magnetic sensor
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Posts: 46,084
I'm attempting to construct an ID and weigh bridge system for seabirds I'm
studying. I've got a load cell hooked up to a BS2sx to log my data, but
am having problems with the ID part of the system and would like any
creative input.
My study species, "Rhinos", are related to puffins and nest underground in
natural burrows and also nest boxes I have provided. The ID/weigh system
will be placed underneath the entrance tunnel to the nest boxes (PVC
pipe). My original idea was to tag 1 of a pair of birds with a magnet so
that weights in conjunction with a magnet reading signify one bird, and
weights without a magnet reading signify the other. Weights under 450g
signify the chick. The tag for the adult is a single Rare Earth magnet
epoxied on a plastic leg band. I'm attempting to determine weights of
males and females over time, the amount of fish they bring their chicks,
and the growth rate of the chicks, all part of a project for seabird
conservation and fisheries management. Weight of the fish brought to a
chick equals the weight of an adult upon entering the tunnel minus the
weight of the adult upon exit.
I have Hall effect sensors (Allegro Microsystems A3515), but am not able
to get a reliable reading using these, as a good read distance for the
sensor is only ~1/4-1/2 inch. I thought I could get a reading from up to
6 inches away, as detailed in Radio Shack's "Electronic Sensor Circuits &
Projects" book, p. 89, "Ultra-sensitive magnet switch", using two A3515s
placed side by side. But it didn't work! I need at least a 3-4 inch
accurate read distance for my project.
I also got Honeywell HMR1021Z magnetic sensors to try, but not many, as
they're expensive, and I fear the same problem.
I'm looking for suggestions as to how to make my original idea work or as
a last resort, a new, inexpensive idea on how to ID the birds. Laser
trips won't work, because I need to distinguish the individuals. I would
love to use PIT tags (passive transponders), but can't afford them, at
least the ones I've seen commercially available (AVID systems, etc.) in
the size and durability I need (~10mm, water and depth-proof). Hopefully
I can get this thing up and running before the birds leave for the year!
Any suggestions?
Thanks,
Julie Thayer
Marine Science Program
Point Reyes Bird Observatory
and
Wildlife, Fisheries & Conservation Biology
University of California, Davis
studying. I've got a load cell hooked up to a BS2sx to log my data, but
am having problems with the ID part of the system and would like any
creative input.
My study species, "Rhinos", are related to puffins and nest underground in
natural burrows and also nest boxes I have provided. The ID/weigh system
will be placed underneath the entrance tunnel to the nest boxes (PVC
pipe). My original idea was to tag 1 of a pair of birds with a magnet so
that weights in conjunction with a magnet reading signify one bird, and
weights without a magnet reading signify the other. Weights under 450g
signify the chick. The tag for the adult is a single Rare Earth magnet
epoxied on a plastic leg band. I'm attempting to determine weights of
males and females over time, the amount of fish they bring their chicks,
and the growth rate of the chicks, all part of a project for seabird
conservation and fisheries management. Weight of the fish brought to a
chick equals the weight of an adult upon entering the tunnel minus the
weight of the adult upon exit.
I have Hall effect sensors (Allegro Microsystems A3515), but am not able
to get a reliable reading using these, as a good read distance for the
sensor is only ~1/4-1/2 inch. I thought I could get a reading from up to
6 inches away, as detailed in Radio Shack's "Electronic Sensor Circuits &
Projects" book, p. 89, "Ultra-sensitive magnet switch", using two A3515s
placed side by side. But it didn't work! I need at least a 3-4 inch
accurate read distance for my project.
I also got Honeywell HMR1021Z magnetic sensors to try, but not many, as
they're expensive, and I fear the same problem.
I'm looking for suggestions as to how to make my original idea work or as
a last resort, a new, inexpensive idea on how to ID the birds. Laser
trips won't work, because I need to distinguish the individuals. I would
love to use PIT tags (passive transponders), but can't afford them, at
least the ones I've seen commercially available (AVID systems, etc.) in
the size and durability I need (~10mm, water and depth-proof). Hopefully
I can get this thing up and running before the birds leave for the year!
Any suggestions?
Thanks,
Julie Thayer
Marine Science Program
Point Reyes Bird Observatory
and
Wildlife, Fisheries & Conservation Biology
University of California, Davis
Comments
How about placing the coil of a metal detector at the entrance. Placing
a small piece of ferrous metal on the
band of a bird could be detected by a metal detector. Circuit Cellar of a month
ago had an article on a metal detector
using a micro to detect the frequency of the metal detector output. Different
size pieces of metal would give different
frequencies, allowing you to ID more than one subject.
