Simple oscillator circuit

[Gone Fishin']

I want a simple oscillator circuit that will give 30 kilohertz.

<http://tinypic.com/m/9quype/3>

Which of these components do I change to achieve this?

What values should these be?

If I want a little variance (~10 percent) it should be the resistor, right?

What other opamps can I use?

Thank you.

 

[Sjouke Burry]

I want a simple oscillator circuit that will give 30 kilohertz.

<http://tinypic.com/m/9quype/3>

Which of these components do I change to achieve this?

What values should these be?

If I want a little variance (~10 percent) it should be the resistor, right?

What other opamps can I use?

Thank you.

The opamp needs to be able to feed the lamp, so you need a
high-output one.
Then bild it, check frequency against the value of C, change
C accordingly.
The lamp makes sure of a stable output without distortion.

 

[Phil Allison]

"Gone Fishin'"

I want a simple oscillator circuit that will give 30 kilohertz.

<http://tinypic.com/m/9quype/3>

Which of these components do I change to achieve this?

What values should these be?

** The formula for frequency is:

f = 1 / 2.pi.R.C

So with the values shown, oscillation is at 159 Hz.

Change both R values and both C values together and do not go under 1kohm
for R.

Many other op-amps could be used, but the NE5534 is a good choice.



..... Phil

 

[Gone Fishin']

The opamp needs to be able to feed the lamp, so you need a

high-output one. Then bild it, check frequency against the value
of C, change C accordingly.
The lamp makes sure of a stable output without distortion.

I calculate 50pF with 100K gives 31.8KHz.

But which of the C do I change? The one connected to ground? Which of the R
is part of the RC circuit? (The circuit is a bit confusing because it uses 2
identical R & C values.)

If I want to make the RC variable, which R do I replace with a pot (or fixed
+ pot)?

Also, this op amp (LF155) is specified as dual-supply type. I need a single
supply op amp. Will the R-C connection to ground of this circuit be connected
to -Vcc regardless if it is a single or dual supply op amp?

Thank you.

 

[Gone Fishin']

Change both R values and both C values together and do not go under 1kohm

for R.

Many other op-amps could be used, but the NE5534 is a good choice.



.... Phil

Thanks for your reply Phil.

So changing both R to 50pF and leaving both R at 100K will give 31.8KHz?

 

[Phil Allison]

"Gone Fishin'"

So changing both R to 50pF and leaving both R at 100K will give 31.8KHz?

** You must reduce the two R values to a few kohms at most and then pick C
to suit.

2.2 kohms and 2.2 nF is about right.

Fine adjustment can be done with a pot of about 10% the value of R in series
with one of them.



..... Phil

 

[Gone Fishin']

** You must reduce the two R values to a few kohms at most and then pick C

to suit.

2.2 kohms and 2.2 nF is about right.

Fine adjustment can be done with a pot of about 10% the value of R in series
with one of them.

Thanks Phil. Much appreciated.

 

[Sjouke Burry]

I calculate 50pF with 100K gives 31.8KHz.

But which of the C do I change? The one connected to ground? Which of the R
is part of the RC circuit? (The circuit is a bit confusing because it uses 2
identical R & C values.)

If I want to make the RC variable, which R do I replace with a pot (or fixed
+ pot)?

Also, this op amp (LF155) is specified as dual-supply type. I need a single
supply op amp. Will the R-C connection to ground of this circuit be connected
to -Vcc regardless if it is a single or dual supply op amp?

Thank you.

You change them both, both circuits have to balance at the
wanted frequency.
Changing only one will degrade oscillator quality.
If you can lay your hands on a tuning cap, they often contain
two sections, and make testing rather easy.

 

[Gone Fishin']

I need some advice regarding the grounding of the parallel R & C.

<http://tinypic.com/m/9quype/3>

The LF155 is a dual-supply amp. I need a single-supply amp.

I presume that in this circuit the ground is chosen because it is the
mid-point between the dual supplies (ie, +/-15). With a single-supply amp,
this point is not mid-point but rather it is the "negative supply" point.

How should this circuit change for use with a single-supply amp?

Thanks.

 

[Baron]

Gone Fishin' Inscribed thus:

I calculate 50pF with 100K gives 31.8KHz.

But which of the C do I change? The one connected to ground? Which of
the R is part of the RC circuit? (The circuit is a bit confusing
because it uses 2 identical R & C values.)

If I want to make the RC variable, which R do I replace with a pot (or
fixed + pot)?

Also, this op amp (LF155) is specified as dual-supply type. I need a
single supply op amp. Will the R-C connection to ground of this
circuit be connected to -Vcc regardless if it is a single or dual
supply op amp?

