Dan's Data letters #132Publication date: 24-Nov-2004.
Last modified 03-Dec-2011.
Alternatively, light the room on fire
I have read your photo tutorial and its really great! I learned a lot from it! But there is a little question left that I would like to ask you: Which kind of diffuser do you use to fade out the shadows and get light from everywhere?
Where did you position the lights to do this CMoy amp picture?
I would be more than happy to get some clues from you!
These days, I'm using three flashes with my EOS-D60; two 420EX slaves and one 550EX on the camera. If you set up your photo area in the corner of a white-painted room, just bouncing flashes off the walls and ceiling will give you good fill light without any special reflectors; I also use a high-tech A3 piece of thick paper as an adjustable top reflector, and fiddle about with its angle and the 550EX's aiming for best effect. Usually just bouncing light straight down onto the object from the main flash does the trick, though; you only need to spend more time fooling with reflectors if you need to get light into crevices of some object or other.
You can get similar effects cheaper with natural light (from one side, with a white cardboard reflector on the other), or with hot lights (a cheap floodlight here, a cheap floodlight there...). Gimcrack contraptions made out of white cardboard and broomsticks will do perfectly fine as reflectors for these purposes; professional ones are just easier to adjust and more durable.
I'm looking for some low-power lighting solutions, for my flat. I know you're a pretty big fan of LEDs, and I'm myself no fan of unnecessary IR energy expenditure nor of narrow-spectrum solutions.
I've been hunting the market a bit for 230V 50Hz-powered LED based bulbs, and so far the only one I was able to find is a €15 unit in GU10 socket from Selectronic - their site is so horrible to use it looks like an IBM 3270 to HTML translator, but the specification sheet is as follows:
- socket: GU10 (same as small halogens here)
- power: 230V AC
- 20 white LEDs
very precise, as you can see.
I'd like to light the whole flat with LEDs; not necessarily those LEDs, but my needs range from "equivalent 40W" to "equivalent 120W" (using the "compact fluoro" lighting units). The big question is: Am I asking this too early, or do I just not know where to look (I suspect both)?
Yes, you're asking too early. LEDs don't yet have enough brightness per unit to be useful for general purpose lighting, and white LEDs don't have very exciting brightness per watt, either. The heftiest super-LEDs can be driven to five watts for reasonably long periods with decent cooling, but they're no brighter then than a five watt halogen - though their bluer light does mean you're likely to be able to get away with somewhat fewer watts for a given perceived illumination level. You're still not going to be able to get "40W-equivalent" light with fewer than six super-LEDs, though, and if you're using little 5mm LEDs you're still talking about ten LEDs per watt. White LEDs remain well behind fluorescents of all types in the lumens-per-watt stakes.
If you want halogen downlight replacements that're just as bright over a much smaller area (for reading-lamp or lighting-a-sculpture sorts of purposes), you can already get reasonably priced LED options - reasonably priced when you remember that you may never have to replace them, anyway. And for coloured accent lighting, LEDs are great - coloured LEDs are considerably more efficient than white ones. But for general illumination, you still can't get a single LED that can output more light than a 10 watt halogen lamp no matter how well you heatsink the LED.
Various low to medium brightness mains-powered LED lamps are out there, but the ones that have better than night-light brightness are still thrillingly expensive. They're aimed at people who really really want to never have to change a bulb - contaminated areas, amazingly inaccessible locations, and so on.
Wait a few years and what you want to do will be more feasible. In the meantime, LEDs are only good for decorations and other little lights.
Thinking of calling it "Winchester"
Just wondering what your thoughts are of I my idea for a "twin actuator" hard drive design. Two actuators, located on opposite sides of the platter, working in parallel.
With the correct control algorithms etc (NCQ or some such variant), would this effectively reduce the latency & increase read speed? Kind of like a RAID array but in a single device and much more efficient?
Sorry - it's been done!
I don't know whether any two-actuator drives exist today; I guess the extra expense needed to efficiently control the two actuators as data densities shot up (and spindle speed crawled up) made them uneconomical.
