Simple oscillator circuit

G

Gone Fishin

Guest
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.
 
Gone Fishin' wrote:
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
Click to expand...
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.
 
"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?
Click to expand...

** 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
 
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.
Click to expand...
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.
 
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
Click to expand...
Thanks for your reply Phil.

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


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

** 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
 
** 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.
Click to expand...
Thanks Phil. Much appreciated.
 
Gone Fishin' wrote:
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.

You change them both, both circuits have to balance at the
Click to expand...
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.
 
"Phil Allison" <phil_a@tpg.com.au> wrote in message
news:hpekgk$ar0$1@news-01.bur.connect.com.au...
"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.


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


Could you use a single supply with a voltage divider to set a virtual
Click to expand...
"ground" node without causing distortion of the output waveform, or would it
be necessary to put a voltage follower there?
 
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.
 
Gone Fishin' Inscribed thus:

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.
Click to expand...
Sounds like home work !

--
Best Regards:
Baron.
 
Sounds like home work !
Click to expand...
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.
 
Gone Fishin' Inscribed thus:

Sounds like home work !

It is... of my own making.

I've been out of school for 30-plus years, now.
Click to expand...
Oops. :)

Do you have any suggestions re. a solution?

Thanks.
Click to expand...
Google "Wien Bridge Oscillator".

--
Best Regards:
Baron.
 
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'" <gone@fishin.net> wrote in message
news:0001HW.C7E0EDDB00526AEEB01AD9AF@news.eternal-september.org...

Take a look here:

http://english.cxem.net/home/home69.php



--- news://freenews.netfront.net/ - complaints: news@netfront.net ---
 
On Tue, 6 Apr 2010 13:55:39 -0700, Gone Fishin' <gone@fishin.net> wrote:

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?
Click to expand...
---
Does the output have to be sinusoidal?

Does it have to be centered around zero volts?

Does it have to be symmetrical?

JF
 
"Gone Fishin'" <gone@fishin.net> wrote in message
news:0001HW.C7E103ED00579739B01AD9AF@news.eternal-september.org...
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.

Among conventional op-amps, there isn't much that really makes a
Click to expand...
single-supply op-amp special. Often the only thing about an op-amp that
inspires the manufacturer to call it a single-supply op-amp is the fact that
the common mode range (the input) includes the negative supply. At least
that's my take on it.
More to the point is that your APPLICATION appears to require a dual supply.
Almost any old op-amp will do, like the one Phil named or even a good old
741.
You need a central reference point for that circuit, as indicated by the
ground symbol. It's actually not hard to take a single supply and
effectively split it in two. You need a voltage divider and a voltage
follower. The voltage divider is two resistors in series connected across
your power supply that creates a voltage reference at the midpoint between
Vcc+ and Vcc-. But it has high impedance, which means that drawing current
from it will drag the voltage up and down, something you don't want. So you
put a buffer in there, a voltage follower. If you get a dual op-amp you
can use the spare op-amp as the voltage follower.
To use an op-amp as a voltage follower you connect the non-inverting input
to the voltage divider, and connect the inverting input to the op-amp's
output. The op-amp's output is then a low-impedance source at the midpoint
of your power supply. It's like taking a 12 volt battery and magically
turning it into two 6 volt batteries in series.
You can also use a bjt as a voltage follower.
 
Does the output have to be sinusoidal?

Does it have to be centered around zero volts?

Does it have to be symmetrical?

JF
Click to expand...
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.
 
"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/stores/servlet/ProductDisplay?langId=-&storeId=10001&catalogId=10001&productId=23270
Click to expand...


** The link is to an LM1875 audio amp.

One could use that as the oscillator.



...... Phil
 
** The link is to an LM1875 audio amp.

One could use that as the oscillator.

..... Phil
Click to expand...
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.
 
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