Wikipedia:Reference desk/Archives/Science/2014 November 1

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November 1

do soundcards produce voltages below 0

if I make a sine wave in, say, Audacity, and play it, is the voltage on the soundcard's output, is it a sine line centered on the soundcrad's ground or does it lie completely above it (i.e. is there a DC component)? and if I wanted to amplify the signal using an opamp in the inverting config, what should the (+) terminal of the opamp go to to keep the signal from clipping, the ground or a voltage divider? can it go to ground if the signal is capacitor-coupled (which should remove the DC component anyway)? Thank you in advance and sorry if the questions are dumb Asmrulz (talk) 01:13, 1 November 2014 (UTC)

This is a very reasonable question!

The answer is complicated. Voltage is always measured relative to a reference. So the question you are implicitly asking is whether any sound-cards produce a negative voltage relative to some standard reference point - most probably, the main system's ground plane (or chassis, or case, or the grounded power supply safety ... or whatever). The answer is "almost certainly" yes: some system somewhere does so.

But, this is uncommon on personal-computer hardware. Most audio output amplifiers that are built into computers will produce a signal whose dc level is at or above the system ground. This kind of digital-to-analog output signal is easier to generate.

Some audio amplifiers have a floating ground. Those amplifiers are susceptible to popping, clicking, and other turn-on/turn-off transients.

If you're connecting your soundcard's audio output to a secondary amplifier, you need to look up your card's nominal output voltage and impedance. We can probably help track that kind of thing down if you know your audio card model.

For example: here's the data sheet for the Realtek ALC850, a "top of the line" AC97 audio DSP and analog output chip (this is the sort of thing that used to be soldered onto motherboards, in the era after soundcards were plug-in peripherals, but before they were built into the main logic board's chipset, i.e. before analog audio was commonly built into the silicon of the system's "south bridge" or its modern equivalent). As you can see, the analog input can be whatever you want (within reason); but the DAC output will be scaled between ground and V_DD. Unlike the amp you'd find in a really old dinosaur hi-fi system's audio system, there is definitely not a negative voltage rail.

Keep in mind that PC audio output is usually driving a headphone or a separately-powered speaker-amplifier. It only needs to generate a very low power, very low current, very low voltage signal. For such amplifiers, it is not necessary to force a zero dc-mean current or voltage; the circuit doesn't have to be balanced. If you look at big amps - like a hi-fi loudspeaker amp - there are more reasons to choose a balanced design with a positive and negative voltage supply - reasons that have to do with engineering practicalities, like line losses, parasitics, power supply noise, ground bounce, and so on.

Nimur (talk) 03:53, 1 November 2014 (UTC)

thanks! by ground I meant simply the terminal which is designated ground in the standard 3.5 mm jack (bottom ring.) I suspect it's the same as the chassis and all other ports (the D-shaped thing on the VGA connector, for example), but I just said "the soundcard's ground" in case it isn't Asmrulz (talk) 09:22, 1 November 2014 (UTC)

I just had this idea, what if the left channel was CLK and the right was data, could one transmit serial data using the soundcard (for example to drive a counter or a shift register with a 7-segment display, only to see if it works) but I need to amplify the signal to 0..5 V that TTL understands Asmrulz (talk) 09:29, 1 November 2014 (UTC)

I don't think the answer is the same for all computers. Some of them are AC coupled - meaning that the signal may vary as to where it's mid-point is over time, others are not. I've been following a Kickstarter project "The Peachy Printer" which is working on driving a crazily low-cost 3D printer from the headphone jack of a desktop or a laptop (and are now trying to get it to work with a cellphone, an MP3 player or even a radio)! They are deflecting a couple of mirrors to position a laser using the left channel of the audio for one mirror and the right channel for the other. They have run into all of the problems that you're going to hit, (and there are many) and have outlined solutions in their project updates. It would be well worth trawling through those documents - and perhaps even contacting the project owner, who seems an amenable kind of a guy. To solve some of these problems, they had to resort to using an amplitude modulation technique where they send a continuous carrier signal from the sound port in an effort to keep the voltages referenced to some kind of a standard level. SteveBaker (talk) 13:24, 1 November 2014 (UTC)

Interesting, thanks Asmrulz (talk) 18:37, 1 November 2014 (UTC)

