Dan's Data letters #124Publication date: 9 September 2004.
Last modified 03-Dec-2011.
I have a Samsung 950P which I bought about five years ago. It has seen constant use, but it is now noticeably dim. It's interesting because I also have a Panasonic P50 Pro that is even older which is still very bright.
I remember you once mentioning that there exists a way to brighten aging monitors but it shortens their life. Elaborate.
I don't need to elaborate, because other people have elaborated for me!
Note that pretty much all tube-brightening strategies have to do with boosting the voltage to the cathode filaments, and thereby require you to rummage around inside a CRT, which gives many opportunities to Light Yo'self Up.
Any funeral expenses will not be borne by me.
A few years ago, I bought (non-rechargeable) 9V lithium batteries to put in the smoke detectors in my house. They look exactly like a normal alkaline or other cheap 9V battery, but obviously they cost several times as much. They appear to have been worth it, because it's three and a half years later and they show no signs of wearing out (blinky-light still blinks every few seconds, and they self-test fine). "They" recommend replacing alkaline batteries in smoke detectors once or twice a year.
So my actual question is: how long can I expect these to last? I've looked at various Web sites and was unable to find any information about these things. I can't even find a mention of them on the Duracell site, and the ones I have were made by them!
Smoke detectors draw very little quiescent current - something in the vicinity of 50 microamps. What this means is that a battery's shelf life may be more important than its capacity when it's running a smoke alarm.
You can expect a cheap carbon-zinc ("dry cell") 9V battery (PDF datasheet) to have a capacity of about 400mAh when delivering 5mA. It may manage a fair bit more into a much lighter load, like a smoke detector. A detector may well have pretty relaxed voltage specs, too, so it may keep running OK well down below the 4.8V mark (0.8 volts per cell) that was used to define the battery capacity.
Even with only 400mAh, though, you'll get most of a year of continuous service; take the low load and voltage tolerance into account and you may get two years.
The usually quoted shelf life for carbon-zinc batteries, though, is about 18 months. This isn't a clear figure either, as carbon zinc, alkaline and lithium batteries may still be useable (for a while) long after their expected shelf life has expired, provided they haven't started leaking. 18 months is a decent guess for carbon zinc cells, though; five years is a good guess for alkaline, and ten years is a good guess for lithium. Note that this is since they were made, not since you bought them; it seldom matters much if you buy year-old alkaline batteries for immediate use, but it's quite important that carbon-zinc batteries be fresh.
An alkaline 9V (PDF) rated at 625mA from 25mA drain might give three years of service in a smoke detector, depending on the abovementioned variables. Lithium 9V batteries, though (PDF), are likely to be rated at an impressive 1200mAh into a constant 900 ohm load (starting at 10mA-odd and tapering off), and could last an easy four or five years.
When the alarm's sounding a smoke alarm will draw a lot more current, of course - 100 milliamps, say. That high load (by 9V battery standards) will eat up the battery's capacity faster than the current number suggests, so one minute of alarm time may use up more than two days worth of standby time. But if the detector doesn't trip very often, the above numbers should hold.
This doesn't mean you should push the boundaries, though, especially with carbon-zinc and alkaline batteries, which may leak if left in service for years (lithiums are quite safe in that department).
If, however, you're buying a smoke detector with the intention of throwing it into someone's roof cavity so that its eventual "low battery chirp" will drive them utterly nuts, bear in mind the above timings. A lithium-powered detector concealed today may not start chirping until late 2009!
With all of your audiophilic myth-busting experience, especially in the area of $500/ft speaker cords, have you run into any information on using plain old power cords as speaker wire? If you trim the ends off of the cord that detaches from a newly deceased lamp, or just pare away at the growing mountain of PC power cords still in their packages to use on your stereo, would you be better off than with cheap speaker wire from Radio Shack?
Or is size not the best gauge of performance?
Power cord works fine as speaker wire. Just about any big chunky wire will work as speaker cable, actually, and the toughness of even medium duty household power cables makes them good choices if you don't need a nice flat wire to run under your carpet. Heavy duty power cable is overkill for ordinary use, but can be great for PA and/or outdoor applications.
Do make sure the wire isn't very twisted, though, which power cable shouldn't be anyway. If it is, though, it'll raise the cable inductance, which in extreme cases can eat some of the high frequency response.