Regards, Theron
Julie Thayer wrote:
> I'm attempting to construct an ID and weigh bridge system for seabirds I'm
> studying. I've got a load cell hooked up to a BS2sx to log my data, but
> am having problems with the ID part of the system and would like any
> creative input.
>
> My study species, "Rhinos", are related to puffins and nest underground in
> natural burrows and also nest boxes I have provided. The ID/weigh system
> will be placed underneath the entrance tunnel to the nest boxes (PVC
> pipe). My original idea was to tag 1 of a pair of birds with a magnet so
> that weights in conjunction with a magnet reading signify one bird, and
> weights without a magnet reading signify the other. Weights under 450g
> signify the chick. The tag for the adult is a single Rare Earth magnet
> epoxied on a plastic leg band. I'm attempting to determine weights of
> males and females over time, the amount of fish they bring their chicks,
> and the growth rate of the chicks, all part of a project for seabird
> conservation and fisheries management. Weight of the fish brought to a
> chick equals the weight of an adult upon entering the tunnel minus the
> weight of the adult upon exit.
>
> I have Hall effect sensors (Allegro Microsystems A3515), but am not able
> to get a reliable reading using these, as a good read distance for the
> sensor is only ~1/4-1/2 inch. I thought I could get a reading from up to
> 6 inches away, as detailed in Radio Shack's "Electronic Sensor Circuits &
> Projects" book, p. 89, "Ultra-sensitive magnet switch", using two A3515s
> placed side by side. But it didn't work! I need at least a 3-4 inch
> accurate read distance for my project.
>
> I also got Honeywell HMR1021Z magnetic sensors to try, but not many, as
> they're expensive, and I fear the same problem.
>
> I'm looking for suggestions as to how to make my original idea work or as
> a last resort, a new, inexpensive idea on how to ID the birds. Laser
> trips won't work, because I need to distinguish the individuals. I would
> love to use PIT tags (passive transponders), but can't afford them, at
> least the ones I've seen commercially available (AVID systems, etc.) in
> the size and durability I need (~10mm, water and depth-proof). Hopefully
> I can get this thing up and running before the birds leave for the year!
>
> Any suggestions?
>
> Thanks,
> Julie Thayer
> Marine Science Program
> Point Reyes Bird Observatory
> and
> Wildlife, Fisheries & Conservation Biology
> University of California, Davis
>
> To UNSUBSCRIBE, just send mail to:
> basicstamps-unsubscribe@yahoogroups.com
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Body of the message will be ignored.
>
>
> Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
used in window/door sensors for alarm systems. if it worked from far
enough away it would be even easier to read than a hall sensor
Jason
Julie Thayer wrote:
>
> I'm attempting to construct an ID and weigh bridge system for seabirds I'm
> studying. I've got a load cell hooked up to a BS2sx to log my data, but
> am having problems with the ID part of the system and would like any
> creative input.
>
> My study species, "Rhinos", are related to puffins and nest underground in
> natural burrows and also nest boxes I have provided. The ID/weigh system
> will be placed underneath the entrance tunnel to the nest boxes (PVC
> pipe). My original idea was to tag 1 of a pair of birds with a magnet so
> that weights in conjunction with a magnet reading signify one bird, and
> weights without a magnet reading signify the other. Weights under 450g
> signify the chick. The tag for the adult is a single Rare Earth magnet
> epoxied on a plastic leg band. I'm attempting to determine weights of
> males and females over time, the amount of fish they bring their chicks,
> and the growth rate of the chicks, all part of a project for seabird
> conservation and fisheries management. Weight of the fish brought to a
> chick equals the weight of an adult upon entering the tunnel minus the
> weight of the adult upon exit.
>
> I have Hall effect sensors (Allegro Microsystems A3515), but am not able
> to get a reliable reading using these, as a good read distance for the
> sensor is only ~1/4-1/2 inch. I thought I could get a reading from up to
> 6 inches away, as detailed in Radio Shack's "Electronic Sensor Circuits &
> Projects" book, p. 89, "Ultra-sensitive magnet switch", using two A3515s
> placed side by side. But it didn't work! I need at least a 3-4 inch
> accurate read distance for my project.
