precision low frequency generation (redux)

[[email protected]]

It's really a shame somebody decided to change the subject line to
"what a fucking moron" as some useful messages will simply get lost in
the aether. Here are two good solutions:


50. YD
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More options Nov 21, 3:01 am
Newsgroups: sci.electronics.design
From: YD <[email protected]>
Date: Wed, 21 Nov 2007 08:01:58 -0300
Local: Wed, Nov 21 2007 3:01 am
Subject: Re: Precision low frequency generation
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Late at night, by candle light, Dirk Bruere at NeoPax

I'm thinking of creating a precision low frequecy generator (<20HZ) by
taking a computer generated stereo sinewave output with (say) one
channel o/p 5000Hz and the other (say) 5002.5Hz, feeding into a
summing input of an op amp and then putting the signal through a low
pass filter to recover a 2.5Hz sine wave. Do you think this will work,
or have I missed something?

Dirk

Generate a PWM square wave at a couple 100 Hz. Then all you'll need is
a LPF and whatever gain and DC block/restore required. Might try FM
too.

- YD.

--
Remove HAT if replying by mail.
================================================================================

I'm thinking of creating a precision low frequecy generator (<20HZ) by
taking a computer generated stereo sinewave output with (say) one
channel o/p 5000Hz and the other (say) 5002.5Hz, feeding into a
summing input of an op amp and then putting the signal through a low
pass filter to recover a 2.5Hz sine wave. Do you think this will work,
or have I missed something?

Dirk

You need to define precision.

How about this. You can make a simple sine wave generator feeding a
square wave to a switched capacitor filter. Now if the clock for the
switched capacitor filter was the output of the sound card, you would
get a much lower frequency sine wave than the clock. The square wave
generator is made by dividing down the switched capacitor filter
clock.

Let's do a simple example. The sound card is putting out 100Hz. Let
the clock to corner of the filter be 100. Now you have a filter at
1Hz. Divide the switched capacitor clock by 128 to make things simple.
This gives you a square wave at 0.78125Hz. This is in the passband of
the switched capacitor filter. The first harmonic you need to worry
about is the 3rd, or 2.34375Hz. Use an elliptic switched capacitor
filter with a transition ratio less that 2, and the 3rd harmonic and
the remaining harmonics will be filtered.

The frequency of the sine wave will be very precise. Fidelity is
another story. You would be doing well to get about 70db down.

There are trick you can do to reduce the harmonics fed to the switched
capacitor filter. One simple trick is to feed a signal that is 1 1 1
0 -1 -1 -1 0 , that is, reduce the size of the jump, which in turn
reduces the harmonics. You could also generate a signal with resistor
taps to reduce the jumps further.

If you have a bigger budget, use a digital sine wave generator scheme
(dac and rom), where again the clock is from the sound card.

I saw a DAC on the parallel port mentioned. This doesn't work well
unless you use DOS. The port control timing is not very good in modern
operating systems.

 

[Phil Allison]

It's really a shame somebody decided to change the subject line to
"what a fucking moron"

** No shame in outing a lying, rabid, psychopathic nut case like Dirk
Bruere.

Generate a PWM square wave at a couple 100 Hz. Then all you'll need is
a LPF and whatever gain and DC block/restore required.

** The problem is that sound cards incorporate capacitors in the output
signal path - so low ( sub audio) frequencies are attenuated and lost.

Any attempt to use a PWM rectangular wave to transfer such low frequencies
via a small capacitor will suffer the exact same fate.

BTW

" PWM square wave " = a self contradiction.




......... Phil

 

[Winfield]

** No shame in outing a lying, rabid, psychopathic nut case like ...

It makes a total mess of the threads, and exposes you
as a class-A #1 troublemaker, to put it mildly. Give
it a rest, and join in the community, that's my advice.
Stop the juvenile namecalling, and the grandstanding.

 

[Phil Allison]

"Winfield"

It makes a total mess of the threads,

** Who the hell cares about such a triviality ?

Way preferable to having psychopathic arseholes running loose, unopposed and
making a total mess of a public forum.

Oh - that is what we have right now ......

and exposes you
as a class-A #1 troublemaker, to put it mildly.

** Your ill informed opinions and unsupported views are not facts - it is
grossly dishonest of you to present them as such and the act of a pathetic
bully.

There is simply nothing for me to answer in them.

This worthless post and others like it from you in the past are PURE ABUSE
!!

Constantly failing to see this simple point goes to proves how grossly
autistic you are - Win.

Give
it a rest, and join in the community, that's my advice.

** Shove it where the sun don't shine - pal.

Your "advice" is nothing but worthless, disguised personal abuse.

Stop the juvenile name calling, and the grandstanding.

** More asinine, unsupported personal abuse posing as fact.

Makes you look an absolute WANKER - Win.

