Search results

  1. K

    Normal gun underwater.

    You guys must've all come in at the end of that episode of Mythbusters... Supersonic rounds disintegrated within a foot or two of the surface. Subsonic rounds, as I recall, made it 5 or 10 feet.
  2. K

    make your own PC? **Nastalgia**

    I've designed three motherboards and built systems around them... that should count...
  3. K

    What is a laser

    And what's the worry there, really? I mean, wouldn't a cheap polarized film on cockpit windows clear that right up?
  4. K

    Is Heavy Water Poisonous?

    If you've got a centrifuge at home, sure - you could separate it from light water that way... Boil it and use gaseous diffusion - that would work, too...
  5. K

    separate 12v rails better than one?

    Hrm. I'm not sure how to answer that. :) Seriously - there's a safety requirement that says any power supply with a rail that can source >240W has to be in an unopenable cage with warning stickers and stuff. And since the power supply cable comes out of its box, the "unopenable cage" would...
  6. K

    separate 12v rails better than one?

    None of the above, and it's very very doubtful you'll ever find a power supply that sources over 20A on any 12V rail. There's a UL requirement that any power supply which can source more than 240W (for DC; I think the requirement's really 240VA, but for DC supplies, same thing) has to be in...
  7. K

    The rectifier problem, backwards...

    okay, that makes sense. I hadn't considered that 120VDC would be sufficient, but I should have - that saves me the trouble of doing the 555 timer, but I'd still have to do one hell of a charge pump. As for actually building the thing, no problem - I do know how to do that sorta stuff. :) 3A...
  8. K

    The rectifier problem, backwards...

    I've got the opposite problem of the guy with the homework problem to take 120VAC and get 6VDC. I've got a lovely Christmas wreath with some lights. It's got a power cord, which implies it wants 120VAC. I wish to hang it on my front door, where there's no convenient outlet, so I'd really...
  9. K

    Needed: Hosptial technicians,signal processers.

    You could just use the RNG in the Firmware Hub, if you're on an Intel chipset with an FWH...
  10. K

    Product need: External PCI Express breakout box

    $800 to $1500? How many units would you expect to build/sell?
  11. K

    Need an electricity formula

    A bunch of AAs in parallel would kinda work; only concern is if they don't have exactly the same voltage - you'd want small resistors in series with each. With a 9V, you'd want to do some sort of a high-efficiency stepdown voltage regulator to get it to 1.2V (or whatever your target is)...
  12. K

    Need to reduce voltage using as few and as small components as possible

    Be careful doing it this way... what everyone's describing here is a linear regulator from 12V to 1.5V, and you're gonna be burning 7 watts as heat in your pass element (the resistor or LM317, depending on what ya pick) for every watt you deliver to your device. I realize that's probably the...
  13. K

    OPAMP troubles

    Uhm, someone did figure out that's a 10k potentiometer, and not a fixed resistor, RIGHT?
  14. K

    Mulitple PCI-Express 16 slots

    There's another way to do it; if you're willing to share bandwidth, you could use a PCI-E fanout switch (analogous to a PCI-to-PCI bridge) to hook multiple x16 devices to a single x16 interface...
  15. K

    Electrical/Electronics wiring circuit HELP! Need to convert 0-150Vdc 10 ~15vdc

    Something screams "perpetual motion machine" here, it seems. The alternator's rectified output creates the electric field that the alternator needs to provide a rectified output?? Anyway, if I black-box that out of the way, the rest is how to step an unregulated high-voltage DC input down to...
  16. K

    Electrical/Electronics wiring circuit HELP! Need to convert 0-150Vdc 10 ~15vdc

    Why? What's the bigger picture of the thing you're trying to make?
  17. K

    gameboy afterburner resistor question

    I've never seen the original thing, so I'm shooting completely from the hip here. Is the original a surface-mount resistor (kinda a box that lays flat on a circuit board) or a resistor with wires coming off the ends?
  18. K

    Persistence of Flash Memory

    Sure - in the flash components' datasheets. Now, everything in those sheets is done through extrapolation; a lot of those estimates are on the order of a hundred years, and since there wasn't any flash memory around in 1904, that's kinda hard to empirically test... :)
  19. K

    Reverse Engineering the BIOS

    That's why the fun job's creating the reference designs. ;)
  20. K

    Can anyone give a formal Mathematical proof to this one.

    Okay - I'm not quite there yet, but I do think this is awfully similar to a Putnam Exam problem I remembered... Turns out it's problem B3 from 1996: From the NIU Putnam archive:
  21. K

    Can anyone give a formal Mathematical proof to this one.

    This looks like fun. I never get to play with my math degree...
  22. K

    How do I get 24 volts from ATX PS? EE's please?

