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Notebook computer sized cells..... Where to buy ?
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Don Bruder
electronics forum Guru Wannabe


Joined: 03 May 2005
Posts: 190

PostPosted: Tue Jun 28, 2005 6:43 pm    Post subject: Re: Can you explain this? (lightning experience today) Reply with quote

In article <42c1a4c2.297953@news.individual.net>,
AL205refirst@phoneyaddy.com (AL) wrote:

Quote:
Hi folks,
I was working away in my attic office here at home in England this
afternoon, while a thunderstorm approached.

As I sat, reading an email, with my right hand resting on my mouse ,
there was a very loud clap of thunder very close-by. At that same
moment, I received an electric shock in my right hand and
similtaneously heard a sharp "crack" in the same vicinity. The shock I
felt was very brief, but it felt at least as powerful as a shock from
our domestic mains (240+ volts). Surprisingly, my PC continued to
function as normal, although I lost my internet connection at that
same moment.

Can anyone explain what happenned? I am just curious....

Al (England)

Simple: You took part of the lightning strike that most likely hit the
phone lines and/or power line nearby.

Think about it - That lightning bolt has just jumped anywhere from half
a quarter of a mile to as much as ten miles of air-gap. Do you *REALLY*
think that the quarter inch of plastic wrapped around your mouse is
sufficient to insulate you from its power?

The fact that your computer survived is a testament to the bizarre
behavior of lightning - It'll take out every electronic device in a room
*EXCEPT* the radio, while in the next room, it'll blow a TV set into a
million pieces scattered about the room, yet leave thousands of dollars
worth of video gear plugged into the same power strip untouched, and in
the room next to that, leave the alarm-clock blinking "12:00", and the
telephone dead.

It all depends on the ground ("earth", to you Brits) paths.

--
Don Bruder - dakidd@sonic.net - New Email policy in effect as of Feb. 21, 2004.
Short form: I'm trashing EVERY E-mail that doesn't contain a password in the
subject unless it comes from a "whitelisted" (pre-approved by me) address.
See <http://www.sonic.net/~dakidd/main/contact.html> for full details.
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CWatters
electronics forum Guru


Joined: 02 May 2005
Posts: 494

PostPosted: Tue Jun 28, 2005 7:20 pm    Post subject: Re: Can you explain this? (lightning experience today) Reply with quote

A similar event took out the modem on my mothers PC last year.
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steamer
electronics forum addict


Joined: 10 May 2005
Posts: 66

PostPosted: Tue Jun 28, 2005 8:15 pm    Post subject: Re: How to make inside of tube reflective?...tia sal Reply with quote

--How reflective and what material is the tube made of?

--
"Steamboat Ed" Haas : Just another fart in
Hacking the Trailing Edge! : the Elevator of Life...
http://www.nmpproducts.com/intro.htm
---Decks a-wash in a sea of words---
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John
electronics forum beginner


Joined: 07 Jun 2005
Posts: 14

PostPosted: Tue Jun 28, 2005 10:19 pm    Post subject: Re: portable VHF receiver problem Reply with quote

On Tue, 28 Jun 2005 21:44:17 +0100, "tg" <tg@nospamevereverever.net>
wrote:

Quote:
I'm in the UK and have a Shure EC11 bodypack transmitter with lavalier mike
on 174.8MHz. (I've also got an ECI transmitter on 173.Cool I want to use this
pack with a camcorder so I need a portable receiver for the camera end.
Shure used to do a VP3 portable receiver for just this purpose but the VP3
has been discontinued in the UK. The chances of my finding a second hand VP3
on 173.8MHz or 174.9MHz is about nil. I see VP3's still sell in the US but
not on this frequency, and VP3's rarely seen on ebay use frequencies that
are illegal in the UK. Could I make a decent VHF receiver from a kit? Would
a radio scanner do the job? Is there any other solution to this problem? I
can't afford a new wirless mike system. Thanks for any help.


The scanner radio may have a bandwidth too narrow for high quality
audio, but would work OK for voice bandwidth.

