Today's Message Index:
----------------------
1. 05:43 AM - Re: coil tuning anyone? (Dan Billingsley)
2. 10:14 AM - Re: coil tuning anyone? (Robert L. Nuckolls, III)
3. 12:33 PM - Re: AOA circuitry (user9253)
4. 01:57 PM - Re: PM capacitor inrush (Jan de Jong)
5. 01:58 PM - Re: Re: AOA circuitry (Jared Yates)
6. 03:45 PM - Re: coil tuning anyone? (Dan Billingsley)
7. 06:01 PM - Re: PM capacitor inrush (Robert L. Nuckolls, III)
8. 07:39 PM - Re: Turning simple-ideas into working hardware. (Robert L. Nuckolls, III)
9. 08:09 PM - Re:hi!5c (leesafur@aol.com)
Message 1
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Subject: | Re: coil tuning anyone? |
Bob,
Thanks for the reply. My equipment is at school so I will send the make and
models to you Monday. Below I attached the link to where I got the plans. We are
making our search coil at about 12" diameter. I know if I followed the sizes
they gave it would come out fine, yet I would like to teach the kids how to do
coil tuning. In my electronics I class we wind coils to make crystal radios and
it would be good to cover tuning here as well. If you have any suggestions on
what might make the following project work better, I'm all ears.
http://www.easytreasure.co.uk/bfo.htm
Thanks a Bunch for taking a look!
Dan
----- Original Message ----
> From: "Robert L. Nuckolls, III" <nuckolls.bob@aeroelectric.com>
> To: aeroelectric-list@matronics.com
> Sent: Fri, February 25, 2011 8:48:27 PM
> Subject: Re: AeroElectric-List: coil tuning anyone?
>
><nuckolls.bob@aeroelectric.com>
>
> At 09:29 PM 2/25/2011, you wrote:
><dan@azshowersolutions.com>
> >
> >
> > I have found plans on building a simple BFO metal detector. I will have them
> > making their own PCB's and constructing the entire project from raw
>materials.
> > The area I am needing help with is tuning the coils. They should be wound to
> > match as close as I can get them so the fine tuner will be effective + or -
> > 250hz (the frequency target is 100khz)
>
>
>
>
> > The tools I have available to me include an oscilloscope and a function
> > generator...the questions;
>
> What are the make/model of your test equipment items?
>
> > 1. Do I have what I need to assist / measure my coil windings to get them in
>the
> > frequency ball park?
>
> There are coil winding calculators all over 'net.
> I presume your plans call out the electrical size
> of the components. Can you scan the schmematic and/or
> point me to a link where you might have downloaded it?
>
> > 2. Would someone be kind enough to give me a clue how it is done?
>
> Not a problem once we fill in some numbers. For example,
> A 10" search coil wound of 104 T #22 wire will yield
> about 5.4 mH. Parallel this with a 470 pF capacitor and
> you find the thing resonates around 100 KHz. The fixed
> oscillator coil might better be a purchased item. It will
> need a LOT of wire in a small space to get into the 5.4 mH
> class of inductor. Do your plans call for any torroidal
> inductor cores?
>
>
>
> Bob . . .
>
>
>
>
>
Message 2
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Subject: | Re: coil tuning anyone? |
>If you have any suggestions on
>what might make the following project work better, I'm all ears.
>http://www.easytreasure.co.uk/bfo.htm
>
>Thanks a Bunch for taking a look!
Hmmm . . . what's the 'lesson plan' for this endeavor?
You mentioned having students lay out an ECB. Is this
a paper exercise or are you planning on fabrication
as well? This is a complicated project (read
high risk) for a class-room exercise. The device is
rich in simple-ideas (physics) each of which
presents an opportunity for teaching. At the same
time, it takes only one solder joint, one bad component,
one wiring error to 'disappoint' even the most
interested members of the class. Without a solid
personal understanding of that which you hope to
illustrate and demonstrate, your own ability to
trouble shoot and fix a defect offers risk for this
being more of a "turn-off" than a "lights-on" experience
for the students. It wouldn't help your personal
credibility either.
What are the design goals for the experience?
There are thousands of examples of kit-built
technologies where following clearly written
instructions will produce a functional product.
Unfortunately, the experience adds little to
a student's understanding of the simple-
ideas that make it work. Heathkits come to mind.
