Chip with simple program for Toy

"Matt" <valid@email.com> wrote in message news:umHsd.261$MC.71@lakeread04...
hello all. I have a simple question. What makes a 5v relay rated at 5v?
Is it limited by the voltage or really by the current? I have a bunch of
5
volt relays that'd I'd like to use with 12 volts. is it possible to add a
small resister in line with the terminals that switch the relay and have
it
turn on with a 12 volt supply? They will be one for a while, so I do not
want to risk them heating up too much.

on the other hand, relays are pretty cheap. does it make sense to just
get
some proper ones? Either way, I'm curious to know! Thanks!

-matt
Click to expand...

Why not use a voltage regulator if you are going to run several 5 volt
relays
on a 12 volt supply. Use an LM7805 and a heat sink. If your total current
requirements are low, you may be able to use a zener diode and a limit
resistor.

Where is your 12 volts coming from? If it's a car, there are other
considerations.
 
In article <umHsd.261$MC.71@lakeread04>, Matt <valid@email.com> wrote:
hello all. I have a simple question. What makes a 5v relay rated at 5v?
Is it limited by the voltage or really by the current? I have a bunch of 5
volt relays that'd I'd like to use with 12 volts. is it possible to add a
small resister in line with the terminals that switch the relay and have it
turn on with a 12 volt supply? They will be one for a while, so I do not
want to risk them heating up too much.

on the other hand, relays are pretty cheap. does it make sense to just get
some proper ones? Either way, I'm curious to know! Thanks!
Click to expand...
There are two voltage ratings for relays. One if for the contacts and is
almost always higher than 5V. The other is the voltage rating of the
coil. I assume that the coil's rating is what you have.

The coil has some resistance. It is usually specified by the maker and
does not vary much from unit to unit. If you use that resistance and an
external resistor to work out the yusual voltage divider design, you will
have 5V on the coil when it is operating.

The coil has some inductance. This inductance will cause the voltage on
the coil to be 12V very breifly when you first apply power. 12V isn't
high enough to break down the insulation and won't last long enough to
cause any other trouble so don't worry about it.


BTW:

There is a fairly simple trick that can save you some power. The relay
takes a higher current in the coil to pull the armature in than it takes
to hold it in. If you know the holding current, you can design the
resistor so that you get a bit more than that in the steady state. You
then will need to put a capacitor across the resistor to give an initial
pulse of current to pull the armature in.

--
--
kensmith@rahul.net forging knowledge
 
Yes, the relay is rated at 5v to turn on, and 250v for whatever it is
running. I have 12v to the coil now, it is getting a bit hot. I'm not sure
if they are supposed to get hot since they are such low resistance.

Can you tell me more about the power saving trick? Do I put a low value
resister in series w/ the coil and put a cap in parallel with this resister?
what value do you suggest?

BTW - are there any simple RC circuits to delay the turn on of the relay for
a couple seconds?

Thanks!
-matt


"Ken Smith" <kensmith@green.rahul.net> wrote in message
news:covhqe$8g1$2@blue.rahul.net...
In article <umHsd.261$MC.71@lakeread04>, Matt <valid@email.com> wrote:
hello all. I have a simple question. What makes a 5v relay rated at 5v?
Is it limited by the voltage or really by the current? I have a bunch of
5
volt relays that'd I'd like to use with 12 volts. is it possible to add a
small resister in line with the terminals that switch the relay and have
it
turn on with a 12 volt supply? They will be one for a while, so I do not
want to risk them heating up too much.

on the other hand, relays are pretty cheap. does it make sense to just
get
some proper ones? Either way, I'm curious to know! Thanks!

There are two voltage ratings for relays. One if for the contacts and is
almost always higher than 5V. The other is the voltage rating of the
coil. I assume that the coil's rating is what you have.

The coil has some resistance. It is usually specified by the maker and
does not vary much from unit to unit. If you use that resistance and an
external resistor to work out the yusual voltage divider design, you will
have 5V on the coil when it is operating.

The coil has some inductance. This inductance will cause the voltage on
the coil to be 12V very breifly when you first apply power. 12V isn't
high enough to break down the insulation and won't last long enough to
cause any other trouble so don't worry about it.


BTW:

There is a fairly simple trick that can save you some power. The relay
takes a higher current in the coil to pull the armature in than it takes
to hold it in. If you know the holding current, you can design the
resistor so that you get a bit more than that in the steady state. You
then will need to put a capacitor across the resistor to give an initial
pulse of current to pull the armature in.

