Daqarta and Function generator

[Kari Laine]

Hi,

I am total beginner with electronics....

I am learning this Daqarta scope program (www.daqarta) and at the moment
I am wondering the power output of function generator. I am planning
to buy (when I have the money) two velleman applifiers K4004B -
http://www.velleman.eu/distributor/products/view/?id=352782
I will configure them for mono.

That should give me enough power. Problem is that manual says the
outputs should be connected before power is applied. When testing things
it is quite possible that I forget this. And it is quite possible I will
short them for prolonged time. Velleman says that there is protection of
10s for shorts - that is not enough.

Any way to solve these problems?

Then I would need a power supply for +/- 28 DC for these amplifiers.
It is not clear to me what the maximum amperage should be - anyone?
Where in the EU area to buy these?
(I am also building my own power supply but I won't use it with anything
valuable)

Now when waiting the money come to my way, I have discrete components
and I would like to make simple amplifiers with just 1-4 transistor.
I found some examples with Google but they had max input of 1 volt.
My sound card gives out max 3V when maximum volume. Do anyone have a
connection example for an amplifier which takes 0-3(5)V and gives out
something like 0-6(10)V.

I have an idea of dividing the input voltage with resistors and test
with different base-resistors - right?


Best Regards
Kari

--
PIC - ARM - DISPLAYS - RELAYS - MODULES - CONVERTERS - I2C - SPI -
KEYPADS - ACCESSORIES
http://www.byvac.com (I am just a satisfied customer)

 

[Hammy]

On Tue, 16 Mar 2010 13:23:14 +0200, Kari Laine <klaine8@gmail.com>
wrote:

Hi,

I am total beginner with electronics....



Now when waiting the money come to my way, I have discrete components
and I would like to make simple amplifiers with just 1-4 transistor.
I found some examples with Google but they had max input of 1 volt.
My sound card gives out max 3V when maximum volume. Do anyone have a
connection example for an amplifier which takes 0-3(5)V and gives out
something like 0-6(10)V.

I have an idea of dividing the input voltage with resistors and test
with different base-resistors - right?


Best Regards
Kari

What you want is something with high input impedance to buffer your
sound card this could be an emitter follower. Then you feed the output
of this to a gain stage like say a Common Emitter how many stages
depends on the amount of gain, you could then buffer this with a diode
compensated push pull stage.

Heres a pic of what I said. Output stage of a DDS based signal
generator.

http://i43.tinypic.com/10if0hf.png

You will need a separate power supply for the amplifier!
Be careful you don't fry your soundcard!

Keywords to use for your power supply are "current limiting" and
"foldback current limiting"

Some bjt tutorials.

http://www.sentex.ca/~mec1995/tutorial/xtor/xtor3/xtor3.html

http://www.electronics-tutorials.ws/transistor/tran_1.html

I strongly suggest you read and understand the tutorials and
understand your soundcard before arbitraly hooking components to it.
This could get expensive.

There is enough information to get you started.

Good luck

 

[Hammy]

On Tue, 16 Mar 2010 09:06:44 -0400, Hammy <spam@spam.com> wrote:

On Tue, 16 Mar 2010 13:23:14 +0200, Kari Laine <klaine8@gmail.com
wrote:

Hi,

I am total beginner with electronics....



Now when waiting the money come to my way, I have discrete components
and I would like to make simple amplifiers with just 1-4 transistor.
I found some examples with Google but they had max input of 1 volt.
My sound card gives out max 3V when maximum volume. Do anyone have a
connection example for an amplifier which takes 0-3(5)V and gives out
something like 0-6(10)V.

I have an idea of dividing the input voltage with resistors and test
with different base-resistors - right?


Best Regards
Kari

What you want is something with high input impedance to buffer your
sound card this could be an emitter follower. Then you feed the output
of this to a gain stage like say a Common Emitter how many stages
depends on the amount of gain, you could then buffer this with a diode
compensated push pull stage.

Heres a pic of what I said. Output stage of a DDS based signal
generator.

http://i43.tinypic.com/10if0hf.png

That is an example only!!