My good friend an mentor of over 40 years, former
dean of engineering at Wichita U, assembled his
first color TV from a Heathkit. Worked good, lasted
a long time . . . but he had not the foggiest
notion of how or why things worked the way they
did. His thing was aerodynamics and mechanics.
The article you cited has a clever application
of some simple-ideas. The oscillators are of
a configuration I've never seen before: the
collector and base of the transistor are tied
together via the dc resistance of the coil.
Power to the oscillator comes through a 10K
resistor. This means that the DC power available
to the collector cannot exceed the Vbe drop
of the transistor. I spider-webbed the oscillator
Emacs!
. . . and powered it up.
Emacs!
Sho'nuf. It WAS a weak oscillator given that the transistor had
to run on about .6 volts. Further, I couldn't get it to oscillate
at much below 15 volts. Here's the 20v trace showing about 100 mV
pk-pk signal.
Emacs!
Here's the signal with a 30 volt supply (about 3 milliamperes through
the 10K resistor). The signal is much stronger, nearly 200 mV pk-pk.
I can't argue with the author's claimed success and the notion that
the circuit has been duplicated thousands of times. However, before
I stepped in front of a class with this project as a proposed teaching
exercise, I would want to have a 99.99% SOLID circuit that had a
very high probability of student success.
The classroom is no place to be debugging design flaws. Your
students will not be impressed. Can we talk about some other
experience to introduce your kids to silicon and rosin smoke?
I think the metal detector needs to be solidly vetted as at
teaching tool before you drag it into the classroom.
Bob . . .
Message 3
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Subject: | Re: AOA circuitry |
If you have an old hard drive that you do not want, you can take it apart and remove
the powerful magnets. Do not get your fingers between them!
Joe
--------
Joe Gores
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=332155#332155
Message 4
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Subject: | Re: PM capacitor inrush |
I was not too worried about the once per flight high current event, but
having derived some numbers I thought I 'd share them anyway (I found
the 45% overshoot from a 15 mOhm 30' wire to 15 mF interesting - glad
I'm not building a 747).
But thank you for your comments!
Jan de Jong
Message 5
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Subject: | Re: AOA circuitry |
If you want an old hard drive to take apart and don't have one, send me an
email and I'll fill up a flat-rate envelope for you.
On Sat, Feb 26, 2011 at 3:27 PM, user9253 <fran4sew@banyanol.com> wrote:
> >
>
> If you have an old hard drive that you do not want, you can take it apart
> and remove the powerful magnets. Do not get your fingers between them!
> Joe
>
> --------
> Joe Gores
>
>
> Read this topic online here:
>
> http://forums.matronics.com/viewtopic.php?p=332155#332155
>
>
Message 6
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Subject: | Re: coil tuning anyone? |
=0A=0AWell, I certainly appreciate and respect your opinion ( I wouldn't ha
ve asked if =0AI didn't). And, you are right concerning having a solid proj
ect that has been =0Aput through the paces prior to having the kids get fru
sterated with it. I can =0Atell you I am a bit frusterated as a new electro
nics teacher ( have been =0Ateaching Intro classes for 2 years). The curric
ulum I have developed (as =0Amentioned) includes building a crystal radio a
nd this has been quite successful. =0AWe then build a simple amplifier whic
h uses an LM386 along with resistors and =0Acaps on a perf board. This has
turned out to be a good conclusion to that class. =0AMy frusteration-come
s in trying to advance a bit-into-a project that will be a =0Astep up
-in-challenging skill levels and not blowing them out of the water. We
=0Aare also-financially limited due to a $15 cap on what we can charge fo
r a lab =0Afee, so as far as kits go...there are a bunch- out there but o
ut of the dollar =0Arange. This forces me to find circuits that I can purch
ase the-parts and keep =0Athings cost effective. I suppose I can keep thi
ngs simple with bread boards and =0Atiming circuits, but I am open to -su
ggestions for projects if you have any in =0Ayour bag of tricks. My bag is
just beginning to grow along with my experience. =0AThanks for testing that
circuit! Back to the-drawing board.=0ADan=0A=0A=0A>=0A>From: "Robert L.