The statement that "voltage is always measured against a reference" is incorrect or at best misleading. A simple volt meter is proof. It has two terminals and voltage is always a relative measurement between two terminals. There is no absolute voltage scale. Grounding became a practice precisely because of this. Namely, shorts to surfaces tended to place humans between dangerous potentials, whence grounding was created to make humans and other non-terminals at a known potential as well as a creating an interruptible fault before killing someone. The point of "ground" is that if another terminal shorts to it, the fault protection will kick in and the stray voltage eliminated. You can certainly find balanced audio amplifiers that are 3 terminal but ground isn't a signal terminal. You can also find audio transformers (1:1) that can isolate circuitry (Midcom used to make them a long time ago for telephones and other applications). The drawback of 1 terminal being grounded is that the impedance is different for each terminal and noise will couple differently. Matched impedance makes the noise common mode. --DHeyward (talk) 00:53, 2 November 2014 (UTC)

That's more a matter of linguistics. The voltmeter can be said to measure against a reference that's determined by placing the black probe onto that reference and the red probe against the thing you want to measure. The black probe is the way you tell the voltmeter what the reference is. If you put the black probe on the signal wire and the red probe onto the ground pin, you'll get some negative voltage - but what you're doing is using the signal as the "reference" and measuring the ground voltage relative to that reference. The point here is that it is utterly meaningless to say "This wire is at 5 volts" unless you say "5 volts relative to ground" or "5 volts relative to this other wire". In most circuits, the implied reference is "ground" - but if you have a laptop and you're looking at the audio output, the voltage is relative to the ground pin on the connector - which may be wildly different to the ground of the thing you're connecting it to...or (in principle) different from (say) the negative terminal of the laptop's battery. SteveBaker (talk) 14:42, 3 November 2014 (UTC)

I think the "reference potential" for a portable multimeter is (definitionally) "the black probe, or whatever the black probe is touching." My statement shouldn't be interpreted to mean that the reference-point is guaranteed to be a good choice - only that the voltage of some other position is only a meaningful number in comparison to a reference (any reference, where-ever it may be). I apologize if this was a confusing choice of terminology.

It's the same way that tape-measures are used to measure distance, relative to a reference datum. If you tried to measure the distance to a point, and you just left one end of the tape measure flopping around, ... you'd still measure a "distance," but it would be an irrelevant distance. You'd probably want to hold the first end of the tape measure against some meaningful reference-point. Nimur (talk) 16:26, 3 November 2014 (UTC)

It seems like the question is trying to send digital data through an audio port. The first problem is how you could actually send the data, you will probably need to encode the data in one Audio file format. There is a big difference between digital and analog signals. Digital signals switch between two values something like a square wave. Trying to send a square wave through a sound card would cause a lot of problem - there would be a lot of distortion, a steady state signal might not actually appear. You might be better using a Modulation technique, like the way modems switch the frequency of a sin wave down audio phone lines.--Salix alba (talk): 23:47, 2 November 2014 (UTC)

I thought sine waves plus schmitt triggers on the input. Asmrulz (talk) 09:12, 3 November 2014 (UTC)

Yes, obviously to do a GREAT job of sending digital data through an audio channel, you're essentially re-inventing a good old-fashioned 56 kbaud audio-frequency modem such as you can still find in Fax machines and such. And if you do that, you'll get a baud rate in the tens of kilohertz range. But to build that yourself requires an actual modem chip and probably some external discrete components...or maybe you can do it with a lot of fancy software. If you need just low speed communication (hertz, but not kilohertz) and minimal external hardware - then maybe using the sound port without modulation will work well enough. SteveBaker (talk) 21:23, 3 November 2014 (UTC)

I think there are much simpler methods than what dialup modems use(d) (Trellis, QAM etc), such as FSK. But yes, I'd like to try with no modulation first. As you and User:Salix alba rightly noted, the soundcard can't produce steady voltage, but it doesn't have to because I'm only sending short pulses Asmrulz (talk) 02:18, 4 November 2014 (UTC)

