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To fuse equipment or not to?
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mike
electronics forum Guru


Joined: 25 Mar 2005
Posts: 382

PostPosted: Thu Mar 24, 2005 6:00 pm    Post subject: Re: To fuse equipment or not to? Reply with quote

Fred wrote:
Quote:
I'm putting together a circuit board to take in 12V at less than 1/2 amp
from a wall wart. The unit will have a power jack to suit.

In this design a fuse will be very large or non-resettable or expensive. I
already have a diode so reverse polarity won't be a problem but what exactly
are the rules regarding fuses? Do I need one?

I'm in the UK.



I called the psychic hotline to fill in the gaps.
They said that the actual safety of the device is independent of
location. The ONLY reason it might matter that you're in the UK
is that you need third party agency approvals for the device.
The cost of a fuse is inconsequential unless you're in high volume
commercial production of a very low priced item.

While it's fun to let people vote on the internet, the only vote that
counts is that of the safety test engineer that will approve your
product. Read the regulations and/or call the testing agency. You'll
save yourself a LOT of grief.
And if you expect to sell one outside the UK, you might wanna be reading
many other safety standards. You might find that the presence or
absence of the fuse is the least of your problems. Back in the day,
standards for different countries required mutually exclusive wire
colors. This is probably fixed by now.

Wall Warts dramatically reduce, but do not eliminate your need to
understand the safety rules.

Don't get me started on product liability laws. Say you specify a wart
and it all passes the test. Next year, some bean counter substitutes a
different wart. Same specs and certifications on the wart, but it's 8
cents cheaper. Nobody else even knows it happened, much less tested it.
Creates new fire hazard...somebody's gonna get sued...
Or maybe someone substitutes a car battery for the wart.
If the cord ain't permanently attached, you're at risk.

So, even if your safety test engineer says you don't need a fuse, your
attorney might disagree.

Are we having fun yet?
mike

--
Return address is VALID but some sites block emails
with links. Delete this sig when replying.
..
Wanted, PCMCIA SCSI Card for HP m820 CDRW.
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Joerg
electronics forum Guru


Joined: 05 May 2005
Posts: 3533

PostPosted: Thu Mar 24, 2005 6:00 pm    Post subject: Re: TL082 input current? Reply with quote

Hi Chris,

Quote:
Yeah, maybe I'll give that a shot, after I figure out a bunch of other
troubles with my Linux permanent-headache.


I thought Linux is better than Windows. But probably not as good and
simple as DOS. Come to think of it, there isn't much that I can do with
a 'modern' OS that I couldn't with DOS. It's the same with cars, they
become ever fancier. Then something breaks and even an engineer can't
fix it.

Quote:
Now that's a perfectly respectable thing to do! I have been proposing
a switch to all tube front ends around here since I started. Can't
beat 'em for ESD and fault tolerance. Very Happy


Another advantage was that the tube had a dynamic range from here to the
Klondike. Huge signals left it unfazed. Also, it certainly outdid its
guaranteed 10,000 hour lifetime and kept going until we had to move.
Reminds me of why Bob Pease hung on to his VW Beetle.

Regards, Joerg

http://www.analogconsultants.com
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Joerg
electronics forum Guru


Joined: 05 May 2005
Posts: 3533

PostPosted: Thu Mar 24, 2005 6:00 pm    Post subject: Re: TL082 input current? Reply with quote

Hi Ian,

Quote:
In many FET type inputs, the failure is due to excessive current.
However, this is not external current.

It's current flowing through a weak point in the internal capacitance of the
input.
Once the junction is charged up high enough, the capacitance discharges
through a defect, and literally explodes part of the junction.



That can be even more nasty than a total failure because the device may
still 'kind of' work. I have had quite a few JFETs that were biasing ok
and all but where the noise figure had become lousy. After replacement
everything was fine. I guess that is why my first scope had all the
JFETs in sockets.

Regards, Joerg

http://www.analogconsultants.com
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Joerg
electronics forum Guru


Joined: 05 May 2005
Posts: 3533

PostPosted: Thu Mar 24, 2005 6:00 pm    Post subject: Re: Scope Trigger for digital scope Reply with quote

Hi Jim,

Quote:
Why not just run the A/D "balls to the wall" all the time, throw away
all but a little of the data, and do the triggering in soft(firm?)ware?



It won't work if he wants to measure frequencies well above 40MHz. The
only way to do that with a slower ADC is via multiple shots delayed by a
sliver each time. For that the clock of the ADC needs to be precisely
started by the trigger signal, plus x many pico- or nanoseconds for the
subsequent acquisition and so on.

