magnetic field

[Fred Abse]

On Wed, 04 May 2005 22:45:53 +0200, Zak wrote:

Fred Abse wrote:

Vertical scan collapse, on a TV or computer monitor screen will burn it in
minutes. A stationary spot will do it in seconds. The old Schmitt system
back-projection TVs had circuitry to kill the EHT and bias the CRT hard
off in the event of a scan failure, since a stationary spot could melt the
glass.

Monitors have this as well.

Some do, some don't

I think that aging CRTs fail from cathode exhaustion mostly. Th emission
spot inreases in size, and the image gets fuzzy as a result.

Secondary emission due to electrode contamination can cause similar
effects.

--
"Electricity is of two kinds, positive and negative. The difference
is, I presume, that one comes a little more expensive, but is more
durable; the other is a cheaper thing, but the moths get into it."
(Stephen Leacock)

 

[Fred Abse]

On Wed, 04 May 2005 21:18:29 +0000, Tom MacIntyre wrote:

As I recall, thought, monitors have a faster (I forget the exact term)
loss of brightness per line, so don't have such a tendency to burn in.

Depends on application. Industrial and medical monitors can have quite
slow (15-25KHz) scan rates.

Even at high rates, burn-in will be noticeable after a couple of years
running 24/7 on a stationary image, especially if it's text.

--
"Electricity is of two kinds, positive and negative. The difference
is, I presume, that one comes a little more expensive, but is more
durable; the other is a cheaper thing, but the moths get into it."
(Stephen Leacock)

 

[John Fields]

On 6 May 2005 19:39:45 -0700, cheian07@yahoo.com wrote:

hi, can anyone out there can give me ideas on how to use the output
jack of my multimeter. i have one on my meter but i dont know how to
use it. any help would be greatly appreciated.

---
Go to:

http://www.simpsonelectric.com/pdf/manuals/test/260-8man.pdf

and read the section on making measurements using the OUTPUT function.


--
John Fields
Professional Circuit Designer

 

[CWatters]

"John Fields" <jfields@austininstruments.com> wrote in message
news:f5sp71duk2im267jlprdet81nmq97pnffe@4ax.com...

Go to:

http://www.simpsonelectric.com/pdf/manuals/test/260-8man.pdf

and read the section on making measurements using the OUTPUT function.

I'm not the OP but thanks! I hard to believe but... I've been an
electronice engineer for 20+ years and never come across this useful feature
on a meter before.

Colin

 

[Michael Black]

"eeh" (eehobbyist@yahoo.com.hk) writes:

Hi,

Often doing prototype casings are nightmares for many electronic
hobbyists with limited resource. We can design, draw and make a
soplicated electronic PCB but not a good-looking housing. Often we do
not have tools such as milling machines in home to open rectangular
ports.

And I have an idea about prototype house making: Is there a thing in
the world which is like LEGO toy but pinpoints on prototype making so
that we can make the casing just by stacking fundamentary elements?

Thanks!

There is a near infinite number of possibilities for the hobbyist.

You can solder scrap circuit board together, and make little boxes.

You can put things in tin cans that food originally comes with, indeed
I once tried some seitan that came a in a tiny can and while I wasn't
that happy with the food item, I bought some more for the cans.

Decades ago, someone at school was more interested in the finished product
than the electronics. So he'd buy kits, and then put his effort into
making nice wooden boxes for them. For some people, wood is something
they can work with easily.

Get a metal brake, and bend sheet metal for your boxes.

Electronic equipment that's tossed out can often provide interesting
boxes. Either the whole thing (such as an old stereo receiver with
the guts taken out and a new front panel, again circuit board
can be that panel), or inside where there may be small tin boxes
for shielding sections.

At least in North America, you can get metal utility boxes
that have two halves in the shape of a "u". I've cut those
down when a standard size has been too big.

Michael

 

[keith]

On Sun, 08 May 2005 16:39:55 -0700, hhc314 wrote:

It isn't easy to do, since the PCI technology is totally different from
the comparatively simple ISA bus.

Your best bet will be to locate an adapter card, or a motherboard
having both PCI and ISA slots.

Actually, it's not hard to do at all, unless the ISA card is a bus master
(_very_ few were). Many devices use the PLX9050 PCI to ISA bridge to do
exactly this.

--
Keith

 

[Pooh Bear]

keith wrote:

On Sun, 08 May 2005 16:39:55 -0700, hhc314 wrote:

It isn't easy to do, since the PCI technology is totally different from
the comparatively simple ISA bus.

