Dan's Data letters #142
Publication date: 4 March 2005.Last modified 03-Dec-2011.
Noises, desired and otherwise
I have an Asus M5200n laptop running Debian Sarge. I have a Celeron III box as a Debian server that is plugged into a "Something from the early 80s with wood panels" amplifier.
While the laptop is plugged into the mains power I get really bad static through the speakers plugged into the "Something from the early 80s with wood panels" amplifier. I only have one power point in the room, and seven powerboards. Can you think of any way of stopping the interference?
Also, how can I plug the line-in from the "Something from the early 80s with wood panels" into the headphone jack of the laptop rather than the Celeron based Sound Blaster Live card, for watching movies? Or do I just have to get an external USB sound card?
Gareth
Answer:
The static is noise from the laptop's switching power supply. Wrapping the power brick and/or the receiver in earthed
aluminium foil may deal with the problem, but is not the world's most elegant solution. The RFI is probably being
emitted by the laptop's power cord - probably the DC portion, but maybe the AC portion as well - so try getting some
ferrite beads from an electronics store (Jaycar have plenty) and running the
cable through them. You can get hinged snap-on ones, and solid ones that're only usable if you can thread the cable
through their holes (you can also make transformers
out of the solid ones). Putting multiple turns of cable through the hole will increase the bead's effectiveness.
(Those computer cables with weird heavy lumps in them have pre-fitted ferrites.)
Regarding your seven powerboards: I suggest you make a small amount of money by getting the Fire Brigade's publicity department to come and photograph this arrangement for use as a "DON'T" on one of their safety posters. Then, spend that small amount of money on getting an electrician to install some more outlets in that room.
Connecting the laptop's headphone out to a line in on the amp is no big deal; just use a standard 1/8th inch stereo to twin RCA plug lead. There's a small impedance mismatch issue, but it should sound fine with an appropriate volume setting.
Spinning, yet not spinning
Would it be possible to easily use the third wire (the one that's used by the tachometer) of a 3-wire fan connector to power an LED strobe? I mean a strobe like you (at least in the dark ages) used to set the timing on an automobile, not like the kind photographers use.
Such a thing might be a hit with the people who trick out the insides of their computers with lights and windows and the like; it would look pretty cool to have a fan seemingly not rotating.
Dave
Answer:
You couldn't do this directly, because the fan tacho wire is an "open collector" signal; a transistor on the fan circuit
board connects that wire to ground twice per revolution, leaving it unconnected to anything the rest of the
time. The mobo makes this signal readable by using a "pull-up resistor" - a resistor between some power rail and the
fan wire, which'll cause the fan wire to rise to the voltage of the power rail when it's not being pulsed, and to
drop to zero volts when it's earthed. You can't get power from the tacho wire.
It wouldn't, of course, take much silicon to make a widget that would flash an LED in time with the tacho pulses, or only once per revolution. You'd probably also need to reduce the duration of the pulses, as a proper strobe effect needs very brief flashes, and the tacho pulses may be too long.
Here's a marginally relevant project.
Box chopping
This is in reference to your review of the SNT-2316C.
I'm confused about something. Why would I want to pay about twice the money for the WiebeTech DriveDock, when I could get the SNT-2316C, or any other external box that uses the Oxford 911 chipset, and get the same functionality? Does the DriveDock have some performance advantage? Or any other advantage, besides being easier to access when you want to swap a drive?
I'm planning on using this for an external audio drive for my laptop (as well as for backing up data). I really don't care about the case itself. Were the WiebeTech solution cheaper, I'd go for that. You mention in your review that the SNT is a bit noisy. This could indeed be problematic for me. Is it possible to disconnect the fan entirely? I would be perfectly happy leaving the box open to let heat dissipate.
Is it possible to remove the sides of the box in order to be able to use it for 5.25 inch drives (like CD-RW drives)? I know what you're thinking: why not just get a 5.25" case? Because I'm on a budget, and I prefer buying something that has been reviewed, and there's not a ton of stuff with Oxford 911 available where I live.
Steve
Answer:
The DriveDocks (and their cheap competitors) are just for fast-swap
purposes. The WiebeTech products are really nicely made, as opposed to the merely good-enough fit and finish of the
SNT and other Taiwanese products, and I guess the WiebeTech ones are better supported as well - but most users don't
need any support for this kind of thing.