You will need a separate power supply for the amplifier!
Be careful you don't fry your soundcard!

Keywords to use for your power supply are "current limiting" and
"foldback current limiting"

Some bjt tutorials.

http://www.sentex.ca/~mec1995/tutorial/xtor/xtor3/xtor3.html

http://www.electronics-tutorials.ws/transistor/tran_1.html

I strongly suggest you read and understand the tutorials and
understand your soundcard before arbitraly hooking components to it.
This could get expensive.

There is enough information to get you started.

Good luck

 

[John Fields]

On Tue, 16 Mar 2010 13:23:14 +0200, Kari Laine <klaine8@gmail.com>
wrote:

Hi,

I am total beginner with electronics....

I am learning this Daqarta scope program (www.daqarta) and at the moment
I am wondering the power output of function generator. I am planning
to buy (when I have the money) two velleman applifiers K4004B -
http://www.velleman.eu/distributor/products/view/?id=352782
I will configure them for mono.

That should give me enough power. Problem is that manual says the
outputs should be connected before power is applied. When testing things
it is quite possible that I forget this. And it is quite possible I will
short them for prolonged time. Velleman says that there is protection of
10s for shorts - that is not enough.

Any way to solve these problems?

---
I suspect a couple of hits to the pocketbook will shorten the learning
curve and lengthen the attention span appreciably.
---

Then I would need a power supply for +/- 28 DC for these amplifiers.
It is not clear to me what the maximum amperage should be - anyone?

---
According to the specifications, 4 amperes.

JF

 

[Bob Masta]

On Tue, 16 Mar 2010 13:23:14 +0200, Kari Laine
<klaine8@gmail.com> wrote:

Hi,

I am total beginner with electronics....

I am learning this Daqarta scope program (www.daqarta) and at the moment
I am wondering the power output of function generator. I am planning
to buy (when I have the money) two velleman applifiers K4004B -
http://www.velleman.eu/distributor/products/view/?id=352782
I will configure them for mono.

That should give me enough power. Problem is that manual says the
outputs should be connected before power is applied. When testing things
it is quite possible that I forget this. And it is quite possible I will
short them for prolonged time. Velleman says that there is protection of
10s for shorts - that is not enough.

Any way to solve these problems?

Kari:

You don't mention what you intend to use the
amplified function generator outputs for... that
might make a big difference in recommendations.

The best and cheapest amplifier will probably be a
home-stereo amp (or the amp part of a receiver).
You may already have one on hand, or pick up an
older model (cheap or free) from someone who is
upgrading. The Velleman kit is 50 watts/channel
into 4 ohms or 40 into 8 ohms (real watts, not
"music power") which are fairly common home stereo
specs.

Note that sound card outputs are AC-coupled, just
like stereo amps (including the Velleman, I
suspect, since they don't claim otherwise), so you
will not be driving any DC loads.

It's possible to modify a cheap sound card to have
DC outputs, and it's fairly easy to modify most
stereo amps to have DC outputs, but these are not
good projects for beginners since it is too easy
to "let the magic smoke out."

If you are just in the process of setting up a
general purpose home lab, I'd advise against any
external amplifier for the function generator
until you have a specific need. You may discover
you don't need anything more than the sound card
puts out already.

Sound cards are usually well protected against
output load problems, and in fact handle (or at
least tolerate) low-impedance headphones. The raw
output is likely all you need to drive most test
situations, like frequency response and distortion
measurements.

Best regards,


Bob Masta

DAQARTA v5.10
Data AcQuisition And Real-Time Analysis
www.daqarta.com
Scope, Spectrum, Spectrogram, Sound Level Meter
Frequency Counter, FREE Signal Generator
Pitch Track, Pitch-to-MIDI
DaqMusic - FREE MUSIC, Forever!
(Some assembly required)
Science (and fun!) with your sound card!

 

[Kari Laine]

Hammy wrote:

On Tue, 16 Mar 2010 13:23:14 +0200, Kari Laine <klaine8@gmail.com
wrote:

There is enough information to get you started.