Your best bet will be to locate an adapter card, or a motherboard
having both PCI and ISA slots.

Actually, it's not hard to do at all, unless the ISA card is a bus master
(_very_ few were).

How can an ISA card be a *bus master* ?

ISA is just the micro's data and address bus basically with a few extra pins
to the interrupt controller !

I think only EISA and MCA cards had that ability prior to the adoption of
PCI.

Then goes and wonders over some of the earlyish Adaptec SCSI controllers e.g
AHA1540/1542. In which case how did they do it ?

Graham

 

[Michael Redmann]

Fred Abse schrieb:

On Wed, 04 May 2005 21:18:29 +0000, Tom MacIntyre wrote:

As I recall, thought, monitors have a faster (I forget the exact
term) loss of brightness per line, so don't have such a tendency to
burn in.

Depends on application. Industrial and medical monitors can have quite
slow (15-25KHz) scan rates.

Even at high rates, burn-in will be noticeable after a couple of years
running 24/7 on a stationary image, especially if it's text.

I'm not sure burn-in is dependent on refresh rates. I think that at any
refresh rates the screen phosphor is "illuminated" the same amount of
time (more or less) by electron beam. Perhaps the different types of
phosphor (monitor vs. TV) have different decay rates and that's the
reason for TVs to tend to burn-in.

Regards
--
Michael Redmann
"It's life, Jim, but not as we know it." (Spock)

 

[Keith Williams]

In article <4281BA04.5F1D2E6E@hotmail.com>,
rabbitsfriendsandrelations@hotmail.com says...

keith wrote:

On Sun, 08 May 2005 16:39:55 -0700, hhc314 wrote:

It isn't easy to do, since the PCI technology is totally different from
the comparatively simple ISA bus.

Your best bet will be to locate an adapter card, or a motherboard
having both PCI and ISA slots.

Actually, it's not hard to do at all, unless the ISA card is a bus master
(_very_ few were).

How can an ISA card be a *bus master* ?

The device asserts a DRQ, waits for the corresponding DACK, then
asserts MASTER, at which point it can drive the address/data/control
lines as needed.

ISA is just the micro's data and address bus basically with a few extra pins
to the interrupt controller !

It's a *little* more than that.

I think only EISA and MCA cards had that ability prior to the adoption of
PCI.

No, it was there in ISA too, though not often used.

Then goes and wonders over some of the earlyish Adaptec SCSI controllers e.g
AHA1540/1542. In which case how did they do it ?

Yep. There was also the IBM Multi-media Modem (sound card/modem
combined on one DSP) that used bus mastering to swap its OS and data in
and out of system memory.

--
Keith

 

[Dirk Bruere at Neopax]

rgregoryclark@yahoo.com wrote:

I've seen the designs for low-cost home-built nitrogen lasers. But
these were for unfocused beams.
Is there a low-cost method to focus the beam to a spot in the range of
say a few hundred microns wide?

Quartz lens?

--
Dirk

The Consensus:-
The political party for the new millenium
http://www.theconsensus.org

 

[Sam Goldwasser]

Dirk Bruere at Neopax <dirk@neopax.com> writes:

rgregoryclark@yahoo.com wrote:

I've seen the designs for low-cost home-built nitrogen lasers. But
these were for unfocused beams.
Is there a low-cost method to focus the beam to a spot in the range of
say a few hundred microns wide?

Quartz lens?

The problem isn't the lens material as much as the beam quality. It will be
hard to focus the typical home-built N2 laser's output to a very small spot.

--- sam | Sci.Electronics.Repair FAQ Mirror: http://repairfaq.ece.drexel.edu/
Repair | Main Table of Contents: http://repairfaq.ece.drexel.edu/REPAIR/
+Lasers | Sam's Laser FAQ: http://repairfaq.ece.drexel.edu/sam/lasersam.htm
| Mirror Sites: http://repairfaq.ece.drexel.edu/REPAIR/F_mirror.html

Note: These links are hopefully temporary until we can sort out the excessive
traffic on Repairfaq.org.

Important: Anything sent to the email address in the message header above is
ignored unless my full name is included in the subject line. Or, you can
contact me via the Feedback Form in the FAQs.

