Circuit for Randomized Pulse Width Modulation

also somwwhat temporary.

photocell and lava lamp, portable, but heavy, somewhat fragile and slow to start.

When I needed about 8 low frequency noise signals, I used a noisy zener diode, amplified its noise with a video opamp to about 4volts/15MHZ. Put heavy shielding around that, to avoid radio interference.

I then used 16 sample/hold amplifiers, and let them sample the 15mhz signal, each shifted a handful of microseconds. That gave me 6 outputs, each nicely uncorrelated, Filter/amplify to clean up the outputs.

You can change the bandwidth by changing the clock for the 16 bit shift register controlling the s/h amps.

Used to produce wind and engine noise in a car simulator.

I still have the backplane of sounds generator.

So, it's an audio memory module. Interesting. There are ones based on the WTV020SD that accpt an SD card. A few dollars each out of China. But again, not what I was looking for.

Nice but a bit kinky.

Robert Martins

Perhaps you could use a electronic tea light. If you prefer to build it using standard chips then consider using a noice generator with a BJT.

Yup, the central limit theorem will make the duty cycle approach 50% as the division ratio goes up. That's actually pretty useful sometimes, e.g. in building noise servos based on false-count rates.

A PRBS generator's output is periodic, and so consists entirely of harmonics of f_clk/(2**N -1), where N is the register length. Filtering just changes the harmonic amplitudes.

To make that look continuous, so as to get good noise down below 1 Hz, you need a fair few bits and a lowish clock frequency, so that the period is much longer than your measurement.

The OP seems to be making very heavy weather of a simple job. "Too small to produce a workable result" is a typical example.

An ordinary op amp running with a closed loop gain of 100 dB will produce a lot of low frequency noise, and give some lowpass filtering as a bonus. (The amp would need at least 120 dB of open-loop gain, but there are lots of those around.)

Assuming its 0.1-10 Hz p-p noise is 5 uV, the amplitude would be around

If he uses a chopamp, the noise would even be reasonably close to white, but it would probably need two stages to get enough gain. An OPA378 has very flat noise of about 20 nV/sqrt(Hz), so in a 10-Hz bandwidth with a gain of 100000, that would be about 6 mV. A second stage could make that anything he likes.

Cheers

Phil Hobbs

Yeah that might work (gain up the 1/f noise of an opamp.) or use my favorite noise source a 20V zener run at ~10 uA of current.

George H.

All you'll end up making with that setup is a thermal gradient/ microphonics detector that outputs a bunch of off scale DC level jumps that take minutes to settle back down.

If your layout is sufficiently horrible and you pick the wrong parts. A chopamp and a couple of SMT resistors isn't going to give any problems in a sane layout.

I gather you're speaking from experience? ;)

Cheers

Phil Hobbs

How about if I use junction white noise, add a 1KHz LPF and bias the input of an op amp so it only sees the highest amplitude spikes.

I have no idea what the rep rate of those spikes might be, but I may be able to adjust so it is primarily within the sub audio range.

These could used as is, or to trigger a square wave which in turn could be filtered to approximate a sine.

Robert Martin

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You could use agc to set the trigger level.

NT

"I have no idea" apparently equals "I don't want to spend the time to actually design a real solution." Or, maybe, "I don't know how to do this but I don't want to use somebody else's idea."

You've had a lot of smart people giving you advice. That's a wonderful thing, except that you keep adding conditions such as "minimal parts count" and "too small to produce a workable result". Those are irrelevant for a hobby project.

I'm far from dissing hobby projects--I've learned a lot from them myself--but parts count is hardly relevant. "I have no idea" ought to mean "I'm eager to learn", but that doesn't seem to be the case.

If you're too lazy to wire up one op amp and two resistors, none of us can help that.

Cheers

Phil Hobbs

Frankly, I've had it with the pointless sniping and nitpicking on this group. I do have my limit. You have no idea what my personal circumstances are.

Apparently some here think it is intolerable to canvas ideas before starting a project, and then cannot even agree among themselves.

It's obviously all my fault for asking the question. I have unsubscribed. Sorry to have bothered you.

