need help on random noise generator circuit

[cradlemess]

Can anyone tell me how to construct a random noise generator with a frequency range of 0-500hz or better yet can someone give me a schematic diagram of it?

 

[55pilot]

Go to a website called google.com In the text box type "random noise generator circuit" and hit the search button.

Now a question: Does this post belong in the "Homework help" section?

---55p

 

[cradlemess]

i already did that.. but what comes out are either programs, random number generators, non linear or chaotic diagrams. what i need is a circuit that can be implemented to a physical system that can be used as a laboratory test input. Im looking for a simple yet agreeable schematics not complicated ones and from my experience, forums are the best ways to get them.

 

[(*steve*)]

I googled for "random noise generator circuit", clicked on the first link (Noise Generators-- White and Pink Electronic Circuits) and browsed through those.

Is there any reason you want the max frequency to be 500Hz?

Do you want an audio signal, or a logic signal?

What is the purpose of this? (it may help us help you)

 

[NickS]

I have built several noise generators making use of zener noise but I don't know about frequencies that low(0-500Hz) because DC blocking has always been required for mine. But you should be able to set up a real quick test using a variation of the schematic found here...
noise

Replace the amplifiers shown with your favorite opamps set up as gained LPF's with the fc = 500Hz. You will also need much larger coupling caps too get closer to your DC goal.

Another note, you see from the plots on the linked page the noise levels are pretty small
(-50dBm or 10nW) after 40dB of gain. What do you plan on measuring it with(audio precision?).

Best of luck to you. And let me know how low in frequency you were able to go.

 

[cradlemess]

sir steve,

i was advised to keep the frequencies at 0-500hz, we need it to be an audible signal. we kept it at that range to lessen the computational load of the controller. We are designing an ANC algorithm and it needs to be implemented in real time.

 

[cradlemess]

Sir Nicks,

thanks for the circuit i'll try it out. Can it produce unpredictable random noises in varying length of time?

 

[(*steve*)]

The sound you get will probably be a low rumbling sound.

Perhaps you can tell us *why* you need this. It sounds like something fairly specific you're after.

 

[cradlemess]

well sir, our proposed system will be another algorithm to cancel out noise coming from one end of a ventilation duct. Random noises of 0-500hz seems like good test inputs because it gives our controller lesser computational load and at the same time it's fairly audible.

well the system will look something (not exactly) like this:

http://www.hindawi.com/journals/aav/2008/647318.fig3.html

 

[NickS]

Sir Nicks,

thanks for the circuit i'll try it out. Can it produce unpredictable random noises in varying length of time?

Go here for a good starters definition of white noise. The linked page will also let you listen to a white noise soundbyte

However if you are attempting noise cancelling of your ventilation duct I would bet that the sound you want cancelled is not white noise at all. You could test this by capturing the sound of your duct and then processing the data to produce a FFT(frequency domain) plot.

From what I know of noise cancellation I would say you have a good chance of cancelling specific repetitive noise(like a motor turning a squirrel cage, or tires on the road)but you will be hard pressed to notice a noise improvement on white noise.