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On Saturday 07 October 2006 04:17 pm, Shawn Upton wrote:

What about an LM231? Voltage to frequency converter.
You could then measure DC levels on the computer

Hmm, that'd be a bit strange: trying to measure a
changing voltage by correlating the frequency... Waay
too math to convert back to something that looks like
"normal" signal. But sounds like a good senior design
project for those guys who come on here once in a
while looking for one: take a signal with a DC
component and some known BW of AC signal (think TTL
1kHz square wave), and measure that DC and AC
component on a soundcard (ie, recover on the PC the
high/low level and some portion of the edges too,
inspite of the AC coupling of the soundcard).

That is an inteeresting idea. I never messed with any of those chips, though
I did have one I picked up at Radio Shack some years ago, I think it was
called a "9400C" or something pretty close to that, and I never did run
across any real data for it. Tried getting it working once in a breadboard
but didn't have much success. And it wanted multiple power supply voltages,
as I recall.

But I have seen V/F and F/V circuits somewhere or other.

Dealing with DC can be a PITA, particularly when you're dealing with very
small values of it, noise and offset and such can really mess things up.
Back before modern components it was common to chop such stuff, and then
amplify and otherwise process it as an AC waveform, only averaging it out
later on. Betcha a bunch of those students that come around from time to
time that you mention don't know much about such "prior art", nor consider
it worthwhile to look at how things were once done.

--
Member of the toughest, meanest, deadliest, most unrelenting -- and
ablest -- form of life in this section of space, a critter that can
be killed but can't be tamed. --Robert A. Heinlein, "The Puppet Masters"
-
Information is more dangerous than cannon to a society ruled by lies. --James
M Dakin

--- "Stefan Trethan" <stefan_trethan@...> wrote:
*snip*

Anyway, i think Chris really wants a storage scope (and i would
recommend it for his type of work), so the 7704 is out (at least
without 7D20 plugin). Since he already had bad luck with one used
scope, i reckon he doesn't want to take that risk again.

As others said standard probes will fit the velleman thing, 10:1,
100:1, even 1000:1, to increse the input range. This seems a
fairly decent one for PC scope standards, with 1Gsample.
You'd have to set it up properly with a PC or laptop so it is
somewhat comfortable to use.

ST

*snip*

Once again, I think Stefan hit the spot. Chris indicates that he
wants storage / retrieval. As for the software, the advertiement
indicates that "a DLL is supplied, which allows you to create your
own application." If you have decent programming skills, and the DLL
is decent, you can probably make something pretty fancy or specific,
if needed.

Ultimately, I also want storage in a scope. Like Chris, I do not
know if this would be a great help to me, but I believe it would.
The "belief" makes it a "must have" feature for my next 'scope.

Ultimately, I would like to take some readings over a fairly long
period of time (say 20 seconds to 1 minute or more?) and watch the
signals coming down the wire over that time period. Then, I will
scroll back and forth looking for transients, and trying to analyze
these. I s'pose I would have to do this because I do not have the
depth of experience of some of you. Thus, what you might instantly
understand is a Ground Loop problem or a transient coming across the
power supply line might take me days to analyze. I think that
storage / retrieval, with the ability to store LOTS of data, would
accelerate that analysis.

I have been looking at various PC based 'scopes for some time, but
have yet to pull the trigger. That day may come soon.


Side Questions:

- When analyzing a scope, what are the most important specifications
to focus on (e.g. sps, bandwidth, dynamic range, time base, etc.)

- If you had to put 4 or 5 'scopes through the paces to see which
performs the best under various lab conditions, what testing would
you recommend?


Thanks,

Bob H.

Hello, can someone please help me to identify a part I have. It looks
like a small MOSFET, but it has 4 legs. The wrighting on it says "CDT
33?? -04 0544. It is used on a "inline" LED Flasher circuit.

It's a fairly simple circuit. If you do a google search you should be able to find a few schematics for curve tracers that utilize an oscilloscopes X-Y function. At it's most basic you just need a 10v transformer, a few resistors, probes, and some BNC connectors like this one: . I'm planning on doing a little bit more of an elegant version that would use the PCs soundcard as the X-Y scope leaving my o-scope free. I've got a preliminary schematic using CMOS logic for control but it still needs some work and I'll probably use a PIC in the final product instead: .

Hi William

In a previous post you discussed about a sound card based curve tracer. I
would request you to share information about the same.
I am looking for the following information

1) Is it a circuit you made yourself or did you buy it
2) What is the software for it.

