Dan's Data letters #6
Publication date: 1-Nov-2002.Last modified 03-Dec-2011.
Vacuum cleaner fun
I am writing in response to one (or more) of the articles on your website, which refer(s) to vacuum cleaners and their ability to generate circuit board-frying levels of static electricity by the friction between the dust/air and the tube.
Would it not be possible simply to attach an anti-static wrist strap to the tube in question (if, that is, the tube is metal, which, fortunately, mine is) to ground the offending static so that one can vacuum clean one's computer with relative impunity?
This might, I suspect, be a cheaper option than buying a special kit for converting vacuum cleaners for computer use, especially since I have never seen one of those on sale here in the U.K. I suspect, however, that it would still be best to avoid using the vacuum cleaners designed to wash the floor, steam cleaners, and "Shake 'N' Vac" to clean the computer.
James
Answer:
Yes, earthing the tube would work, with a metal tube. Any plastic fittings
on the end might still be able to build up a dangerous charge, though; very
small static charges can be enough to damage hardware.
You'd still want to be careful, though, because household vacuum cleaners have a lot of suction, and can mechanically damage computer components quite easily. If the cleaner's got a "curtain" setting, though, it ought to be quite safe if you earth the tube.
The pages in which I talk about vacuum cleaners and the havoc they can cause, by the way, are here and here.
Luxeon power?
I have seen the ratings/ reviews /mods of Luxeon Star LEDs, and they do appear to be bright. But how many candlepower do they have?
I have a 3-D Mag-Lite, and I want to use the brightest bulb possible (I dont care about battery life).
I have read that Streamlight's Stinger HP bulb is about 40,000 candlepower. Is there a brighter Luxeon Star?
Dmitriy
Answer:
The candlepower rating of a Luxeon LED, or any other kind of lamp, depends
on how you focus it. Tighter focus means more candlepower; it's not an absolute
lamp-power rating.
I talk more about relative power measurements in my old review here.
If you want maximum power from your Mag-Lite, then you don't want an LED. The current top-of-line five watt Luxeon Stars (some of which are on my to-review pile at this moment) are up there with the brighter flashlight bulbs, if you run them at full power. It's not easy to do that, though, as the Stars need serious cooling if you want to run them at full power for any significant length of time.
There are lots of after-market incandescent bulbs for Mag-Lites that are just drop-in replacements, and don't have that problem. Incandescent bulbs like running hot.
Mail tracing?
I've been reading your letters columns, comments about Mailwasher, and all the wonderful spam. It appears, despite my best efforts, that I have made it onto The List again. I only get a couple a day, but like Elvis, it's prolly not going to go away.
Sometimes I open them instead of sensibly hitting the shotgun delete button, and I began to wonder this morning, am I shooting myself in the foot by doing so? I don't know if you are familiar with it, but there is a site called iTraceYou.com where, after signing up, it becomes possible to "trace" an email. Is it possible the spammers could be using something like this service? Simply by looking at something, have I gotten myself on the "send this guy everything" list?
No, I'm not paranoid, but seems these clowns will do just about anything to get me to join the MLM or buy the whatever.! Thanks for reading, even if you haven't time or don't want to reply. KRS
Krstofer
Answer:
The way iTraceYou works, when it does, is simple enough. The site embeds
a "Web bug" in the HTML-mail messages it sends (well, it's meant to, anyway;
the message I got from you doesn't seem to be HTML mail at all...), and
HTML-capable mail clients (all of the popular PC clients, these days) load
the bug when you open or preview the message.
The bug is just a weeny little invisible GIF file or something, but it'll have a distinctive name, unique to that one message. When someone requests that particular file from the iTraceYou server, bing, they know that someone on that IP address read the mail, just as they'd know if the same file were requested by the recipient's Web browser.
Is it possible that spammers could be doing something like this?
Yes, just by looking at an HTML spam, you could attract more of the stuff.
But I wouldn't be too worried about it. You probably would have been on the list anyway. Receive one message from Spammer X, receive every message from Spammer X, until he dies of old age or, more fairly, is drowned in a sewage treatment pond by a cackling troop of Boy Scouts wielding boat-hooks.
Since the incremental cost of sending a zillion extra messages approaches zero, spammers don't bother to prune their lists much, if at all. Web bugs in mail won't get you on to a spam-list, since they can only be sent to you by someone who already knows your e-mail address. They'll only have an effect if someone who's already spammed you is one of the few spammers that're interested in seeing how many of the addresses he's spamming are alive.
Does NAT need firewalling?
A question for you if I may... Talking Internet routers here that have Network Address Translation. Everyone tells me that you need a firewall with such a router, because NAT isn't enough protection. But nobody can tell me why. Do you know how it's possible for somebody on the outside to get access through the router into one of the computers on the LAN? Simple setup, say 10 computers and the router all plugged into a hub. Assume that there are no ports mapped, and that the telnet port has been disabled on the router, so a password hack isn't possible.
Daryl
Answer:
"Everyone" may tell you you need a firewall on top of your router, but everyone
is wrong.
No, I wouldn't use nothing but a NAT box between my Fortune 500 company and the Internet. One of these appliances is more than adequate for small and home office purposes, though.
The confusion may arise from the fact that a lot of "NAT boxes" are actually Windows boxes running Internet Connection Sharing or some similar software. They may well be insecure, because all Windows flavours are riddled with insecurities, especially if they're not completely up to date with Microsoft's security patches. Linux/BSD sharers and stand-alone sharer appliances, though, don't have these problems. They may have vulnerabilities - anything may - but it's really not something that's worth worrying about.
