Search found 104 matches

by pnyxtr
Tue Nov 15, 2011 1:39 am UTC
Forum: Science
Topic: Need a variable resistor/load to test solar panel power
Replies: 6
Views: 3110

Re: Need a variable resistor/load to test solar panel power

Seriously. This is a textbook case of asking for something so wrong it's hard to answer.

Especially: " What we would like to have is a 1 megaohm variable resistor which is rated at up to 180W, up to 48V, and up to 10A"
What. The. Fuck.

Do you really want something the size of a car?
by pnyxtr
Tue Nov 15, 2011 1:14 am UTC
Forum: Science
Topic: Kelvin vs. Celsius
Replies: 60
Views: 13973

Re: Kelvin vs. Celsius

Pfft! 30°C is nothing. :) It's not unusual during a hot spell here for the temperature to stay above 30°C for several days in a row, although I will admit it's not so easy to get to sleep in weather like that without air conditioning. I'm currently living in the sub-tropical part of Australia, but ...
by pnyxtr
Mon Nov 14, 2011 11:25 pm UTC
Forum: Science
Topic: Electronic equivalent of a syphon
Replies: 11
Views: 3857

Re: Electronic equivalent of a syphon

They couldn't come up with a lamer name for it?

Edit: To people who know a little bit what they're doing, that would be a self-resonant flyback converter. A somewhat unusual beast (and for good reason), but it's quite obvious what it does just from looking at it.
by pnyxtr
Fri Nov 11, 2011 9:54 pm UTC
Forum: Science
Topic: Electronic equivalent of a syphon
Replies: 11
Views: 3857

Re: Electronic equivalent of a syphon

If you made what's usually known as a "Vbe multiplier", only with a MOSFET instead of a bipolar transistor, you'd get a "Vgs multiplier" instead. And those can be made to draw ridiculously low current. The problem is that Vgs has a lot larger spread over different devices than Vb...
by pnyxtr
Fri Nov 11, 2011 9:47 pm UTC
Forum: Science
Topic: Kelvin vs. Celsius
Replies: 60
Views: 13973

Re: Kelvin vs. Celsius

I used to have to think a little about this stuff whenever someone asked. But after having made control systems for cryocoolers for a couple of years, Celcius isn't more natural to me than Kelvin, it's obvious that it's just popular because it's a quite convenient scale for people. (The reasons for ...
by pnyxtr
Sat Jun 04, 2011 6:17 pm UTC
Forum: Hardware
Topic: Ground Plane
Replies: 9
Views: 3638

Re: Ground Plane

Old USB is not high-speed digital. 12Mbit signals are practically DC, as far as I'm concerned.
by pnyxtr
Fri May 20, 2011 1:41 am UTC
Forum: Hardware
Topic: hardware recommendations
Replies: 21
Views: 4352

Re: hardware recommendations

Oh, man... You have a disaster in the making, there. He actually *wants* to control real things in perl? I was forced to, once, and I still shudder at the thought. (Well, to be honest, I was the one who forced me to. But let's pretend that did not happen.) And the only thing I can think of that he c...
by pnyxtr
Tue May 10, 2011 7:45 pm UTC
Forum: Hardware
Topic: Electronics Education and Experimentation
Replies: 13
Views: 6595

Re: Electronics Education and Experimentation

LTSpice is The Shit(tm). I'm not saying this just because it's free. I'm often tasked with designing the DC/DC parts for things the sell for a couple 10k$ up to... a magnitude more, at least. And I would have no whatsoever problem getting one or three of the commercial simulators. It's just that, I ...
by pnyxtr
Sun May 08, 2011 4:49 pm UTC
Forum: Science
Topic: Neurotoxin as a Preservative
Replies: 14
Views: 3169

Re: Neurotoxin as a Preservative

As long as you're going for that sort of thing, you might as well theorise that the rooms were held at very low temperatures all that time. It would probably be much more effective than removing the air (though, not as efficient, it would probably require a lot more energy).
by pnyxtr
Sat May 07, 2011 1:44 am UTC
Forum: Hardware
Topic: New Headphone Recommendations
Replies: 17
Views: 2545

Re: New Headphone Recommendations

I've used a pair of HD555 for my everyday 'phones for years. They're seriously good value, and comfier than they look (the look is a little too plasticky for my taste). I can have them on for a day without even playing anything and completely forget that they're there. Sure makes me feel pretty stup...
by pnyxtr
Wed May 04, 2011 12:39 am UTC
Forum: Science
Topic: Ghosts at 19hz?
Replies: 15
Views: 10563

Re: Ghosts at 19hz?