Regards, Joerg

http://www.analogconsultants.com
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Mac
electronics forum Guru


Joined: 25 Mar 2005
Posts: 409

PostPosted: Thu Mar 24, 2005 6:00 pm    Post subject: Re: 40 amp power supply ??? Reply with quote

On Wed, 02 Feb 2005 04:11:01 +0000, rijo1 wrote:

Quote:
Hi , I need to build a 40 amp power supply that has an input voltage
of 120 volts and an output voltage of 12 volts - 13.5 volts . The power
supply will be used for amateur radio so it needs to be quiet . The
transformer I want to use will come out of a battery charger . I need to
regualte the voltage to DC at the voltages I have specified .
I don't want to use a battery charger and a battery for a power
source .
If anyone has a good design and is willing to send me schematics on
it , please send it to me . Be sure to remove no in front of (
nemonet.com.)
Thanks , Rick

The transformer is part of the schematic. If someone sent you a schematic
with a particular transformer in it, how could you be sure you'd find that
in an old battery charger?

Or do you already have the transformer? If so, it would help a lot if you
could measure the open circuit RMS voltage on the secondary, and then also
the loaded voltage with some load to approximate your worst case scenario.
Maybe 0.25 Ohms or so. Note that the power dissipation at "12" Volts is
144/0.24 = 576 Watts. So use a big resistor. Or maybe a bunch of light
bulbs in parallel.

--Mac
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Clarence_A
electronics forum addict


Joined: 02 May 2005
Posts: 66

PostPosted: Thu Mar 24, 2005 6:00 pm    Post subject: Re: OT: reaction to Iraqi elections Reply with quote

"Dirk Bruere at Neopax" <dirk@neopax.com> wrote in message
news:36btqiF5017baU1@individual.net...
Quote:
keith wrote:
On Tue, 01 Feb 2005 14:49:23 +0000, Dirk Bruere at Neopax
wrote:
keith wrote:
On Mon, 31 Jan 2005 20:30:37 +0000, Richard the Dreaded
Libertarian wrote:
On Mon, 31 Jan 2005 08:21:00 +0000, Pooh Bear wrote:

What I've never seen adequately explained is just who these
*insurgents*
actually are or what agenda they're pursuing.
Iraqi freedom fighters, resisting the invasion.
Sure, that's why they're killing their own! You do live in a
drug-induced alter-world!
Ecer heard of 'collaborators'? What do you suppose happens to
them?
Collaborators, my ass. They're simply people caught in the
wrong place
when the Saddamites are in their death throes. It seems
you're a
Saddamite too.

Like policemen, soldiers etc when recruiting stations are
bombed.
The rest falls under the heading of 'collateral damage' to use
an American term.
If someone invaded my country I would be doing exactly the same.

You mean "Getting Killed?" Figures! Probably what you deserve!
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Clarence_A
electronics forum addict


Joined: 02 May 2005
Posts: 66

PostPosted: Thu Mar 24, 2005 6:00 pm    Post subject: Re: PID Control Primer, $17. Companion Software $11 Reply with quote

"Tom" <tom_systek@msn.com> wrote in message
news:1107322477.165819.42030@o13g2000cwo.googlegroups.com...
Quote:
This is blatant spam, doesn't even give his real email address.


Relax, His book is worth it and he is otherwise retired.
He is NOT a pill pusher or scammer!

He is also a regular here. OTOH I've never hear of you.
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Fred Bloggs
electronics forum Guru


Joined: 25 Mar 2005
Posts: 2468

PostPosted: Thu Mar 24, 2005 6:00 pm    Post subject: Re: Sine generator IC solution? Reply with quote

Tony Williams wrote:
Quote:
In article <41FD0BE4.2030700@nospam.com>,
Fred Bloggs <nospam@nospam.com> wrote:


You're not going to do much in the way of a 10:1 tuning range in
Wien bridge- fussy little high Q and amplitude unstable thing
that it is. These days the most practical and high performance
approach, at these frequencies, would be to generate a variable
frequency square wave at fundamental and 100x fundamental which
are then processed by cheap switching tracking filter.


An 8038-variety is still the easiest approach if
not much better than 1% THD is ok.

Your approach is nifty and could be very handy if
(say) something like a 2-phase sine/cosine was required.

Note that there is a 3-step square-wave approximation
of a sine which has zero third harmonic content, very
useful if going into a low pass filter.