Nuckolls, III" <nuckolls.bob@aeroelectric.com>=0A>To: aeroelectric-list@mat
ronics.com=0A>Sent: Sat, February 26, 2011 10:08:08 AM=0A>Subject: Re: Aero
Electric-List: coil tuning anyone?=0A>=0A>=0A>If you have any suggestions o
n =0A>>what might make the following project work better, I'm all ears. =0A
>>http://www.easytreasure.co.uk/bfo.htm=0A>>=0A>>Thanks a Bunch for taking
a look!=0A- Hmmm . . . what's the 'lesson plan' for this endeavor?=0A-
You mentioned having students lay out an ECB. Is this=0A- a paper exercis
e or are you planning on fabrication=0A- as well? This is a complicated p
roject (read=0A- high risk) for a class-room exercise. The device is=0A
- rich in simple-ideas (physics) each of which=0A- presents an opportun
ity for teaching. At the same=0A- time, it takes only one solder joint, o
ne bad component,=0A- one wiring error to 'disappoint' even the most=0A
- interested members of the class. Without a solid=0A- personal underst
anding of that which you hope to=0A- illustrate and demonstrate, your own
ability to=0A- trouble shoot and fix a defect offers risk for this=0A-
being more of a "turn-off" than a "lights-on" experience=0A- for the stu
dents. It wouldn't help your personal=0A- credibility either.=0A=0A- Wh
at are the design goals for the experience?=0A- There are thousands of ex
amples of kit-built=0A- technologies where following clearly written=0A
- instructions will produce a functional product.=0A- Unfortunately, th
e experience adds little to=0A- a student's understanding of the simple-
=0A- ideas that make it work. Heathkits come to mind.=0A- My good frien
d an mentor of over 40 years, former=0A- dean of engineering at Wichita U
, assembled his=0A- first color TV from a Heathkit. Worked good, lasted
=0A- a long time . . . but he had not the foggiest=0A- notion of how or
why things worked the way they=0A- did. His thing was aerodynamics and m
echanics.=0A=0A- The article you cited has a clever application=0A- of
some simple-ideas. The oscillators are of=0A- a configuration I've never
seen before: the=0A- collector and base of the transistor are tied=0A-
together via the dc resistance of the coil.=0A=0A- Power to the oscillato
r comes through a 10K=0A- resistor. This means that the DC power availabl
e=0A- to the collector cannot exceed the Vbe drop=0A- of the transistor
. I spider-webbed the oscillator=0A=0A=0A=0A--- . . . and powered it
up.=0A=0A=0A=0A--- =0A--- Sho'nuf. It WAS a weak oscillator giv
en that the transistor had=0A--- to run on about .6 volts. Further, I
couldn't get it to oscillate=0A--- at much below 15 volts. Here's th
e 20v trace showing about 100 mV=0A--- pk-pk signal.=0A=0A=0A=0A-
-- Here's the signal with a 30 volt supply (about 3 milliamperes throug
h=0A--- the 10K resistor). The signal is much stronger, nearly 200 mV
pk-pk.=0A=0A--- I can't argue with the author's claimed success and
the notion that=0A--- the circuit has been duplicated thousands of ti
mes. However, before=0A--- I stepped in front of a class with this pr
oject as a proposed teaching=0A--- exercise, I would want to have a 9
9.99% SOLID circuit that had a=0A--- very high probability of student
success.=0A=0A--- The classroom is no place to be debugging design f
laws. Your=0A--- students will not be impressed. Can we talk about so
me other=0A--- experience to introduce your kids to silicon and rosin
smoke?=0A--- I think the metal detector needs to be solidly vetted a
s at=0A--- teaching tool before you drag it into the classroom.=0A=0A
=0A=0A- Bob . . .
Message 7
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Subject: | Re: PM capacitor inrush |
At 04:54 PM 2/26/2011, you wrote:
>
>I was not too worried about the once per flight high current event,
>but having derived some numbers I thought I 'd share them anyway (I
>found the 45% overshoot from a 15 mOhm 30' wire to 15 mF interesting
>- glad I'm not building a 747).
>But thank you for your comments!
To be sure, the severity of the 'problem' increases
with physical size of the system (long runs of wire)
and complexity (lots of electrical wigglers).
I think one of my Florida seminar attendees was
a space shuttle techi . . . he commented that it
was the electrically noisiest vehicle he'd ever
worked on.
But there are ways to cope. For example, the signals
from GPS satellite signals are so weak at the earth's
surface, they cannot be distinguished from atmospheric
noise were it not for a predictable pattern in their
emissions. When you know precisely what you're looking
for, the extraneous stuff can be filtered/ignored as
long as it's not overwhelmingly strong.
