Yes, of course you're right. However, there are several considerations here. First, as I said, I had no idea Bob Masta had responded to my post- a problem I hope to fix very soon. Second, I don't use Windows, which is the OS he writes programs for. Third, I do this stuff for fun, so I have not the slightest objection to reinventing the wheel or doing things the "hard" way.
The circuit I found contains six parts. If I had the zener I could slap it together in about ten minutes.
But mostly I just didn't see Bob's post. Even if I didn't like his idea (and I do like it), I'd have been courteous enough to reply, had I seen the post.
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No apology needed. If you go with a hardware solution you will need to be able to convince yourself that it is not picking up an AM station, so be sure to compare one-ear listrening to two-ear listening if you get an effect.
As for Zeners, I haven't tried the 20V units George mentioned... but that sounds like a good aproach if it avoids the need for a lot of gain. I used a reversed-bias EB junction from an NPN back in the "olden days"... I think this was pretty common. You ground the base and feed the collector through 100k from +15, and tap off the noise via a big cap (0.47 or whatever) and a bunch of gain.
If you go with a pseudo-random generator, you have to be careful: "Back in the day" the single-chip units were notorious for having a short repeat pattern. They were designed for transient uses like snare drums, and if you ran them continuously you'd hear "shoop, shoop, shoop" from the repeats. Make sure whatever you use has at least a minute or more, and for your purpose best if it's hours or beyond.
In the past, when computers had easily-controlled hardware, it was fairly easy to do this with code that drove the printer port. Alas, no more.
Best regards,
Bob Masta DAQARTA v6.02 Data AcQuisition And Real-Time Analysis
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You know, you reminded me that my system has a random function built into it - not sure exactly how it works, but it spews out (pseudo)random bytes at a pretty fast rate (A few seconds worth created a file > 100M). Now the trick is to convert that to sound... I suppose I can figure that out. I might pass it through an FFT program just to see whether it's even close to being white noise... I just don't know how this "random" function works. As John von Neumann said, "Anyone who attempts to generate random numbers by deterministic means is, of course, living in a state of sin."
I don't see much problem with gain - if I can't do it with a few transistors (maybe in a Darlington arrangement?), then I can always use a couple of op amps.
I'm probably not going to try this. I don't have the parts handy.
Sure, back when you just about had to write your own drivers for everything. I had a lot of fun back then, but I wouldn't really want to go back to it now.
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Dumb looks are still free.
Sometimes you want (or need) to use a noise source (or whatever) when there is no computer close enough. A laptop solves that problem - but the zener source solves it a whole lot cheaper.
Then there was the circuit in "Electronics", Designer's Casebook or Engineer's notebook, that just used a noisy op-amp and amplified it, as a noise source. No diode needed.
That's very close to what I did - cat /dev/urandom > randomfile. Then I imported that as a raw file into audacity, converted it to ogg format. When I looked at its spectrum, it was suspiciously flat all the way from zero to 20kHz, where it fell off at > 30 dB per octave. Just a little
*too* perfect. I go by the maxim that, if everything goes according to plan, you've obviously overlooked something.
Anyway, it's a nice, noisy signal, but I'm still going to do the other one just for fun (amplified diode noise). As someone pointed out, having a quick noise source around could be handy for other reasons besides talking to ghosts.
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With the a 20V zener you don't need any amplifictaion, just a buffer. I wrapped this together on the top of a power supply.
+15 | 1 Meg | +--0.1uF--+---->scope (use x10 probe, | | not a crappy clip lead.) Z 100k ^ | | GND -15V
I saw a random RC step response with a time constant of ~2us. With something like a few hundred mV step size (on average) (Driving home I realized that the ~80pf in the clip lead I used to connect to the scope was my RC.. so I can't pull any 'real' numbers out.) You can try it yourself with a x10 probe and report results. You should do better than two micro seconds.
Actually, the spectrum of random-amplitude samples should be flat. So I'd be more suspicious of the roll-off above 20 kHz. I haven't delved into ogg format, but my guess is that it may be rolling things off above the audio range.
Note that when an FFT generates a spectrum, it doesn't really know anything about frequency... it just operates on a set of numbers. If the numbers are random, the resulting spectrum is flat. The frequency interpretation comes by knowing the sample rate of the raw data values.
If audacity can't look at the spectrum of the raw data, can you convert to WAV instead of ogg? WAV is just a simple header in front of the raw data... it doesn't actually convert anything. The header holds the sample rate info and related stuff.
Best regards,
Bob Masta DAQARTA v6.02 Data AcQuisition And Real-Time Analysis
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Scope, Spectrum, Spectrogram, Sound Level Meter Frequency Counter, FREE Signal Generator Pitch Track, Pitch-to-MIDI Science with your sound card!
So here=92s a few =91scope shot with 1 Meg Ohm bias resistor. And a x10 scope probe (C =3D 16pF) The step is ~10ns or so... But I may be hitting the limit of the 40MHz scope.
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The same at slower time base.. showing the RC =91recharging=92
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You can average the FFT when watching on the =91scope but a single FFT trace is pretty noisy... but it looks flat to about 500kHz.
If you reduce the bias resistor to 100k you can get improve the bandwidth.
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The FFT looks flat out to near 10MHz!
and a fast shot still with 100k ohm
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From the slope (1 volt in ~170ns) (at a current of 100uA) I get a C of
17pf... I=92m still looking at the C of my probe!
Any ideas on reverse biased zener capacitance? This is the best data sheet I could find.
One trick, at least at RF is to use the Zener breakthrough in a regular transistor, the base - emitter diode backwards can give a very good noise source ranging upp to 1GHz and even above.
Yes, and someone's already warned about that, but the issue isn't because of it's an LED but because of the seethrough casing.
I remember one article about a VCO where the author suggested trying different types of diodes for the varactor. And he mentioned trying some small signal diodes and having AC hum on the output, until he realized the hum was coming from the desk lamp that was shining on the clear-cased diode.
I've seen other mentions of problems because of light. I recall one article warning about it, but not because of hum, but because the external light was affecting diodes, and they were biased wrong or something, or maybe turning on when they shouldn't.
Since LEDs have been used as low voltage zeners, perhaps they do have some ability to better generate noise at a lower voltage or something. With a breadboard, it costs very little to try. If it works, simply paint the LED, get rid of any external problem.
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