FLASHING BULB CIRCUIT WANTED.....

I wonder if the old NE2 RC oscillators did that. I'm almost curious enough to get 25 NE2's and caps and R's and make a ~90V supply. But I don't know how I would be able to look at 25 neons blinking and come away with the impression that they are random or not.

With high R (say 10 meg) and a stiff source, I guess that would be the equivalent of phenominal Vdd filtering.

That leads to the next thought - if the above gave the appearance of randomness that the OP needs, how could it be interfaced to incandescant drivers? Maybe phototransistors?

Ed

I recall a similar NE2 multivibrator:

(Note the change in capacitor position. Once upon a time I took one of those plastic gum-drop trees and wired it up with a few hundred NE2's in that configuration... making a "twinkling" table-top Christmas tree. Powered by a 90V "B" battery :-)

I vaguely remember a string of NE2's series connected like that, called (IIRC) a "foo counter"... some with a wild-sounding audio output ;-) ...Jim Thompson

On Mon, 19 Oct 2009 16:02:33 -0700 (PDT), Bill Sloman wrote:

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JF

te:

If Steve (the OP) were interested enough to ask me for details, I'd produce a circuit diagram. I'd want to know a bit more about what he wants - the power dissipation of the lamps, whether he can order his own components (including prototyping boards and a power supply) in order to give him something he can use.

Without that kind of detail, producing a more detailed solution would be a waste of time.

You don't seem to have seen anything you can undertand, which isn't quite the same thing.

I think the last time that I used one was back in 1978 - one of my friends wanted to generate tolerably narrow-band white noise to test the spectral sensitivity of the sonar her bats were using, and I used pseudo-random binary sequece generator as the basic noise source, then put together an finite impulse response filter out of resistors to band-limit it. My first filter didn't work too well - the H-P article that described the system didn't both mentioning truncation error - but the second try, with a Hamming raised cosine windowing function, worked just fine.

-- Bill Sloman, Nijmegen

e:

Clunky it might be, but it has two advantages over your solution. One is that it involves fewer components and less soldering, and the other is that it would probably give the OP the random flashing that he asked for.

Your solution (as Petrus Bitbyter pointed out) depends on having a bunch of 555 type bistables running asynchronously from a common power supply, while they are notoriously prone to self-synchronise, and you rely on component tolerance to provide for frequency differences between your 25 "independent oscillators" despite the fact that if you buy 25 nominally identical components in one batch you are very likely to get 25 componets out of the same manufacturing batch, which may differ from one another by a lot less than the guaranteed tolerance,

As dubious, clunky solutions go, yours has to be a good deal less satisfactory.

-- Bill Sloman, Nijmegen

I gave him the reference to the relevant page in "Mastering the Art of Electronics" which gives everything that he'd need, and he could always have e-mailed me - my e-mail adress is real, and does work - if he'd wanted more detail.

The OP didn't specify his level of expertise, he didn't specify the power source he wanted to use - presumably 12V but the the "12V" power supply in a car ahs a lot bigger voltage spikes than the 12V you get out of a wall-wart - he didn't specify the actual wattage of his 12V "low wattage" lamps and he didn't specify the range of frequencies he wanted his lamps to flash at.

And John Fields' solution doesn't actually specify every part - "Opto", R, Rt, and Ct leave quite a lot to the OP's judgement.

This is sci.electronics.design, not sci.electronics.basics, and my solution does strike me as being presented with sufficient detail for this group. John Fields does post more stuff on sci.electronics.basics, as you'd expect from someone who seems to want to use the venerable 555 to solve most of the electronic problems that he runs into.

Far from it. But why post a schematic when I could refer the poster to "The Art of Electronics"?

-- Bill Sloman, Nijmegen

ill flash

I just

Funny that you should mention that. The 7555 itself may exhibit only a miniscule switching spike, but each of yours is switching a "low- wattage" incandescent lamp between on and off. The turn-on transistion for incandescent lamps is tolerably fierce - the filament draws quite a lot more current when cold than it does when it has got up to temperature, and while the extended wiring around the lamps won't have a great deal of inductance, it will have quite a bit of mutual inductance, so the switching spikes will show up all over.

You haven't specified the optoisolator. Cheap optoisolators tend to have pretty broad tolerances on the current transfer ratio, which could create problems in a real circuit.

You post a trivial circuit and want me to analyse it?

I doubt if Steve would think so. And in general, a useful way of estimating the construction cost of a circuit is simply to count the number of pins - nodes - on the circuit diagram. On that basis, your solution isn't exactly competitive.

For your value of "properly". The OP's opinion is presumably the only one that actually counts.

A wet-back is just an illegal immigrant who can be expected to work for less than the legal minimum wage.

Do you think that the people from Mexico who are - presumably - over- represented in your illegal immigrant work force - belong to a different branch of the human race than you do?

Your calling me a "racist" doesn't say anything about my attitudes to race, but it does say a mouthful about you.

-- Bill Sloman, Nijmegen

One of your test circuits uses the Fairchild MOC205 opto-isolator which offers a current transfer ratio between 40% and 80%

The other uses the Sharp PC817D

which offers between 300% and 600%. Farnell stocks it, at nearly twice the price of the 80% to 160% selection (PIC817A). This does assume that the OP is able and willing to buy stuff from a broad-line distributor.

Twenty five of these at roughly a dollar each (in small quantities) don't exactly make your solution the cheapest available.

-- Bill Sloman, Nijmegen

I know you don't know much about this newfangled digital logic, but it is a bit easier to stop the switching transients from messing up a clocked pseudo-random binary sequence generator than it is to stop them creating mutual interference between 25 555 oscillators.

Dream on. These are decorative lights. intended to be looked at, and the wiring will be all over the place.

You may have gotten lucky there, but a stopped clock is right twice a day.

You've finally noticed?

The question is whether your circuit does offer the results he wanted. You object to the pseudo-randon binary sequence generator because some of the lights will go on and off at the same time, whch you feel would not provide the degree of randomness that you imagine he wants, but your solution is very likely to leave him with 25 nominally independent oscillators, most of which are likely to self-synchronise via the switching transients, and he's got a do a lot more soldering to put your scheme together.

-- Bill Sloman, Nijmegen

Why would I post a LFSR design here? This isn't sci.electronics.basics so you can refer people to the relevant chapter in "Mastering the Art of Electronics" and leave them to get on with it.

This isn't cheating anybody who has any business posting to this group. You may not appreciate this, since it seems unlikely - based on your persistent wailing - that you could follow the Horowitz and Hill exposition, but you don't really have the expertise to contribute here anyway.

-- Bill Sloman, Nijmegen

te:

Since your idea of of offering "real help" mostly seems to involve pushing the 555, which has been obsolescent for some thirty years now, and only shows up in recycled legacy designs, some would suggest that the idiocy might lie in your point of view, which is rather restricted.

-- Bill Sloman, Nijmegen