Some vaguely related drives (only one head assembly, but reading both sides of a platter at once) have also existed in the past; see this column.
Neodymium Sphere Of Doom
I was reading your article on magnets - kind of interesting! I would like to a buy a magnet shaped as a sphere, about five inches in diameter. How much would this cost? I would like it to have a very strong magnetic field.
It'd cost a lot. I don't think anybody has such a thing as a line item; even just made out of regular ferrite material, it'd cost you quite a bit, because it'd be a special fabrication. The extra expense of making a rare earth version of it probably wouldn't actually add much to the price. I have no real idea how much it'd be, but I think $US1000 would probably be the absolute minimum.
A magnet this big with typical neodymium-iron-boron magnet field strength would be extremely dangerous. Big rare earth magnets don't just want to break people's hands; they also want to smash themselves into tiny jagged pieces that explode all over the place and blind people. I have two mere two-by-one-inch rare earth disc magnets here (mentioned in this review), and I would never even consider handing them both to someone at the same time. It helps if you've only got one magnet to deal with, but the thing will still want to nail itself to anything ferromagnetic nearby, and if it's a sphere magnet then the contact patch will be small and the pressure high.
Hanging in there
I was looking for a replacement for my Sennheisers and happened across your evaluation of the HD 555, which I did find useful even if I didn't understand much of the technical stuff at the end.
My Sennheisers are a bit long in the tooth; I bought them in 1981 and they introduced me to a completely new world, what music was supposed to sound like. I adored them, it was a love affair and my relationship with the HD 420's lasted longer than my marriage.
But all good things, etc, and after several house moves with attendant accidents the headphones were pronounced dead, and buried in my garden with full military honours.
What I would like is something akin to them. My music interests are what I believe is called catholic, nothing to do with the religion, just covers everything, except rap and reggae, which I am afraid I don't understand but then, the look on my face is probably similar to the look on my father's face when he first heard my big band sounds. I am now 71 and still in love with Abba.
The old 420s are open (or "semi-open", which usually amounts to the same thing) headphones with, I think, quite high input impedance; anything that can drive them to reasonable volume should also be perfectly happy driving the lower impedance HD 555s. You'd probably be very happy with a set of 555s - you'll probably find their circumaural earpads quite a lot more comfortable than the 420s, too.
At your age, your ears' high frequency response is probably pretty lousy. You don't have to have listened to a lot of loud music in your youth to have crummy high frequency hearing by the time you're three-score-and-whatever. For this reason, you're unlikely to be able to hear a whole lot of difference between a quality mid-range set of headphones like the 555s and a much more expensive high-end set.
This just firms up my recommendation of the 555s - I bet they'll suit you down to the ground.
I have recently built Jaycar's version of Silicon Chip's FM Stereo Micromitter. I have also recently taken the plunge and bought a laptop (I hate calling them notebooks!)- an Asus A2D series. Now I want to add my Micromitter to my laptop "toolkit". I would like to power it from a USB port on my laptop so that I don't have to worry about flat AAA's or bulky plugpacks. The Micromitter will run from 5V directly. It will never draw more than about 60mA, so that shouldn't be a problem either.
I'm planning to buy a cheap USB cable and chop off the right end to give me the connector to plug into my laptop and a length of cable. From this site, it looks like I can just take pins 1 and 4 to get my 5 volts. My question is, will I have to tie the data lines (pins 2 and 3) to ground with capacitors, or will they be all right floating? I don't want my laptop being confused by noise being picked up on my "power cable". Should I bypass the +5V to ground with a capacitor? Should I use a ferrite bead?
I'm pretty sure every goofy little USB-powered gizmo on the market just leaves 'em floating. They probably don't have conductors going all the way to the end of their cable, of course, but since the host port should have 45-ohm-to-ground termination for the data wires and the signalling voltage is meant to be 3.0 to 3.6V, I don't think a few feet of loose wire hanging off the port would be able to come close to creating an interference-level signal, unless your house is built on top of the Superconducting Supercollider or something. I don't know whether interference on one port would be a problem for another port, either.