--
--
kensmith@rahul.net forging knowledge
Click to expand...
 
In sci.electronics.design Matt <valid@email.com> wrote:
Yes, the relay is rated at 5v to turn on, and 250v for whatever it is
running. I have 12v to the coil now, it is getting a bit hot. I'm not sure
if they are supposed to get hot since they are such low resistance.
Click to expand...
They are designed to be run at the specified voltage.
Much more may cause heating, and poorer contact life (they bang
together too hard).
Can you tell me more about the power saving trick? Do I put a low value
resister in series w/ the coil and put a cap in parallel with this resister?
what value do you suggest?
Click to expand...
Measure the resistance of the coil.
Multiply by 12/5.
Now, subtract the resistance of the coil.
So, if 500 ohms, that's 1200 ohms - 500 ohms = 700 ohms.

You can add a R/C delay by adding this resistor, then putting a capacitor
across the relay. (with the correct polarity)

Time constant is about R*C, so for 2 seconds, you might try 2/500 of a
farad, or .004F (400uF)

In inverse proportion to the coil resistance.
 
On Sun, 5 Dec 2004 13:59:37 -0500, the renowned "Matt"
<valid@email.com> wrote:

Yes, the relay is rated at 5v to turn on, and 250v for whatever it is
running. I have 12v to the coil now, it is getting a bit hot. I'm not sure
if they are supposed to get hot since they are such low resistance.
Click to expand...
You will burn the relay out if you do that. The coil is dissipating
perhaps 5 times as much power as it should (a bit less than the
theoretical 5.76:1 because the wire is getting so hot). Put a series
resistor that is 7/5 = 1.4 times the nominal resistance of the coil
and rated at least at 1.4 times the power dissipation of the coil.

For example, a 360mW 5V miniature relay might have a coil resistance
of 69 ohms. If you put a 0.5W 100 ohm resistor in series you should be
okay.

Can you tell me more about the power saving trick? Do I put a low value
resister in series w/ the coil and put a cap in parallel with this resister?
what value do you suggest?

BTW - are there any simple RC circuits to delay the turn on of the relay for
a couple seconds?
Click to expand...
Use a 2N6028 and a 2N5064, four resistors and a capactor (see the data
sheet for the former for circuit examples). Reduce the series resistor
a bit to account for the 2N5064 forward drop.

Best regards,


Best regards,
Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
speff@interlog.com Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com
 
Matt wrote:
Yes, the relay is rated at 5v to turn on, and 250v for whatever it is
running. I have 12v to the coil now, it is getting a bit hot. I'm not sure
if they are supposed to get hot since they are such low resistance.

Can you tell me more about the power saving trick? Do I put a low value
resister in series w/ the coil and put a cap in parallel with this resister?
what value do you suggest?

BTW - are there any simple RC circuits to delay the turn on of the relay for
a couple seconds?

Thanks!
-matt
Click to expand...
It takes a particular voltage, usually something like 80% of the nominal
coil voltage, to close a relay. However, it takes much less than that to
keep it closed. You can take advantage of this by using an arrangement
whereby turning it on generates a larger voltage.


7V
+------+
| |
|< .-.
CTRL ---| | | 4.7k
|\ | |
| '-'
| |
o------|--------------------o-----\
| | | 12V
| | - Relay
.-. | || ^ Coil
10k| | o-----------||-------o-----/
| | | || |
'-' | V
| |/ C -
'----| |
|> |
| |
'--------------------'
GND

(created by AACircuit v1.28 beta 10/06/04 www.tech-chat.de)

Quick turn on will result in a 14V pulse across the relay coil, which
then relaxes to 7V as the cap charges back to ground through the coil.

Assuming a coil resistance of R, this will save (12^2 - 7^2)/R watts.

The circuit will require some time to recharge the cap, so it isn't good
for very quick close-open-close cycles.

The danger is that production coils will vary, possibly causing issues
with some units. However, I believe that most mfgrs publish minimum
voltages above which the relay is guaranteed to stay closed. If you make
sure your voltage is above that, then this is ok.

--
Regards,
Robert Monsen

"Your Highness, I have no need of this hypothesis."
- Pierre Laplace (1749-1827), to Napoleon,
on why his works on celestial mechanics make no mention of God.
 