Good luck

THANKS ! indeed ....

Kari


--
PIC - ARM - DISPLAYS - RELAYS - MODULES - CONVERTERS - I2C - SPI -
KEYPADS - ACCESSORIES
http://www.byvac.com (I am just a satisfied customer)

 

[John Fields]

On Tue, 16 Mar 2010 19:18:50 +0200, Kari Laine <klaine8@gmail.com>
wrote:

John Fields wrote:
On Tue, 16 Mar 2010 13:23:14 +0200, Kari Laine <klaine8@gmail.com
wrote:


---
I suspect a couple of hits to the pocketbook will shorten the learning
curve and lengthen the attention span appreciably.
---
What you mean with this...Do you mean I should buy some books or
something?

---
No, just a tongue-in-cheek way of saying that if you spend enough money
on being careless with amplifiers you'll eventually probably discipline
yourself so that it doesn't happen.
---

My attention span is very bad indeed, it has always been. Nowadays they
even have a diagnosis for it...

---
"Attention deficit disorder" or something like that?

Be very careful working around electricity if your mind has a tendency
to drift; it's easy to hurt or kill yourself and the equipment you're
working with if you lose track of what you're doing. :-(
---

Then I would need a power supply for +/- 28 DC for these amplifiers.
It is not clear to me what the maximum amperage should be - anyone?

---
According to the specifications, 4 amperes.
Thanks did not notice it.

---
You're welcome.

JF

 

[Kari Laine]

John Fields wrote:

On Tue, 16 Mar 2010 13:23:14 +0200, Kari Laine <klaine8@gmail.com
wrote:


---
I suspect a couple of hits to the pocketbook will shorten the learning
curve and lengthen the attention span appreciably.
---
What you mean with this...Do you mean I should buy some books or

something? If so ISBN is?
My attention span is very bad indeed, it has always been. Nowadays they
even have a diagnosis for it...

Then I would need a power supply for +/- 28 DC for these amplifiers.
It is not clear to me what the maximum amperage should be - anyone?

---
According to the specifications, 4 amperes.
Thanks did not notice it.

Best Regards
Kari

 

[Michael Black]

On Tue, 16 Mar 2010, Kari Laine wrote:

John Fields wrote:
On Tue, 16 Mar 2010 13:23:14 +0200, Kari Laine <klaine8@gmail.com
wrote:


---
I suspect a couple of hits to the pocketbook will shorten the learning
curve and lengthen the attention span appreciably.
---
What you mean with this...Do you mean I should buy some books or
something? If so ISBN is?

I had an analog meter when I was 12, and soon it no longer worked, the
needle having wrapped around the stop too hard. I was careful of any
later meters, having learned the lesson.

Or, that time when I touched high voltage and when I pulled away my elbow
slammed into a hard surface enough to hurt, I was careful of high voltage
after that.

In other words, actually doing mild damage may be a better way of
preventing accidents than merely warning someone to not do something
because it might cause an accident.
Michael

My attention span is very bad indeed, it has always been. Nowadays they
even have a diagnosis for it...



Then I would need a power supply for +/- 28 DC for these amplifiers.
It is not clear to me what the maximum amperage should be - anyone?

---
According to the specifications, 4 amperes.
Thanks did not notice it.

Best Regards
Kari

 

[Kari Laine]

Bob Masta wrote:

On Tue, 16 Mar 2010 13:23:14 +0200, Kari Laine
klaine8@gmail.com> wrote:

You don't mention what you intend to use the
amplified function generator outputs for... that
might make a big difference in recommendations.
Well...main reasons - it would be "cool".

I though that it would open possibilities to test different things.
- solenoids
- transformers
- inductors
- PWM

and so ... mainly I am just curious.
But like you say I might not even need it.

The best and cheapest amplifier will probably be a
home-stereo amp (or the amp part of a receiver).
You may already have one on hand, or pick up an
older model (cheap or free) from someone who is
upgrading. The Velleman kit is 50 watts/channel
into 4 ohms or 40 into 8 ohms (real watts, not
"music power") which are fairly common home stereo
specs.
This is a good idea - I try to find used amplifier which I don't mind

destroying.