Langer VS Hamburger invention

How can it be that Hratog Hamburger invented the saline only in 1896 while Langer invented the Langer's solution in 1882? (both of the information are from Wiki). In addition, Is Hartog Hamburger considered the first who discover the levels of the salt in our bodies before Langer? "Normal saline was invented by Dutch physiologist Hartog Hamburger in 1896. Hamburger's solution was only intended for in vitro study of RBC lysis and was never intended for clinical use.". In the next source, it also appears in reverse chronological order - I don't know why. 213.57.114.161 (talk) 14:39, 1 November 2014 (UTC)

Ringer's solution (not "Langer's", incidentally), is a rather ad-hoc mixture of electrolytes, which is isotonic with human blood. What Hamburger did was to establish that a normal solution of sodium chloride only (with no other electrolytes) could also be used for medical purposes. It would be more accurate to say that Hamburger invented the medical use of normal saline, rather than that he invented the actual substance. Tevildo (talk) 02:28, 2 November 2014 (UTC)

Soviet spacecraft atmosphere

I was going over the Valentin Bondarenko article. His story, of course, bears some tragic similarities to the fates of Grissom, White, and Chaffee in Apollo 1—both were the result of fires that engulfed the (in the American case, 100%, and at least 50% in Bondarenko's case) oxygen atmosphere that was apparently not thought to be a terrible idea (launch weight was the primary concern, as I understand it). After Apollo 1, NASA realized that it actually was a terrible idea, and began using a nitrogen-oxygen mixture roughly similar to earth atmosphere. What I haven't been able to find any record of is when the Soviet space authorities did the same. Did Vostok 1 launch with a primarily oxygen atmosphere? If so, when did (or did) the Soviets switch to a less-likely-to-result-in-fire-and-death American-style atmospheric mixture? Evan ^{(talk|contribs)} 18:51, 1 November 2014 (UTC)

Did NASA switch to a nitrogen-oxygen mixture during flight for the later Apollo capsules? My understanding (and I've not been able to locate a reference yet) is that while they switched over to nitrogen-oxygen while on the ground (to avoiding the super-flammability induced by 100% oxygen at 1.15 bar), they ran 100% oxygen at low pressure during flight. I'll keep looking, but I'd appreciate it if anyone can point me to some references which discuss atmosphere content and pressure for various spacecraft (particularly the post Apollo-1 capsules), and what hardware and procedural changes were implemented to support this. For instance, did the crew pre-breathe pure oxygen via masks while on the pad to avoid decompression sickness when the cabin pressure dropped during ascent, what was done to keep any oxygen leaks around their mask from increasing the oxygen content in the capsule during the countdown, and what was done to purge the nitrogen in the cabin once the pressure dropped to flight level. -- 190.58.249.5 (talk) 01:50, 2 November 2014 (UTC)

Bondarenko's accident occurred on "the tenth day of a 15-day endurance experiment in a low pressure altitude chamber ... . The chamber's atmosphere was at least 50% oxygen." This means that the chamber could have been pressurized to only 0.4 bar and still be normoxic (0.2 bar partial pressure oxygen). Is it publicly know what the pressure was? -- 190.58.249.5 (talk) 01:59, 2 November 2014 (UTC)

Offhand: I don't know about the USSR spacecraft. My memory is that after the Apollo 1 fire, they used regular air at a slightly increased pressure - 15.something PSI instead of 14.7. And once they were in space they gradually switched over to pure oxygen at lower pressure, something 3-4 PSI. I'll try to look it up. Bubba73 ^{You talkin' to me?} 02:30, 2 November 2014 (UTC)

It is an interesting story. After the Apollo fire, when it was on the ground they used 60% nitrogen and 40% oxygen, at 10% or so above normal pressure. They could not use low pressure on the ground because the spacecraft was not designed for that pressure from the outside. If was pressurized above normal pressure to check for leaks. As the rocket ascended, when the pressure outside dropped to 60% of sea-level pressure, they started bleeding off the nitrogen/oxygen mix, while maintaining 40% of seal-level pressure. By the time it reached orbit, the pressure was about 35% of sea-level pressure, and most of the nitrogen was gone. Then they maintained about 35% pressure of almost pure oxygen.

