Generating signal, varying amplitude & frequency: 0-4 kHz 1

[SmeX]

I need to generate signals with varying amplitude and frequency ( 0 - 4 kHz) on a circuit without the use of an external signal generator / oscilloscope. There is also the aspect of frequency stability and accuracy; which in my case is extremely important. I`ve been loking into various VCO / VCXO`s but was unable to find any in my frequency range / spec`s.

I case you wondered: This is to simulate the rotational speed and vibration of a turbine blade.

Any suggestion would be greatly appreciated !

 

[itsmoked]

If you understand micros that could be pretty easy and accurate.

 

[itsmoked]

If you have only certain patterns of interest then you could use Direct Sequence. Running thru a ROM filled with pre-calculated values then fed sequentially to a D2A.

 

[logbook]

Just buy/rent an "arbitrary waveform generator".

 

[ScottyUK]

The venerable Intersil 8038 function generator is simple to interface to as a voltage-controlled variable-frequency source, although it won't achieve a true 'zero' frequency because that is DC. It goes pretty low though.

http://www.intersil.com/data/an/an013.pdf

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Start each day with a smile. Get it over with.

 

[itsmoked]

logbook he said on-board I believe....

 

[SmeX]

Yes,I did mean on-board but thanks nevertheless.

itsmoked; by micros - do you mean micro controllers ? If possible please elborate.

ScottyUK; that was exactly what I was looking for, thanks a lot

(Although not the one you pointed to; it is for some reason not recommended for new designs ? -

http://www.intersil.com/data/FN/FN2864.pdf)

did find this one though;

http://www.maxim-ic.com/appnotes.cfm/appnote_number/650

 

[VEBill]

You might want to look at some old music generator and MIDI chips. Some of those chips can be loaded with waveforms and then played-back with only a few high-level commands. 4kHz is obviously within their range. They're clock-locked so stability can be as good as you want.

The ones I've played with (years ago) can do arbitrary frequencies and sweeps as well as notes.

The biggest issue might be that they're sort-of 1980s and there might not be as many to choose from these days. But MIDI is still going strong so they're out there.

 

[ScottyUK]

Pleased to help - thanks.

You might try the Exar XR8038 if the Intersil chip is hard to find.

Both are still available, but I guess it has been EOL'd by Intersil and production is being ramped down. OK for a one-off, but buy a handful of IC's in case one fails in service.

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Start each day with a smile. Get it over with.

 

[itsmoked]

SmeX;
Yes I meant microprocessor. The 4kHz you need is easy for a micro running at 4 or 8 or 20Mhz. If you said you needed 100kHz I would maybe think harder about a micro doing the job but might still use one to coordinate whatever other solution I reached for. But actually the new DSP micros could even handle that with out much problem.

A lot of designers are thinking this way. That is why chips as offered by others here are starting to disappear. Since designs now need micros for ohter desired features they just use the micros for sine-wave synthesis.

Micros are sooo flexible. I always grab for them.
They come with PWM blocks that can be used to create sine waves and triangles and squares and pulse trains and sweeps, etc, etc. And they automatically provide other stuff you end up needing but didn't think of earlier like; synchronization, start, stop, timing, delays, monitoring and indication.

Here is an example application note on generating DTMF tones (harder than your requirement) using a simple micro.

http://ww1.microchip.com/downloads/en/AppNotes/00655a.pdf

 

[felixc]

If precision and stability is important, it is not sure that an analog oscillator will do it. But you did not tell what kind of precision and stability, and the possibility to generate a very precise frequency, that you are expecting for your product. All of the answers above can work. If you want cheaper, a 555 can also fit the bill. Do you need a sine wave? Or would a square wave do?