"Ian Stirling" <root@mauve.demon.co.uk> wrote in message
news:41b35f87$0$50902$ed2619ec@ptn-nntp-reader01.plus.net...
In sci.electronics.design Matt <valid@email.com> wrote:
Yes, the relay is rated at 5v to turn on, and 250v for whatever it is
running. I have 12v to the coil now, it is getting a bit hot. I'm not
sure
if they are supposed to get hot since they are such low resistance.

They are designed to be run at the specified voltage.
Much more may cause heating, and poorer contact life (they bang
together too hard).

Can you tell me more about the power saving trick? Do I put a low value
resister in series w/ the coil and put a cap in parallel with this
resister?
what value do you suggest?

Measure the resistance of the coil.
Multiply by 12/5.
Now, subtract the resistance of the coil.
So, if 500 ohms, that's 1200 ohms - 500 ohms = 700 ohms.

You can add a R/C delay by adding this resistor, then putting a capacitor
across the relay. (with the correct polarity)

Time constant is about R*C, so for 2 seconds, you might try 2/500 of a
farad, or .004F (400uF)

In inverse proportion to the coil resistance.
Click to expand...

I believe a cap across the relay will delay it turning off, not on, as the
charged cap will give voltage to the coil and leave it on.
 
On 05 Dec 2004 19:20:39 GMT, the renowned Ian Stirling
<root@mauve.demon.co.uk> wrote:

In sci.electronics.design Matt <valid@email.com> wrote:
Yes, the relay is rated at 5v to turn on, and 250v for whatever it is
running. I have 12v to the coil now, it is getting a bit hot. I'm not sure
if they are supposed to get hot since they are such low resistance.

They are designed to be run at the specified voltage.
Much more may cause heating, and poorer contact life (they bang
together too hard).

Can you tell me more about the power saving trick? Do I put a low value
resister in series w/ the coil and put a cap in parallel with this resister?
what value do you suggest?

Measure the resistance of the coil.
Multiply by 12/5.
Now, subtract the resistance of the coil.
So, if 500 ohms, that's 1200 ohms - 500 ohms = 700 ohms.

You can add a R/C delay by adding this resistor, then putting a capacitor
across the relay. (with the correct polarity)

Time constant is about R*C, so for 2 seconds, you might try 2/500 of a
farad, or .004F (400uF)
Click to expand...
The source impedance in this case is less than 300 ohms. If we assume
RC (63% pull-in), that's C ~= 6800uF. If it's a typical small 360mW
power relay, the required capacitance will be more like 50,000uF.

In inverse proportion to the coil resistance.
Click to expand...
The relay contact life may be significantly reduced by not switching
it cleanly.



Best regards,
Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
speff@interlog.com Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com
 
Matt wrote:

"Ian Stirling" <root@mauve.demon.co.uk> wrote in message
news:41b35f87$0$50902$ed2619ec@ptn-nntp-reader01.plus.net...

In sci.electronics.design Matt <valid@email.com> wrote:

Yes, the relay is rated at 5v to turn on, and 250v for whatever it is
running. I have 12v to the coil now, it is getting a bit hot. I'm not
sure
if they are supposed to get hot since they are such low resistance.

They are designed to be run at the specified voltage.
Much more may cause heating, and poorer contact life (they bang
together too hard).

Can you tell me more about the power saving trick? Do I put a low value
resister in series w/ the coil and put a cap in parallel with this
resister?
what value do you suggest?

Measure the resistance of the coil.
Multiply by 12/5.
Now, subtract the resistance of the coil.
So, if 500 ohms, that's 1200 ohms - 500 ohms = 700 ohms.

You can add a R/C delay by adding this resistor, then putting a capacitor
across the relay. (with the correct polarity)

Time constant is about R*C, so for 2 seconds, you might try 2/500 of a
farad, or .004F (400uF)

In inverse proportion to the coil resistance.



I believe a cap across the relay will delay it turning off, not on, as the
charged cap will give voltage to the coil and leave it on.
Click to expand...
That is also true, but at turn-on there is zero volts across the cap.
because you now have a series resistor, the cap slowly charges up (time
constant = R*C seconds)

At turn-off the cap starts fully charged (5V if you picked your external
resistor right) and will ring with the coil inductance at f =
1/(2*pi*sqrt(L*C))

Cheers
Terry
 
"Terry Given" <my_name@ieee.org> wrote in message
news:ISKsd.22309$9A.386132@news.xtra.co.nz...
Matt wrote:

"Ian Stirling" <root@mauve.demon.co.uk> wrote in message
news:41b35f87$0$50902$ed2619ec@ptn-nntp-reader01.plus.net...