The switched capacitor filters make an application like this virtually
digital- no analog involved, no tuning, no fussing with voltages, a
simple embedded programming application: Digitally Controlled Sine-Wave
Generator-
http://www.maxim-ic.com/appnotes.cfm/appnote_number/2081
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John Fields
electronics forum Guru


Joined: 24 Mar 2005
Posts: 3260

PostPosted: Thu Mar 24, 2005 6:00 pm    Post subject: Re: Triac or relay to switch AC power? Reply with quote

On 1 Feb 2005 12:29:33 -0800, Robijean@hotmail.com (Jean) wrote:

Quote:
Triac or relay to switch AC power?

I want to use a controller to switch for an hour the AC power of a
light bulb.
Should I use a triac or a relay?
Besides the circuit needed to drive the triac or the relay, what are
the parameters I should be aware of to choose between the triac and
relay?
In both cases, the controller has to keep sending the signal for an
hour; The circuit around the controller will use current for an hour
and I am concerned about this consumption and want to keep this
consumption as low as possible.

---
How do you want to start and stop the timer?

--
John Fields
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Bill Sloman
electronics forum Guru


Joined: 12 May 2005
Posts: 1080

PostPosted: Thu Mar 24, 2005 6:00 pm    Post subject: Re: Which website would you send to Issac Newton? Reply with quote

Probably something encapsulting Dale Carnegie's "How to Win Friends and
Influence People". Newton eventually mastered the second skill, but he
was even worse at winning friends than Gerardus 't Hooft is today.
-----------
Bill Sloman, Nijmegen
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Armin Steinhoff
electronics forum beginner


Joined: 24 Mar 2005
Posts: 3

PostPosted: Thu Mar 24, 2005 6:00 pm    Post subject: Re: CHEAP Serial bus, control 200 devices, 50 meters Reply with quote

Brook Stevens wrote:
Quote:
Rene Tschaggelar wrote:


I'd go for RS422, a bidirectional bus with one leading in
each direction. Physically identical to the RS485, it doesn't
require you to switch direction at the cost of an additional
line pair. There are input impedances that limit the number
of devices to 32 or 128, depending on the receivers.
So after the number of devices is reached, just add a
repeater.
I'd use 6 wires for the bus. 4 wires for the signal plus
one for GND and +5V. This would enable you to have the local
RS422_to_CMOS plus perhaps isolators powered from the bus.


Thanks Rene. RS-422 seems like a good option for the bus.

RS-422 is not the right choice for a BUS. RS-422 can be used for a
one-to-one (or one to many) communication structure.

Use RS-484 ... or simply CAN and you go with a standard.

Armin


Quote:
But, then what
protocol should the devices use to communicate with the PC? The PC needs to
address one out of 200 devices and tell it to set it's outputs, or to send
it's inputs.

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Bill Sloman
electronics forum Guru


Joined: 12 May 2005
Posts: 1080

PostPosted: Thu Mar 24, 2005 6:00 pm    Post subject: Re: [OT]: Who should God take 1st? Supreme court justice, Pat Robertson, Sponge-Bob, Dr. Dobson, Hillary or Bush? Reply with quote

"martin griffith" <martingriffith@yahoo.co.uk> schreef in bericht
news:4251015c6vv2j698g64un2i4d1qmdppal8@4ax.com...
Quote:
On Wed, 02 Feb 2005 01:59:05 -0600, in sci.electronics.design Scott
Stephens <scottxs@comcast.net> wrote:

Pat Robertson recently prophesied that a supreme court justice would go
home for their reward, freeing up a seat for a righteous judge.

Well, one of the conservatives has cancer, so it seems God is, once
again, working in mysterious ways that are beyond the reason of we mere
mortals.

But if you were God, whom would you smite for snicks 'n grins?

I would smite the creators of such great American cartoons as the Family
Guy, South Park, and the Simpsons. I can't understand why a fundee like
Dr. Dobson is attacking Sponge-Bob, while leaving alone the Christians
whipping-boys in those other cartoons, which are seem to come strait
from the anti-jew propaganda Hilter made.

Last night I heard the "Family Guy" using Disney's "Wish upon a star" as
a paradodee of "Fiddler on the Roof". I hope its a Jew writing those
scripts, and not a Christian!
Hi Scott
1) I'm in Europe
2) I'm an aethist
3) I dont know or care who Pat Robertson is
4) S.E.D in an international english speaking newsgroup, not a US
newsgroup

Please could you post your very OT non electronic ideas to a more
appropriate newsgroup

Thus, we have another candidate for God's attention, though granting Scott
Stephens performances here, the Devil might be more interested in him.