I would request you to share the information around it with me.

Thanks
Regards

Gaurav

Great find! Should be just what I need for my soundcard curve tracer.

I'm using my Ghodlike listowner powers to repost the entire message,
because Stefan hit it on the head.

We keep rehashing this over and over again.

Steve Greenfield

--- In Electronics_101@..., "Stefan Trethan"
<stefan_trethan@...> wrote:

Joe,

in this group there is as far as i know no rule for top/bottom

posing. If

i remember correctly Steve (moderator) said a few times he doesn't

mind.

So since there is no rule, you can't break it.

I would say the common points that are agreed on are:

*) TRIM posts (Steve says that all the time)
*) SUBJECT LINE must correspond with topic (change it if you change

the

topic)

What most people would additionally like to see:

*) avoid HTML email since it destroys quoting.
*) use standard quoting (which is a > in front of each quoted line,

for

double quoting).
*) don't use ALL CAPITALS, use polite and correct language (as good

as one

can will do, we are international after all)

I think if you do that most people will be happy, no matter if your

text

is written below or above or between the quoted text.
What is important is that it is clearly visible which is your text, so
people don't have to start a lengthy search and re-read the whole

message

to find whatever is new to them. This is easy if > is used properly

(in

front of the old text and _not_ your answer).

That was basically my comment which started this topic - it would be

good

if one could identify what someone wrote. It's not a big thing - you

don't

have to stand in the corner if you speak without raising your hand

;-).

But often the poster will not notice the quoting malfunctions for his
posts, so i pointed it out, maybe it can be fixed easily.

ST

--- In Electronics_101@..., "lcdpublishing"
<lcdpublishing@...> wrote:

Hmmm, that sounds neat. I will have to look through my box of
computer "Guts" and see if I have an old card. Chances are good
though they would be surface mount though wouldn't they?

Chris

Chris,

If you decide to jumper the input capacitors on your sound card, you
put your computer at significant risk. In fact, I think I,
personally, would pass on the sound card thing altogether: my computer
is too important to leave to luck (like my not sampling the line
voltage). It might be possible to blow out the input capacitors
pretty easy. Who knows, they might short through rather than blowing
open.

In the scheme of things, that Vellman digital scope isn't all that
expensive. If you don't like it, sell it on eBay for half, or whatever.

Or, put some money with it and look at the BN310 at www.bitscope.com

Richard

The one I am working with the most right now is the free one from
Virtins.



Scroll all the way down to the bottom where they list the "OLD
VERSIONS". I am using V2.0. The biggest reason I like this one is
that it works full screen

Chris



--- In Electronics_101@..., <william.kroyer@...> wrote:

Which soundcard scope are you toying with? I've been looking for

a free soudcard based scope program to try and make a little PC bsed
curve tracer for trouble shooting.

----- Original Message -----
From: lcdpublishing
To: Electronics_101@...
Sent: Saturday, October 07, 2006 3:54 PM
Subject: [Electronics_101] Re: How limitting do you think a

scope would be if it were limitted to 35 volts?

This kind of neat. I can shut down the scope, re-start it and

the

traces are showing the same as before. I don't have to push

every

button on the computer like I had to do with my "real" scope ;-)

It still isn't the greatest thing, but it's a heck of a lot
more "Trusty" than what I had.

The one problem with this type of scope is accurately

calibrating

the voltage (vertical) scale. These things (SOundcard versions)
cannot measure a steady DC voltage - it must be alternating to
different levels and at some magical, Minimum frequency.

I am digging it! Especially the price for the ones I have ;-)

Chris

--- In Electronics_101@..., "Stefan Trethan"
<stefan_trethan@> wrote:
>
> On Sat, 07 Oct 2006 21:10:18 +0200, lcdpublishing
> <lcdpublishing@> wrote:
>
> >
> > More tinkering with this to do, but I have quickly gained
respect for
> > these sound card scopes - so far it's working a thousand

times

better
> > than my HP scope has - not that HP scopes are bad, mine is

just

seen
> > much better days!
> > Chris
>
>
> Ok, then maybe you should get the USB scope. Because that is
working a
> thousand times better than a soundcard - litterally, 50Msps
instead of
> 50ksps. Working a million times better than the HP scope seems

a

good deal
> ;-)
>
> ST
>






[Non-text portions of this message have been removed]

Hmmm, that sounds neat. I will have to look through my box of
computer "Guts" and see if I have an old card. Chances are good
though they would be surface mount though wouldn't they?

