Dan's Data letters #56
Publication date: August 2003.Last modified 12-Sep-2012.
Infuriating emanations
I am confused about all the interference coming off of electronic equipment. In the battle to block out EMI and RFI, I've Googled my fair share of sites, yet no one seems to have a set answer. Since you're an electrician, I thought you may have run across these "enemies of mankind and his toys" before.
For example, we all see these rounded cables with aluminum "shielding"... but does it help? I hear from one source that aluminum is worthless for blocking EMI, and that only ferrous metal will do... but how does having iron in the material help?
Why do I care so much? Well, the side of the room that houses my main computer has the power cable from the entire house running behind it. Thus, if some bloke in the house decides to give me a hard time, they can turn on something high-draw (like a hairdryer) and cause my monitor to go into an almost degauss type of spaz-attack.
And it ain't power quality either, 'cause I have my system plugged into a UPS, and I've unplugged the UPS from the wall before, and the monitor still went haywire when I turned on the hairdryer in the other room. I was even stupid enough to pick up the 19" CRT and try it in different positions, only to find that as I got further away from the wall, the better things got.
I've got to find a way to shield that wall, cause this is the only wall that would be practical for my main system. I bought an LCD monitor to avoid the degauss-like effect, but now the LCD has a high-pitched whine!
Nathan
Answer:
I'm not an electrician, nor do I play one on TV. I did once lick 240 volts,
but I understand that you also need to know the secret handshake before
the Sparkies' Guild will award you the Cheap Chinese Linesman's Pliers of
Apprenticehood.
Anyway, I suggest you stop listening to the source that told you about ferrous metals being the best EMI shield. Generally speaking, any reasonably conductive metal will do as good a job as any other for EMR blocking purposes. Ferrous metals are the ones to choose if you want to channel a magnetic field, but channelling isn't the same as blocking; an iron box won't protect a monitor from magnetic interference.
And it's magnetic interference you're dealing with, here. Degauss-ish waviness and colour changes mean a moving magnetic field.
There's nothing you can do about magnetic interference but move the computer, assuming the problem's not being caused by an actual wiring fault. If it is being caused by a fault, like for instance lots of current running to ground or from one ground to a mismatched one through a water pipe or steel conduit, then it could be dangerous, not just a nuisance. If it only happens when people use an appliance, and if it happens with various appliances and various outlets, then I think it's unlikely to be this sort of problem. It could still be worth checking, though.
Magnetic shielding is theoretically possible (I talk about it a bit here), but not at all practical for domestic users.
Assuming the problem isn't curable (an electrician might or might not be able to help), you're just going to have to use your magnetic-perturbation-immune-LCD monitor. Its whining problem is unlikely to be related to the CRT's problem; it's probably a defective inverter for the LCD backlight.
Warranty, ahoy!
Sound sans wires
The goal: Wireless headphones that don't cut out when you turn your head, and don't fall and break because of the awkward built in receiver. In short, a STEREO wireless arrangement that does not suck.
I found an FM transmitter here, but I need to know exactly what this means:
"Clarity is approximately 40dB stereo separation."
Anyway, this thing might be great, that is, if it works like a good, powerful local FM station, you know? I could then grab some small FM belt size Walkmans and have a cheap wireless headphone system using whatever headphones I favour.
Infrared is out. 900MHz (and above) would be nice if the design didn't insist on Martian headwear. FM is a compromise, for sure, but should work. Again, I have this picture in my mind of awesome reception and separation duplicating the performance of our local FM blowtorch. Am I out of my mind?
NOMAD
Answer:
The 40dB separation thing means the left channel only cross-talks into the
right one, and vice versa, at about its signal level minus 40dB. That's
a lot; it's fine.
There are lots of companies that sell mini FM transmitters like this, pre-made or in kit form. The problem with this idea is that you'll be using a fleapower transmitter to send to a portable stereo, and portable stereos aren't very good FM receivers. They usually use the headphone lead as the antenna, which is clever but not very effective. You'll probably have noticed already that the quality of the sound from a "Walkman"-type FM receiver can vary enormously as you move around.
The range figures for the little transmitters are often very optimistic. They generally seem to assume a good quality receiver (a regular speaker-equipped portable radio with a telescopic antenna, for instance), and may also assume you're not actually interested in stereo (mono FM is much easier to clearly tune). The position and type of transmitter antenna matters, as well; these transmitters often just have a dangling bit of wire for an antenna.
Radio systems that use a much higher frequency than ordinary FM are more sensitive to obstacles - you pretty much need line of sight to the transmitter - but can also use much smaller antennas, so a reasonably omnidirectional receive antenna can be built into the headphones. You can't do that with FM, unless you stick at least one telescopic antenna to the side of your head.
Bulletproof LEDs
I have followed with interest your evaluations of LED devices. Although your focus is flashlights (broadly defined) I am trying to find an ambient lighting solution for an indoor firing range. Because of the shock waves when firing, the recommended lights are outdoor floods (fluorescents break). The floods are large and must be protected from less than stellar aim, which can result in a significant amount of steel protruding into an expensive concrete box and reducing the available space.
