Viewing an ohms change on an oscope???

[scanner80]

Hello,
I'm looking for a circuit I can build or equipment I can buy
so I can time how long an ohms change is. I would like to build it if
possible . I would like to view it on a scope.
One example would be a starting ohms reading from a device of 1355 ohms. It
will increase by approx. 20 ohms
and then return to 1355 ohms. The time it will take is approx. 19 seconds. I
will need to be able to see a change as small as 1 ohm if possible , but the
most important thing is to see the reading change from 1355 and return to
1355 ohms. I need to then measure the time with cursers on a scope.
I know a respiration monitor can see and display an ohms change , but I need
a way to exactly measure the change.
I will be greatful for any help.
Thank you,
Jeff

 

[DBLEXPOSURE]

"scanner80" <scanner80@charter.net> wrote in message
newsEUIe.5352$Tt6.4270@fe04.lga...

Hello,
I'm looking for a circuit I can build or equipment I can buy
so I can time how long an ohms change is. I would like to build it if
possible . I would like to view it on a scope.
One example would be a starting ohms reading from a device of 1355 ohms.
It
will increase by approx. 20 ohms
and then return to 1355 ohms. The time it will take is approx. 19 seconds.
I
will need to be able to see a change as small as 1 ohm if possible , but
the
most important thing is to see the reading change from 1355 and return to
1355 ohms. I need to then measure the time with cursers on a scope.
I know a respiration monitor can see and display an ohms change , but I
need
a way to exactly measure the change.
I will be greatful for any help.
Thank you,
Jeff

Jeff:



To measure resistance you need to apply a voltage and then
measure the current. Another way is to use a "voltage divider", put your
changing resistance in series with a known resistance, apply a voltage to
the circuit and monitor the voltage dropped across the known resistor. As
your changing resistance decreases current in the circuit will increase and
the voltage drop across your known resistor will increase. This will all be
linear so you will be able to make notations on your scope graticule so that
you can directly readout the display in ohms.



You will want to use a regulated voltage source. A look into Ohms law will
provide the math for you to make the calculations..

 

[scanner80]

I just want to be able to measure the time it takes from when the resistance
leaves 1355 ohms and returns to 1355. I can do it with a meter and a
stopwatch, but I was looking for a more verifiable way to do it. I want to
remove human error. This is for calibration purposes.
Is there any type of simple timer or timer circuit that can will trigger as
the ohms changes and stop when it returns?
Jeff
"DBLEXPOSURE" <celstuff@hotmail.com> wrote in message
news:N4adnYfOl4fDgWnfRVn-qg@rapidnet.com...

"scanner80" <scanner80@charter.net> wrote in message
newsEUIe.5352$Tt6.4270@fe04.lga...
Hello,
I'm looking for a circuit I can build or equipment I can buy
so I can time how long an ohms change is. I would like to build it if
possible . I would like to view it on a scope.
One example would be a starting ohms reading from a device of 1355 ohms.
It
will increase by approx. 20 ohms
and then return to 1355 ohms. The time it will take is approx. 19
seconds.
I
will need to be able to see a change as small as 1 ohm if possible , but
the
most important thing is to see the reading change from 1355 and return
to
1355 ohms. I need to then measure the time with cursers on a scope.
I know a respiration monitor can see and display an ohms change , but I
need
a way to exactly measure the change.
I will be greatful for any help.
Thank you,
Jeff



Jeff:



To measure resistance you need to apply a voltage and then
measure the current. Another way is to use a "voltage divider", put your
changing resistance in series with a known resistance, apply a voltage to
the circuit and monitor the voltage dropped across the known resistor. As
your changing resistance decreases current in the circuit will increase
and
the voltage drop across your known resistor will increase. This will all
be
linear so you will be able to make notations on your scope graticule so
that
you can directly readout the display in ohms.



You will want to use a regulated voltage source. A look into Ohms law
will
provide the math for you to make the calculations..

 

[DBLEXPOSURE]

"scanner80" <scanner80@charter.net> wrote in message
news:aSWIe.1770$Mq4.1350@fe05.lga...