From How Apollo Flew to the Moon, pp. 170-72. Bubba73 ^{You talkin' to me?} 02:51, 2 November 2014 (UTC)

When I've heard Apollo 1's story told, it has always been emphasized that the high pressure pure oxygen atmosphere was what caused the increased flammability, and it is usually implied (and occasionally stated outright) that at a lower pressure (as during flight) the 100% oxygen atmosphere would not have been a problem. I was therefore very surprised when I was reading NASA's Recommendations for Exploration Spacecraft Internal Atmospheres and ran across this:

By contrast with human respiration that depends primarily on oxygen partial pressure in the atmosphere, materials flammability depends strongly on oxygen concentration (volume percent) and to a lesser extent on total pressure. (pg 11)

So I asked about that here two weeks ago, and while Stephan Schulz provided a couple mechanisms as to how the addition of inert gases could reduce flammability in a atmosphere where the partial pressure of O₂ remained constant, no references were provided either for the mechanisms or giving any numbers or graphs showing the magnitude of the effect on flammability of pO₂ compared to %O₂. For instance, what percent O₂ in a 1.0 bar O₂/N₂ atmosphere yields the same flammability in various substances as a 100% O₂ 0.21 bar atmosphere? -- 190.58.249.5 (talk) 03:12, 2 November 2014 (UTC)

Well, one reason that it was thought that 100% oxygen in space would not be a fire hazard is because that it was thought that a fire in zero-G could not be sustained. On Earth, the CO₂ produced goes up and away. In zero-G it was thought that it would stay around the flame and deprive it of oxygen. In tests in the space shuttle, I think they found that this isn't exactly true. Bubba73 ^{You talkin' to me?} 03:51, 2 November 2014 (UTC)

The NASA document isn't inconsistent, it just fixes a different knob than the one you are used to turning and comparing. If, say, you fix the number of oxygen molecules in the capsule so that it's the same number as a 30%, 1 Atmosphere, the resulting 100% oxygen, low pressure environment will be more flammable than the 1 Atm case. This is because the amount of vapor from the object that will burn will increase in both the lower pressure case and also heat will need to be added to keep the temperature constant. The key to understanding the statement is that the partial pressure of oxygen and cabin temps must be habitable. Over that range of pressures/temps, flammability will be determined by how much fuel vapor is available. It is much more sensitive to concentration than pressure because of the added heat and the lower overall pressure in the high percentage case. The higher the concentration of oxygen, the more vapor will be available since the cabin pressure will drop and heat will be added to maintain temperature. Think of a petrol can that is sealed at 1 Atmosphere. Start pumping out only nitrogen molecules. Add heat to keep the temperature constant. That's my take, anyway. --DHeyward (talk) 08:41, 2 November 2014 (UTC)

Well stated. Still, I'd like to see some data.

Regarding the OP's question about Soviet spacecraft, our Soyuz and Voskhod articles indicate that they both used O₂/N₂ at 1.0 bar, and the Voskhod first flew in 1964, three and a half years after Bondarenko's death. Our Vostok article does not give atmosphere information. (Has that information been published?) Vostok 1 with Gagarin flew only three weeks after Bondarenko's death, so there wouldn't have been time to redesign the capsule to take advantage of lessons learned. And back to Apollo, our Apollo–Soyuz Test Project article mentions the need for an airlock connecting the two capsules "as the Apollo was pressurized at 5.0 psi using pure oxygen, while the Soyuz used a nitrogen/oxygen atmosphere at sea level pressure". It goes on to mention that the Soyuz was modified to "operate, during the docking phase, at a reduced nitrogen/oxygen pressure of 10.2 psi, allowing easier transfers between the Apollo and Soyuz". -- 190.58.249.5 (talk) 12:33, 2 November 2014 (UTC)

Thanks for the replies, everybody. It is definitely interesting that the Soviets started using nitrogen-oxygen mixtures before NASA did, and it does raise the question as to how NASA engineers would have reacted had they known. With all the "disappearing cosmonaut" rumors that were floating about it is disappointing, if not quite surprising, that there wasn't enough flow of information across the Curtain to result in NASA catching on. Evan ^{(talk|contribs)} 18:34, 2 November 2014 (UTC)

Through Apollo, they used nitrogen/oxygen only on the ground. Before an Apollo was very high in the atmosphere, they started venting that and replacing is with oxygen at lower pressure (see above). Bubba73 ^{You talkin' to me?} 23:02, 2 November 2014 (UTC)

I saw. The significance of pressure and partial pressure vis a vis flammability isn't quite what I expected. Evan ^{(talk|contribs)} 01:48, 3 November 2014 (UTC)

One thing I always wondered about was why they didn't fill the capsule with 100% oxygen at low pressure prior to launch, to reduce the weight. Some thoughts:

1) As noted above, while less flammable than 100% oxygen at 1 atm, it's still worse than normal air at 1 atm.