>
> I also got Honeywell HMR1021Z magnetic sensors to try, but not many, as
> they're expensive, and I fear the same problem.
>
> I'm looking for suggestions as to how to make my original idea work or as
> a last resort, a new, inexpensive idea on how to ID the birds. Laser
> trips won't work, because I need to distinguish the individuals. I would
> love to use PIT tags (passive transponders), but can't afford them, at
> least the ones I've seen commercially available (AVID systems, etc.) in
> the size and durability I need (~10mm, water and depth-proof). Hopefully
> I can get this thing up and running before the birds leave for the year!
>
> Any suggestions?
>
> Thanks,
> Julie Thayer
> Marine Science Program
> Point Reyes Bird Observatory
> and
> Wildlife, Fisheries & Conservation Biology
> University of California, Davis
>
> To UNSUBSCRIBE, just send mail to:
> basicstamps-unsubscribe@yahoogroups.com
> from the same email address that you subscribed with. Text in the Subject and
Body of the message will be ignored.
>
>
> Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
--
_______________________________________________
Jason Lavoie
jlavoie@e...
jlavoie@o...
ICQ#:10604243
Electrical Engineering III, Carleton University
around $50 ea and can work as magnetometer reading absolute N and W
earth field values. I believe it can detect even small magnets at 4".
(magnets will affect the birds orientation ? ) Another way may be a
metal detector coil.
ACJacques
Julie Thayer wrote:
>
> I'm attempting to construct an ID and weigh bridge system for seabirds I'm
> studying. I've got a load cell hooked up to a BS2sx to log my data, but
> am having problems with the ID part of the system and would like any
> creative input.
>
> My study species, "Rhinos", are related to puffins and nest underground in
> natural burrows and also nest boxes I have provided. The ID/weigh system
> will be placed underneath the entrance tunnel to the nest boxes (PVC
> pipe). My original idea was to tag 1 of a pair of birds with a magnet so
> that weights in conjunction with a magnet reading signify one bird, and
> weights without a magnet reading signify the other. Weights under 450g
> signify the chick. The tag for the adult is a single Rare Earth magnet
> epoxied on a plastic leg band. I'm attempting to determine weights of
> males and females over time, the amount of fish they bring their chicks,
> and the growth rate of the chicks, all part of a project for seabird
> conservation and fisheries management. Weight of the fish brought to a
> chick equals the weight of an adult upon entering the tunnel minus the
> weight of the adult upon exit.
>
> I have Hall effect sensors (Allegro Microsystems A3515), but am not able
> to get a reliable reading using these, as a good read distance for the
> sensor is only ~1/4-1/2 inch. I thought I could get a reading from up to
> 6 inches away, as detailed in Radio Shack's "Electronic Sensor Circuits &
> Projects" book, p. 89, "Ultra-sensitive magnet switch", using two A3515s
> placed side by side. But it didn't work! I need at least a 3-4 inch
> accurate read distance for my project.
>
> I also got Honeywell HMR1021Z magnetic sensors to try, but not many, as
> they're expensive, and I fear the same problem.
>
> I'm looking for suggestions as to how to make my original idea work or as
> a last resort, a new, inexpensive idea on how to ID the birds. Laser
> trips won't work, because I need to distinguish the individuals. I would
> love to use PIT tags (passive transponders), but can't afford them, at
> least the ones I've seen commercially available (AVID systems, etc.) in
> the size and durability I need (~10mm, water and depth-proof). Hopefully
> I can get this thing up and running before the birds leave for the year!
>
> Any suggestions?
>
> Thanks,
> Julie Thayer
> Marine Science Program
> Point Reyes Bird Observatory
> and
> Wildlife, Fisheries & Conservation Biology
> University of California, Davis
>
> To UNSUBSCRIBE, just send mail to:
> basicstamps-unsubscribe@yahoogroups.com
> from the same email address that you subscribed with. Text in the Subject and
Body of the message will be ignored.
>
>
> Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
financial constraints but you might be able to detect
a non linear junction like that found in a cheap diode
or transistor at a distance. The trick is to radiate
the pn junction with enough RF energy to cause
harmonics to re-radiate and then be able to detect
them. I'm not an EE but you might be able to use a
car's radar detector as your receiver/detector if you
could build a transmitter on the right frequency to
generate a harmonic in the radar detector's passband.
