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'[EE] Detecting vehicles by magnetism'
2005\05\17@220059 by Debbie

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PICers,
Looks like I might have an actual job in spec - hah! I'd need to detect moving
vehicles, I'd guess via their magnetism. Probably need to detect presence +
direction of travel. Anyone had experience with devices for magnetic vehicle
detecting that they'd wish to share? I'm mentally kicking round Honeywell's MR
detectors. Are there other types on the market? Any tips most appreciated
Thanks - Debbie.

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2005\05\17@224223 by Jinx

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This detects vehicles magnetically with a coil

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

There are other options, depends on the actual application

Could use broken beam/reflected beam, pressure sensor/air
pipe, shadow etc

2005\05\18@040844 by Michael Rigby-Jones

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>-----Original Message-----
>From: spam_OUTpiclist-bouncesTakeThisOuTspammit.edu [.....piclist-bouncesKILLspamspam@spam@mit.edu]
>Sent: 18 May 2005 03:01
>To: Microcontroller discussion list - Public.
>Subject: [EE] Detecting vehicles by magnetism
>
>
>PICers,
>Looks like I might have an actual job in spec - hah! I'd need
>to detect moving vehicles, I'd guess via their magnetism.
>Probably need to detect presence + direction of travel. Anyone
>had experience with devices for magnetic vehicle detecting
>that they'd wish to share? I'm mentally kicking round
>Honeywell's MR detectors. Are there other types on the market?
>Any tips most appreciated Thanks - Debbie.


I guess some more details on the application (if possible) would be
helpfull.  With the explosive growth of speed cameras here in the UK,
there are several different technologies in current use for vehicle
speed and direction detection.

Inductive loops in ground
Piezo cables in ground
Radar
Laser
ANPR Automatic Number Plate Recognition (or License plate for non UK
readers).

We now have a network of plate reading cameras on major roads throughout
the UK ("TrafficMaster") that is currently used for traffic congestion
monitoring, though it's potential for (mis)use for detcting speeding
drivers or simply for surveilance is surely tempting the powers that be.
However, it shows that the technology must now be relatively
inexpensive.

Regards

Mike

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2005\05\18@172104 by Debbie

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Thanks for those ideas Mike. That NVE website looks pretty interesting too.The
app will be - **if** it goes ahead? - to photograph cars on a country road.
It's a big station abutting a nat park and they want to monitor who uses roads
at back of their property by photographing vehicle rego plates. It's semi arid
Outback country so I think dust will be the killer - how do you photo thru a
dust cloud thrown up as the vehicle moves away? If go for a forward shot, you'd
have probs with the vehicle's headlights at night. Plus flash/illumination
probs. Still thinkin' about that.

Don't want to use inductive loops or anything that needs cables spread out - it
needs to be smallish & easy to deploy so solid state sensors look attractive.
The range of the sensor would be an issue - it needs to detect a vehicle from
the side of the road. That's not far as we're talking dirt tracks & large 4x4
vehicles mostly. don't need auto rego-number reading. Hmmm ... a laser bounced
off a corner reflector is a possibility, maybe. Would you say solid state MR
sensors could detect a vehicle in a situation like that?
Debbie

--- Michael Rigby-Jones <Michael.Rigby-JonesspamKILLspambookham.com> wrote:
{Quote hidden}

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2005\05\18@174957 by Jinx

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> Outback country so I think dust will be the killer - how do you
> photo thru a dust cloud thrown up as the vehicle moves away?

Can they put down scoria on a 10m, 20m section of road so
there wouldn't be dust to throw up ?

> Plus flash/illumination probs

Could use IR



2005\05\18@175330 by Dave VanHorn

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At 04:21 PM 5/18/2005, Debbie wrote:
>Thanks for those ideas Mike. That NVE website looks pretty interesting too.The
>app will be - **if** it goes ahead? - to photograph cars on a country road.
>It's a big station abutting a nat park and they want to monitor who uses roads
>at back of their property by photographing vehicle rego plates. It's semi arid
>Outback country so I think dust will be the killer - how do you photo thru a
>dust cloud thrown up as the vehicle moves away? If go for a forward
>shot, you'd
>have probs with the vehicle's headlights at night. Plus flash/illumination
>probs. Still thinkin' about that

Solid state cameras are pretty amazing that way. You can get the
pixels inbetween the overexposed ones, IF you disable any sort of
auto-exposure, and use your own ambient light sensor, and illumination.