Note that sound card outputs are AC-coupled, just
like stereo amps (including the Velleman, I
suspect, since they don't claim otherwise), so you
will not be driving any DC loads.
Ok

It's possible to modify a cheap sound card to have
DC outputs, and it's fairly easy to modify most
stereo amps to have DC outputs, but these are not
good projects for beginners since it is too easy
to "let the magic smoke out."
Ok - I won't try it yet.

If you are just in the process of setting up a
general purpose home lab, I'd advise against any
external amplifier for the function generator
until you have a specific need. You may discover
you don't need anything more than the sound card
puts out already.
I put it in the back burner - the Velleman that is.

One other helpful person gave two links and I am going to spend some
days reading those - very good sites!

Sound cards are usually well protected against
output load problems, and in fact handle (or at
least tolerate) low-impedance headphones. The raw
output is likely all you need to drive most test
situations, like frequency response and distortion
measurements.
OK

Now when I have you attention you hopefully don't mind a question.

How to find out capacitance and inductance with using function generator
and scope? Is it easy,not so easy, hard, very hard or impossible?
I remember seeing this somewhere in the net, but don't find it now.


Best Regards
Kari

Bob Masta

DAQARTA v5.10
Data AcQuisition And Real-Time Analysis
www.daqarta.com
Scope, Spectrum, Spectrogram, Sound Level Meter
Frequency Counter, FREE Signal Generator
Pitch Track, Pitch-to-MIDI
DaqMusic - FREE MUSIC, Forever!
(Some assembly required)
Science (and fun!) with your sound card!

--
PIC - ARM - DISPLAYS - RELAYS - MODULES - CONVERTERS - I2C - SPI -
KEYPADS - ACCESSORIES
http://www.byvac.com (I am just a satisfied customer)

 

[John Fields]

On Tue, 16 Mar 2010 19:29:12 +0200, Kari Laine <klaine8@gmail.com>
wrote:

Now when I have you attention you hopefully don't mind a question.

How to find out capacitance and inductance with using function generator
and scope? Is it easy,not so easy, hard, very hard or impossible?
I remember seeing this somewhere in the net, but don't find it now.

---
It's pretty easy.

If you have a capacitor and inductor and you know the value of one of
them only, to find the value of the other you can hook up your equipment
like this: (View in Courier)


+-------+
+-----[10K]----+<----[X10 PROBE]---|VERT |
| | | |
| [L] | |
[FUNCTION GEN] | | SCOPE |
| [C] | |
| | | |
+--------------+-------------------|GND |
+-------+

Set your generator to output sine waves and adjust its output amplitude
and the scope's vertical gain control for some convenient display and
then vary the generator frequency until the scope displays a null.

At the very bottom of that null is where the circuit is resonant, and
since we know that, at resonance, capacitive reactance (Xc) equals
inductive reactance (Xl) we can determine the reactance of the component
which we know the value of and then solve for the value of the unknown
component by using that reactance.

For example, let's say we have a 0.1ľF capacitor which resonates with an
unknown coil at 10kHz.

In order to determine the reactance of the capacitor we can say:

1 1
Xc = --------- = ---------------------- ~ 159 ohms
2pi f C 6.28 * 1e4Hz * 1e-7F

Now, since we know that the reactance of the coil has to be the same as
the reactance of the cap, we can calculate the inductance like this:


Xl 159R
l = ------- = -------------- = 2.504e-3H ~ 2.1 millihenrys
2pi f 6.28 * 1e4Hz


If you know the value of the inductor, but not the capacitor, you can
find its reactance by rearranging the second equation to:


Xl = 2pi f L


and then find the value of the cap by rearranging the first equation to:

1
C = ----------
2Pi f Xc

Finally, you can check your work with:


1
f = ---------------
2pi sqrt (LC)


so, plugging in the results we got earlier, we'll have:


1
f = ------------------------------- = 10998Hz
6.28 * sqrt (2.1e-3H * 1e-7F)


About 10% high because there are rounding errors in there, but you get
the picture, yes?