Which * is * 100 % appropriate.





....... Phil

 

[[email protected]]

** No shame in outing a lying, rabid, psychopathic nut case like Dirk
Bruere.


** The problem is that sound cards incorporate capacitors in the output
signal path - so low ( sub audio) frequencies are attenuated and lost.

Any attempt to use a PWM rectangular wave to transfer such low frequencies
via a small capacitor will suffer the exact same fate.

BTW

" PWM square wave " = a self contradiction.

........ Phil

Well, then my SCF approach will work since the signal I require is
within the audio range. I used the design years ago to generate a
telecom guard tone.

Getting back to the other approach (PWM), you could generate an AM
signal with the sound card, then put an envelop demod on it to recover
the low frequency tone. It is probably the simplest approach regarding
hardware. Trivial if the original poster understands AM radio.

 

[Phil Allison]

Well, then my SCF approach will work since the signal I require is
within the audio range.

** Insane drivel.

The required ( 2 Hz) signal is not in the audio range.

I used the design years ago to generate a
telecom guard tone.

** Yawn.....

Grandiose crap.

Getting back to the other approach (PWM), you could generate an AM
signal with the sound card, then put an envelop demod on it to recover
the low frequency tone.

** Bout the only way to go using a sound card and simple methods.



........ Phil

 

[[email protected]]

<[email protected]>
"Phil Allison"







** Insane drivel.

The required ( 2 Hz) signal is not in the audio range.


** Yawn.....

Grandiose crap.


** Bout the only way to go using a sound card and simple methods.

....... Phil

Well there are those that do, and then those that post.

Have a really nice day.

 

[Phil Allison]

"YD"

The PWM carrier is in the audio range.

** Total fallacy.

No such " carrier " exists with PWM.

It should be lowish for good
resolution but high enough to be easily filtered. Extracting the
sub-AF from the variable duty cycle is done by the external circuitry.
Makes perfect sense if you think about it.

** Makes total BULL SHIT obfuscation to anyone with a clue.

You are nothing but a STINKING FUCKING LIAR !!!!!!!!!

Well, whatever. I was too lazy to write "variable duty cycle pulse
train".

** Just as you are too lazy to think straight and too dishonest to admit
even the grossest error.

Drop fucking dead - you fuckwit WOG shithead !~!~!





....... Phil

 

[YD]

Late at night, by candle light, "Phil Allison"

** The problem is that sound cards incorporate capacitors in the output
signal path - so low ( sub audio) frequencies are attenuated and lost.

Any attempt to use a PWM rectangular wave to transfer such low frequencies
via a small capacitor will suffer the exact same fate.

The PWM carrier is in the audio range. It should be lowish for good
resolution but high enough to be easily filtered. Extracting the
sub-AF from the variable duty cycle is done by the external circuitry.
Makes perfect sense if you think about it.

BTW

" PWM square wave " = a self contradiction.

Well, whatever. I was too lazy to write "variable duty cycle pulse
train".

- YD.

 

[John Devereux]

Late at night, by candle light, "Phil Allison"


OK, what do you call it?

I'll type really slow and make pretty pictures for you to understand.

Do you know how to create a rectangular waveform in the audio range?
Do you know how it may be created by the sound card? Do you understand
duty cycle? Can it be done in software?

Let's see...

What's the average of the following waveforms, assuming 0 and 1 V?


__________ __________
a) __________| |__________| |______...


_ _
b) ___________| |___________________| |_______________...



_________ ___________________ _________________...
c) |_| |_|

The average *after you run it through the soundcard output capacitor*
will be zero.

Let's say the pulse frequency is a few hundred Hz and you run it
through a LPF with sub-audio corner while you *slowly* vary the duty
cycle, what will you see after the LPF?
Zero.

Possible in principle, but it needs more than just your low pass
filter.

 

[Jan Panteltje]

The average *after you run it through the soundcard output capacitor*
will be zero.

That may be true, but a simple diode to ground will fix that

audio ----- C--------- pulse -.7 to + whatever.
from |
soundcard |
k
DIODE
a
|
///

 

[John Devereux]

That may be true, but a simple diode to ground will fix that

audio ----- C--------- pulse -.7 to + whatever.
from |
soundcard |
k
DIODE
a
|
///

Yes - DC restoration.

 

[YD]

Late at night, by candle light, "Phil Allison"

"YD"



** Total fallacy.

No such " carrier " exists with PWM.

OK, what do you call it?

I'll type really slow and make pretty pictures for you to understand.

Do you know how to create a rectangular waveform in the audio range?
Do you know how it may be created by the sound card? Do you understand
duty cycle? Can it be done in software?

Let's see...

What's the average of the following waveforms, assuming 0 and 1 V?


__________ __________
a) __________| |__________| |______...


_ _
b) ___________| |___________________| |_______________...