I just want to be able to measure the time it takes from when the
resistance
leaves 1355 ohms and returns to 1355. I can do it with a meter and a
stopwatch, but I was looking for a more verifiable way to do it. I want to
remove human error. This is for calibration purposes.
Is there any type of simple timer or timer circuit that can will trigger
as
the ohms changes and stop when it returns?
Jeff
"DBLEXPOSURE" <celstuff@hotmail.com> wrote in message
news:N4adnYfOl4fDgWnfRVn-qg@rapidnet.com...

"scanner80" <scanner80@charter.net> wrote in message
newsEUIe.5352$Tt6.4270@fe04.lga...
Hello,
I'm looking for a circuit I can build or equipment I can buy
so I can time how long an ohms change is. I would like to build it if
possible . I would like to view it on a scope.
One example would be a starting ohms reading from a device of 1355
ohms.
It
will increase by approx. 20 ohms
and then return to 1355 ohms. The time it will take is approx. 19
seconds.
I
will need to be able to see a change as small as 1 ohm if possible ,
but
the
most important thing is to see the reading change from 1355 and return
to
1355 ohms. I need to then measure the time with cursers on a scope.
I know a respiration monitor can see and display an ohms change , but I
need
a way to exactly measure the change.
I will be greatful for any help.
Thank you,
Jeff



Jeff:



To measure resistance you need to apply a voltage and then
measure the current. Another way is to use a "voltage divider", put your
changing resistance in series with a known resistance, apply a voltage to
the circuit and monitor the voltage dropped across the known resistor.
As
your changing resistance decreases current in the circuit will increase
and
the voltage drop across your known resistor will increase. This will all
be
linear so you will be able to make notations on your scope graticule so
that
you can directly readout the display in ohms.



You will want to use a regulated voltage source. A look into Ohms law
will
provide the math for you to make the calculations..

Typically they prefer that you bottom post in this group. Doesn't bother me
but, when in Rome..........


Well, I don't have time at the moment to work out all the details; maybe
someone else will chime in with more help. But I can at least get you
started.



First, use the voltage divider circuit I talked about in the previous post.
Instead of monitoring the voltage across the known resistance with your
scope, use that voltage to drive the Vin of a simple "Op Amp non inverting
comparator" circuit. Here is a link to get you started with the comparator.
http://home.maine.rr.com/randylinscott/learn.htm



The idea is when your voltage across the known resistance of the voltage
divider exceeds the Vref of the comparator the output of the comparator will
go high.



This output voltage can be used to drive a reed relay. You can find reed
relays that will energize with very little coil current. The relay will be
used instead of the transistor depicted in the schematic of the
non-inverting comparator shown on the link provided.



Now get yourself a cheap stopwatch that has one button that will both start
and stop. Wire the switch contacts of the relay across the start/stop
switch of the watch.



There are more eloquent ways to go about it but this will be a pretty easy
and cheap way to get the job done. I have left a lot of the design to you,
resistor sizes, voltages etc.. Newark Electronics might be a good place to
find the relay. The 741 op-amp crosses to a NTE941M, which can be found
here http://www.weisd.com/store2/ntesemi/NTE941M.html



Well, duty calls, gota run for now.........

 

[John Fields]

On Fri, 5 Aug 2005 23:23:22 -0500, "scanner80"
<scanner80@charter.net> wrote:

I just want to be able to measure the time it takes from when the resistance
leaves 1355 ohms and returns to 1355. I can do it with a meter and a
stopwatch, but I was looking for a more verifiable way to do it. I want to
remove human error. This is for calibration purposes.
Is there any type of simple timer or timer circuit that can will trigger as
the ohms changes and stop when it returns?

---
You could do it with something as simple as a voltage comparator
detecting the resistance change and using its (the voltage
comparator's) output to gate a counter, but you need to supply more
details about the resistance before we can help you much. For
example, what is the resistance, physically, and how is it being
used? Does it have a voltage across it?

--
John Fields
Professional Circuit Designer

 

[JeffM]

...reading from a device of 1355 ohms...
Jeff (scanner80)

Posting the same question individually to multiple groups
is not only foolish (worse than linked cross-posting), it is selfish.