Component clashes
I have come across one problem with the Aopen H600A case. When I tried to put a CD-ROM drive in the bottom 5 1/4" bay I found that it was on course to collide with a protruding motherboard component. I had the same problem with a removable hard drive rack too. I didn't spot this in your review - it definitely wasn't listed as the worst feature.
The motherboard is an ASUS A7V133.
Nicholas
Answer:
This can happen with lots of cases. Motherboards that're about as big as
an ATX board is allowed to be, and whose designers have taken the not very
wise step of putting sticky-up components (like big capacitors) in the top
corner, cause it. Clashes can also be caused by unusually long drives -
removable racks are often longer than the average CD-ROM drive, and CD writers
and changers can also stretch into space normally reserved for motherboards.
You can't blame the case makers, because they're sticking to the ATX spec. It's just a bad combination of dimensions.
Fan as generator
If I manually spun a fan (backwards maybe?) would this create a small electric charge? If so, why?
Carey
Answer:
No, it wouldn't, not if it was a regular computer fan. Computer fans use
electronically commutated brushless motors, which rely for their operation
on a timing circuit that energises coils in the right order. Without power,
the timing circuit doesn't work, so spinning the rotor doesn't give you
anything at the input terminals. If you spin the rotor really fast, though
(with compressed air, for instance), you can and will barbecue the electronics.
A fan attached to a simple brush motor, on the other hand, will work as a generator (or dynamo); brush motors are mechanically commutated, and work both ways, as it were. Cheap DC "hobby motors" are all brush units, and allow you to do all of the basic Learning About Electricity stuff with them - connecting the motor to a little light bulb, manually spinning the rotor, and making the bulb light up, for instance.
Here's a good place to start learning about electric motors.
Widening a webcam
I am building a robot, and I just added a PYRO FireWire webcam to it. It uses a Sony 1/4" CCD sensor. It works well, but I would like to change to a wider angle lens. The lens screws off easily. Are the lenses on webcams interchangeable, and is it possible to get a wide-angle lens without physically modifying the camera?
Allan
Answer:
The little one-block camera modules that sit inside all somewhat recent
webcams should have standard threads on them; there are a few different
thread sizes, but the most common one seems to be 12mm diameter with 0.5mm
thread pitch. Other lenses are available to fit those threads.
This is the
lenses catalogue of a local seller of video-security stuff, here in Australia;
there are 12mm-thread lenses with horizontal fields of view from 10 to 108
degrees, if they're used on a camera module with a 1/3rd inch sensor. The
1/4 inch sensor in your camera will give a proportionally narrower field
of view.
You can get super-concealable pinhole lenses as well; there might be fisheyes and other super-wides available, if you need that wide a view.
To actually get one of these lenses to fit on your webcam, though, you may need to hack off some of the casing, or remove a decorative lens-surround focus ring, or something; the lens may or may have exactly the same exterior dimensions as the stock one. And if your webcam doesn't have a popular thread on its sensor module, you're out of luck. I think the Sony modules should be fine, though.
Crossing over
Does a typical small 4 or 5 port router have a crossover cable port? As in, can I use a crossover cable (which I have and which is like 15 m long, so I don't want to throw away) to connect between a PC and the router, instead of an ordinary network cable?
Wai
Answer:
Yes and no.
The way you connect together 10/100BaseT hubs and switches and routers and such is that each connection between such devices must be crossed over, in the cable, or at the port. "Uplink" ports, which you'll find on a lot of switches and hubs, are just ordinary ports with the data wires crossed over inside; they're usually wired in parallel with a normal, un-crossed-over port, so you can use only one of those two sockets at a time.
Crossover ports are just a convenience feature, to let you connect devices together without bothering with a special crossover cable. A crossover cable (which will often be green, to indicate that it's not a normal network cable) lets you do the exact same thing by connecting two regular ports together. Crossover cables also let you connect two (and only two) computers together with no hub or switch at all.
I don't think there's any standard for cable-router products in this regard. A router with a non-crossed-over LAN port can be connected to a hub or switch with a regular cable, or to a single PC directly with a crossover cable; the reverse applies for a router with a crossed-over LAN port. Both kinds exist.
Note that nothing will explode if you plug the wrong kind of cable in; it just won't work.
Cheap projector?
I have seen kits sold in backs of magazines on making a projection TV (or monitor) out of common stuff, namely a BIG Fresnel lens.
Have you ever done this? If not, you should make an article on it, as you have infinite knowledge on all things neat. Plus it would save me 50$ :D
Matthew
Answer:
Those things work, for suitably small values of "work". There are always lots of eBay ads for them; eBay is the
new back-pages-of-Popular-Mechanics.
I don't want one, though, so you're out of luck :-).
Projectors that use a regular CRT of some sort, turned upside down, with a big Fresnel lens in front of it, give a really dim image. The parts cost is very small, and you can goose up the image brightness by twiddling the TV (and shortening its tube life considerably), but they'll never come anywhere near the brightness of a "proper" projector.
The best of the cheap-and-cheerful options is an overhead projector (which gives you good brightness and decent optics) with some kind of LCD panel sitting on its bed. Dedicated LCD panels for business presentations exist, and you can also dismantle a computer LCD monitor if you're feeling brave. These setups are better than the TV-plus-lens ones, but they're still massively outclassed by pretty much any one-box projector.
Find lots of blather on this subject here.