There are VHF receiver kits that would probably work, but I only know
the US suppliers.
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Yukio YANO
electronics forum addict


Joined: 27 May 2005
Posts: 66

PostPosted: Wed Jun 29, 2005 2:01 am    Post subject: Re: How to make inside of tube reflective?...tia sal Reply with quote

sal@spp.net wrote:
Quote:
Greetings, All

I have a tube which I would like to make the inside reflective.
Does anyone know if there is a reflective type of spray or dip that I can coat the inside of the tube with
to give it a mirror type of coating?

TIA
sal


40 years ago, I would have said look in the Yellow pages under mirrors,

for a re-silvering shop. These people would use a modification of "John
A. Brashear's " silvering process. In this process a Silver
Nitrate/Ammonium Hydroxide solution would be Reduced to a metallic
Silver film on any surface using a Glucose solution . This is very much
equipment simpler than Vaccumn evaporation for large or irregular objects.
This is or was the method of choice for "Thermos Bottles", Dewar Flasks.

Most "Silvered objects are now Vaccumn Coated with Aluminum, very
cheaply once you acquire a suitable Chamber.

For a one time, application 25 grams of Silver Nitrate would probably
coat several square Meters. A tube would be simple to silver, using the
tube itself as your reaction chamber. I did silver my first Telescope
Mirror using this method. I recently Aluminized it in a Vaccumn Chamber,
very much cleaner and easier, but then how many people have easy access
to an Electron Microscope Lab.

Yukio YANO
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CWatters
electronics forum Guru


Joined: 02 May 2005
Posts: 494

PostPosted: Wed Jun 29, 2005 10:19 am    Post subject: Re: How to make inside of tube reflective?...tia sal Reply with quote

"Yukio YANO" <yano@shaw.ca> wrote in message
news:T2pwe.1823044$6l.114406@pd7tw2no...
Quote:
sal@spp.net wrote:

40 years ago, I would have said look in the Yellow pages under mirrors,
for a re-silvering shop.

If it's a metal tube you could get it chrome plated easily.
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kell
electronics forum Guru


Joined: 25 Mar 2005
Posts: 383

PostPosted: Wed Jun 29, 2005 6:56 pm    Post subject: Re: Simple current supply for thermistors? Reply with quote

redbelly wrote:
Quote:
CWatters wrote:

http://www.vishay.com/document/70596/70596.pdf

Thank you.

view in proportional font (if you are using google, click on "show
original")

this circuit gives very tight current regulation:
load n-channel
(thermistor) mosfet R (see below)
_____/\/\/\_________ _______________/\/\/\____________
| _|___|_ _|_ | |
| _ / \ | |
| |_______/ \____________| |
| | c e |
| / npn transistor |
| \ |
| / 1K |
|_____________________\ |
| ground
__|__
_
_____ battery
_ or power supply
_____
_
|
|
ground

for R start with a value of .6 divided by desired current and adjust
until you get the current you want

This is a sink. If you want a source you could turn everything upside
down and do it with a p-channel mosfet and a pnp transistor, and put
the thermistor grounded.

The base-emitter voltage of the current-sensing transistor varies with
temperature -- the only source of any significant inaccuracy in the
circuit, as long as your power supply has stable voltage. Regulation's
pretty independent of load. You should look up the b/e temperature
coefficient for a bjt, I don't remember offhand.
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John Fields
electronics forum Guru


Joined: 24 Mar 2005
Posts: 3260

PostPosted: Thu Jun 30, 2005 6:18 pm    Post subject: Re: Simple current supply for thermistors? Reply with quote

On 30 Jun 2005 12:46:58 -0700, "kell" <kellrobinson@billburg.com>
wrote:

Quote:


He's going to have to face some hard realities. At 100 uA,
if it can be achieved, physical construction becomes critical.
Assuming 5V Vcc, a 100 meg resistance draws 50 uA.

---
E 5V
I = --- = ------ = 5E-8a = 0.05µa
R 1E8R
---


Quote:
His spec
was .5% accuracy. 100uA * .005 = .5 uA
So if dirt/humiditity/whatever on his pc board yields a 100
meg or lower path for current to follow, he's blown away by
two orders of magnitude, or more.

