Precision low frequency generation

[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

 

[Mark]

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

if you are making a linear summing amplifier, then YES you have missed
something, the difference between addition and multiplication.

Mark

 

[Phil Allison]

"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?

** Yep - the regular, prescription, anti-psychotic drugs that keep you
just inches away from committing suicide.

Please do continue as you are ......

( Wot a ** fucking MORON ** )




....... Phil

 

[Dirk Bruere at NeoPax]

"Dirk Bruere at NeoPax"




** Yep - the regular, prescription, anti-psychotic drugs that keep you
just inches away from committing suicide.

Please do continue as you are ......

( Wot a ** fucking MORON ** )

...... Phil

You're projecting again Phil.

Dirk

 

[[email protected]]

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

A whole lot simpler to produce the 2.5Hz signal directly from your
computer.

 

[Phil Allison]

"Dirk Bruere at NeoPax"


** This vile psychopathic pile of SHIT must be exterminated.

http://www.neopax.com/

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

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


May take any number of wooden stakes driven through the vile zombie's heart.

Show no mercy - it is not human.




....... Phil

 

[Vladimir Vassilevsky]

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?

Wow. You don't have a slightest clue, do you?

VLV

 

[Dirk Bruere at NeoPax]

A whole lot simpler to produce the 2.5Hz signal directly from your
computer.

I need to use any computer, without specialised hardware.
Soundcards typically will not go down below 10Hz.
I suppose I could simplify it by generating a high frequency sine wave
100% amplitude modulated with the low frequency component in something
like Audacity.

Dirk

 

[Dirk Bruere at NeoPax]

"Dirk Bruere at NeoPax"

** This vile psychopathic pile of SHIT must be exterminated.

http://www.neopax.com/

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

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

May take any number of wooden stakes driven through the vile zombie's heart.

Show no mercy - it is not human.

...... Phil

"Human" is not something to aspire to, but something to transcend.

Dirk

 

[Dirk Bruere at NeoPax]

Wow. You don't have a slightest clue, do you?

VLV

Your usual helpful self.
Why do you bother being such a jerk?

 

[Phil Allison]

"Dirk Bruere at NeoPax"


** This vile psychopathic pile of SHIT must be exterminated.

http://www.neopax.com/

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

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


May take any number of wooden stakes driven through the vile zombie's heart
to kill it.

Show no mercy - it ain't human.




....... Phil

 

[Phil Allison]

"Dirk Bruere at NeoPax"

** 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 ain't human.




....... Phil

 

[John Larkin]

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'd get no output at 2.5 Hz. You need a nonlinear mixer ahead of the
filter, ideally a linear multiplier.

John

 

[[email protected]]

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

Dirk, to get the difference frequency you need to multiply, not add,
the signals.

Here is a cheap man's solution:

0V --potentiometer-- +12V +12V
| |
100kOhm 2200 Ohm
C 1 |
| C4
f1---- 100nF----------------g2
drain---------------------------- 100uF---------------- out
BF961
|
C 2 dual gate MOSFET
1uF
f2---- 100nF----------------g1 source-- |
C3
|
| ///
100kOhm
|
| ///
///

C1 and C2 decouple the input.
The potentiometer sets the voltage at gate2 so the drain is at about
7V.
The 2200 Ohm together with C3 form a lowpass.
The second gate in the BF961 dual gate MOSFET modulates the signal
caused by the voltage on the first gate.
Here is a similar diagram, note the mixer, it is for higher input
frequencies however..
http://panteltje.com/panteltje/lorentz/experiment.ps

Select C3 for adequate low pass filtering.

Does output need to be a precise sinewave?
If so, use an EPROM with a binary counter on the address lines, driven
from a 74HC4046 VCO, output
EPROM into a simple DAC.

 

[Ecnerwal]

I need to use any computer, without specialised hardware.

Given that you are adding "specialized hardware" in the form of external
circuits, why not just make the external circuits be a ROM full of
digitized waveforms and a DAC to spit them out? You can get a uP that
has both enough ROM and a DAC on-board...