Those people who do not visit each of the groups
will not benefit by the intelligence of the responses at those other
groups.

Despite those folks who warn about EXCESSIVE cross-posting,
posting the same question individually to 4 groups
is a really bad approach.
http://groups-beta.google.com/groups?filter=0&q=ohms-change&enc_author=OnQYWRUAAAAyzOE-dhhFNNxnTzSF4k0hZk8LRyw6Fzc364xXu3mYhA

This practice robs those people
who do not habitually visit all the groups
of the wisdom of others on the topic.
It also doesn't let everyone know
when the question has been answered sufficiently.

Most importantly, it does not allow those in 1 group
to gain from further details revealed in another group.
http://groups-beta.google.com/group/sci.electronics.basics/browse_frm/thread/afeafaf14bf3f345/4a59ccea8c81d035?q=The-device-will-use-an-opamp-circuit-to-create-the-resistances

If the query is relevant to multiple groups,
put the names of ALL the groups in which you would like it to appear
on the Groups line (the To line) THE FIRST TIME you post it.

Proper use of the Followup-To line is also useful.

 

[Jasen Betts]

In article <PEUIe.5352$Tt6.4270@fe04.lga>, scanner80 wrote:

Hello,

I'm looking for a circuit I can build or equipment I can buy
so I can time how long an ohms change is. I would like to build it if
possible . I would like to view it on a scope.
One example would be a starting ohms reading from a device of 1355 ohms. It
will increase by approx. 20 ohms
and then return to 1355 ohms. The time it will take is approx. 19 seconds. I
will need to be able to see a change as small as 1 ohm if possible , but the
most important thing is to see the reading change from 1355 and return to
1355 ohms. I need to then measure the time with cursers on a scope.
I know a respiration monitor can see and display an ohms change , but I need

a computer with apropriate software could do that using the 16-bit ADC in the
soundcard for input, or you can buy specialised devices that come with
software too...

or a microcontroller could be combineed with a current source and sensitive
DAC to output resistance readings 100 or so times a second...

Bye.
Jasen

 

[Day Brown]

Jasen Betts wrote:

a computer with apropriate software could do that using the 16-bit ADC in the
soundcard for input, or you can buy specialised devices that come with
software too...

or a microcontroller could be combineed with a current source and sensitive
DAC to output resistance readings 100 or so times a second...
Waitaminit. I've long wondered if the soundcard could not take input

as data. Rather like the com port? where's this software? Linux?

 

[Chris Head]

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Day Brown wrote:

Waitaminit. I've long wondered if the soundcard could not take input
as data. Rather like the com port? where's this software? Linux?

Sure thing. See:

http://polly.phys.msu.su/~zeld/oscill.html

for details. Try not to blow anything up.

Chris
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[Jasen Betts]

In article <1u3Ke.2257$_b6.74727439@typhoon.cei.net>, Day Brown wrote:

Jasen Betts wrote:
a computer with apropriate software could do that using the 16-bit ADC in the
soundcard for input, or you can buy specialised devices that come with
software too...

or a microcontroller could be combineed with a current source and sensitive
DAC to output resistance readings 100 or so times a second...
Waitaminit. I've long wondered if the soundcard could not take input
as data. Rather like the com port? where's this software? Linux?

in linux you can do

od -tx1 < /dev/audio

and get a crude hexadecimal dump of the soundcards input mixer
(so to read line-in or mic you need to turn them on using aumix etc)

if you want something better google for this:

soundcard software oscilloscope linux


Bye.
Jasen

 

[Day Brown]

Jasen Betts wrote:

Waitaminit. I've long wondered if the soundcard could not take input
as data. Rather like the com port? where's this software? Linux?
in linux you can do

od -tx1 < /dev/audio

and get a crude hexadecimal dump of the soundcards input mixer
(so to read line-in or mic you need to turn them on using aumix etc)

if you want something better google for this:

soundcard software oscilloscope linux
Way kewl. thanx. got http://radio.linux.org.au/?sectpat=All&ordpat=title

which seems to have what I'm looking for.