    Thanks, Geniere. Damonpip - while you're right about silver boxes being switch-mode supplies, and I assume you're right about why that's so (transformers and magnetics really aren't in my area of expertise), I still think the full-wave bridge rectifier is the right way to model the power supply...
  23. K

    How do I get 24 volts from ATX PS? EE's please?

    Uhm, yeah, actually, I do. For instance, here's a lovely picture of what I spent my summer designing... Anyway: Full-wave bridge rectifier? That's what's inside the power supply; it's the most common topology for an AC to DC converter. I've never designed a silver box myself, so a...
  24. K

    what is th emin amount of layers for a pcb to fully implement DDR-SDRAM?

    Depends what else you've got going on and how much room you have to route :) You should be able to route a 64-bit DDR SDRAM channel in 2 routing layers + 2 reference plane layers, so 4L should be doable. You MIGHT be able to get two channels into that space - I've heard that's doable, but never...
  25. K

    How do I get 24 volts from ATX PS? EE's please?

    Egads! If your pump wants to draw 2.5A at 24V, and you connect it between the +12V and -12V rails, you're going to draw 2.5A from the +12V rail, and you're going to push 2.5A INTO the -12V rail. And I don't know whether that's gonna trip the power supply or not (tho if i thought long enough...
  26. K

    CD audio: quality loss seen in copies?

    All that assumes it's a bit-for-bit copy. If, for instance, the CD copying software decided to re-normalize the audio levels, it might sound quieter or louder... and if the data got compressed and uncompressed for some reason, then all bets are off. But yeah - a bit-for-bit copy that's the...
  27. K

    Determining periodic/aperiodic signals

    Sure, Fourier series would be one way to look at it. A periodic function has a Fourier sequence (not series, since it's only a countably infinite number of Fourier coefficients) with zero coefficients everywhere BUT at a fundamental frequency f_0, and harmonics 2f_0, 3f_0, ... (It could be...
  28. K

    Predicting Random Numbers

    (woohoo! I was right!)
  29. K

    Predicting Random Numbers

    tinyabs - your example simply doesn't clarify anything. In the first half, you're assuming that your spinning wheel has an equal probability distribution for each of the 1000 values which is unrelated to any previously generated value. In the second half, you're talking about physical...
  30. K

    Help!!! How dp you measure PCI bus utilization

    Aw, be fair. Troubleshooting or not, any question whose answer is "Hook up a logic analyzer" belongs here. :) (I don't think that theory works, either; no way should a PCI device get horked because the bus is full.)
  31. K

    Reference for checking temperature

    More general question: What IS a precise way to determine temperature? Does the range over which the temperature is measured matter when choosing the instrument?
  32. K

    electrical resistor/motherboard/traces question

    Yeah, there's no way in hell I could do it without the stereo microscope, tho I've got technicians who can solder freakin' 0402s with the naked eye. (Unbelievable.) The right equipment's the fine-tipped soldering iron, the stereo microscope, solder wick, and a bottle of flux. Oh, and solder...
  33. K

    Would it be possible to make my own motherboard?

    Aaaaah. For some reason I thought Peter meant 5 to 10 years out of school till one got one's first mainboard project, which I thought was a little pessimistic. 5 to 10 years from NOW, sure :) (And if you're gonna start learning now, shoot ahead of the duck and be sure to take at least one...
  34. K

    Would it be possible to make my own motherboard?

    Flat-out impossible for anything modern, for the same reason you can almost never use 2 layer PCBs. Signal traces need to be kept REALLY close (thousandths of an inch) to a power or ground plane, such that when current flows one direction in the trace, it can complete the loop by flowing in...
  35. K

    Math book that deals with real world senarios?

    My university had/has a math class designed for education majors, based around precisely that premise. It's called Contemporary Math, or something like that. The text was pretty great - 's called For All Practical Purposes, and it's written by a group of authors called COMAP. 5th Ed at...
  36. K

    Anyone know how to reveal the email adress in Bcc field of an email?

    Wouldn't that kinda defeat the purpose of BCC?
  37. K

    What is a logic design project that I can do in two weeks or so during Xmas break?

    Elemental, I'm guessing you're a frosh or sophomore in CmpEn or a related field. I've got a BS CmpEn and another BS (Mathematics); graduated in '98. If I could go back to my freshman year and have my now-self tell my then-self something, it would be to spend less time studying and more time...
  38. K

    What is "mass"?

    Excellent point, Rjain. To the best of my knowledge, there's no consensus as to why inertial mass (the one in F=ma, which describes how matter "resists" acceleration) happens to be the same as gravitational mass (the one in F = G(m1)(m2)/r^2, which explains how matter attracts other matter)...
  39. K

    itanium systems

    Some of the usual Asian suspects were showing off whiteboxable Itanium motherboards at Fall IDF...