WiebeTech target the Macintosh market. Can you tell?
Yes, you can disconnect the fan in the SNT box; it's got a little plug onto the box's circuit board, so you don't even have to cut wires. And then, indeed, you'll need to leave the lid off to keep the drive cool.
Regarding a 5.25 inch conversion: Well, yes, you could carve out a bit of plastic from the side lips of the tray to remove the width restriction, and you'd even still be able to slide the metal case back on afterwards if you wanted to use the box as designed again. But PATA hard drives have a jumper block between their power connector and their IDE socket, and 5.25 inch optical drives don't, and there's not enough adjustment in the SNT box's sliding power plug widget to get it to fit an optical drive. You could free the power plug completely and carve it up or use a little extension cable or something, but seeing as SNT make 5.25 inch boxes with, I presume, the same electronics, that don't cost very much, I think you'd do much better to just buy one of those. There's a good chance that anywhere that sells the 3.5 inch boxes will be able to get the 5.25 inch ones too.
Star topology power!
Lately, I got the idea of powering all the stuff I could from one source, so my router, switch, media converter, access point, battery charger and cordless phone all run from the same 12V source. It's a switching PSU, an old HP laptop brick (12V, 5A). The total current rating (measured) during operation of all this stuff is hovering around 3 to 3.5 amps.
Being totally happy at having removed more than 10 wall-brick PSUs from my life, I would want to ask you a pair of questions:
1) Is what I've done safe? I've simply made a plugbox that outputs 10 coaxial outs, wired in parallel, from the 1 coaxial in that comes from the power brick. Besides the amp meter, nothing else. I've used hefty gauge wire to be sure, and the brick is regulated, but should I add some capacitors (or something) to ease the life of the brick (and the peripherals)?
2) A pair of the peripherals run on 9VDC instead of 12. I used a simple linear voltage regulator (LM7809) attached to a beefy heatsink to do the job, again without the use of capacitors (that against the whitepapers of the regulator which do suggest to do so, but they do mention noisier power sources, while mine shouldn't be). Is this OK?
3) (last!) Wanting to take out the only source of noise in my Web server (an otherwise passively cooled Celeron T 1.3GHz), I would want to switch to one of those 12VDC-to--ATX PSUs sold by Mini-Box, something like the PW-200. Hence, I would have one plug less in my room and some 3 to 4 amps more load on my brick - definitely too much.
They do sell a 9A brick, but it's described as a 12-17VDC, 9A unit. Since they do seem not to reply to my e-mails, I'm thinking this could be an unregulated PSU... even if this does sound a bit strange to me, since it's a switching one... so what can it be?
I've searched for ages on eBay for a similar PSU, but without luck. The beefiest one I could find was a Gateway 12V, 6.67A, but that is still too few amps for me. Any hints?
Lorenzo
Answer:
Assuming you haven't got screwed-up solder joints slowly overheating or some other weird problem, then your multi-adapted
laptop PSU should run all of the 12V gear without a problem. As long as the power supply is within its current rating,
it should be fine.
Laptop power supplies are generally of quite good quality and expect to be running close to their rating for long periods, so there's little risk. Old cheap heavy linear PSU wall warts, in contrast, quite often fail in alarming ways if driven hard continuously. I've carried more than one of those out into the garden by its cable, listening to its molten guts hiss and spit.
Note, by the way, that you can ease the thermal load on fanless AC adapters of all kinds by just getting them up off the floor a bit, for better air circulation. I used to have my old Amiga 500's PSU up on a couple of glass jars, until I upgraded it to a 150W AT PSU.
The un-smoothing-capacitored regulators ought to be OK too, again assuming you haven't done anything... whimsical... like left the regulators out in the breeze waiting for conductive dust to land on them, et cetera.
Regarding running your server from the same source, I think you'd do better to try a mains powered fanless PSU, provided of course that the computer's PSU fan isn't essential to its system cooling at the moment. If it's not running practically "nude", you'll probably find it gets surprisingly hot without a gentle breeze through it all the time.
Anyway, assuming a fanless PSU won't be a problem, one like this would probably suit you.
Ia! Ia!