2) This would require an additional procedure to depressurize the capsule after the crew enters, and repressurize it if the mission is aborted, complicating the launch process.

3) The capsule is meant to withstand pressure differentials, but only with higher pressure inside the capsule than outside. Reversing that may not work. Engineering it to withstand differentials in both directions might very well add more weight than would be saved. StuRat (talk) 13:06, 5 November 2014 (UTC)

Why don't dogs and cats get sick from licking, tasting, and even eating everything?

Dogs and cats constantly lick, taste, and even eat or drink many things that are usually considered unhygienic to humans: their own anus and the anus of other animals, their own feces and the feces of other animals, mud, shoe soles, dirty water, dirty balls and other dirty toys, garbage, etc. Why don't they get sick when humans doing the same thing would? —SeekingAnswers (reply) 20:56, 1 November 2014 (UTC)

They do pass on some diseases that way, but they just live with them. Humans sometimes do too! Most of us in the developed world are over-fussy about hygiene. Dbfirs 21:05, 1 November 2014 (UTC)

Most carnivores don't take apart their prey with flint knives (or better). They tear into the guts of an animal with apparent pleasure. Usually a mighty "predator", such as a wolf, is in reality part predator, more scavenger, and spends a lot of time eating scats (feces) it encounters. One visible difference of humans from most other mammals is in the stomach, which is much simplified, reflecting the substitution of fussy primate behaviors. Humans also have dramatically reduced odor-sensing capabilities (many mutated odorant receptors) ... hmmm, I wonder if this makes it harder for us to tell "good" rotten meat from "bad" rotten meat than it is for dogs? The simplest bottom line though is that most species are very well adapted to survive doing what they do - humans, a species of recent origin and ever-changing behavior, being a most notable exception.

That said, also recall felching. There are more things in heaven and earth..... Wnt (talk) 22:07, 1 November 2014 (UTC)

Supposedly, antifreeze tastes good to dogs, who will eagerly lap it up and then die from it. Or for that matter, chocolate. So they're not immune to everything. ←Baseball Bugs ^{What's up, Doc?} carrots→ 22:12, 1 November 2014 (UTC)

According to Mogens Eliasen's book:"Raw Food For Dogs - the Ultimate Guide for Dog Owners" in order to digest the large chunks of raw food that they swallow without much chewing, a dog's stomach produces very acidic digestive juices with a pH between 1 and 2, compared to a pH of 5 in humans. This is why they can eat things we can't. However, dogs do often end up being operated on to remove things they've eaten, such as shoe soles and rubber balls that they can't digest. I'm not sure though if this lower pH also breaks down toxins from bacteria. I do have a question about the original post though - why do you think we need links to dogs, cats, lick, taste and the other fourteen common terms you've linked? Richerman (talk) 22:59, 1 November 2014 (UTC)

Our article on gastric acid suggests that the pH in a human's stomach ranges from 1.5 to 3.5, not 5. Matt Deres (talk) 00:47, 2 November 2014 (UTC)

Hmm... it says that here too. I don't know where Eliansen gets 5 from. Richerman (talk) 01:08, 2 November 2014 (UTC)

Bear Grylls has demonstrated that you can actually violate pretty much most of the hygiene rules we stick to when living in the Wild: "The show has featured stunts including Grylls climbing cliffs, parachuting from helicopters, balloons, and planes, paragliding, ice climbing, running through a forest fire, wading rapids, eating snakes, wrapping his urine-soaked t-shirt around his head to help stave off the desert heat, drinking urine saved in a rattlesnake skin, drinking fecal liquid from elephant dung, eating deer droppings, wrestling alligators, field dressing a camel carcass and drinking water from it, eating various "creepy crawlies" [insects], utilising the corpse of a sheep as a sleeping bag and flotation device, free climbing waterfalls and using a bird guano/water enema for hydration.[41][42] Grylls also regales the viewer with tales of adventurers stranded or killed in the wilderness." Count Iblis (talk) 03:36, 2 November 2014 (UTC)

a truly terrible example. He has been hospitalised after filming his shows.Greglocock (talk) 21:24, 3 November 2014 (UTC)