Another way is to use a resistor of a known value in series with the
unknown cap or coil:


+-------+
+-----[10K]----+<----[X10 PROBE]---|VERT |
| | | |
| | | |
[FUNCTION GEN] [DUT] | SCOPE |
| | | |
| | | |
+--------------+-------------------|GND |
+-------+

I've gotta go do some chores, but I want to get this off instead of
waiting until later to send the whole thing, so I'll finish it when I'm
done...

JF

 

[Hammy]

On Tue, 16 Mar 2010 19:29:12 +0200, Kari Laine <klaine8@gmail.com>
wrote:

Now when I have you attention you hopefully don't mind a question.

How to find out capacitance and inductance with using function generator
and scope? Is it easy,not so easy, hard, very hard or impossible?
I remember seeing this somewhere in the net, but don't find it now.


Best Regards
Kari

Johns giveing you a nice detailed instruction but I see from your sig
that you are at least familiar with PIC's so you could build your own.

Here is a pretty good one.

http://ironbark.bendigo.latrobe.edu.au/~rice/lc/

 

[Kari Laine]

Michael Black wrote:

I had an analog meter when I was 12, and soon it no longer worked, the
needle having wrapped around the stop too hard. I was careful of any
later meters, having learned the lesson.

Or, that time when I touched high voltage and when I pulled away my elbow
slammed into a hard surface enough to hurt, I was careful of high voltage
after that.

In other words, actually doing mild damage may be a better way of
preventing accidents than merely warning someone to not do something
because it might cause an accident.
Michael
I should have mentioned that I am not totally ignorant about electricity

and electronics. I know the passive components quite well but transistor
has always been difficult to me. I had electronics as hobby when I was a
kid up to something round 16 years old. Then I was in the UNI and
learned something(I am a dropout). Then worked in computer business.
Now I am retired and though that why not...

I have had 220V chocks something round 5 times totally in my lifetime
and they really hurt. Luckily the hart was not stopped. Nowadays I
triple check before touching anything. But naturally accidents could
happen. I am mainly interested the low-voltage electronics (at least now).

The amplifier thing I mentioned turned up nicely.
I got used car audio amplifier for about $90 from auction site in Finland.

Specs:

APA4400G
100W x 4 Channel Amplifier
Maximum Power Output 300 W (75 W x 4)
Continuous Average Power Output 200 W (50 W x 4 into 4 ohms 20Hz-20kHz @
0.04% THD)
Maximum Power Output 700 W (175 W x 4)
Continuous Average Power Output 400 W (100 W x 4 into 4 ohms 20Hz-20kHz
@ 0.02% THD)
Typical 2-ohm Stereo 130 W x 4 @ 0.2% THD
Typical Bridged Power 250 W x 2 @ 0.2% THD
Dynamic Output Control Bass Extender Control 0-12dB
Adjustable 4-Channel 50Hz-200Hz, 24dB/oct. High/Low Pass Crossover
2-Channel Non-Fade Line-Level Output
Mixed-Mode Operation
Bridgeable 4-, 3-, or 2-Channel Operation
Pulse-Width Regulated MOSFET Power Supply

So is this good one or bad?

I have never worked with car amplifiers. But I think it must be single
supply 12V with lot of amperes (I have a lab power supply which probably
can cope). And what is good that according the manual there seems to be
all possible protections for misuse. I only hope the seller is honest...

Well another new tool to play...

By the way these newsgroups are great. I have learned a lot when reading
these groups. I use GigaNews which has retention to year 2003.
Groups about electronics, interesting me contains about
1200000 messages



Best Regards
Kari


--
PIC - ARM - DISPLAYS - RELAYS - MODULES - CONVERTERS - I2C - SPI -
KEYPADS - ACCESSORIES
http://www.byvac.com (I am just a satisfied customer)

 

[Ron M.]