19Hz is _not_inaudible. It is, however, much less audible than things that are a little higher in frequency.
It's not an on and off thing, hearing is not a brickwall filter at 20Hz and 20kHz, like a lot of fools seem
to think.
by pnyxtr
Tue Apr 12, 2011 11:33 pm UTC
Forum: Language/Linguistics
Topic: Varsågoda och ... tala svenska! [Swedish Practice]
Replies: 41
Views: 13634

Re: Varsågoda och ... tala svenska! [Swedish Practice]

Självklart betyder det inte så mycket för förståelsen, om man brukar en fel artikel. Även om det ju är bäst att kunna språket helt korrekt, tycker jag att det är viktigast, att man bara förstår varandra inom dom skandinaviska länderna, och man skall inte vara rädd för at säga eller skriva något fel...
by pnyxtr
Sun Apr 03, 2011 1:11 am UTC
Forum: Language/Linguistics
Topic: Varsågoda och ... tala svenska! [Swedish Practice]
Replies: 41
Views: 13634

Re: Varsågoda och ... tala svenska! [Swedish Practice]

Du skriver jäkligt bra, måste jag säga, även om du missar några småsaker. Till exempel finns inte fordi över huvud taget på svenska (det blir formellt "därför att", mer informellt "för att"). Däremot så undrar jag (eftersom jag förstår precis vad du menar) om det inte finns på no...
by pnyxtr
Sun Apr 03, 2011 12:21 am UTC
Forum: Science
Topic: Lasers, and focusing optics
Replies: 14
Views: 1905

Re: Lasers, and focusing optics

I think the ambient light saturation problem can be solved by putting the receiver at the bottom of a tube, if it does become an issue. The only high frequency noise source I can think of at the moment is fluorescent lights, depending on how the ballast is built. However, that can hopefully be solv...
by pnyxtr
Sat Apr 02, 2011 10:32 pm UTC
Forum: Science
Topic: Lasers, and focusing optics
Replies: 14
Views: 1905

Re: Lasers, and focusing optics

Ordinary remote controls use a trick to improve reception range that might be useful if you run into serious problems with the reception. The light signal is modulated as a continuous carrier wave at around 40kHz, and then the data signal turns the carrier wave on and off. The reciever has a tuned ...
by pnyxtr
Wed Mar 30, 2011 10:58 pm UTC
Forum: Science
Topic: Lasers, and focusing optics
Replies: 14
Views: 1905

Re: Lasers, and focusing optics

You are correct in much, and I am correct in much too. Just for reference, I build infrared cameras. (No, not "near" IR.) Which apparently means we approach the subject from two quite different directions. This is, of course, a Good Thing(tm). (I did build a zoom for 890nm recently, though...
by pnyxtr
Wed Mar 30, 2011 9:44 pm UTC
Forum: Science
Topic: Lasers, and focusing optics
Replies: 14
Views: 1905

Re: Lasers, and focusing optics

1) Beg, borrow or steal (probably best if you stick to the first three*( a telescope, binocular, spotting scope, or gun scope. Focus on y'all's transmitter (laser OFF), then swap the detector in place of the eye. A bit of fiddling could focus the beam on the detector, greatly extending y'all's rang...
by pnyxtr
Wed Mar 30, 2011 8:43 pm UTC
Forum: Hardware
Topic: hardware recommendations
Replies: 21
Views: 4352

Re: hardware recommendations

My point isn't that the article is bad, or that you yourself suck at control systems. My point is that in order to have a complete novice design a control system, even just one that's barely good enough for a simple system (and good enough == good, by my standards, even if it's barely), you need a l...
by pnyxtr
Wed Mar 30, 2011 7:44 pm UTC
Forum: Science
Topic: Lasers, and focusing optics
Replies: 14
Views: 1905

Re: Lasers, and focusing optics

#1 depends entirely on how you drive it, at least at the speeds you're going for. It's rarely a limitation of the diode itself, you'll just have to read the data sheet of the module. I've used kinds that could be modulated on and off at 10Hz or so, at best, and I've used kinds that go to 17 bazillio...
by pnyxtr
Fri Mar 25, 2011 3:28 am UTC
Forum: Hardware
Topic: EE Project Help
Replies: 16
Views: 3561

Re: EE Project Help

You know, you can pretty much always get components for free, at uni or at work, as long as it's just one or two. (Not that that matters to me, I just have to make sure the components don't cost, like, a hundred bucks.)
But 10 bucks for a D/A? They were obviously clueless in the extreme.
by pnyxtr
Fri Mar 25, 2011 2:25 am UTC
Forum: Hardware
Topic: EE Project Help
Replies: 16
Views: 3561