The lighting along the range, other than target illumination, is only to avoid looking into a black hole. I do not have a feel for the actual light output of the Luxeon LEDs. Is it reasonable to use these for lighting in this application for their low profile and durability? Each light would have a deflector in front of it to avoid the errant chunk of lead problem. A 30 degree angled piece of 1/8" steel. But the LED would make that very small vs a floodlight bulb.
The range is an eight by eight foot tunnel. Any thoughts about how many devices need to be used?
Harold
Answer:
If you'd be OK with a light level that'd mean someone trying to (unadvisedly)
read a newspaper in the middle of the tunnel would have to squint, then
you could do it with white one watt Luxeon Stars. Use the no-optics versions
(not Star/Os), get the Lambertian High Dome models (which have the widest
angle output - they're closest to a regular bulb), and you'll be in business.
One of those every six feet or so, staggered on either side of the ceiling
of the tunnel (one on the left, three feet, one on the right, three feet,
one on the left...) might well be perfectly adequate.
You could also use green Stars, if you liked; they're the brightest-appearing of the Luxeon LEDs for a given power input. Or, heck, alternate RGB all the way, and then hang some disco balls in polycarbonate tubes!
The protective steel would also be useful to avoid a line of tiny twinkly lights making shooters feel as if they're about to launch from the Battlestar Galactica - even from a distance, a Star emitter is a REALLY bright little point. White or silver paint on the LED side of the deflector would give it a bit of reflection capability.
I wouldn't bet my life on Luxeons being a great solution for you, since it's possible that there's bright lighting at the shooter's end that'd mean you really need a buttload of illumination all down the tunnel for it to seem to be lit at all.
Luxeons are certainly not out of the question, though, and they're so small and easy to replace that you could, ignoring the dazzle factor, just leave them completely unshielded and notify all shooters that a $20 replacement fee will apply for any Chief Wiggums who manage to blow one away.
More hopes dashed
I have a few monitors laying around in my garage waiting to be used but there's nothing I need them for. However, I have a Playstation 2 that I'd LOVE to see work on my monitor, but it's expensive to spent $70+ on one of those VGA converter boxes. Do you have any ideas? I was thinking there could be a way I could cut and mod the wires to work with the PS2 video output, but I don't know where to start or if it's even possible, since a monitor is way more complicated (resolution, refresh rate) then a TV.
John
Answer:
Sorry; can't be done. The PS2 has RGB component output, but only at TV scan
rates, unless software asks for something more - which games don't, as I
discussed in this letters column.
Some monitors that can sync to 15-point-something kilohertz video can be made to work with a PS2, but no normal "VGA" monitor can do it. They all need at least twice that scan rate.
Still some magic smoke left
Our IT department was swapping out video cards from the imaging department, upgrading to Radeon 9700 Pros. Apparently one of our techs was not really sure what an AGP Pro slot was, and tried to force the card in the wrong way (with the power connected, no less). A spark and fizzle erupted and I had a heart attack watching this out of the corner of my eye. I took over the system and installed the card properly and booted and prayed. To my surprise it worked. After closer testing, though, I noticed some anomalies that I can only describe as "weird".
First off the motherboard (Soyo KT400), has "lost" the option for 8X and 4X AGP. The BIOS shows only 1X and 2X modes, even after flashing. Secondly, the hardware monitor shows the AGP voltage as 3.24V. This is waaay too high. But everything seems to work correctly. I even took the computer home and gamed on it with UT2003 and Unreal 2 to test the video to make sure that everything is working well. From my experience, and some benchmarks, the system is performing to specs.
My questions are:
1. The computer is functional, but can long term damage occur if the AGP voltage is too high? (I have used many software monitors and they all see the AGP as 3.24V).
2. Since the company that I work for is in publications and frequently do 3D rendering, is the loss of 8X and 4X AGP going to matter?
Andrew
Answer:
AGP 2X isn't terribly much slower than 4X, and 8X isn't much faster than
4X, so that isn't a major problem. Modern PCs do more with the AGP bus than
good old AGP texturing, but there still isn't generally a whole lot of traffic
on that bus.
So if it works, keep using it. If your application involves a lot of AGP chatter, then yes, it could have a significant impact - but if you haven't noticed one, don't sweat it.
The AGP voltage isn't high; it's actually a bit low. The AGP supply voltage is always meant to be 3.3 volts. When you hear people talking about "1.5 volt" or "0.8 volt" AGP cards, they're talking about the signalling voltage.
3.24V, assuming you're getting the right numbers from the hardware monitoring chip, is well within tolerance.
Tasteful art photography. No, seriously.
An aspiring artist in my family wishes to create a digital portfolio. She'd then like to print 8x10 inch inkjet copies of her work at reasonable quality to show prospective buyers. The former has proven more difficult than I'd hoped.