Just a thought. Another idea might be just a simple
magnetometer or "metal detector" placed under the
entrance. You might check with an alarm supply place
for the loop device that you place under the ground to
detect a passing vehicle, under the close distances
maybe it would be sensitive enough to detect a metal
leg band. Good Luck.
--- Julie Thayer <jathayer@u...> wrote:
>
> I'm attempting to construct an ID and weigh bridge
> system for seabirds I'm
> studying. I've got a load cell hooked up to a BS2sx
> to log my data, but
> am having problems with the ID part of the system
> and would like any
> creative input.
>
> My study species, "Rhinos", are related to puffins
> and nest underground in
> natural burrows and also nest boxes I have provided.
> The ID/weigh system
> will be placed underneath the entrance tunnel to the
> nest boxes (PVC
> pipe). My original idea was to tag 1 of a pair of
> birds with a magnet so
> that weights in conjunction with a magnet reading
> signify one bird, and
> weights without a magnet reading signify the other.
> Weights under 450g
> signify the chick. The tag for the adult is a
> single Rare Earth magnet
> epoxied on a plastic leg band. I'm attempting to
> determine weights of
> males and females over time, the amount of fish they
> bring their chicks,
> and the growth rate of the chicks, all part of a
> project for seabird
> conservation and fisheries management. Weight of
> the fish brought to a
> chick equals the weight of an adult upon entering
> the tunnel minus the
> weight of the adult upon exit.
>
> I have Hall effect sensors (Allegro Microsystems
> A3515), but am not able
> to get a reliable reading using these, as a good
> read distance for the
> sensor is only ~1/4-1/2 inch. I thought I could get
> a reading from up to
> 6 inches away, as detailed in Radio Shack's
> "Electronic Sensor Circuits &
> Projects" book, p. 89, "Ultra-sensitive magnet
> switch", using two A3515s
> placed side by side. But it didn't work! I need at
> least a 3-4 inch
> accurate read distance for my project.
>
> I also got Honeywell HMR1021Z magnetic sensors to
> try, but not many, as
> they're expensive, and I fear the same problem.
>
> I'm looking for suggestions as to how to make my
> original idea work or as
> a last resort, a new, inexpensive idea on how to ID
> the birds. Laser
> trips won't work, because I need to distinguish the
> individuals. I would
> love to use PIT tags (passive transponders), but
> can't afford them, at
> least the ones I've seen commercially available
> (AVID systems, etc.) in
> the size and durability I need (~10mm, water and
> depth-proof). Hopefully
> I can get this thing up and running before the birds
> leave for the year!
>
> Any suggestions?
>
> Thanks,
> Julie Thayer
> Marine Science Program
> Point Reyes Bird Observatory
> and
> Wildlife, Fisheries & Conservation Biology
> University of California, Davis
>
> To UNSUBSCRIBE, just send mail to:
> basicstamps-unsubscribe@yahoogroups.com
> from the same email address that you subscribed
> with. Text in the Subject and Body of the message
> will be ignored.
>
>
> Your use of Yahoo! Groups is subject to
> http://docs.yahoo.com/info/terms/
>
>
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An ordinary pocket compass can pick up a rare earth magnet several
inches away, provided it passes by at a favored orientation, and
provided there are no ferrous materials in the vicinity (weighing
pan?). The compass at least provides a way to "visualize" the field
produced.
Perhaps a compass needle partially blocking and modulating a light
beam would serve as a more sensitive "low-tech" detector. Hall
effect sensors do not work reliably below 1 gauss. I can easily see a
twitch in a compass needle that is caused by a field much less than
the earth's 0.5 gauss.
What size and type of magnet you are using, what polarization in
relation to the leg band? A reason to use two sensors is to assure
that at least one of them is at a favored orientation to the magnet.
You may get more mileage out of the solid state sensor by amplifying
the AC component of the signal. Hook the output of your sensors up
to an oscilloscope set on a sensitive AC range, and see if you can
detect any twitches above the noise level as the magnet walks by.
The noise and instability will probably be in a wide band of
frequencies, with lots of 1/f noise and temperature dependence. A
great improvement in the signal to noise ratio can be had by forcing
the signal to fall in a narrow frequency band. This was the
principle of the old "flip coil" for measuring small magnetic fields.
The sensor is simply a coil of wire rotated or shaken at a steady
frequency in the area where the field is to be detected. That moves
the signal to a single known frequency where super noise reduction is
possible using a lock-in amplifier or synchronous detection. The
same techniques might work with a hall-effect sensor.