Basically - don't sweat it. Tap the cable and it'll probably work fine.
Holodeck, here we come
Modified air? Get out!
This just HAS to be vapourware for sure!
You'll be unsurprised to learn that about 90% of the people who find out about the alleged Heliodisplay make the same joke you did.
IO2 have been promoting their Heliodisplay, whatever it is, for more than a year now. It may be inching towards real-product status, since they're now at least taking orders, but nobody seems to have been able to do a review of the thing yet. IO2's claims about what the Heliodisplay is supposed to be doing to the air to make it diffuse light are, as you say, difficult to believe, or even understand.
Slashdot chewed the Heliodisplay over last September.
Too bad to be true
A friend of mine found this the other day.
The warning at the end is priceless.
"In that case, someone with evil intent could re-engineer the process to reverse the machine itself. This would give it the capability to consume energy without outputting any. Such a weapon could suck all the energy out of a city or small country in one fell swoop. Basement tinkerers who are ignorant of physics are playing with dangerous stuff. They may desire the salvation of the world, but they could inadvertently cause its total destruction."
It should be noted that Donald Simanek's site, where you found this, is a great ANTI-perpetual-motion resource. Since he co-authors that paper, which propounds a theological proof of the possibility of perpetual motion (among other things), you can be pretty sure that he's kidding.
The document in question is linked from the "Cutting Edge Science" page, which mentions the fact that you can find some "explanatory notes" in the HTML source code. The "view source" function of any good browser should colour-code the comments for ease of reading.
But then again
While trawling eBay for knick-knacks and doo-hickeys of questionable worth but with good impulse buy appeal, I came across this eBay store.
Never have I seen such a collection of rip-offs, overpriced rare earth magnets and books on black magic. If I was to make a mockery of an eBay store that sold that sort of thing I don't think I would have done this well.
I find the fact that they have a feedback score of 444 and 99.6% positive very disturbing....
My challenge to my readers: Find something there that isn't a scam.
(A reader's now pointed out that they're currently selling Dante's "The Divine Comedy" as an e-book on CD, which is, at least, likely to actually be what they say it is. But since you can download an illustrated version for free, I think the e-book only qualifies as the least scammy thing they're selling.)
Another one of those special moments
One Matt Greenwood recently received one of those "See my homepage with my weblog and last webcam photos!" spams, bearing my e-mail address in its "reply-to" or "from" fields, and decided to say "you suck" to me, because he didn't know I hadn't sent the spam. No problem, we were all newbies once. I replied as follows:
I did not send the spam to which you are responding - if you look at my Web site, you should be able to see that I'm not really in that business.
Someone else sent the spam, and used my (well-known) e-mail address as the reply address. This is common practice among spammers. Their reply and "from" addresses are seldom real at all; when they're real, they belong to an innocent victim like me.
Feed the e-mail in question to Spam Cop, for instance, and you'll be able to see where it really came from.
I wasn't envisaging putting this up as part of a letters column, since pretty much everybody reading this probably already knows it and it's information you can find in lots of other places. But it doesn't do any harm to put it out there one more time, since there are still plenty of people like Matt who haven't got the message yet and make spam worse by complaining to the wrong people.
Anyway, Matt's reply to me was "I don't care."
At this point, I checked with him to make sure he actually meant that he didn't care that I didn't do what he said I did, and informed him that I was considering holding him up to public ridicule on these grounds, and invited him to persuade me not to.
Redicule [sic] me on your pathetic website for me not caring about something you didn't do to write over 5 words in my previous 2 responses. I truly don't care.
I'm sure everyone will think that this is a blast.
Well, I never.
I gave Matt's e-mail address and invited people to drop him a line on the subject of willful ignorance, discourtesy to people who try to help you out, and anything else that occurred to them, and needless to say lots and lots of them did, and his blood pressure had a bit of a spike. Now he's apologised, though (not yet to me, mind you, but by proxy while begging other people to stop e-mailing him), so you'll find no more mailto: links here.
Move along, folks. Nothing to see here.