--
Dirk

The Consensus:-
The political party for the new millenium
http://www.theconsensus.org

 

[Dirk Bruere at Neopax]

Sam Goldwasser wrote:

Dirk Bruere at Neopax <dirk@neopax.com> writes:


rgregoryclark@yahoo.com wrote:


I've seen the designs for low-cost home-built nitrogen lasers. But
these were for unfocused beams.
Is there a low-cost method to focus the beam to a spot in the range of
say a few hundred microns wide?

Quartz lens?


The problem isn't the lens material as much as the beam quality. It will be
hard to focus the typical home-built N2 laser's output to a very small spot.

Depends on the length of the laser cavity I assume, since its single pass.

--
Dirk

The Consensus:-
The political party for the new millenium
http://www.theconsensus.org

 

[Sam Goldwasser]

Dirk Bruere at Neopax <dirk@neopax.com> writes:

Sam Goldwasser wrote:

Dirk Bruere at Neopax <dirk@neopax.com> writes:

rgregoryclark@yahoo.com wrote:


I've seen the designs for low-cost home-built nitrogen lasers. But
these were for unfocused beams.
Is there a low-cost method to focus the beam to a spot in the range of
say a few hundred microns wide?

Quartz lens?

The problem isn't the lens material as much as the beam quality. It
will be hard to focus the typical home-built N2 laser's output to a
very small spot.

Depends on the length of the laser cavity I assume, since its single pass.

More than that. It depends on the mode structure of the beam.

--- sam | Sci.Electronics.Repair FAQ Mirror: http://repairfaq.ece.drexel.edu/
Repair | Main Table of Contents: http://repairfaq.ece.drexel.edu/REPAIR/
+Lasers | Sam's Laser FAQ: http://repairfaq.ece.drexel.edu/sam/lasersam.htm
| Mirror Sites: http://repairfaq.ece.drexel.edu/REPAIR/F_mirror.html

Note: These links are hopefully temporary until we can sort out the excessive
traffic on Repairfaq.org.

Important: Anything sent to the email address in the message header above is
ignored unless my full name is included in the subject line. Or, you can
contact me via the Feedback Form in the FAQs.

 

[Mark Fergerson]

Sam Goldwasser wrote:

Dirk Bruere at Neopax <dirk@neopax.com> writes:


Sam Goldwasser wrote:


Dirk Bruere at Neopax <dirk@neopax.com> writes:


rgregoryclark@yahoo.com wrote:



I've seen the designs for low-cost home-built nitrogen lasers. But
these were for unfocused beams.
Is there a low-cost method to focus the beam to a spot in the range of
say a few hundred microns wide?

Quartz lens?


The problem isn't the lens material as much as the beam quality. It
will be hard to focus the typical home-built N2 laser's output to a
very small spot.

Depends on the length of the laser cavity I assume, since its single pass.


More than that. It depends on the mode structure of the beam.

I was going to mention mirror quality and how they're positioned
vs. cavity proportions...

Mark L. Fergerson

 

[Uncle Al]

rgregoryclark@yahoo.com wrote:

I've seen the designs for low-cost home-built nitrogen lasers. But
these were for unfocused beams.
Is there a low-cost method to focus the beam to a spot in the range of
say a few hundred microns wide?

337 nm. Fused silica, alkali halide, or alkaline earth fluoride
lens. A meniscus lens is preferred to lessen aberrations. Down to
microns is gonna take some work - superradiant lasers are not coherent
and you'll need a large diopter rating (thick lenses are problems on
several fronts). I doubt Fresnel or binary optics configurations can
pull it off, especially if you need imaging in addition to
concentration.

--
Uncle Al
http://www.mazepath.com/uncleal/
(Toxic URL! Unsafe for children and most mammals)
http://www.mazepath.com/uncleal/qz.pdf

 

[Uncle Al]

Mark Fergerson wrote:

Sam Goldwasser wrote:
Dirk Bruere at Neopax <dirk@neopax.com> writes:


Sam Goldwasser wrote:


Dirk Bruere at Neopax <dirk@neopax.com> writes:


rgregoryclark@yahoo.com wrote:



I've seen the designs for low-cost home-built nitrogen lasers. But
these were for unfocused beams.
Is there a low-cost method to focus the beam to a spot in the range of
say a few hundred microns wide?

Quartz lens?


The problem isn't the lens material as much as the beam quality. It
will be hard to focus the typical home-built N2 laser's output to a
very small spot.

Depends on the length of the laser cavity I assume, since its single pass.


More than that. It depends on the mode structure of the beam.