Re: EE Project Help

Why are some people here so hell bent on resistor ladders? A D/A in (say) SOT23-6 is hella smaller and magnitudes better. I wouldn't be surprised if it was also cheaper.
by pnyxtr
Fri Mar 25, 2011 1:34 am UTC
Forum: Hardware
Topic: hardware recommendations
Replies: 21
Views: 4352

Re: hardware recommendations

It's not that hard. I'm sure your typical programmer would have no problem independently inventing proportional control just by thinking it through. All the additional knowledge you need is probably just derivative and integral control and how to tune it, which is easily found on the wikipedia page...
by pnyxtr
Sun Mar 20, 2011 12:47 am UTC
Forum: Hardware
Topic: simple pic microntoller question
Replies: 3
Views: 1362

Re: simple pic microntoller question

If your PIC uses the same supply voltage as your LCD (5V, perhaps?), then they should work fine together, no need for level translating buffers.

(This is much oversimplified, of course. But if you know enough to pick nits about it, you also know why I didn't want to complicate it further.)
by pnyxtr
Sun Mar 20, 2011 12:38 am UTC
Forum: Hardware
Topic: hardware recommendations
Replies: 21
Views: 4352

Re: hardware recommendations

[...]Now, the problem my friends and I are having is... well, we're all computer science majors. And our education hasn't even been that high on programming/computers. It's been 90% theory and such. But we feel we have a handle on the code. The problem we have is, we're not electrical engineers and...
by pnyxtr
Sun Mar 20, 2011 12:07 am UTC
Forum: Science
Topic: Cooling Avalanche Photodiodes to Run in Geiger Mode
Replies: 24
Views: 2891

Re: Cooling Avalanche Photodiodes to Run in Geiger Mode

We need our dark counts to be as low as possible. We don't really have a problem with afterpulsing, as we are looking for coincidences of entangled photons, and we just adjust the width of the logic pulse on our discriminator to compensate for any afterpulsing. Also: We are using passive quenching....
by pnyxtr
Sat Mar 05, 2011 12:05 am UTC
Forum: Science
Topic: Voltages (International Differences, and Dangers Therein)
Replies: 34
Views: 3309

Re: Voltages (International Differences, and Dangers Therein

I looked a bit for that, and it appears a lot of electricity companies actually synchronize the grid with a very precise clock. In the 50s and 60s, accurate clocks were expensive, and many official buildings and schools used clocks synchronized on the grid. Reducing or increasing the grid frequency...
by pnyxtr
Fri Mar 04, 2011 11:36 pm UTC
Forum: Science
Topic: Cooling Avalanche Photodiodes to Run in Geiger Mode
Replies: 24
Views: 2891

Re: Cooling Avalanche Photodiodes to Run in Geiger Mode

What kind of budget are you on, anyway? I cool down stuff to below liquid nitrogen temperatures all the time. (In fact, part of my job consists of keeping things within, say, 65,002 K and 64,998K, but let's not get into the details of that. Much because the security people would be very cross with m...
by pnyxtr
Fri Mar 04, 2011 11:18 pm UTC
Forum: Hardware
Topic: Ground Plane
Replies: 9
Views: 3638

Re: Ground Plane

Umm, I think the "what" is the circuit board. He clearly stated it is a double-sided board - i.e. only two copper layers. dukederek: you really don't give enough information about your design for anyone to give you the right answer - there is no single right answer. I can offer some initi...
by pnyxtr
Fri Mar 04, 2011 11:10 pm UTC
Forum: Hardware
Topic: What's with all these electronics questions?
Replies: 13
Views: 4047

Re: What's with all these electronics questions?

If you can't change it other than by manual labour, it's hardware. Which most definitely makes electronics hardware.
by pnyxtr
Fri Mar 04, 2011 11:06 pm UTC
Forum: Hardware
Topic: Magnetic core memory: Just like mom used to make!
Replies: 33
Views: 18093

Re: Magnetic core memory: Just like mom used to make!

so, to apply a zero, you would apply a voltage in the opposite direction of the voltage you apply to make a 1? Sort of. You would apply a flux to the core in the opposite direction. Which usually means you would apply a current. But I see lots of opportunities for controlling flux by doing a consta...
by pnyxtr
Fri Feb 18, 2011 10:49 pm UTC
Forum: Science
Topic: Voltages (International Differences, and Dangers Therein)
Replies: 34
Views: 3309