When I was in college, I remember someone telling me at an, ah, smoky party that there was an entry in the library's card catalog for the Necronomicon. Not the H.R. Giger picture book, not the repeated-nonsense L. Sprague version, not the Donald Tyson version (which didn't even exist when I was in school), not the Simon version (one of my buddies had a copy of that; I note that it's been debunked by people who should know). None of those. The real, genuine, authentic, evil Book Of The Dead.
I can't recall whether I ever found the card myself, possibly because of the abovementioned smoke. But a couple of friends of mine who went to different colleges turn out to have heard the same rumor about their libraries.
I can't find any such listing in Melvyl or the UCLA catalog. Has there ever been any such listing anywhere? Is it real?
Grant
Answer:
It's quite possible that there was a listing in the card catalogue; such listings, and ones for other fanciful
books, were often put in catalogues as jokes by bored librarians. The Necronomicon was, traditionally, permanently
listed as "lost".
To add an Australian slant, I've checked the online University of Sydney, UNSW and Macquarie Uni catalogues too, and had no luck; I'm also very disappointed to say that MIT's catalogue contains no entry for the John Dee Necronomicon - and that's the one place I'd expect to have a listing.
Mind you, to be fair, people unable to find the listing (or the book itself) might just not be looking for it during a planetary alignment, while drenched in the blood of babies, and wearing the tanned skin of a nun. Or they might just not look enough like a frog.
And there may indeed be a "real" 1589 John Dee Necronomicon, at least insofar as there may exist a publication of that title which alleges within its own pages that the famous alchemist, magician and all-purpose later-life flim-flam artist John Dee did indeed translate it upon that date, in accordance with H.P. Lovecraft's 1927 "History of the Necronomicon".
Unfortunately for people seeking to rend the fabric of space and time and raise incomprehensible horrors from the oceans, like everything else Lovecraft and his contemporary horror writers at the time wrote about the Cthulhu mythos, the History was entirely fiction (though some people didn't get that memo). Some of the other writers might have toyed with enthusiasts who thought they were reading stories inspired by genuinely ancient myths, but Lovecraft himself apparently never did so, and always clearly stated, when asked, that it was all made up.
It's my understanding that there is no evidence to suggest that the "1589 translation" actually existed before demand for The Book Of The Dead had been stirred up by Lovecraft's work, the popularity of which peaked decades after he died. The "1589" book is not listed in the Library of Congress catalogue - they list a Necronomicon by "Alhazred, Abdul", but that's the 1973 version with a preface by L. Sprague de Camp. The body of that work contains, as you say, eight pages of pseudo-Arabic repeated over and over to fill the book. I don't think the LOC catalogue contains any joke entries. They're not renowned for their sense of humour.
The Straight Dope, naturally, has a piece on this subject. It makes reference to the fact that there are "bogus card catalog entries at a number of university libraries" for the Necronomicon.
And the H.P. Lovecraft Archive's mini-FAQ makes explicit reference to the abovementioned work: "There are many known library references to the Necronomicon by Abdul Alhazred, Michael Tice's entry at UCLA being perhaps the most notorious; these are pranks engineered by students or librarians."
Of course, if everybody who reads the Necronomicon is driven to immediate murder-suicide, or explodes into a flailing mass of ichor-drenched tentacles, or vanishes with a pop into a dimension where humans are immortal, rapidly regenerating food animals for seven-legged creatures with barbed and rotating mouthparts who love the sound of screams, then proper verification of the existence of the work will, naturally, be somewhat difficult.
Incidentally, if you're looking for an impressive rendition of the Necronomicon in TV or movies, I think the second episode of the 2005 Masters Of Horror series nails it. It's not so much a modernised version of Dreams in the Witch-House as a story about what happened in that house (which, uh, hadn't been demolished quite as thoroughly as H.P. thought) 80 years later. Judging by the fact that the bottom has still not fallen out of Arkham, Massachusetts' housing market, it would appear that people just don't learn that it's one of those places like Stephen King's Maine or the various little towns featured in murder mystery series, than which absolutely anywhere else is a much better place to live.
Ezra Godden's the protagonist; the boy just can't get enough of ghastly otherworlds.
Anyway, that episode gives you a close-up look at a far nicer Necronomicon prop than the one in the obvious movie (not to mention the various other options, and disregarding the even more obvious but lousy movie).
The Masters of Horror book seems to have been bound in the skin of a rather small human, but that detail only improves it, if you ask me.