I was going to mention mirror quality and how they're positioned
vs. cavity proportions...

Superradiant nitrogen lasers have messy output, as such or one pass
with a rear mirror. The cavity is irrelevant. The output is not
coherent. You might as well try focusing a flashbulb to a few microns
image radius.

--
Uncle Al
http://www.mazepath.com/uncleal/
(Toxic URL! Unsafe for children and most mammals)
http://www.mazepath.com/uncleal/qz.pdf

 

[Gary Cavie]

In article <42825C8D.CBD4B3BD@hate.spam.net>, UncleAl0@hate.spam.net
says...

Mark Fergerson wrote:

Sam Goldwasser wrote:
Dirk Bruere at Neopax <dirk@neopax.com> writes:


Sam Goldwasser wrote:


Dirk Bruere at Neopax <dirk@neopax.com> writes:


rgregoryclark@yahoo.com wrote:



I've seen the designs for low-cost home-built nitrogen lasers. But
these were for unfocused beams.
Is there a low-cost method to focus the beam to a spot in the range of
say a few hundred microns wide?

Quartz lens?


The problem isn't the lens material as much as the beam quality. It
will be hard to focus the typical home-built N2 laser's output to a
very small spot.

Depends on the length of the laser cavity I assume, since its single pass.


More than that. It depends on the mode structure of the beam.

I was going to mention mirror quality and how they're positioned
vs. cavity proportions...

Superradiant nitrogen lasers have messy output, as such or one pass
with a rear mirror. The cavity is irrelevant. The output is not
coherent. You might as well try focusing a flashbulb to a few microns
image radius.

As a young boy, about 8 or so, I read about lasers, and spent many weeks
pocket money buying up loads of toy magnifying glass lenses, stacking
them in a piece of PVC waste pipe, and fitting a torch at one end. Can
you imagine my disappointment when I didn't end up with a laser gun from
'Star Wars'?

 

[AES]

In article <42825C8D.CBD4B3BD@hate.spam.net>,
Uncle Al <UncleAl0@hate.spam.net> wrote:

Superradiant nitrogen lasers have messy output, as such or one pass
with a rear mirror. The cavity is irrelevant. The output is not
coherent. You might as well try focusing a flashbulb to a few microns
image radius.

Never actually played with one of these, but my hypothesis would be that
if you used a long cavity -- longer the better -- with flat or
long-radius mirrors (radius longer than the mirror spacing) and equal
sized apertures at each end, the angular spread in the output would be
roughly equal to the angular spread of either aperture seen from the
center of the aperture at the other end. Would be a bit delicate to get
and keep the mirrors aligned, however.

 

[John Fields]

On Wed, 11 May 2005 15:17:07 -0700, AES <siegman@stanford.edu> wrote:

In article <42825C8D.CBD4B3BD@hate.spam.net>,
Uncle Al <UncleAl0@hate.spam.net> wrote:


Superradiant nitrogen lasers have messy output, as such or one pass
with a rear mirror. The cavity is irrelevant. The output is not
coherent. You might as well try focusing a flashbulb to a few microns
image radius.


Never actually played with one of these, but my hypothesis would be that
if you used a long cavity -- longer the better -- with flat or
long-radius mirrors (radius longer than the mirror spacing) and equal
sized apertures at each end, the angular spread in the output would be
roughly equal to the angular spread of either aperture seen from the
center of the aperture at the other end. Would be a bit delicate to get
and keep the mirrors aligned, however.

---
Mirrors???

Apertures???


--
John Fields
Professional Circuit Designer

 

[Baugh]

Sam Goldwasser wrote:

Dirk Bruere at Neopax <dirk@neopax.com> writes:


rgregoryclark@yahoo.com wrote:


I've seen the designs for low-cost home-built nitrogen lasers. But
these were for unfocused beams.
Is there a low-cost method to focus the beam to a spot in the range of
say a few hundred microns wide?

Quartz lens?


The problem isn't the lens material as much as the beam quality. It will be
hard to focus the typical home-built N2 laser's output to a very small spot.

Cannot you by placing the lens far enough away from the laser obtain a
better focus? The distance will correlate off-line output with lateral
displacement. A lens of sufficient quality and wide enough for the
spread beam will then redirect more accurately to the focus.

Think of it in terms of the focused image for the distance to the laser
will move closer to the focus from infinity as you move the lens farther
away. (Again assuming no spherical aberation in the lens.)


Regards,
James Baugh.