---
No, at 100 megohms he's an order of magnitude better than the spec.
---

Quote:
Frankly, I'm clueless as to how to meet his specs. You
could use an op amp to get even better current regulation,
but I don't know how to accomodate that on a PC board with
those specs. Thompson could design it inside a chip,
combining the thermistor function with regulation and
whatever else, and yielding an output that is not critical.
I don't think it can be done with discretes.

I can't find the original post. What purpose does the OP have in mind
for this circuit... maybe he'll find a solution off the shelf, like a
temperature sensor chip.

--
John Fields
Professional Circuit Designer
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redbelly
electronics forum Guru Wannabe


Joined: 29 May 2005
Posts: 210

PostPosted: Thu Jun 30, 2005 6:45 pm    Post subject: Re: Simple current supply for thermistors? Reply with quote

kell wrote:

Quote:
I can't find the original post. What purpose does the OP have in mind
for this circuit... maybe he'll find a solution off the shelf, like a
temperature sensor chip.

Here is the OP, courtesy of the OP. For some odd reason, it is showing
up as the third message in the thread, at least when read at Google
Groups:

I'm looking for a basic, easy-to-build constant current source to drive
thermistors, nominally at 0.1 mA. The thermistors would be the common
10 k-ohm @ 25 C variety.

I spent time Googling this topic without success. One site mentioned
that an LM317 can be used to generate a current, but the current would
have to be a minimum of 5 or 10 mA. I need a 0.1 mA source.

I'd like to build something, preferably for under $10.00, with better
than 0.5% accuracy (that should correspond to temperature readings
within 0.1 or 0.2 C). My plan is to have several thermistors in series
driven with the circuit, and then I can read off the voltage of each
thermistor with an A/D hooked up to a PC, and be able to monitor
temperature readings over several hours or up to a day.

TIA,

Mark
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redbelly
electronics forum Guru Wannabe


Joined: 29 May 2005
Posts: 210

PostPosted: Thu Jun 30, 2005 7:48 pm    Post subject: Re: Simple current supply for thermistors? Reply with quote

I'm currently considering 3 options, based on what I've read here:

1. Resistor divider network, with 1 fixed, low temperature coefficient
resistor plus up to three thermistors, all in series. Ratio of each
thermistor voltage to fixed-resistor voltage gives accurate thermistor
resistance (where fixed resistance is known), so a stable current or
voltage source is not required.

2. The LM134/234, probably using the "zero temp coefficient"
configuration.

3. Off-the-shelf temperature sensor.

Thanks,

Mark
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Mike Berger
electronics forum Guru Wannabe


Joined: 06 Jun 2005
Posts: 283

PostPosted: Fri Jul 01, 2005 7:40 pm    Post subject: Re: portable VHF receiver problem Reply with quote

Get one on the wrong frequency but in the right band and
recrystal and retune it.

John wrote:
Quote:
On Tue, 28 Jun 2005 21:44:17 +0100, "tg" <tg@nospamevereverever.net
wrote:


I'm in the UK and have a Shure EC11 bodypack transmitter with lavalier mike
on 174.8MHz. (I've also got an ECI transmitter on 173.Cool I want to use this
pack with a camcorder so I need a portable receiver for the camera end.
Shure used to do a VP3 portable receiver for just this purpose but the VP3
has been discontinued in the UK. The chances of my finding a second hand VP3
on 173.8MHz or 174.9MHz is about nil. I see VP3's still sell in the US but
not on this frequency, and VP3's rarely seen on ebay use frequencies that
are illegal in the UK. Could I make a decent VHF receiver from a kit? Would
a radio scanner do the job? Is there any other solution to this problem? I
can't afford a new wirless mike system. Thanks for any help.



The scanner radio may have a bandwidth too narrow for high quality
audio, but would work OK for voice bandwidth.

There are VHF receiver kits that would probably work, but I only know
the US suppliers.

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John Larkin
electronics forum Guru


Joined: 29 Apr 2005
Posts: 4320

PostPosted: Sun Jul 03, 2005 9:55 pm    Post subject: Re: Cockroft-Walton question. Reply with quote

On 3 Jul 2005 15:13:08 -0700, rgregoryclark@yahoo.com wrote:

Quote:
Why couldn't you have the output of a CW voltage doubler lead into the
input of a another doubler? It seems to me that instead of the voltages
being additive with additional stages as done now, with this method you
could double the voltage each time.
So with 10 repetitions you could multiply the voltage by 2^10 = 1024.