In sci.electronics.design Matt <valid@email.com> wrote:

Yes, the relay is rated at 5v to turn on, and 250v for whatever it is
running. I have 12v to the coil now, it is getting a bit hot. I'm not
sure
if they are supposed to get hot since they are such low resistance.

They are designed to be run at the specified voltage.
Much more may cause heating, and poorer contact life (they bang
together too hard).

Can you tell me more about the power saving trick? Do I put a low value
resister in series w/ the coil and put a cap in parallel with this
resister?
what value do you suggest?

Measure the resistance of the coil.
Multiply by 12/5.
Now, subtract the resistance of the coil.
So, if 500 ohms, that's 1200 ohms - 500 ohms = 700 ohms.

You can add a R/C delay by adding this resistor, then putting a capacitor
across the relay. (with the correct polarity)

Time constant is about R*C, so for 2 seconds, you might try 2/500 of a
farad, or .004F (400uF)

In inverse proportion to the coil resistance.



I believe a cap across the relay will delay it turning off, not on, as
the charged cap will give voltage to the coil and leave it on.

That is also true, but at turn-on there is zero volts across the cap.
because you now have a series resistor, the cap slowly charges up (time
constant = R*C seconds)

At turn-off the cap starts fully charged (5V if you picked your external
resistor right) and will ring with the coil inductance at f =
1/(2*pi*sqrt(L*C))
Click to expand...

Is it not really feasible to use an RC circuit to delay because of the low
resistance of the coil? sounds like it will take a large capacitance.

-matt
 
Ian Stirling wrote:

In sci.electronics.design Matt <valid@email.com> wrote:
big snip

Is it not really feasible to use an RC circuit to delay because of the low
resistance of the coil? sounds like it will take a large capacitance.


It will.
But, it's probably easier than learning the proper way to do it.
(some sort of transistor/IC circuit)
Click to expand...
ditto.

I always used to use a very crude scheme - an npn transistor to drive
the relay, with a base pullup resistor split in two, a cap to ground at
the split, and a base pull-down resistor. That way Rb is perhaps 10k, so
for 2s you would be looking at a cap around the 100uF mark. By suitably
choosing the voltage divider ratio this can be reduced further, but is
certainly a lot better than the 100mF or so required for the brute force
approach. Were I not so lazy I would draw an ASCII schematic.

Cheers
Terry
 
"Roger Hamlett" <rogerspamignored@ttelmah.demon.co.uk> wrote in message

"Anthony Fremont" <spam@anywhere.com> wrote in message

Isn't it really just I2C protocol with a chip select as the "third"
wire?

I'd be very 'wary' about chosing this chip, since it is no longer
listed
by Dallas/Maxim, with the data sheet 'links', going to a blank page...
Click to expand...
Hmm.... I just went to www.maxim-ic.com and typed in ds1393 in the part
number search field, clicked the "PART NO. SEARCH" button and came up
with this page:
http://www.maxim-ic.com/quick_view2.cfm/qv_pk/4359

The datasheet link worked fine for me as well. It's one datasheet for
the DS1390, DS1391, DS1392, and DS1393. Where did you look?
 
"Denis Gleeson" <dgleeson-2@utvinternet.com> schrieb im Newsbeitrag
news:184c35f9.0412040855.6a4a25df@posting.google.com...
the possibility of allowing the identification of items through a
persons sense of touch.
Click to expand...

Since the late 1970s there were devices available called Optacons.
http://www.nfbae.ca/publications/index.php?id=375

Unfortunatly this technology has disappeared from the market. It essencially
consists of a neadle array (20 x 5) where such trigger is stimmulated by
vibrating certain sets of these pins at a time.
This in fact allows detailed pattern recognition without the effect of
distress on the finger.
I am using such device for 25 years now myself and as an engineer I am
constantly looking for techniques to replace / rebuilt it.

Applying electricity directly to the finger is imho not a good idea. Apart
from safety considerations and possible long-term electrolytic effects I
would assume that you'll lose sensitivity for this after a while.
Vibrating mechanics of some kind triggered by something like an AC current
would work but in order to provide useful information this requires a
complex mechanical setup - just like on the Optacon.

The most promissing approach that I ever considered is to create haptical
stimulation by electrostatic / magnetic fields similar to what you can
experience if you switch your old model color TV off and touch the tube
glass.
If one would switch such fields on and off quickly, shield the whole thing
by some polymer with a suitable electronegativity characteristic and then
put the finger right on this plastic it may be possible to trigger a certain
part of the finger for a short time and - as a result - produce a picture.
This is what the optacon does but the approach could result in a much less
gragil technology with higher resolution and lower costs.