Knowing what's on the power bus is the first step toward
being sure that you can artfully reduce its effects
to insignificance.
Bob . . .
>Jan de Jong
>
>
>-----
>No virus found in this message.
>Checked by AVG - www.avg.com
Bob . . .
Message 8
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Subject: | Re: Turning simple-ideas into working hardware. |
At 06:35 PM 2/26/2011, you wrote:
Well, I certainly appreciate and respect your opinion ( I wouldn't
have asked if I didn't). And, you are right concerning having a solid
project that has been put through the paces prior to having the kids
get frustrated with it. I can tell you I am a bit frustrated as a new
electronics teacher ( have been teaching Intro classes for 2 years).
The curriculum I have developed (as mentioned) includes building a
crystal radio and this has been quite successful.
Great!
We then build a simple amplifier which uses an LM386 along with
resistors and caps on a perf board. This has turned out to be a good
conclusion to that class.
Another good one.
My frustration comes in trying to advance a bit into a project that
will be a step up in challenging skill levels and not blowing them
out of the water.
That is where the artful side of teaching must prevail.
We are also financially limited due to a $15 cap on what we can
charge for a lab fee, so as far as kits go...there are a bunch out
there but out of the dollar range. This forces me to find circuits
that I can purchase the parts and keep things cost effective. I
suppose I can keep things simple with bread boards and timing
circuits, but I am open to suggestions for projects if you have any
in your bag of tricks. My bag is just beginning to grow along with my
experience. Thanks for testing that circuit! Back to the drawing board.
I'm pleased that you've already got a general
notion for what the path to success looks like.
I've had several teachers approach me who were
looking to launch their first endeavor. There
the challenge was greater . . . I had to teach
the teacher. You've worked past those early
hurdles and can focus on refinement.
Some years ago I was working with a teacher who
wanted to go the next step above a crystal set
but with some attention to history too. How about
a one-tube radio? Most folks don't know what
tubes are. But they're a whole lot easier to teach
than transistors! Further more, you can take one
apart and hold the pieces in your hand. No such
luck with a 2N2222.
One of the ideas that grew out of our discussions
was the development of a one-tube radio module.
As with the crystal set, the major performance driver
was the 'front end' work. It all happened with the
tuner. Further, risks to success were based more on
techniques (soldering fragile little gizmos together)
and parts selection (being able to duplicate or artfully
substitute a bill of materials).
So how about starting with a 'stock' module that
reduced the risks while evaluating performance gains
demonstrated by the student work-product.
I came up with this proposal:
http://www.aeroelectric.com/Catalog/AEC/9050/9050-600a.pdf
The idea was that these modules would belong to the
school and be re-usable from one class to the next.
The goal was to go through the now 'ancient' texts
on DIY radios and duplicate some of the tuner
designs. Then evaluate performance for selectivity
and sensitivity using some calibrated test equipment
(also built by the teacher or an advanced student).
This reduced the class-to-class costs dramatically
and reduced risks for no-learning-events driven
by assembly and/or parts selection snafus.
We thought that I would kit the modules and
he would have some of the more advanced students
build them.
That teacher got laid off and I've not heard from
him again. That was about 4 years ago.
How would you proposed to introduce and teach ECB
fabrication? There's a free ECB design package
that is VERY powerful. I use it all the time for
my projects. When the work product needs to be
converted to useable hardware, their prices are
quite reasonable and they're quick 1 day turn with
two day UPS delivery of finished boards.
http://expresspcb.com
This same package could be used for a paper design task.
Students could lay out boards, print the artwork
and swap it with other teams for proofing. This is
exactly the way we did boards at Electro-Mech and
Beech for about 30 years. For a class, three
or four teams could do layouts. Swap between
teams for proofing. Then vote on the best looking
layout and order that one for the class project
to move forward. Alternatively, you could have a
'stock' ECB that had been previously ordered in
quantity to get the cost down.
I wouldn't give up on the metal detector. But
I think it wise to have a working model
in class on Day One. Throw a schematic up on the
screen and dissect the simple-ideas. Again,
packaging, coil winding, and mechanical fabrication
presents some challenges that could blow a perfectly
good lesson plan out of the water.
Let's talk about ways to refine the metal detector
(or any other circuit) into a teaching tool. How many
students are in the typical class?
Bob . . .
Message 9
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