On Mar 16, 1:26 pm, Michael Black <et...@ncf.ca> wrote:

On Tue, 16 Mar 2010, Kari Laine wrote:
John Fields wrote:
On Tue, 16 Mar 2010 13:23:14 +0200, Kari Laine <klai...@gmail.com
wrote:

---
I suspect a couple of hits to the pocketbook will shorten the learning
curve and lengthen the attention span appreciably.
---
What you mean with this...Do you mean I should buy some books or
something? If so ISBN is?

I had an analog meter when I was 12, and soon it no longer worked, the
needle having wrapped around the stop too hard.  I was careful of any
later meters, having learned the lesson.

Or, that time when I touched high voltage and when I pulled away my elbow
slammed into a hard surface enough to hurt, I was careful of high voltage
after that.

In other words, actually doing mild damage may be a better way of
preventing accidents than merely warning someone to not do something
because it might cause an accident.
    Michael


How about 15 watts VHF right into the palm of your hand. That is an

attention getter. Won't touch that again.

My attention span is very bad indeed, it has always been. Nowadays they
even have a diagnosis for it...

Then I would need a power supply for +/- 28 DC for these amplifiers.
It is not clear to me what the maximum amperage should be - anyone?

---
According to the specifications, 4 amperes.
Thanks did not notice it.

Best Regards
Kari- Hide quoted text -

- Show quoted text -

 

[Kari Laine]

John Fields wrote:

On Tue, 16 Mar 2010 19:29:12 +0200, Kari Laine <klaine8@gmail.com
wrote:


Now when I have you attention you hopefully don't mind a question.

How to find out capacitance and inductance with using function generator
and scope? Is it easy,not so easy, hard, very hard or impossible?
I remember seeing this somewhere in the net, but don't find it now.

---
It's pretty easy.

Thank you! Even I understood. If you have time the second method would
be interesting.

Best Regards
Kari

 

[Kari Laine]

Hammy wrote:

On Tue, 16 Mar 2010 19:29:12 +0200, Kari Laine <klaine8@gmail.com
wrote:

Johns giveing you a nice detailed instruction but I see from your sig
that you are at least familiar with PIC's so you could build your own.

Here is a pretty good one.

http://ironbark.bendigo.latrobe.edu.au/~rice/lc/

Ok thanks. That should be interesting project to make.
And also easier to use. Will save the link and do it later.

Best Regards
Kari

 

[Bob Masta]

On Tue, 16 Mar 2010 22:01:43 +0200, Kari Laine
<klaine8@gmail.com> wrote:

I should have mentioned that I am not totally ignorant about electricity
and electronics. I know the passive components quite well but transistor
has always been difficult to me. I had electronics as hobby when I was a
kid up to something round 16 years old. Then I was in the UNI and
learned something(I am a dropout). Then worked in computer business.
Now I am retired and though that why not...

I have had 220V chocks something round 5 times totally in my lifetime
and they really hurt. Luckily the hart was not stopped. Nowadays I
triple check before touching anything. But naturally accidents could
happen. I am mainly interested the low-voltage electronics (at least now).

The amplifier thing I mentioned turned up nicely.
I got used car audio amplifier for about $90 from auction site in Finland.

Specs:

APA4400G
100W x 4 Channel Amplifier
Maximum Power Output 300 W (75 W x 4)
Continuous Average Power Output 200 W (50 W x 4 into 4 ohms 20Hz-20kHz @
0.04% THD)
Maximum Power Output 700 W (175 W x 4)
Continuous Average Power Output 400 W (100 W x 4 into 4 ohms 20Hz-20kHz
@ 0.02% THD)
Typical 2-ohm Stereo 130 W x 4 @ 0.2% THD
Typical Bridged Power 250 W x 2 @ 0.2% THD
Dynamic Output Control Bass Extender Control 0-12dB
Adjustable 4-Channel 50Hz-200Hz, 24dB/oct. High/Low Pass Crossover
2-Channel Non-Fade Line-Level Output
Mixed-Mode Operation
Bridgeable 4-, 3-, or 2-Channel Operation
Pulse-Width Regulated MOSFET Power Supply

So is this good one or bad?