Chris



--- In Electronics_101@..., "Roy J. Tellason"
<rtellason@...> wrote:

On Saturday 07 October 2006 03:54 pm, lcdpublishing wrote:

The one problem with this type of scope is accurately calibrating
the voltage (vertical) scale. These things (SOundcard versions)
cannot measure a steady DC voltage - it must be alternating to
different levels and at some magical, Minimum frequency.

There's a way to get around that, particularly if you have a

spare sound card

to mess with. You remove the coupling capacitors that are

blocking the DC

from the input connector, and jumper the pads...

--
Member of the toughest, meanest, deadliest, most unrelenting -- and
ablest -- form of life in this section of space, a critter that

can

be killed but can't be tamed. --Robert A. Heinlein, "The Puppet

Masters"

-
Information is more dangerous than cannon to a society ruled by

lies. --James

M Dakin

--- John Popelish <jpopelish@...> wrote:

I thought you were driving your transformer with a
current
source. If so, the primary current should be
independent of
the cores state. The output current will diminish
as the
core saturates, because more and more of the primary
current
will be going into stored magnetic energy as the
core saturates.

Yep, still using a current source. I wanted to remove
the effect of the secondary, thus I can only watch the
voltage across the inductor to see what happens. That
way, I can see if the flux cancelation (due to
transformer action) does make an impact.

I'd think that the voltage would clip if the core
material saturates--if the flux cannot build any
higher (no more stored field), then the voltage should
clamp or even droop, even as current goes higher.

Sounds like you need 4 pieces, 4 times as long, in
parallel.
Fold each into a hair pin to get the ends close
together,
and keep the inductance down.

That's a good idea, hadn't thought of it. Thanks.

Have you tried a fat ferrite bead over the source
leads of
the fets? A low value wire wound source resistor
might also
help.

No, haven't built it yet, just simulating first in
LTSPICE, to check for problems. And problems show up,
so I'm hesitant to build just yet.

The FET's have a 20 ohm gate resistor, originally I
put them in there just to prevent the op-amps from
oscillation (with the gate capacitance). I tried to
insert some inductance, but I couldn't get it stable,
and the gate voltage starts swinging real hard. I've
seen RF amps take more than the spec'd +/-20V gate
limit, but I'm not so sure at these relatively low
frequency levels.

I also tried a lead network here on the gate, still no
luck (RC across the gate resistor, to try to get some
positive phase shift). Frequency of oscillation just
moves around.

I tried to add some lead to the feedback, but that
hasn't helped either. I think I have to sit down and
figure out the phase response over frequency, and do
the math and see what I actually need to do in order
to compensate this: I tried some "standard" fixes here
and there (bigger gate resistor, caps here and there)
to no success.

Shawn Upton, KB1CKT

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Shawn Upton wrote:

Ah, took me a moment--for powdered iron cores, the
higher the permability, the more conductive the core
is. The core I'm playing with is ferrite though, and
I don't think they are conductive as a rule. Haven't
read up on their construction yet though. My core is
like mu r = 10,000, based upon some measurements.

Powdered metal cores are almost all good insulators, because the bonding material between the grains is good insulation. Only a few very high permeability, low frequency materials have significant conductivity. They are also easily recognized by colored paint and a gray, grainy appearance if chipped. Ferrite looks black and glassy if chipped.

There are two basic families of ferrite in wide use. The high permeability family, including the high flux power supply core types are made of manganese ferrite and are semi conductive. The high frequency types, including most f the EMI suppression cores (except for a few exceptions) are made of nickel zinc ferrite and are pretty good insulators. They are such good insulators, that you can't sort them with an ohm meter, except to tell that they are nickel zinc. But the manganese zinc family have the general property that the higher the permeability (and lower the frequency capability) the lower the resistivity, and can be fairly accurately sorted with an ohm meter. The data sheets for the various materials should include a spec for the bulk resistivity.

I experimented around, and indeed I have not been able
to saturate my core, even at stupid high currents. There is something that I need to go back and look at,
a pecularity that I couldn't quite figure out. Basically, I figure, if the core saturates, I should
see flattopping in the current:

I thought you were driving your transformer with a current source. If so, the primary current should be independent of the cores state. The output current will diminish as the core saturates, because more and more of the primary current will be going into stored magnetic energy as the core saturates.