/Roland
 
Roland Zitzke wrote:
I am using such device for 25 years now myself and as an engineer I am
constantly looking for techniques to replace / rebuilt it.
Click to expand...
Roland, is this a device to help you see? I've read about these, but
never actually had any direct contact. Can you recognize different
faces? Or the fact that a face is in front of you?

--
Regards,
Robert Monsen

"Your Highness, I have no need of this hypothesis."
- Pierre Laplace (1749-1827), to Napoleon,
on why his works on celestial mechanics make no mention of God.
 
Roland Zitzke wrote:

"Denis Gleeson" <dgleeson-2@utvinternet.com> schrieb im Newsbeitrag
news:184c35f9.0412040855.6a4a25df@posting.google.com...


the possibility of allowing the identification of items through a
persons sense of touch.




Since the late 1970s there were devices available called Optacons.
http://www.nfbae.ca/publications/index.php?id=375

Unfortunatly this technology has disappeared from the market. It essencially
consists of a neadle array (20 x 5) where such trigger is stimmulated by
vibrating certain sets of these pins at a time.
This in fact allows detailed pattern recognition without the effect of
distress on the finger.
I am using such device for 25 years now myself and as an engineer I am
constantly looking for techniques to replace / rebuilt it.

Applying electricity directly to the finger is imho not a good idea. Apart
from safety considerations and possible long-term electrolytic effects I
would assume that you'll lose sensitivity for this after a while.
Vibrating mechanics of some kind triggered by something like an AC current
would work but in order to provide useful information this requires a
complex mechanical setup - just like on the Optacon.

The most promissing approach that I ever considered is to create haptical
stimulation by electrostatic / magnetic fields similar to what you can
experience if you switch your old model color TV off and touch the tube
glass.
If one would switch such fields on and off quickly, shield the whole thing
by some polymer with a suitable electronegativity characteristic and then
put the finger right on this plastic it may be possible to trigger a certain
part of the finger for a short time and - as a result - produce a picture.
This is what the optacon does but the approach could result in a much less
gragil technology with higher resolution and lower costs.

/Roland




After I have read this post, I have had the idea, that I would be able
Click to expand...
to propose a novel idea for this purpose, that may be very attractive,
because this allows to makes devices with even large surfaces, that can
produce even large pictures. This idea is based on may experience, and
this is the reason, whyI think, that this will work, but it requires
some money for the development. The device will not contain any moving
elements.

If somebody is interested in it, I would be able to do this development
and create a product. This can be surely patented.


Wieslaw Bicz

---------------========== OPTEL sp. z o.o. ===========---------------
------===== R&D: Ultrasonic Technology/Fingerprint Recognition ====------
ul. Otwarta 10a PL 50-212 Wroclaw Tel.:+48 71 3296854 Fax.:+48 71 3296852
--------==== mailto:W.Bicz@optel.pl -=- http://www.optel.pl ====-------
 
"Mike Deblis" <mdeblis@hotmail.com> wrote in message
news:bc45f679.0412080157.6676b4cd@posting.google.com...
Hi,

Has anyone tried talking to a DS1393 or similar 3-wire RTC from either
a PIC or AVR (or similar) - these RTCs are not SPI - they have a
bi-directional I/O pin.

Thanks,

Mike
Click to expand...
I'm using a DS1302 for a project which also has only 3 wires. It's really
simple and just like SPI, except that it's half duplex.

You can easily bit bang it. Switch the data in/output to output, make /CS
low, output 8 databits+clocks, then change the in/output to input, and issue
the neccessary clocks and sample the input. 20-25 lines of C code.

something like:

(assuming AVR, port B... 0=cs 1=dat 2=clk)

#define CS 1
#define DAT 2
#define CLK 4
..
..
..
DDRB|=DAT; // switch the data line to output
PORTB&=~CS; // select the chip
for (i=0;i<8;i++) // output 8 bits of command
{
if (command & 128) PORTB|=DAT;
else PORTB&=~DAT;

PORTB|=CLK; // Toggle clk. DS sample the data bit
command<<=1; // Shift command, maybe insert some NOPs here to delay
if it goes too fast
if (i!=7) PORTB&=~CLK; // Don't set CLK low at the last bit to prevent
shorting two outputs together
}

DDRB&=~DAT; // Switch to input
PORTB&=~CLK; // Set CLK low, DS13XX switches to output, takes at max 160ns

data=0;
for (i=0;i<8;i++) // Fetch 8 bits
{
data<<=1;
if (PORTB & DAT) data|=1;

PORTB|=CLK;
nop();
PORTB&=~CLK;
}

PORTB&=~CS; // End transfer

I've successfully interfaced many chips this way and for an RTC, speed is
not really an issue. Just follow the timing diagrams in the datasheet.

