Simple oscillator circuit

[Phil Allison]

"Gone Fishin"
" Phil Allison "

** The link is to an LM1875 audio amp.

One could use that as the oscillator.


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]

On Mon, 5 Apr 2010 21:24:27 -0700, Gone Fishin'
<gone@fishin.net> 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.

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
DaqMusic - FREE MUSIC, Forever!
(Some assembly required)
Science (and fun!) with your sound card!

 

[George Herold]

On Apr 7, 12:50 am, "Phil Allison" <phi...@tpg.com.au> wrote:

"Gone Fishin"
" Phil Allison "

** The link is to an LM1875 audio amp.

  One could use that as the oscillator.

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

Yeah, You'd certainly have enough current to turn the light bulb on!
(to OP if you don't try Phil's idea you do need an opamp with a decent
amount of current drive. (at least that's my experience...) you might
check out AN43 from Linear. J. Williams does a nice job describing
the operation... page 29 and beyond.)

Say has anyone used the LM1875? Is it any better/worse than the
LM675? (I've always found little bits of cross-over 'crap' on the
LM675)

George H.