Well, you can't trust everything you see on TV. The article you linked mentions something with a pony... in all seriousness, which do you think would be more repugnant to a TV producer: faking eating elephant dung (bear dung, etc.), or actually eating it? Though I suppose in a sense it's irrelevant -- it's not that eating these things can't be done, just that bad things could happen (Giardiasis being an obvious one that Grylls might conceivably have built up an immunity to at some point?) So whether he fakes it or he simply tries it for the show and gets lucky, the take-home is the same: still not a good idea. Wnt (talk) 04:55, 2 November 2014 (UTC)

Human babys also put allot in their mouth that is everything but "hygienic" without getting sick. On the long run Hygiene gives the impression to "pay out" statistically because it is simply a reduction of possible danger tho medicine tells us today that an Immune system decays if it is not burdened and the rising medical problem of Allergy may often be caused by tomuch Hygiene. --Kharon (talk) 05:08, 2 November 2014 (UTC)

Be careful. Some children do indeed put things in their mouths that harm them. ←Baseball Bugs ^{What's up, Doc?} carrots→ 07:03, 2 November 2014 (UTC)

Unfortunately indeed children to often die from chocking but that probably really happes most with completely hygienic items. --Kharon (talk) 23:18, 2 November 2014 (UTC)

Intestinal flora varies throughout the world. Montezuma's revenge is not mythical but reflects the difference in flora between different countries food supply. This gastro affliction is rarely fatal and takes a few weeks for adjustment. The same is likely true for other species. Once adapted to the local microbes, there is little effect and adaptation is not fatal in most cases. Humans tend to avoid getting getting sick and measure success by not getting sick. We are not so kind to animals, though. Dogs and cats get sick all the time and have the runs or vomit regularly yet unless they are dying from it we don't pay much attention. They may very well be suffering from their lack of hygiene but we simply don't notice/don't care about "Montezuma's revenge" in a dog the same way we feel sorry for (and track it) in humans. --DHeyward (talk) 06:33, 2 November 2014 (UTC)

Dogs and cats barf all the time. I know two dogs that died from some sort of food poisoning (one seems to have been intentional, the other accidental), and one that had to be operated on after eating a turkey carcass out of the trash. Where is the citation that supports a claim that such animals don't get sick form food poisoning or related illnesses? μηδείς (talk) 20:28, 2 November 2014 (UTC)

I agree. Another thing is that dogs, in particular, are able to suffer large amounts of pain without showing any obvious signs that they are suffering. We humans communicate even the slightest stomach discomfort to anyone who'll listen. So we tend to be more sensitive to things that upset our digestive system than we are to that in our dogs...so we assume that they don't get digestive problems when eating food that we wouldn't touch. SteveBaker (talk) 14:33, 3 November 2014 (UTC)

I'm with Count Iblis on this one. A TV show isn't the best example, but many humans survived just fine without modern sanitary practices. Sure, hygiene can be important, and it has saved many lives, especially in hospitals. But for daily routines, humans (and human babies) can eat and lick all sorts of things without necessarily becoming ill. You might be interested in reading up on the hygiene hypothesis, which is what [[User:Kharon was getting at above. It describes how, in some situations, avoidance of contaminants can be harmful to immune systems. SemanticMantis (talk) 15:29, 3 November 2014 (UTC)

Some points:

1) Intestinal parasites do seem to be more common in animals that are careless about what they eat.

2) Indigestion seems to be more common too. As noted, such animals regularly vomit.

3) Acid from a puking dog actually dissolved the pattern off my brother's linoleum floor, so it's pretty acidic all right.

4) During periods of starvation, it makes sense to take more risks with what you eat, as starving to death is more likely than dying from what you eat.

5) People in undeveloped nations often live in less clean environments, and do suffer from more infectious diseases and have a much lower life expectancy as a result (lack of medical care probably has some effect here, too). However, they still manage to survive long enough to reproduce. They may well have fewer allergies (although some of that might just be that people who are sick all the time don't much notice allergies), but I'd still take the longer life expectancy along with allergies any day. StuRat (talk) 12:55, 5 November 2014 (UTC)