Thank you.

Sounds like home work !

 

[Gone Fishin']

Sounds like home work !

It is... of my own making.

I've been out of school for 30-plus years, now.

Do you have any suggestions re. a solution?

Thanks.

 

[Baron]

Gone Fishin' Inscribed thus:

It is... of my own making.

I've been out of school for 30-plus years, now.

Oops.

Do you have any suggestions re. a solution?

Thanks.

Google "Wien Bridge Oscillator".

 

[Gone Fishin']

This TI app note describes a single-supply wien bridge oscillator, which
helps me with a partial solution:

<
http://www-
k.ext.ti.com/SRVS/Data/ti/KnowledgeBases/analog/document/faqs/sscco2.htm>

The note does not describe specific op amp P/N's. Should I limit my design to
a single-supply op amp? Or can a dual-supply op amp and a single supply be
used here?

Thanks.

 

[Gone Fishin']

Does the output have to be sinusoidal?

Does it have to be centered around zero volts?

Does it have to be symmetrical?

JF

Approx 30 KHz, sine, distortion not terribly important. Centered around zero?
Don't know. It's to be the input to an amplifier module like one of these?

<http://www.jameco.com/webapp/wcs/stores/servlet/ProductDisplay?langId=-
1&storeId=10001&catalogId=10001&productId=23270>

Thanks.

 

[Phil Allison]

"Gone Fishin'"

Approx 30 KHz, sine, distortion not terribly important. Centered around
zero?
Don't know. It's to be the input to an amplifier module like one of these?

http://www.jameco.com/webapp/wcs/st...storeId=10001&catalogId=10001&productId=23270


** The link is to an LM1875 audio amp.

One could use that as the oscillator.



...... Phil

 

[Gone Fishin']

** The link is to an LM1875 audio amp.

One could use that as the oscillator.

..... Phil

There seems to have been a mix-up. The link should be this one:

<http://tinyurl.com/y9k83vf>

This is an audio amp. The oscillator will be the input to this.

Thanks.

 

[Phil Allison]

"Gone Fishin"
" Phil Allison "

There seems to have been a mix-up. The link should be this one:

<http://tinyurl.com/y9k83vf>

This is an audio amp. The oscillator will be the input to this.

** No mix up.

My suggestion is to use the LM1875 AS the oscillator - it is an op-amp
itself.

The only drawback is that the output level would become fixed.



..... Phil

 

[Bob Masta]

I want a simple oscillator circuit that will give 30 kilohertz.

<http://tinypic.com/m/9quype/3>

Which of these components do I change to achieve this?

What values should these be?

If I want a little variance (~10 percent) it should be the resistor, right?

What other opamps can I use?

Thank you.

You haven't mentioned what your ultimate goal is,
but I'm guessing that this is to be part of
something that is experimental... maybe in need of
some adjustments (the ~10% variance you mention)
before you get things to work just right.

If so, you might want to use a function generator
during the development phase. Then when you are
sure you can get the desired result, you can
replace that with a circuit.

If you don't already have a function generator,
you can use the free Daqarta Generator, which
works with your Windows sound card. To get to 30
kHz, you'll need a sound card (or built-in
chipset) capable of sampling at 96 kHz. Most
systems will do that these days, but older systems
may be limited to 48 kHz, or even 44.1 kHz if it
is *really* old.

Sound output frequency on any digital system can't
exceed half the sample rate, but at 96 kHz you
should have no problems getting to well past 30
kHz. Note, however, that there are some systems
that can sample at 96 kHz, but which apparently
have analog filters that limit the output
frequency to ~20 kHz. You can easily test if
yours is one of these via a "loopback" cable from
output to input.

Although this may all sound rather cumbersome
compared to a neat little circuit on a breadboard,
the advantage is that you can easily change things
experimentally. Besides fixed-frequency sines,
you can change waveforms at the click of a button,
or add various types of modulation (AM. FM, Phase)
or tone bursts or sweeps. You can even create a
band of noise that covers a chosen frequency
range.

Then, once you find the ideal signal for your
project, you can cast it into hardware.
Otherwise, if you start with the hardware and the
initial design doesn't give the desired results,
you can waste a lot of time pursuing dead ends.
For example, if you think *maybe* it would work
better with an FM warble, that's not easy to add
to your existing design. But if you knew from the
function generator tests that it was needed, you
could get the right circuit for the job.

Note that the Daqarta Generator really is
absolutely free. After the trial period, the
*inputs* stop working unless you buy Daqarta, but
the outputs (ie the Generator) will keep working
forever. Enjoy!

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
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(Some assembly required)
Science (and fun!) with your sound card!