Also, old beat-up power cables may have damaged conductors, and often aren't long enough for many speaker setups anyway. New shiny plugless cable from your local hardware or electronics store shouldn't cost you much.
Are you considering doing a review, or have you even heard of, the Brunton MacroScope?
I'm considering buying one, but I like to be an "informed consumer", and you definitely help me to be informed!
I hadn't heard of it, and I'm not very likely to review it - my telescope reviews are few and far between.
It looks like a pretty neat item, though, if of course you have a use for its close-focus feature. I don't know whether anybody's made a "macro lens for the human eye" before, but if the fun I've had with my camera macro is anything to go by, this thing should be a blast.
Note, however, that it won't be much use for astronomical purposes. Binoculars and monoculars (which are basically just half of a binocular, of course...) can be surprisingly useful for skygazing, but the standard astronomy rule applies - light-gathering ability is, generally speaking, much more important than magnification.
For this reason, lots of small-ish binoculars, monoculars and telescopes that're great for birdwatching or other daytime applications are rubbish for astronomy, because they can't suck up enough light to let you see the various quite large, but quite dim, things that're awaiting your attention in the night sky (light pollution permitting). The MacroScope has a 40mm objective lens, which isn't too awful (and, of course, makes the monocular smaller and lighter), but won't grab a whole lot of light. Most astronomers recommend at least a 50mm objective lens for night-time binoculars, and there's a healthy market for gigantic tripod-mount binocs (often ex-military), with objective lenses of 100 to 150mm. These, of course, aren't terribly portable and can be horrendously expensive, but there are a few models that are relatively affordable.
Getting a set of those could be worth it, just to hear your guests ask where they should insert the coin.
Have you heard of the Zielonka Smellkiller?
I Googled a bit, but it seems no one credible has done any tests on this device. I didn't see any authoritative debunking of it either.
What do you think?
I hadn't heard of the Zielonka products in particular, but odour-eating stainless steel "soaps" and related gadgets are common enough things. And, for some odours at least, they work; rubbing your hands on a stainless steel object under running water will remove garlic, onion and some other sulfur-based odours more effectively than will plain water, or possibly even water and soap. You don't need a special soap-shaped object to do that, though; a stainless steel spoon will do.
These "Smellkiller" gadgets are in a different class, though; they're little objects that're just meant to sit there and deodorise the area around them.
Zielonka's rather lyrical "History of Odors" page ends with a picture of their gadget being used like one of the "soap" gizmoes, and their "how it works" page is singularly unsatisfying, though the LGA report you can download there seems to be genuine. All that report says is that their gizmo appeared to somehow reduce the concentration of methyl ethyl ketone vapour in a room, though; it didn't address the question of the odour molecules you'd actually be likely to find in a house or car (as opposed to a workshop or plastics factory with inadequate ventilation...), and it didn't explain why a little puck of stainless steel would be so much more effective than the great big slab of stainless steel that most kitchens contain - the sink.
The other Smellkiller product pages, and the FAQ, tell you that the gizmoes just sit there next to a damp sponge and zap odours, all odours, as a result. This is news to people who rely on stainless steel to not react with, or catalyse other reactions in, various smelly organic chemicals.
I'd be surprised if these products were actually good for much. I suggest you try spritzing water on the sink in the kitchen instead.
While I'm sure we co-frequent enough sites that you've already seen it, I couldn't risk the possibility that you had missed the world's smallest flying robot.
The tech is of course cool enough on its own, but I confess my favourite part about that little blurb is the pic.
The Epson flyer's a neat little thing, and has more smarts than a traditional R/C helicopter, but it is not the lightest micro-copter humans have made so far.
The Epson product weighs an elephantine 8.6 grams without battery; the Pixelito is 6.9, ready to fly!
Do you know what kind of voltage a gas grill igniter produces? I'm having trouble getting one to spark in a basic spud gun I'm making, and I think it's because of a long wire run from the igniter to the combustion chambers, and because I've got two chambers wired in series. Would I have better success if I used a battery of some sort (AA, 9V, etc.) and a momentary switch (i.e. an ATX power switch)?
A gas grill clicker's good for several kilovolts at least (with minuscule current capacity, of course), but the value varies with the igniter.