 

[Jan Panteltje]

On a sunny day (Tue, 20 Nov 2007 07:25:00 -0800 (PST)) it happened
[email protected] wrote in
<2cccb7f8-56d7-4b7e-903f-350c7b819a6a@b36g2000hsa.googlegroups.com>:


Google screwed up my ASCII art, so here again from a real newsreader;

Dirk, to get the difference frequency you need to multiply, not add, the signals.

Here is a cheap man's solution:

0V --potentiometer-- +12V +12V
| |
100kOhm 2200 Ohm
C 1 | | C4
f1---- 100nF----------------g2 drain---------------------------- 100uF---------------- out
BF961 |
C 2 dual gate MOSFET 1uF
f2---- 100nF----------------g1 source-- | C3
| | ///
100kOhm |
| ///
///

C1 and C2 decouple the input.
The potentiometer sets the voltage at gate2 so the drain is at about 7V.
The 2200 Ohm together with C3 form a lowpass.
The second gate in the BF961 dual gate MOSFET modulates the signal caused by the voltage on the first gate.
Here is a similar diagram, note the mixer, it is for higher input frequencies however..
http://panteltje.com/panteltje/lorentz/experiment.ps

Select C3 for adequate low pass filtering.

Does output need to be a precise sinewave?
If so, use an EPROM with a binary counter on the address lines, driven from a 74HC4046 VCO, output
EPROM into a simple DAC.

 

[Dirk Bruere at NeoPax]

On a sunny day (Tue, 20 Nov 2007 07:25:00 -0800 (PST)) it happened
[email protected] wrote in
<2cccb7f8-56d7-4b7e-903f-350c7b819...@b36g2000hsa.googlegroups.com>:

Google screwed up my ASCII art, so here again from a real newsreader;

Dirk, to get the difference frequency you need to multiply, not add, the signals.

Here is a cheap man's solution:

0V --potentiometer-- +12V +12V
| |
100kOhm 2200 Ohm
C 1 | | C4
f1---- 100nF----------------g2 drain---------------------------- 100uF---------------- out
BF961 |
C 2 dual gate MOSFET 1uF
f2---- 100nF----------------g1 source-- | C3
| | ///
100kOhm |
| ///
///

C1 and C2 decouple the input.
The potentiometer sets the voltage at gate2 so the drain is at about 7V.
The 2200 Ohm together with C3 form a lowpass.
The second gate in the BF961 dual gate MOSFET modulates the signal caused by the voltage on the first gate.
Here is a similar diagram, note the mixer, it is for higher input frequencies however..
http://panteltje.com/panteltje/lorentz/experiment.ps

Select C3 for adequate low pass filtering.

Does output need to be a precise sinewave?
If so, use an EPROM with a binary counter on the address lines, driven from a 74HC4046 VCO, output
EPROM into a simple DAC.

Thanks.
Initially I need to test with sinewaves, but ultimately I want to use
the computer to generate arbitrary LF waveforms.
Modulating a HF signal with the LF waveform in the computer would seem
the best way to go initially. Then it becomes an AM 'radio' problem.
Cat's whisker?

Dirk

 

[Vladimir Vassilevsky]

You'd get no output at 2.5 Hz. You need a nonlinear mixer ahead of the
filter, ideally a linear multiplier.

John,
why did you sell him an ultimate arb generator?

VLV

 

[DJ Delorie]

but ultimately I want to use the computer to generate arbitrary LF
waveforms.

Put a DAC on the parallel port, or buy a DAC dongle that plugs into
USB.

 

[Dirk Bruere at NeoPax]

Given that you are adding "specialized hardware" in the form of external
circuits, why not just make the external circuits be a ROM full of
digitized waveforms and a DAC to spit them out? You can get a uP that
has both enough ROM and a DAC on-board...

That would be a good solution for a standalone unit.
However, I like the idea of selling custom PC progs for specialised
generation for the app I have in mind.
The money, as usual, is in the s/w

Dirk