_________ ___________________ _________________...
c) |_| |_|



Let's say the pulse frequency is a few hundred Hz and you run it
through a LPF with sub-audio corner while you *slowly* vary the duty
cycle, what will you see after the LPF?

** Makes total BULL SHIT obfuscation to anyone with a clue.

You are nothing but a STINKING FUCKING LIAR !!!!!!!!!

Pbhhhh... Same to you.

** Just as you are too lazy to think straight and too dishonest to admit
even the grossest error.

I'm honest enough to agree it could have been worded better. I still
know what I'm talking about.

Pity that after you've flown off the handle over some silly detail you
cease thinking straight but never admit it. When you're sane you're
usually pretty spot on.

Drop fucking dead - you fuckwit WOG shithead !~!~!

WOG? Whassa WOG?

- YD.

 

[Dirk Bruere at NeoPax]

It makes a total mess of the threads, and exposes you
as a class-A #1 troublemaker, to put it mildly. Give
it a rest, and join in the community, that's my advice.
Stop the juvenile namecalling, and the grandstanding.

I wouldn't bother - he's clearly insane.
He's even famous amongst the non-techies for his ranting abuse.
On the plus side he's easy to filter out, and there is nothing to lose
because abuse seems to be his only contribution.

Dirk

 

[Phil Allison]

"Dirk Bruere at NeoPax"

So what would I get from linearly adding two different frequency sine
waves?
When I do it in Audacity (s/w) I get a signal modulated at the
difference frequency.

** Wot an utterly, monumental fuckwit.

This vile psychopathic pile of **SHIT** must be exterminated from
the face of the earth.

http://www.neopax.com/

http://www.neopax.com/dirk bruere.jpg

http://www.neopax.com/asatru/index.html


It may take any number of wooden stakes, driven through this vile zombie's
heart.

Show no mercy - it simply ain't human.






....... Phil

 

[Phil Allison]

"YD"

The PAM carrier is in the audio range.

** Total fallacy.

No such " carrier " exists with PAM.

It should be lowest for good
resolution but high enough to be easily filtered. Extracting the
sub-AF from the variable duty cycle is done by the external circuitry.
Makes perfect sense if you think about it.

** Makes total BULL SHIT obfuscation to anyone with a clue.

You are nothing but a STINKING FUCKING LIAR !!!!!!!!!

Well, whatever. I was too lazy to write "variable duty cycle pulse
train".

** Just as you are too lazy to think straight and too dishonest to admit
even the grossest error.

Drop fucking dead - you bucket CRIMINAL WOG shorthead !~!~!






....... Phil

 

[Phil Allison]

"YD"

The PWM carrier is in the audio range.

** Total fallacy.

No such " carrier " exists with PWM.

It should be lowish for good
resolution but high enough to be easily filtered. Extracting the
sub-AF from the variable duty cycle is done by the external circuitry.
Makes perfect sense if you think about it.

** Makes total BULL SHIT obfuscation to anyone with a clue.

You are nothing but a STINKING FUCKING LIAR !!!!!!!!!

Well, whatever. I was too lazy to write "variable duty cycle pulse
train".

** Just as you are too lazy to think straight and too dishonest to admit
even the grossest error.

Drop fucking dead - you CRIMINAL fuckwit WOG shithead !~!~!




....... Phil

 

[YD]

Late at night, by candle light, John Devereux

Yes - DC restoration.

Yeah, I forgot about that. I was thinking more about the principle of
the thing than the nitty-gritty. So run it through a comparator before
the LPF.

- YD.

 

[YD]

Late at night, by candle light, "Phil Allison"

"YD"



** Total fallacy.

No such " carrier " exists with PAM.

Now where did PAM get from? I do know a Pamela but she's not very
interested in PWM.

- YD.

 

[Robert Baer]

OK, what do you call it?

I'll type really slow and make pretty pictures for you to understand.

Do you know how to create a rectangular waveform in the audio range?
Do you know how it may be created by the sound card? Do you understand
duty cycle? Can it be done in software?

Let's see...

What's the average of the following waveforms, assuming 0 and 1 V?


__________ __________
a) __________| |__________| |______...


_ _
b) ___________| |___________________| |_______________...



_________ ___________________ _________________...
c) |_| |_|



Let's say the pulse frequency is a few hundred Hz and you run it
through a LPF with sub-audio corner while you *slowly* vary the duty
cycle, what will you see after the LPF?




Pbhhhh... Same to you.




I'm honest enough to agree it could have been worded better. I still
know what I'm talking about.

Pity that after you've flown off the handle over some silly detail you
cease thinking straight but never admit it. When you're sane you're
usually pretty spot on.




WOG? Whassa WOG?

- YD.

"WOG"? Maybe "Wily Old Goat"??? or "With Out Gold"?
Too lazy to use WikiPedia...