Bob Clark

Because the input to a c-w stage must be AC, and the output is DC.[1]

John

1. Except that DC doesn't exist.
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Vidar Løkken
electronics forum addict


Joined: 24 Mar 2005
Posts: 79

PostPosted: Mon Jul 04, 2005 9:34 pm    Post subject: Re: Lightning protection Reply with quote

Tom MacIntyre wrote:
Quote:
Hi folks...this was in a baseball newsgroup that I participate in
(rec.sport.baseball). Faraday cages have been mentioned, implying that
it could be safe. I don't know that I'd trust this against lightning
(maybe a Van de Graff generator). What do you think?

"Just wondering if sitting on a wood bench inside a metal cage (i.e.
metal on top and 4 sides) is a safe place to be during a lightning
storm. This is similar to the situation of being in a car (except for
the rubber tires!). I have seen younger kids wait out a passing storm
this way and am wondering if it IS in fact safe? What would the effect
of metal cleats be? I'd appreciate any thoughts from anybody but
especially from physics teachers/physicists. Thanks!"

Tom

Inside a faraday is safe. Absolutely safe. Only problem could be the
potential difference between your legs, due to the resistance of the
copper. But I guess that it'd be small enough to not be lethal. But
remember, copper is a resistor, so if you stand with your feets apart,
you're in paralell with that part of the copper, and will see some of
the current. But since you're in series with the rest of the copper,
you'll only see a fraction of the voltage. So yes, for 1000$ I'd be in a
copper cage on top of a mountain during a thunderstorm.

--
MVH,
Vidar

www.bitsex.net
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Jim Thompson
electronics forum Guru


Joined: 06 May 2005
Posts: 5440

PostPosted: Tue Jul 05, 2005 2:12 pm    Post subject: Re: Cockroft-Walton question. Reply with quote

On 5 Jul 2005 09:09:20 -0700, rgregoryclark@yahoo.com wrote:

Quote:
Jim Thompson wrote:
On 5 Jul 2005 04:43:03 -0700, rgregoryclark@yahoo.com wrote:

Jim Thompson wrote:
On 4 Jul 2005 11:32:25 -0700, rgregoryclark@yahoo.com wrote:


How many times does it multiply the input voltage?


Bob Clark

"ChargePump-4X-Example.pdf" 4X ?:-)

...Jim Thompson


Cockroft-Walker multipliers with fewer components can multiply voltage
8 times:

Cockroft Walton Voltage Multipliers
http://home.earthlink.net/~jimlux/hv/cw1.htm

Read more carefully, it multiplies 8X the PEAK, or 4X the
Peak-to-Peak; mine does the same, just in a fashion that allows
monolithic implementation without forward biasing wells and creating
latch-up, etc.


You can't read what is not there. You ONLY said it multiplies "4
times". The Cockroft-Walton circuit page specifically says 8 times
peak.
You're post is also misleading in that it was in response to the post
by "cnctut" who suggested "charge pumps" could multiply at each
additional stage.
I don't know if this is accurate or not.


Bob Clark

No charge pump MULTIPLIES! A better phrase would be STACKER... stacks
one capacitor on top of another.

...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice:(480)460-2350 | |
| E-mail Address at Website Fax:(480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |

I love to cook with wine. Sometimes I even put it in the food.
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Mark Fergerson
electronics forum Guru Wannabe


Joined: 06 May 2005
Posts: 196

PostPosted: Thu Jul 07, 2005 5:03 pm    Post subject: Re: How can I make a rubber stopper at home? tia sal Reply with quote

sal@spp.net wrote:
Quote:

Greetings all,

I would like to make my own rubber stoppers I have created a mold using plaster of paris,
I have tried epoxy and fiberglass resin but these end up being to hard does anyone know
what I can use to make softer rubber stoppers.

You could try RTV (Room Temperature Vulcanizing) silicone rubber,
but it'll get expensive pretty quick, and you'd probably have to
build them up in layers due to the shrinkage issue.

Why don't you just buy them? Odd-sized glassware?


Mark L. Fergerson
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