Contact me if you would like to talk about this further. I did thesis
work on tagging bumblebees, and I'm located over in Berserkeley.
-- regards,
Thomas Tracy Allen Ph.D.
electronically monitored ecosystems
mailto:tracy@e...
http://www.emesystems.com
510-848-5725
>I'm attempting to construct an ID and weigh bridge system for seabirds I'm
>studying. I've got a load cell hooked up to a BS2sx to log my data, but
>am having problems with the ID part of the system and would like any
>creative input.
>
>My study species, "Rhinos", are related to puffins and nest underground in
>natural burrows and also nest boxes I have provided. The ID/weigh system
>will be placed underneath the entrance tunnel to the nest boxes (PVC
>pipe). My original idea was to tag 1 of a pair of birds with a magnet so
>that weights in conjunction with a magnet reading signify one bird, and
>weights without a magnet reading signify the other. Weights under 450g
>signify the chick. The tag for the adult is a single Rare Earth magnet
>epoxied on a plastic leg band. I'm attempting to determine weights of
>males and females over time, the amount of fish they bring their chicks,
>and the growth rate of the chicks, all part of a project for seabird
>conservation and fisheries management. Weight of the fish brought to a
>chick equals the weight of an adult upon entering the tunnel minus the
>weight of the adult upon exit.
>
>I have Hall effect sensors (Allegro Microsystems A3515), but am not able
>to get a reliable reading using these, as a good read distance for the
>sensor is only ~1/4-1/2 inch. I thought I could get a reading from up to
>6 inches away, as detailed in Radio Shack's "Electronic Sensor Circuits &
>Projects" book, p. 89, "Ultra-sensitive magnet switch", using two A3515s
>placed side by side. But it didn't work! I need at least a 3-4 inch
>accurate read distance for my project.
>
>I also got Honeywell HMR1021Z magnetic sensors to try, but not many, as
>they're expensive, and I fear the same problem.
>
>I'm looking for suggestions as to how to make my original idea work or as
>a last resort, a new, inexpensive idea on how to ID the birds. Laser
>trips won't work, because I need to distinguish the individuals. I would
>love to use PIT tags (passive transponders), but can't afford them, at
>least the ones I've seen commercially available (AVID systems, etc.) in
>the size and durability I need (~10mm, water and depth-proof). Hopefully
>I can get this thing up and running before the birds leave for the year!
>
>Any suggestions?
>
>Thanks,
>Julie Thayer
>Marine Science Program
>Point Reyes Bird Observatory
>and
>Wildlife, Fisheries & Conservation Biology
>University of California, Davis
find inside my books from Borders can't be more than a nickel.
patmat (Go Bears, berkeley 82)
--- In basicstamps@y..., Julie Thayer <jathayer@u...> wrote:
>
> I'm attempting to construct an ID and weigh bridge system for
seabirds I'm
> studying. <snip>
>frequencies, with lots of 1/f noise and temperature dependence. A
>great improvement in the signal to noise ratio can be had by forcing
>the signal to fall in a narrow frequency band. This was the
>principle of the old "flip coil" for measuring small magnetic fields.
>The sensor is simply a coil of wire rotated or shaken at a steady
>frequency in the area where the field is to be detected. That moves
>the signal to a single known frequency where super noise reduction is
>possible using a lock-in amplifier or synchronous detection. The
>same techniques might work with a hall-effect sensor.
You can get high sensitivity without moving parts, with a fluxgate
sensor... A core is wound with two (or three, as in a fluxgate compass)
orthogonal windings. One winding is driven to modulate core permeability
(usually switching it into and out of saturation). The other winding
outputs a signal proportional to magnetic field strength after synchronous
demodulation. The circuitry can be remarkably simple.
Don Lancaster has some useful stuff on magnetic field sensing:
http://www.tinaja.com/glib/muse103.pdf
http://www.tinaja.com/glib/muse104.pdf
Mike Hardwick, for Decade Engineering -- <http://www.decadenet.com>
Manufacturer of the famous BOB-II Serial Video Text Display Module!
Expanding on your multi-axis suggestion, Tracy, the Sentron 3D-H-10
(www.sentron.ch) is a 3-axis Hall generator.