>Don't want to use inductive loops or anything that needs cables
>spread out - it
>needs to be smallish & easy to deploy so solid state sensors look attractive.
>The range of the sensor would be an issue - it needs to detect a vehicle from
>the side of the road. That's not far as we're talking dirt tracks & large 4x4
>vehicles mostly. don't need auto rego-number reading. Hmmm ... a laser bounced
>off a corner reflector is a possibility, maybe.

Bugs?

Anything wider than about half the beamwidth will trigger it.

Critters and rain can be kept off the optics by the same sort of
thing they use for windshield wipers on ships.
Spinning plexiglas disc throws anything that lands off radially.

>Would you say solid state MR sensors could detect a vehicle in a
>situation like that?

It would be best, if the vehicle comes between you and the south pole.
You could also add a local bias magnet.

Be prepared to see this set off by geomagnetic storms.

You can also use a large-ish loop oriented like a sign, not buried.
With two of these, say 10' apart, you can go differential, and geomag
problems should null out.


Then there's the TX-RX method, send 1kHz into one coil, and use
another to pick it up, using synchronus boxcar detector integrator if
need be, to eliminate noise.  Level shifts tell you that the amount
of magnetic coupling has changed.

A tracking window comparator (I can give you details offlist) will
eliminate hits as the coupling varies slowly over time.

Third, you can set up the coils so that the field at the receiver is
nulled out, and adding metal unbalances it.
A bit trickier to set up, but very easy to produce in numbers.



2005\05\18@194855 by Stephen R Phillips

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--- Debbie <.....cyberia429-piclistKILLspamspam.....yahoo.com.au> wrote:
> Thanks for those ideas Mike. That NVE website looks pretty
> interesting too.The
> app will be - **if** it goes ahead? - to photograph cars on a country
> road.
> It's a big station abutting a nat park and they want to monitor who
> uses roads
> at back of their property by photographing vehicle rego plates. It's
> semi arid
> Outback country so I think dust will be the killer - how do you photo
> thru a
> dust cloud thrown up as the vehicle moves away? If go for a forward
> shot, you'd
> have probs with the vehicle's headlights at night. Plus
> flash/illumination
> probs. Still thinkin' about that.
>
I suggest using IR digital camera's instead.  You need to be sure the
paint used on most plates gives adequate contrast.  You can flood the
area with IR without anyone knowing about it, no flash problems.  As
for creating a photo out of that, you could store them on a digital
media card. Would make it quick to get the data out and quick to handle
(no processing fees etc).

> Don't want to use inductive loops or anything that needs cables
> spread out - it needs to be smallish & easy to deploy so solid state
> sensors look attractive.
> The range of the sensor would be an issue - it needs to detect a
> vehicle from the side of the road. That's not far as we're talking
> dirt tracks & large 4x4 vehicles mostly. don't need auto rego-number
> reading. Hmmm ... a laser bounced  off a corner reflector is a
> possibility, maybe. Would you say solid  state MR sensors could
> detect a vehicle in a situation like that?

For optically based sensors sun must be considered for false
triggering. IR is not immune to this problem.  Microwave is immune to
sun problems but might be interfered with in other ways.  You might
also have a range issue for sensors. Namely if you need to detect
something over a wide area (greater than 10 meters).  Through beam for
optical is probably best for that reason. Reflective sensors have too
high of losses. Both are suseptable to sun and light interference.

Stephen R. Phillips was here
Please be advised what was said may be absolutely wrong, and hereby this disclaimer follows.  I reserve the right to be wrong and admit it in front of the entire world.


               
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2005\05\19@042248 by Alan B. Pearce

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>how do you photo thru a dust cloud thrown up as the vehicle
>moves away? If go for a forward shot, you'd have probs with
>the vehicle's headlights at night. Plus flash/illumination
>probs. Still thinkin' about that.