I have never worked with car amplifiers. But I think it must be single
supply 12V with lot of amperes (I have a lab power supply which probably
can cope). And what is good that according the manual there seems to be
all possible protections for misuse. I only hope the seller is honest...

You hit the nail on the head with your observation
about the 12V power supply. My personal feeling
is that even if this amp is free it will not be
worth the effort and expense of getting it working
on your bench. I'd vote to hold out for a cheap
home stereo amp. Even units from 40 years ago
should be fine for this. I imagine that as people
buy 5- and 7-channel "home theater" systems, their
old 2-channel units will be cheap or free.

Best regards,


Bob Masta

DAQARTA v5.10
Data AcQuisition And Real-Time Analysis
www.daqarta.com
Scope, Spectrum, Spectrogram, Sound Level Meter
Frequency Counter, FREE Signal Generator
Pitch Track, Pitch-to-MIDI
DaqMusic - FREE MUSIC, Forever!
(Some assembly required)
Science (and fun!) with your sound card!

 

[John Fields]

On Wed, 17 Mar 2010 10:15:15 +0200, Kari Laine <klaine8@gmail.com>
wrote:

John Fields wrote:
On Tue, 16 Mar 2010 19:29:12 +0200, Kari Laine <klaine8@gmail.com
wrote:


Now when I have you attention you hopefully don't mind a question.

How to find out capacitance and inductance with using function generator
and scope? Is it easy,not so easy, hard, very hard or impossible?
I remember seeing this somewhere in the net, but don't find it now.

---
It's pretty easy.

Thank you! Even I understood. If you have time the second method would
be interesting.

---
Today!

JF

 

[Kari Laine]

Bob Masta wrote:

On Tue, 16 Mar 2010 22:01:43 +0200, Kari Laine
klaine8@gmail.com> wrote:


You hit the nail on the head with your observation
about the 12V power supply. My personal feeling
is that even if this amp is free it will not be
worth the effort and expense of getting it working
on your bench. I'd vote to hold out for a cheap
home stereo amp. Even units from 40 years ago
should be fine for this. I imagine that as people
buy 5- and 7-channel "home theater" systems, their
old 2-channel units will be cheap or free.


Bob Masta

DAQARTA v5.10
Data AcQuisition And Real-Time Analysis
www.daqarta.com
Scope, Spectrum, Spectrogram, Sound Level Meter
Frequency Counter, FREE Signal Generator
Pitch Track, Pitch-to-MIDI
DaqMusic - FREE MUSIC, Forever!
(Some assembly required)
Science (and fun!) with your sound card!

Ok Bob, Thanks!
Will keep eyes open.

Best Regards
Kari



--
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[John Fields]

On Tue, 16 Mar 2010 13:14:36 -0500, John Fields
<jfields@austininstruments.com> wrote:

Another way is to use a resistor of a known value in series with the
unknown cap or coil:

+-------+
+-----[10K]----+<----[X10 PROBE]---|VERT |
| | | |
| | | |
[FUNCTION GEN] [DUT] | SCOPE |
| | | |
| | | |
+--------------+<------------------|GND |
+-------+

I've gotta go do some chores, but I want to get this off instead of
waiting until later to send the whole thing, so I'll finish it when I'm
done...

OK.

For the cap, set up your equipment like this:


E1 +-------+
|<---------------------------------|VERTA |
| E2 | |
+-----[10K]----+<----[X10 PROBE]---|VERTB |
| | | |
| | | |
[FUNCTION GEN] [DUT] | SCOPE |
| | | |
| | | |
+--------------+<------------------|GND |
+-------+

Using the sine wave output of your function generator, set its output,
E1, to any convenient level and then tune it to the frequency which
causes E2 to be 1/2 the voltage of E1.

Then solve:

1
C = ----------
2pi f Xc

where C will be the capacitance in farads,
2pi is 6.28,
f is the frequency which causes E2 to be 1/2 of E1, in Hz,and
Xc is 5800 ohms.

Why 5800 ohms?

That's the capacitive reactance you need in order to get E2 equal to
half of E1 at any frequency.

Ergo, with a constant reactance, capacitance will go inversely with
frequency.

JF