Dennis O'Leary
Original Message
From: Tracy Allen [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=vOFdqB-ebEw3dDEyJRvKw57XB9t-Urlc3W_JdCbOwjzMrv1uGVqSwI6mijo3-2ZZt2dmqxZsM41T2OHYDqM]tracy@e...[/url
Sent: Thursday, June 21, 2001 12:48 AM
To: basicstamps@yahoogroups.com
Subject: Re: [noparse][[/noparse]basicstamps] magnetic sensor
Hi Julie,
An ordinary pocket compass can pick up a rare earth magnet several
inches away, provided it passes by at a favored orientation, and
provided there are no ferrous materials in the vicinity (weighing
pan?). The compass at least provides a way to "visualize" the field
produced.
Perhaps a compass needle partially blocking and modulating a light
beam would serve as a more sensitive "low-tech" detector. Hall
effect sensors do not work reliably below 1 gauss. I can easily see a
twitch in a compass needle that is caused by a field much less than
the earth's 0.5 gauss.
What size and type of magnet you are using, what polarization in
relation to the leg band? A reason to use two sensors is to assure
that at least one of them is at a favored orientation to the magnet.
You may get more mileage out of the solid state sensor by amplifying
the AC component of the signal. Hook the output of your sensors up
to an oscilloscope set on a sensitive AC range, and see if you can
detect any twitches above the noise level as the magnet walks by.
The noise and instability will probably be in a wide band of
frequencies, with lots of 1/f noise and temperature dependence. A
great improvement in the signal to noise ratio can be had by forcing
the signal to fall in a narrow frequency band. This was the
principle of the old "flip coil" for measuring small magnetic fields.
The sensor is simply a coil of wire rotated or shaken at a steady
frequency in the area where the field is to be detected. That moves
the signal to a single known frequency where super noise reduction is
possible using a lock-in amplifier or synchronous detection. The
same techniques might work with a hall-effect sensor.
Contact me if you would like to talk about this further. I did thesis
work on tagging bumblebees, and I'm located over in Berserkeley.
-- regards,
Thomas Tracy Allen Ph.D.
electronically monitored ecosystems
mailto:tracy@e...
http://www.emesystems.com
510-848-5725
>I'm attempting to construct an ID and weigh bridge system for seabirds I'm
>studying. I've got a load cell hooked up to a BS2sx to log my data, but
>am having problems with the ID part of the system and would like any
>creative input.
>
>My study species, "Rhinos", are related to puffins and nest underground in
>natural burrows and also nest boxes I have provided. The ID/weigh system
>will be placed underneath the entrance tunnel to the nest boxes (PVC
>pipe). My original idea was to tag 1 of a pair of birds with a magnet so
>that weights in conjunction with a magnet reading signify one bird, and
>weights without a magnet reading signify the other. Weights under 450g
>signify the chick. The tag for the adult is a single Rare Earth magnet
>epoxied on a plastic leg band. I'm attempting to determine weights of
>males and females over time, the amount of fish they bring their chicks,
>and the growth rate of the chicks, all part of a project for seabird
>conservation and fisheries management. Weight of the fish brought to a
>chick equals the weight of an adult upon entering the tunnel minus the
>weight of the adult upon exit.
>
>I have Hall effect sensors (Allegro Microsystems A3515), but am not able
>to get a reliable reading using these, as a good read distance for the
>sensor is only ~1/4-1/2 inch. I thought I could get a reading from up to
>6 inches away, as detailed in Radio Shack's "Electronic Sensor Circuits &
>Projects" book, p. 89, "Ultra-sensitive magnet switch", using two A3515s
>placed side by side. But it didn't work! I need at least a 3-4 inch
>accurate read distance for my project.
>
>I also got Honeywell HMR1021Z magnetic sensors to try, but not many, as
>they're expensive, and I fear the same problem.
>
>I'm looking for suggestions as to how to make my original idea work or as
>a last resort, a new, inexpensive idea on how to ID the birds. Laser
>trips won't work, because I need to distinguish the individuals. I would
>love to use PIT tags (passive transponders), but can't afford them, at
>least the ones I've seen commercially available (AVID systems, etc.) in
>the size and durability I need (~10mm, water and depth-proof). Hopefully
>I can get this thing up and running before the birds leave for the year!
>
>Any suggestions?
>
>Thanks,
>Julie Thayer
>Marine Science Program
>Point Reyes Bird Observatory
>and
>Wildlife, Fisheries & Conservation Biology
>University of California, Davis