(snip account of surprises)

A fun side note: I attempted to make my own resistor
to measure current, using 23mm of 18g wire. 0.5
milliohm. I was able to get what I think was around
270App at 1kHz, not bad--but the shunt managed to
unsolder the scope probe at that power level!

Sounds like you need 4 pieces, 4 times as long, in parallel. Fold each into a hair pin to get the ends close together, and keep the inductance down.

(snip hot ware story)

Anyhow, I ran a bunch of tests, and then went back to
figure out if I could "trust" my shunt. Well, I
forget what inductance I calculated for 23mm of wire,
but in the end, at 5kHz, I found the wire to have 0.5
milliohm of inductive reactance. Not so good, means
the current waveform as measured isn't what I thought!
Not only that, but above 10kHz, the skin effect
starts to crop up too, increasing the resistance.

I would be thinking of something like a square of brass shim stock with a heavy copper bar soldered across each end as connection points. You can punch the middle with a paper punch to get close and then trim slivers off the sides.

In the end, I'm shifting gears. I'm going to make a
push pull pair, using IRF510's, to drive the
transformer with a different set of windings (probably
6 or 7:1). OPA627's to drive the FET's, one as an
integrator and the other as an invertor, so as to
drive the gates out of phase. 0.1 ohm shunt, so as to
stay resistive past 100kHz, and some feedback so that
the response is flat.
It simulated well. Looked good, was about to build it
until I realized that the DUT is inductive. Adding in
the 60nH of inductance causes a nice oscillation, so I
haven't been able to build it yet. The slight phase
shift between the 60nH inductor and the large phase
shift from the gate capacitance (reacting with the
usual gate resistor) causes a 1.2MHz oscillation. Drat, was so close! Haven't been able to get a lead
network to tame it yet either.

Have you tried a fat ferrite bead over the source leads of the fets? A low value wire wound source resistor might also help.

Guys isnt this conversation getting out of hands. I am sure all the methods
to reply are ok, after all the group has survived communication in past and
we have been able to help each other.
Just a thought.
Gaurav

Shawn Upton wrote:
(snip)

I couldn't tell from your response--are you against
including prior emails or for it? Trimming the
history to just the points being responded to, or not?

(my opinion, not a rule) Include just enough to remind the reader what post and what part of that post you are replying to. If they haven't been reading the recent history, they probably won't read a quoted copy, anyway. But when many people may be involved in a branched thread, a little context is needed, just so the place of this post in the thread can be reconstructed, if desired.

Which soundcard scope are you toying with? I've been looking for a free soudcard based scope program to try and make a little PC bsed curve tracer for trouble shooting.

What about an LM231? Voltage to frequency converter.
You could then measure DC levels on the computer

Hmm, that'd be a bit strange: trying to measure a
changing voltage by correlating the frequency... Waay
too math to convert back to something that looks like
"normal" signal. But sounds like a good senior design
project for those guys who come on here once in a
while looking for one: take a signal with a DC
component and some known BW of AC signal (think TTL
1kHz square wave), and measure that DC and AC
component on a soundcard (ie, recover on the PC the
high/low level and some portion of the edges too,
inspite of the AC coupling of the soundcard).

Shawn


Shawn Upton, KB1CKT

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On Saturday 07 October 2006 03:54 pm, lcdpublishing wrote:

The one problem with this type of scope is accurately calibrating
the voltage (vertical) scale. These things (SOundcard versions)
cannot measure a steady DC voltage - it must be alternating to
different levels and at some magical, Minimum frequency.

There's a way to get around that, particularly if you have a spare sound card
to mess with. You remove the coupling capacitors that are blocking the DC
from the input connector, and jumper the pads...

--
Member of the toughest, meanest, deadliest, most unrelenting -- and
ablest -- form of life in this section of space, a critter that can
be killed but can't be tamed. --Robert A. Heinlein, "The Puppet Masters"
-
Information is more dangerous than cannon to a society ruled by lies. --James
M Dakin

This kind of neat. I can shut down the scope, re-start it and the
traces are showing the same as before. I don't have to push every
button on the computer like I had to do with my "real" scope ;-)

It still isn't the greatest thing, but it's a heck of a lot
more "Trusty" than what I had.

The one problem with this type of scope is accurately calibrating
the voltage (vertical) scale. These things (SOundcard versions)
cannot measure a steady DC voltage - it must be alternating to
different levels and at some magical, Minimum frequency.

