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IC advice to create a regolable oscillator from 0 to 500kHz

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iMo:

--- Quote from: Zero999 on April 02, 2019, 09:05:17 am ---
--- Quote from: imo on April 02, 2019, 07:50:41 am ---If you want to learn something useful, download the LTspice and you will get a tool which works..

--- End quote ---
Does the astable with the 74HC74 work though?

--- End quote ---
Sure, you would need a '74 model with real transistors in it.

Zero999:

--- Quote from: imo on April 02, 2019, 10:19:59 am ---
--- Quote from: Zero999 on April 02, 2019, 09:05:17 am ---
--- Quote from: imo on April 02, 2019, 07:50:41 am ---If you want to learn something useful, download the LTspice and you will get a tool which works..

--- End quote ---
Does the astable with the 74HC74 work though?

--- End quote ---
Sure, you would need a '74 model with real transistors in it.

--- End quote ---
I take that as a no then. How about using slightly different values of R or C, for each side of the timing circuit? It might work then. Simulators often struggle with a perfectly symmetrical astable multivibrator, which doesn't represent reality. I would do it myself, but can't download the 74HC74 model at the moment.

stockvu:
Your spec of 0 to 500 kHz is pretty tough for a discrete circuit to realize (in a repeatable fashion) such that you know what the current frequency (and perhaps duty-cycle).

I'd suggest buying a good bench-top frequency generator as one solution ~$100-200.

Another way is to buy a AD9833 Direct Digital Synthesizer module (~$5 on eBay) and run it using a PIC or Arduino micro-controller board.

That low-cost AD9833 DDS can really deliver (0.1 Hz resolution) from 0 to 12.5 MHz, especially in a Square wave output. I use them for my projects with an Arduino 2560.

I realize this approach is way beyond using a few discrete chips. However, if you what you need MUST be repeatable and accurate, its likely worth considering.

hth

ogden:

--- Quote from: stockvu on April 02, 2019, 12:55:41 pm ---That low-cost AD9833 DDS can really deliver (0.1 Hz resolution) from 0 to 12.5 MHz, especially in a Square wave output.

--- End quote ---

Square wave output of this DDS is just MSB of the DAC - far from DDS resolution with jitter for most (noninteger) frequencies. AD9851 have built-in comparator for proper square wave output, yet it is huge overkill for 0..500KHz application.

Further reading.

iMo:

--- Quote from: ogden on April 02, 2019, 02:55:32 pm ---Square wave output of this DDS is just MSB of the DAC - far from DDS resolution. AD9851 have built-in comparator for proper square wave output, yet it is huge overkill for 0..500KHz application.

--- End quote ---
Nope. The 9833's "MSB" is with 28bit resolution. Therefore the square wave too.
It is the same situation as with the 9851 and its comparator.

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