Your long wire run probably does have a lot to do with the problem you're having. The wire you use needs to have really high dielectric strength - really good insulation between the conductors, and between the "hot" conductor and earth - or you'll lose spark to current leakage through the insulation.
Ordinary PVC insulation that's thick enough to be perfectly safe for mains power applications is likely to be pretty darn permeable when you're talking kilovolts and microamps. You don't need to buy funky high-voltage-rated wire, though; all you have to do is separate the wires with a bit of air. Split some figure-8 cable and cable-tie it to opposite sides of a bit of rubber hose, for instance, and as long as it doesn't get too close to anything earthed (your body will present a pretty good earth, so don't hold onto the cable), it should transmit most of the power well enough. You could also, of course, try an automotive spark-plug lead, though not the resistance "carbon" type.
Check out this for a neat igniter design. It's working with a stun gun as a power supply, but a scaled down version could work with a sparker.
A (reasonably) low voltage source like a battery would only work directly (without a voltage multiplier, as used in stun guns and cattle-prods) if you gave it a suitable, tiny, spark gap. You can get an arc out of a couple of 9V batteries (as many people have discovered, by plugging the negative of one into the positive of the other and then hinging them back and forth to adjust the spark gap), but you need about 20,000 volts per inch to strike an arc in air, so obviously a mere 18-volt supply will need terminals that're pretty darn close together.
(Yes, you can chain 9V batteries to get an arbitrarily high DC voltage, but this is foolish and dangerous, as well as being fun.)
You could make a little spark gap out of pencil leads, but it'd need constant fiddling.
"Electric matches" made for igniting model rocket motors would work, too, but you'd need one per shot.
But really, a good-sized piezo sparker ought to cut the mustard, if you can find some good enough cable.
Here's some more sparker fun.
Is there any news on the automatic porn detector front?
I love it when I get mail from Abby. It always makes me feel as if I should be wearing a silk dressing gown and smoking a pipe.
I haven't been paying a lot of attention to the smut-detection field, but I don't think any great breakthroughs have been made. There exists no before-the-fact way to really effectively prevent people from seeing any particular kind of Internet content. An automatic filter of any kind will inevitably let through some of whatever you're trying to block, even if it's so broadly configured that it blocks lots of stuff you're not trying to block. The notion that an automatic porn-blocker can tell "violent" pornography from non-violent erotica is, of course, laughable, unless you create a government department to administer a universal blacklist, which itself wouldn't work too well; what about P2P downloading, for instance?
After-the-fact solutions, though, like snoop programs that let parents/teachers/librarians/sysadmins see what people have been looking at, or what they're looking at right now, can work just fine. This, of course, does not prevent The Children from occasionally seeing A Penis, and so is unacceptable to our moral guardians.
A few specific replies to parts of the piece you mention:
> Mark Latham's office is understood to have shown "strong interest"
> in controls that would automatically filter out violent pornography
> such as images of rape, torture, bestiality and coprophilia.
As long as I can still get my daily goatse fix, I'm fine with that.
> A confidential paper from the left-wing think tank the Australia
> Institute, which is now being considered by the Opposition Leader's
> office, proposes that ISPs install compulsory filtering programs so
> only adults who can verify their age could view X-rated material.
Since practically every ISP account is paid for by an adult, usually with a credit card which serves as age confirmation, this is of course nonsensical. Not a lot of kids are using their pocket money to hook up their own personal DSL link; they're using their parents' connection, and commonly not even signing in with their own password on a shared machine, much less using some secure authentication system to verify their age as they use the machine.
> The recommendation follows moves in Britain, where the largest ISP,
> British Telecom, began blocking customers in June from accessing child
> pornography sites.
BT's "Cleanfeed" filter uses the UK Internet Watch Foundation blacklist of kiddy-porn sites. I don't think they make their blacklist public - these kinds of outfits never do - so who knows what's on it.
It is unknown how effective Cleanfeed has been so far, but that hasn't stopped the UK government from telling all ISPs to use the IWF list, at least to block whatever kiddy porn sites the IWF happens to decide to put on that list. This is, of course, popular, though not everywhere.
This follow-up piece is also relevant. Or at least, it was, before news.com.au took the page down, in accordance with their ancient and respected policy of making sure that nobody ever thinks of them as an place where any significant amount of information can be found at any one time. (The most of that piece I've been able to find anywhere now is here.)