--------------
Bill Sloman, Nijmegen
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Rene Tschaggelar
electronics forum Guru


Joined: 24 Mar 2005
Posts: 540

PostPosted: Thu Mar 24, 2005 6:00 pm    Post subject: Re: CHEAP Serial bus, control 200 devices, 50 meters Reply with quote

Nico Coesel wrote:

Quote:
Rene Tschaggelar <none@none.net> wrote:


Nico Coesel wrote:

"Dave VanHorn" <dvanhorn@dvanhorn.org> wrote:


There is a protocol which deals better with these sort of setups. It's
called TCP/IP.

Seems like a lot of overhead, I guess you could toss out the parts you don't
need.

There are some very space efficient TCP/IP stacks around. I've noticed
its quite hard to put a reliable communication protocol together. It
takes some serious thought on fault detection, re-transmitting lost
packets, time-outs, packet re-alignment, etc. So why try to invent
something new if you can use something that already exists?


Very efficient ?
TCP/IP allows to transmit block of 2^32bits in random
packet order. To as many as 2^32 devices. It adresses
2^16 different ports per device. This is huge overkill
when the packetlength is shorter than 250 bytes, to
less than 255 devices.


If you use a standard ethernet chip, it will do most of it for you at
high speed using standard cabling, standard hubs / switches, etc.
Besides, the more advanced IP stacks will collect a number of packets
(nagle algorithm) for a given target and send them as one packet to
reduce overhead. If you send a lot of short messages to a target from
-let's say a PC- in a short period, the target will receive 1 or more
long packets.

Yes, the ethernet chip does up to the IP level. Meaning
1500 something bytes, no ports, no retransmit, no reassembly.
It may depend from which platform you look, from an 8bit
micro TCP/IP is a heavy burden. I'd possibly prefer UDP
if it had to be. The random transmissions have to be
controlled somehow to reduce collisions. But a master-
slave setup should do that nicely.

Rene
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Paul Burke
electronics forum Guru


Joined: 06 May 2005
Posts: 444

PostPosted: Thu Mar 24, 2005 6:00 pm    Post subject: Re: [OT]: Who should God take 1st? Supreme court justice, Pat Robertson, Sponge-Bob, Dr. Dobson, Hillary or Bush? Reply with quote

Bill Sloman wrote:

Quote:

Thus, we have another candidate for God's attention, though granting Scott
Stephens performances here, the Devil might be more interested in him.

On God's recent record, he'll ignore all the obvious candidates and just

kill another 30000 kids.

Paul Burke
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Fred Bloggs
electronics forum Guru


Joined: 25 Mar 2005
Posts: 2468

PostPosted: Thu Mar 24, 2005 6:00 pm    Post subject: Re: Triac or relay to switch AC power? Reply with quote

Jean wrote:
Quote:
Triac or relay to switch AC power?

I want to use a controller to switch for an hour the AC power of a
light bulb.
Should I use a triac or a relay?
Besides the circuit needed to drive the triac or the relay, what are
the parameters I should be aware of to choose between the triac and
relay?
In both cases, the controller has to keep sending the signal for an
hour; The circuit around the controller will use current for an hour
and I am concerned about this consumption and want to keep this
consumption as low as possible.

The simplest way to achieve success without knowing much about
electronics is to use an AC relay actuated by a your controller through
a TRIAC. The sizing of the relay driving an incandescent load has to be
adjusted downward from the maximum current rating of the relay to
something like 30-40% because of the cold filament surge and possible
filament failure scenarios. So if your bulb is say 300W @ 240VAC, then
I=W/V=300/240=1.25A -use a relay with contacts rated at 5A @240VAC and
240VAC coil. Then use a 600V TRIAC with 1A or more current rating to
drive the coil like so:

View in a fixed-width font such as Courier.

.
.
. +--------------+
. | / |
. LINE -----------|--+-----o o---|----------------->
. | | | TO LAMP
. | K|| |
. | K|| | +---->
. | K|| | |
. | K|| | |
. | K|| | |
. | | | |
. Rs=100 ohm +--------------+ |
. flameproof | |
. | |
. Cs=0.1u 1000V | |
. | |
. +-----+ |
. | | +-------+ |
. [Rs] | TRIAC |* | |
. | --- | OPTO | |
. | ^ v/ -------| DRIVE | |
. === --- | | |
. Cs | +-------+ |
. | | | |
. NEUTRAL-----+-----+--------------+---------+
.
.
.
. * see http://www.fairchildsemi.com
.
. sold through Mouser
.
.
.
.
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