I am digging it! Especially the price for the ones I have ;-)

Chris



--- In Electronics_101@..., "Stefan Trethan"
<stefan_trethan@...> wrote:

On Sat, 07 Oct 2006 21:10:18 +0200, lcdpublishing
<lcdpublishing@...> wrote:

More tinkering with this to do, but I have quickly gained

respect for

these sound card scopes - so far it's working a thousand times

better

than my HP scope has - not that HP scopes are bad, mine is just

seen

much better days!
Chris

Ok, then maybe you should get the USB scope. Because that is

working a

thousand times better than a soundcard - litterally, 50Msps

instead of

50ksps. Working a million times better than the HP scope seems a

good deal

;-)

ST

Ah, took me a moment--for powdered iron cores, the
higher the permability, the more conductive the core
is. The core I'm playing with is ferrite though, and
I don't think they are conductive as a rule. Haven't
read up on their construction yet though. My core is
like mu r = 10,000, based upon some measurements.

I experimented around, and indeed I have not been able
to saturate my core, even at stupid high currents.
There is something that I need to go back and look at,
a pecularity that I couldn't quite figure out.
Basically, I figure, if the core saturates, I should
see flattopping in the current: flux doesn't increase
as fast as it should in saturation (core saturation is
sudden not gradual), and so current transfer on the
peaks should clip in a soft sort of way. Instead, it
looked like zero crossing error in the current. Could
be the driver.

Next week, I think I'll unhook the secondary and then
watch V vs I and see if I can detect a saturation
level, and then rehook the secondary and see if it
saturates at the same current. My understanding is
obviously wrong about this transformer, in terms of
saturation.

A fun side note: I attempted to make my own resistor
to measure current, using 23mm of 18g wire. 0.5
milliohm. I was able to get what I think was around
270App at 1kHz, not bad--but the shunt managed to
unsolder the scope probe at that power level!

[I had used RG-174 as a probe to the scope, that way I
could measure mV's. Works well. But the coax braid
went to the 3/8" braid I was using as a secondary, and
the shunt was connected to the DUT, and thus the
center conductor could get hot enough to unsolder
itself. It's a fun thing, to be able to smell your
circuit, and know it's working. Maybe I should go
work with some tubes in the future.]

Anyhow, I ran a bunch of tests, and then went back to
figure out if I could "trust" my shunt. Well, I
forget what inductance I calculated for 23mm of wire,
but in the end, at 5kHz, I found the wire to have 0.5
milliohm of inductive reactance. Not so good, means
the current waveform as measured isn't what I thought!
Not only that, but above 10kHz, the skin effect
starts to crop up too, increasing the resistance.

In the end, I'm shifting gears. I'm going to make a
push pull pair, using IRF510's, to drive the
transformer with a different set of windings (probably
6 or 7:1). OPA627's to drive the FET's, one as an
integrator and the other as an invertor, so as to
drive the gates out of phase. 0.1 ohm shunt, so as to
stay resistive past 100kHz, and some feedback so that
the response is flat.

It simulated well. Looked good, was about to build it
until I realized that the DUT is inductive. Adding in
the 60nH of inductance causes a nice oscillation, so I
haven't been able to build it yet. The slight phase
shift between the 60nH inductor and the large phase
shift from the gate capacitance (reacting with the
usual gate resistor) causes a 1.2MHz oscillation.
Drat, was so close! Haven't been able to get a lead
network to tame it yet either.

Shawn

--- John Popelish <jpopelish@...> wrote:

--- In Electronics_101@..., Shawn Upton

If you have several candidate cores on hand, you can
easily find the
high permeability ones that will provide highest
winding coupling by
touching them on two spots with your ohm meter
leads. The lower the
resistance reading, the higher the permeability, as
a general rule.

Shawn Upton, KB1CKT

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You really can't go too wrong with a used Tektronix scope. The two biggest problems I see when they come in for repair are: 1) dirty cam switches (these were used mainly in 5000 and 7000 series), and 2) bad caps in the supply. I've found a couple of 2215/2225/2235 series with bad PWM ICs in the supply but they are $0.80 parts that are readily available through Mouser. So even if something does go wrong with a Tek scope it is usually easily repaired.

The drawback with Tektronix equipment though is that they only support thier products for a few years so if one of the more obscure components go bad or a mechanical part breaks that is specific to that model it can be difficult to impossible to get the part. For example thier old curve tracers are pretty much impossible to find parts for anymore.