Re: Voltages (International Differences, and Dangers Therein

More specifically, this particular kind is normally described with "off line switched power supply" (no, not offline). In jargon it's usually just "switcher" or "AC/DC" or something equally short. (No point in jargon if things end up with longer names, after all.) Anywa...
by pnyxtr
Wed Feb 16, 2011 10:56 pm UTC
Forum: Science
Topic: Voltages (International Differences, and Dangers Therein)
Replies: 34
Views: 3309

Re: Volatges (International Differences, and Dangers Therein

You know, if a clock can run on either 120 or 230V, it would have to be maldesigned to an almost criminal degree if it didn't also autosense 50 or 60Hz. (It's quite easy, I assure you.) But you'd be quite right if what you meant was that it's probably not as simple as using a 230->120V transformer ...
by pnyxtr
Wed Feb 16, 2011 9:16 pm UTC
Forum: Hardware
Topic: Magnetic core memory: Just like mom used to make!
Replies: 33
Views: 18093

Re: Magnetic core memory: Just like mom used to make!

A core dump where this kind of computer is concerned means a bunch of little ferromagnetic rings dropping into your hand. (Sorry, had to say it.) Anyway, this is even older than most core memories I've seen (I have seen a couple of different kinds in real life). And a filename like "kernspeiche...
by pnyxtr
Fri Jun 11, 2010 11:19 pm UTC
Forum: Science
Topic: Relay troubles
Replies: 8
Views: 754

Re: Relay troubles

Normally, for huge and fast pulse currents, you'd use a thyristor. I've used them in the past to do kA pulses with little difficulty. But you know... As usual, I have to question why you think you need to solve the problem in this particular way. It would be a far better question if you asked how to...
by pnyxtr
Fri Jun 11, 2010 11:09 pm UTC
Forum: Hardware
Topic: simple audio amp
Replies: 7
Views: 1367

Re: simple audio amp

You people are probably trying to help, but you're doing a very poor job of it. Don't confuse the poor guy with smokescreens like that. Anyway, there's no reason whatsoever for you to make a -something volt supply. A bridged amp is the way to go for this, and what you need is just more voltage, not ...
by pnyxtr
Wed Jun 09, 2010 9:28 pm UTC
Forum: Science
Topic: Laser power supply ?
Replies: 4
Views: 801

Re: Laser power supply ?

Hmm... Are you sure you actually need modulation? That complicates matters quite a bit, and it seemed from your answer that you just sort of wanted it if it was free. From the other answers, I can at least draw the conclusion that you need something switched, probably a SEPIC. (Or you'd be totally s...
by pnyxtr
Mon Jun 07, 2010 7:43 pm UTC
Forum: Science
Topic: Laser power supply ?
Replies: 4
Views: 801

Re: Laser power supply ?

You're missing a couple of requirements in your question. How (not) heavy? How small? What kind of supply does it have to work from? What temp range does it have to tolerate? Are you going to modulate the output? And, perhaps the most important one, how much electronics are you prepared to build rat...
by pnyxtr
Mon Jun 07, 2010 4:12 pm UTC
Forum: Hardware
Topic: Noninverting amplifiers and measuring resistance
Replies: 10
Views: 2657

Re: Noninverting amplifiers and measuring resistance

Hard to say how effective your internal shielding will be, it depends on which way the noise couples over. If it's capacitive coupling, aluminium foil will do fairly fine. It seems that by far the most noise you'll get in this application will couple over the wires, and shielding will do little or n...
by pnyxtr
Mon Jun 07, 2010 3:04 pm UTC
Forum: Hardware
Topic: Noninverting amplifiers and measuring resistance
Replies: 10
Views: 2657

Re: Noninverting amplifiers and measuring resistance

Well, cutoff frequency for an RC filter is 1/(2*pi*R*C). Or as an example, R=3k3, C=100n gives a cutoff frequency of 483Hz, which might not be a bad place to start. The RC filter is a good idea to have even if you use the buffer. Then it's only used for its filtering abilites, though, not to provide...
by pnyxtr
Sun Jun 06, 2010 7:18 pm UTC
Forum: Hardware
Topic: Noninverting amplifiers and measuring resistance
Replies: 10
Views: 2657

Re: Noninverting amplifiers and measuring resistance

They're usually pretty high impedance at DC , but it's not at all a given that they are at frequencies above that, where the A/D converter does its work. You might very well be able to get away with just an RC filter instead, though, where the filter capacitor will supply the all the tiny fast curre...

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