 Oct 2006 13:48:09 +1000 (EST), Debbie wrote:

{Quote hidden}

Perhaps it's a trap?  It gets metal detectorists to start digging, then the ants swarm out and eat them!  :-)

Cheers,


Howard Winter
St.Albans, England


2006\10\16@042715 by Anand Dhuru

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>Hmmm. Looks like it's either an IR sig, modulated @ 38-40kHz, to a
>reflector
>and back or a magnetic sensor, Honeywell probly.
>The reflector set up would work, I'd say, but needs to be aligned + I'm
>thinking about battery capacity if you're flashing the light non stop all
>day.
>The battery wouldn't have to be particularly small, however.

The alignment at the range you need is really not as difficult as it sounds;
the beam is fairly divergent, both ways, transmitting and reflecting. Its
the shielding to prevent direct reception you will have to be careful about.

Take a look at http://www.rentron.com/PicBasic/infrared_object_detection.htm

This is for PBP users, but you'll get the idea.

Regards,

Anand

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2006\10\16@100200 by Mike Hord

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> Hmmm. Looks like it's either an IR sig, modulated @ 38-40kHz, to a reflector
> and back or a magnetic sensor, Honeywell probly.
> The reflector set up would work, I'd say, but needs to be aligned + I'm
> thinking about battery capacity if you're flashing the light non stop all day.
> The battery wouldn't have to be particularly small, however.

Okay, two things jumping in at the last minute.

First, for an IR trip sensor, you need to modulate a signal at 38 kHz, and then
THAT signal needs to be switched on and off, too.  Most IR receivers will
filter out a constant source of 38 kHz flashing light (or so I'm given to
understand; may bear experimentation).

Second, try NVE's line of giant magnetoresistive sensors.  The most sensitive
ones can detect a screwdriver a foot away; I think they'd have NO trouble with
a car, even up to a couple of meters.  They're also cheap.

Mike H.

2006\10\16@122755 by David VanHorn

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>
>
> Second, try NVE's line of giant magnetoresistive sensors.  The most
> sensitive
> ones can detect a screwdriver a foot away; I think they'd have NO trouble
> with
> a car, even up to a couple of meters.  They're also cheap.



A large diameter coil, and current-voltage amp will detect cars quite a ways
away.
In hawaii, I expeimented with this using a six inch coil of a few turns, and
was able to see traffic on the street three floors down and about 20 feet
away.

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