Actually, Dallas has an appnote of this, app note 2361...

Hope this helps,

Jeroen
 
"Wieslaw Bicz" <W.Bicz@optel.pl> schrieb im Newsbeitrag
news:41B85BA4.3030501@optel.pl...
fragil technology with higher resolution and lower costs.

After I have read this post, I have had the idea, that I would be able to
propose a novel idea for this purpose, that may be very attractive,
because this allows to makes devices with even large surfaces, that can
produce even large pictures. This idea is based on may
Click to expand...
Yes, I guess it would be possible to apply a core technology similar to
displaying TV pictures line by line.

experience, and
this is the reason, whyI think, that this will work, but it requires some
money for the development.
Click to expand...
You are right, and this is probably the problem why such technology is not
further developed or even sold.

The device will not contain any moving
elements.

Sure not, the three things I see as obstacles is
Click to expand...
a) To find a suitable surface material
b) to find components which are able to switch a high voltage on and off
with high frequency and deflect it.
c) Do extensive testing to see if the approach as such works as we think it
might word.
If somebody is interested in it, I would be able to do this development
and create a product. This can be surely patented.
Click to expand...
But I simply don't see a big market for such product since even my old
machine is no longer made.
/Roland
 
In article <41B9E19E.D0C684F2@tinaja.com>, don@tinaja.com says...
... is now available for free download as
http://www.tinaja.com/glib/funfield.pdf

It is on fun with fields.

Additional gurugrams at http://www.tinaja.com/gurgrm01.asp
Consulting services available via http://www.tinaja.com/info01.asp
Click to expand...
I don't understand your assertion that "there is no way you can tell if
a perfectly-uniform magnetic field is stationary or rotating."

If I bring a piece of wire into the field, a detectable current will be
induced by a rotating magnetic field, but not a stationary one. AC
motors would have a hell of a time working otherwise. Is this one of
those Heisenberg-style trick assertions (e.g., the field's no longer
perfectly-uniform once I couple energy out of it with a conductor)?

-- jm

------------------------------------------------------
http://www.qsl.net/ke5fx
Note: My E-mail address has been altered to avoid spam
------------------------------------------------------
 
I read in sci.electronics.design that Roger Johansson <no-email@home.se>
wrote (in <Xns95BBC317B4A5786336@130.133.1.4>) about 'Circuit that
produces a tingling sensation in the fingers.', on Fri, 10 Dec 2004:
I would try the skin on one of my thighs, it is fairly easy to attach a
thin elastic cloth around it and leave it on all day.

Then I need a way to excite the nerves in the skin of my thigh.
Click to expand...
IIRC, you have picked the body area where nerves in the skin are most
sparse.
--
Regards, John Woodgate, OOO - Own Opinions Only.
The good news is that nothing is compulsory.
The bad news is that everything is prohibited.
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk
 
On Fri, 10 Dec 2004 10:30:14 -0800, John Miles wrote:

In article <41B9E19E.D0C684F2@tinaja.com>, don@tinaja.com says...

... is now available for free download as
http://www.tinaja.com/glib/funfield.pdf

It is on fun with fields.

Additional gurugrams at http://www.tinaja.com/gurgrm01.asp
Consulting services available via http://www.tinaja.com/info01.asp


I don't understand your assertion that "there is no way you can tell if
a perfectly-uniform magnetic field is stationary or rotating."

If I bring a piece of wire into the field, a detectable current will be
induced by a rotating magnetic field, but not a stationary one. AC
motors would have a hell of a time working otherwise. Is this one of
those Heisenberg-style trick assertions (e.g., the field's no longer
perfectly-uniform once I couple energy out of it with a conductor)?
Click to expand...
He means that the rotating field is symmetric and is || to the axis
of rotation. Therefore the flux remains constant throughout the
revolutions.

IOW if you flip the bar magnet around, the field is *not* uniform -
it changes.

--
Best Regards,
Mike
 
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