Robert Martin

You have to have a thick skin when you decide to ask for help here. There are quite a few very knowledgeable people here, but they tend to be short of patience. Especially so with people who are obviously no experts, and yet refuse to listen to advice and suggestions.

There are lots of trolls, too. Just ignore the trolls.

As for me, I haven't even understood what you are trying to do. You never really described your purpose, but only what you believe are solutions.

Jeroen Belleman

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Huh, OK bye Robert. I thought your thread was tame compared to some. This is a nice place to fling ideas around, but you do need a thick skin when you first start interacting and don't know who all the people are.

Think on this, Phil H. is a private consultant. (I'm not sure what he calls himself) He probably charges customers ~$100/hr for his time. And here you can get his thoughts for free. More so if you are nice and offer him some of your wisdom.

George H.

Not in any detail, of course, but then that's not highly relevant to the point at hand.

There are quite a few folks that show up here asking questions who don't actually want a solution, and you appear to be one of them. This is a discussion group, so discussion is great, as long as it leads somewhere. (I'm not the owner of the group, I just have an opinion, and that's what it is.) We like to be helpful round here.

Your two threads on this project spanning more than two months (starting on Hallowe'en) have racked up about 70 posts, apparently with zero progress. The gizmo looks like getting built sometime in the twenty-third century.

Questions are fine. It's being super boring about it that's the issue. ;)

I sort of doubt that, but it's nice of you to apologize.

Cheers

Phil Hobbs

ote:

uty

or - it can also be done with long shift registers, and some parts seem to have been designed for the job, but the single-chip microprocessor or a pro grammable logic chip are the minimum part solution.

et the job done.

and the exclusive-OR gate package.

't be bother finding out what parts are available.

nly provide external output from the stages you need to feed into the exclu sive-OR gate, and you can program a programmable-logic device to do all the same jobs in one chip.

on the output you'd see about 2V peak to peak.

l swing - which could be up to 15V with old 4000-series CMOS. More modern p arts are mostly only rated for lower supply voltages - 5V or lower.

Couldn't you low pass filter the bit stream and feed an on chip DAC and dri ve an analog output directly? His actual goal is to produce random waves, right?

Rick C.

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at

Somehow I feel this should be doable with a 555 timer chip... but no idea h ow really. Can every problem be solved with a 555 timer chip or two?

Two 555 timer functions (is that a 556 chip?) with slightly different perio ds exclusive ored together, then low pass filtered.

Rick C.

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"Very knowledgeable" and "useful advice" are often incompatible.

Advice is just that. If someone rejects your advice it often means you either didn't understand the problem or the person. Silly to get an attitude about it. Either people can offer solutions and enjoy the responses or be jerks about it. Whatever.

Rick C.

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What is it with people like that, anyway?

Not referring to the present example in particular, but more generally. It seems to fit a pattern.

A current one that comes to mind (on another forum), is asking about "contra-wound" inductors and their applications to microwave antennas. Just... where do they get these ideas from? Rubbing together two contrary ideas and expecting something to come out?

They seem to usually be conversant, but show absolutely no ability to reason, or even acknowledge that an argument might be made about a given topic.

Our own resident Skybuck seems to fit such a categorization; probably several of the other trollier users too.

I recently watched a sort of biography of a schizophrenic who became obscurely-internet-famous for his, to put it roughly, ravings. Definitely a smart person, but sadly hampered by his condition, and the general lack of mental health care in this country. The highlight of his effort, he created an operating system (of sorts) from scratch, TempleOS. (The name, and content, look to be manifestations of his delusions.) Since the late 90s, he showed up in many places on the internet, from newsgroups to forums to Reddit and beyond (of course, being moderated out of existence in most places). The last few years, his condition continued to spiral downwards; he died last year... struck by a train.

I suppose many conditions may provoke such behaviors, the persistent ideation, delusions, trolling, incapability of reason... I wonder if it's better that those sorts of people have an outlet (whether their voices are heard or not -- not that most people want to hear them, either). I would suppose we shouldn't entertain their ideas. Trolling them back obviously isn't going to help. But actually getting them useful help? Who knows...

Tim