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I am curious on making things oscillate. I would love to do this with one chip, but if there was a chip that oscillated at 2295 Hz, I have no idea where it is. So the question is, how could I use an LC or RLC circuit to oscillate ate 2295 Hz? I have looked at the formulas and looked for calculators and can't see a way to go backwards like I'd like easily.

Or is there any other circuit that can be used to oscillate at this frequency?

Dom
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Kyle
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    Do you need a sine wave or will a square wave do? How accurate must it be? With a microcontroller timer, you can get pretty close (within 1 or 2 Hz). – tcrosley Jan 20 '12 at 03:53
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    ... And what peak voltage and drive capability? – tyblu Jan 20 '12 at 03:59
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    Is this for RTTY ? – Paul R Jan 20 '12 at 08:01
  • The question is very unspecific there are a lot of oscillator chips available. The most common may be the NE555... But you have to specify a little bit more detailed, what you want to achieve. – chrmue Jan 20 '12 at 08:26
  • Yeah for 300 baud or so RTTY, my microcontroller gets choppy around that. – Kyle Jan 25 '12 at 17:46

3 Answers3

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You need to tell us what you are trying to do and why.
BIG picture.
What you ask for is very easy BUT may not be what you really want.

The "best" way may be to use a microcontroller with an inbuilt timer / counter unit (or even one without one). If a square wave is wanted then this allows easy rapid and accurate alteration of frequency once established and a single IC solution. Depending on required accuracy and stabiity this could be controlled by a crystal or a ceramic resonator or use an internal oscillator.

A very easy way & low cost way is to use any hex Schmitt inverter, or in fact and inverting Schmitt gate configured as an inverter.

The IC can be 74C14, 74HC14, 74...14, CD40106, ...
t ~= R x C
Fosc ~= 1/(R x C)
(From here

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Following all from here

Using an op amp

RC Phase Shift:

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or

Wien bridge:

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or

Schmitt:

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or

Using 2 transistors

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or

using 1 MOSFET transistor
Usually used at higher frequencies.

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A zillion leads - each image is live.

Russell McMahon
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  • I would recommend to use trimmers in specific positions, instead of resistors: for instance, using a trimmer in the simple Schmidt trigger allows you to fine-tune the frequency at which the circuit oscillates, and it would be nearly impossible to create a wave with a 4-digit precision with normal components, because of tolerance. – clabacchio Jan 20 '12 at 15:02
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    You should also specify which of these are sinusoidal oscillators (e.g. the Wien bridge) and which are multivibrators (square wave, e.g. Schmidt bridge), because it's not clear what Kyle is looking for. – clabacchio Jan 20 '12 at 15:08
  • Or go higher tech AD9834 – Matt Jan 20 '12 at 15:59
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The big question is what accuracy do you need?

You asked for a very specific frequency. That normally implies you want a high accuracy. 5Hz is about 0.17% of 3KHz, so lets assume you want a 0.1% accuracy.

That is a tough deal for RC based oscilators. Capacitors have a tolerance of about 2% at best so the only way you could get that kind of accuracy with a RC system would be to tune individual devices using variable resistors or capacitors. Doable for a one-off but a PITA for anything you want to put into production. I would also question the log term stability.

You can get dedicated clock generator chips that are designed to drive a crystal and then multiply and divide it but they tend to come in packages that are distinctly unfriendly to beginners and they tend to be designed for higher frequencies.

A suspect a microcontroller is probablly the easiest soloution to driving a crystal and then dividing the output down to product a frequency in the range you want.

Peter Green
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The LTC 6990 is a clever solution, it has an oscillator set by DC input or via a resistor, then that output is divided by one of 8 division ratios due to a second resistor set input. Brilliant! See sheet 6 of the data sheet to see the details.

Shawn
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