You do what Europeans do for speed cameras. Use Infrared flash - the speeder
never knows they got caught until the notice arrives in the post, and other
speeders don't get warned by the flash that the camera is active.

Now there is a thought - I wonder what the market would be for a IR flash
detector so you see if the car in front got flashed, and I can slow down
before the camera ;))))

2005\05\19@042816 by Michael Rigby-Jones

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>-----Original Message-----
>From: Dave VanHorn [EraseMEpiclist-bouncesspam_OUTspamTakeThisOuTmit.edu]
>Sent: 18 May 2005 22:54
>To: Microcontroller discussion list - Public.; Microcontroller
>discussion list - Public.
>Subject: RE: [EE] Detecting vehicles by magnetism
>
>
>Then there's the TX-RX method, send 1kHz into one coil, and use
>another to pick it up, using synchronus boxcar detector integrator if
>need be, to eliminate noise.  Level shifts tell you that the amount
>of magnetic coupling has changed.
>

Developing this idea, how about the other metal detector methods such as
BFO or pulse induction?  Pulse induction in particular can achive pretty
good ranges.

Regards

Mike

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2005\05\19@043222 by Alan B. Pearce
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>Microwave is immune to sun problems but might
>be interfered with in other ways.

Depending on the frequency you use, it might also get detected by traffic
radar detectors, which might not suit you (i.e. it tells the subject where
they were photographed, and depending on end use may result in equipment
vandalisation).

I like Jinx's idea of putting down a dose of scoria to get a low dust area,
and you could bury a coil of wire in the scoria for a traffic detector
similar to those used for traffic lights in cities, and automatic gates. Use
cable with a heavy duty sheath should do it, but you could always put it in
plastic water pipe for extra protection. Run a couple of lengths right
across the roadway each side of a gap in a fence line (so they cannot drive
around them if they suspect a sensor of some sort) and then if the wire is
discovered and ripped up it is easily replaced.

2005\05\19@092718 by Dave VanHorn

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>
> >Then there's the TX-RX method, send 1kHz into one coil, and use
> >another to pick it up, using synchronus boxcar detector integrator if
> >need be, to eliminate noise.  Level shifts tell you that the amount
> >of magnetic coupling has changed.
> >
>
>Developing this idea, how about the other metal detector methods such as
>BFO or pulse induction?  Pulse induction in particular can achive pretty
>good ranges.

BFO is inherently unstable, and rain, temperature, etc would all factor in.

Pulse induction might be workable.

2005\05\19@100306 by alan smith

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Not magnetic but microwave

http://www.wavetronix.com/


               
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2005\05\19@134355 by Peter

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On Thu, 19 May 2005, Michael Rigby-Jones wrote:

> Developing this idea, how about the other metal detector methods such as
> BFO or pulse induction?  Pulse induction in particular can achive pretty
> good ranges.

Pulse induction on a car with ignition on will detect it even if the
pulse is not induced ;-)

What's wrong with a decent road hump and a weight triggered sensor near
it ?

Peter

2005\05\21@173505 by Debbie

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PICers,
Thankz for all the useful i/p on this. To sum all the ideas up, the app would
require the cams to stand unattended for long periods, so battery life is a key
issue. Ideas like coupled coils & BFOs would need an osc running all the time
so battery drain would be an issue there. It looks like either a pressure
pad/vibe sensor or something like Honeywell's or NVE's mag sensors might be the
way to go. Haven't gone thru the data sheets yet but Honeywell's intro "Vehicle
Detection & Compass Applications", Caruso & Withanawasam, says AMR sensors can
detect a vehicle from the curbside. What you need is to put the whole thing to
sleep @ low quiescent current & rely on a passive sensor to wake it up on
interrupt. You might then even want some sort of secondary sensor to confirm
presence of a bandit: and that could allow a higher current drain if for a
short on-time. That sounds like a pretty standard design - but I'll need to log
date/time of events. Have some calendar chips in hand so will work on that part
& read up on the sensors. Thanks everyone.
Debbie

> What's wrong with a decent road hump and a weight triggered sensor near
> it ?
> Peter

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