I initially tried to flatbed scan and piece together smaller pictures, but this presented enormous difficulties in time and consistency for even moderately large ones. Handheld consumer scanners probably more suited to the purpose no longer appear to be in production.
I then attempted to take digital pictures with my 1.3 megapixel Fuji camera, but the end results were inevitably washed out and lacking in detail despite various Photoshop post-corrections.
I don't mind spending a bit if that's what it takes. Is there a better way to pull this off?
David
Answer:
A "1.3 megapixel" (probably something like 1280 by 960, right?) digital
camera won't give you quite enough pixels for good eight by ten prints.
You'll want about 200 pixels per inch, so that's around 1600 by 2000 pixels,
at least.
You could scrape by with your camera if you can tolerate about 150 pixels per inch, which isn't too lousy; between 100 and 150 is acceptable for poster sized prints that won't be viewed very closely.
Anyway, resolution aside, your digital camera is likely to actually be up to the task, provided you use a tripod (a very cheap one will do), don't use flash, light the artwork carefully, and shoot with a relatively long exposure (that's why you need the tripod - well, that and the fact that a tripod makes it much easier to line the shot up perfectly).
You don't need a bunch of expensive photographic lights. Bounce the light from a couple of cheap hardware-store halogen flood lights off a reflector of some kind (white wall, white ceiling, bedsheet...) and you'll probably be OK.
If the artwork's reflective (a lot of paintings are quite shiny) then getting the lighting right can be tricky; angled lighting will emphasise texture, and perpendicular lighting will create glare (that's why you don't want flash). If you can get an add-on polarising filter for your camera, it'll let you minimise the glare.
Once you've got the shots, you'll probably need to twiddle them a bit in the image editing program of your choice, to remove colour casts (the camera's white balance adjustment probably won't compensate quite right for the colour of the lighting), and play with the image contrast and brightness and colour saturation. Then, any six- or seven-ink consumer inkjet will give you portfolio-quality prints on medium-priced paper. The prints may fade or shift colour over the years, but so do a lot of photos. You can just re-print them if that happens.
Exercise avoidance
My company would like to install two webcams on a LAN so people can communicate between the first and second floor work areas without having to run up and down the stairs. I got stuck with the project! Neither of these computers will be connected to the Internet.
I know there's all kinds of software to do this on the Internet, but how would it be done on a LAN? We need both audio and visual capability.
Tom
Answer:
Well, you could use plain old
Netmeeting;
it's included in current versions of Windows and a free download for older
versions, and it works on a LAN. You "call" another user either by computer
name or by IP address. If you go to the "About Netmeeting" option in the
Help menu, it should tell you what your IP address is.
Once you've connected to a given computer once, they should appear in the drop-down connection menu.
There's a quick guide here.
Mobile computing
I came up with an idea which has quite taken my fancy. I would like to draw on your knowledge of RC tank technology to assess whether it is feasible.
I have a PC case that I have customised myself. It is a full tower case finished in solid hardwood and sheet steel. What I would like to do is to fit radio controlled caterpillar tracks to my PC case, partly so that I can drive it around LAN parties like some mutant homage to the Jawa sandcrawler in Star Wars and partly because it would be a very pointless thing to do. I'm an Englishman you see, pointless hobbies are in my blood.
The main problem as I see it is the weight of the case, around 30kg. Obviously the case would have to be very stable on the tracks, but speed and ability to scale gradients would be of little importance.
So what kind of kit should I be looking at, and how much might I expect to pay for it?
Luke
Answer:
I don't know of any cheap kit-parts that'll be able to hold this much weight
without bending axles or wrecking bearings (probably the latter). You could
do it with ludicrous amounts of suspension or super-expensive
large scale tank parts, but
I think there's a better way.
Since you only want it to move very slowly, the drivetrain side of things isn't a big deal. You could use a couple of Tamiya gearboxes and one of their DMD drive systems, as seen on their recent tanks, but you'd get more power if you stripped a couple of cordless drills for the motors, and connected them to a separate controller. That could be as simple as a couple of separate R/C speed controllers running from a normal FM receiver (you'll probably want a PCM radio, if you want good noise rejection for the deafening RFI environment of a LAN party...), one for each side, controlled by a radio that's got one stick for each track. The "two levers" control system is perfectly fine for a small tank, or indeed for a big one; some variant of two levers (like, one throttle and two brakes) is how many full sized tanks steer, or used to at least.
This whole contraption could run from the PSU's 12V rail if you only want the computer to drive around when it's plugged in. Otherwise, you could use various hobby battery packs, or a cheap 12V or 6V sealed lead acid battery, or something. Or a UPS built into the computer, even.
As for the tracks themselves, consider rubber snow-blower tracks (see here, for instance). Rubber tracks have lots of drag, but you won't care much about that. They're strong, there are plenty of tough drivetrain components to go with them onto which you could graft your electric drive system, and they look butch, too. Perfect.
