Dan's Data letters #58

Publication date: August 2003.
Last modified 08-Mar-2015.

 

Playing chords

I bought a keyboard recently (a BTC multimedia keyboard), and was annoyed to find it had a very low minimum number of keys that could be pressed simultaneously before the thing refused to accept any more input. (For example, in a FPS game using the WASD movement keys, I could crouch and move in one direction, but when I went to change direction the keyboard would just lock up and I wouldn't move anywhere. Very difficult if you're wanting to sneak around!)

I've come across this before with other keyboards - some are crap and let you press, say, 3 buttons max simultaneously, whereas other keyboards don't seem to have a problem. I've heard that keyboards are divided into key "quadrants", and that you are limited to a certain number of keys depressed in each quadrant before the thing throws a wobbly. Is this true? And if so, is there any way to determine whether you're buying a lemon before you purchase the keyboard? Do keyboard manufacturers provide this information on the packaging or anything?

Chris

Answer:
Electrically, keyboards are grids of crossed address wires, which can be connected together arbitrarily at their crossover points when you press keys. Every time you press a key, you connect wires together; the keyboard hardware looks at which wires are connected to tell which keys are being pressed.

If more than one connection's being made on a given wire, though, the keyboard hardware won't be able to figure out which keys you're pressing. If a theoretical keyboard had one horizontal address wire for each row of keys, then you wouldn't be able to press any two keys on the QWERTY row simultaneously and have anything happen.

I don't know whether any real keyboards are this simple. I suppose some real cheapies may be. Better keyboards split up the 'board into separately addressed zones, which may or may not all be composed of contiguous blocks of physical keys. There are numerous designs out there, and also differently intelligent hardware on the other end of the matrix, which may or may not be able to handle more than a given number of keys at once no matter where they are.

There's a specific "too many keys" error that keyboards can report, with which the operating system can do what it wishes. I speak from recent experience when I say that Windows generally system-beeps repeatedly at you when it gets this "cat-on-the-keyboard" error. Some keyboards have their own noisemakers and will beep or click at you when the error occurs, no matter what OS you're running.

If I space my hands over my old IBM battleship carefully enough, I can press a key with each finger and not get the too-many-keys beep. This isn't of much interest, though; if I don't space the keys I'm pressing out, I often can't press more than three at a time. Three nearby keys at a time is enough for most gaming purposes, though; press any three of your WASD keys at once and one of them will be contradicting one of the others anyway.

You can work out empirically which combinations of keys a particular keyboard supports, by just fiddling around with a text editor window open. For all of the keys except the modifiers (Control, Alt, Shift) and other special keys, the last one you pressed ought to repeat if the combination's OK, and nothing should happen (possibly with error beeps) if you're pressing too many. It's easy enough to do this before buying a keyboard, if the store staff will let you.

My IBM, for instance, lets me press ASD at the same time with no problem, likewise SDF, or indeed ASDF together. But not DFG, FGH, GHJ or HJK. But JKL is OK again, as is KL;. Not L;', though. Various sub-combinations of non-allowed combinations are OK, though; D and F and any letter on that row except G are fine. Et cetera.

 

Fuzzyvision

I recently bought an MSI Mega PC with the intention of it being plugged into the TV, so I could surf the Web in my living room. But the quality stinks. This is with the proper MSI TV output card and all the requisite drivers. The only way to make text readable is to set the display down to 640 by 480, which isn't really good enough for what I want.

Is there a way of improving the display on the TV - either with a different output card or a software solution - or should I just abandon it and get a big monitor?

Quinn

Answer:
Few non-HD televisions can manage even 640 by 480 with reasonable clarity. That's the principal reason why a 21 inch TV is so much cheaper than a 21 inch computer monitor.

If you want a big, cheap, high resolution screen: Give up.

If you wanted to do home theatre PC sorts of things, and occasionally read small text as well, then you could use a TV from the Mega PC's TV output and a regular monitor from the VGA output. Squint at the little screen when you need to read text, turn it off and use the big screen when you don't. That's not very elegant, but it's cheap, and all you need to make it work is a video adapter capable of mirroring the same output to both screens, which pretty much everything with a TV output can do these days.

You could also save up for a video projector. They give you real high resolution output, and can be quite affordable these days if you shop around, particularly compared with giant TVs. I ramble on about projector pros and cons here.

 

One drop holds a ton

I have a 2GHz P4 with the boxed heatsink. The black layer on the bottom of the heat sink is now well melted onto the CPU. What is the correct way to remove the CPU from the motherboard when the CPU retention lever is covered by the heat sink, and the heat sink is glued to the CPU with that black layer of thermal compound?

I once removed the heat sink to clean dust out of it, and in my attempts to wiggle it off the CPU, the actual CPU came out with it, even though the retention lever was still in the closed position. After a minor heart attack and a careful pin inspection it turned out to be fine, but I am not keen to remove it again unless I know the proper way.

Sam

Answer:
The heat sink should come off fairly easily, if it's warm. If you want to get it really warm, run the computer with the side of the case off (just looking at the BIOS setup screen will do), and unplug the CPU fan. After a few minutes at most, the thermal goop should be quite soft (and the CPU heat sink almost too hot to hold). Once you've undone the clip, twist the cooler off.

Then, remove all of the goop from the CPU and the cooler with lighter fluid or, if you're feeling more energetic, a small amount of dishwashing liquid, and replace it with a smear of thermal grease. "Chewing gum" thermal compound like this should only be used once.

A couple of readers have, by the way, pointed out that I didn't explicitly say that you should turn the computer off before you take the heat sink off the processor.

You should turn the computer off before you take the heat sink off the processor.

Thank you.

 

Wrong number

I recently took possession of a new IntelliMouse Explorer 3.0 mouse from AusPC Market and was wondering why it doesn't seem to have improved sensitivity over my old original Explorer. I more or less bought the new mouse because of its advertised improved resolution, which I thought would translate into more accurate and sensitive mouse control when working with graphics, etc. For all intents and purposes, it really doesn't seem any different from my old Explorer.

Have I misinterpreted or misunderstood the quoted higher resolution that this mouse is supposed to be capable of? I also have a Logitech iFeel Mouse which I used for a while and found it to be capable of very sensitive and accurate movement. However, due to its small size in relation to the size of my hand, I resorted back to my trusty original Explorer. That's when I noticed the particularly coarse resolution of this mouse compared to the Logitech.

Mal

Answer:
You've mistaken a higher imaging rate for higher resolution. The IntelliMouse Explorer 3.0 (reviewed here), like other third-generation-sensor Microsoft optical mouses, has an increased sensor imaging rate - 6000 images per second, versus 2000 from the second-generation sensor and only 1500 from the first generation one. But its resolution remains the same - 400 counts per inch. So the maximum sensitivity you can possibly set it to without skipping over more than one pixel at a time somewhere is 400 screen pixels per inch of mouse mat, not including "acceleration".

400dpi sensitivity is plenty for most purposes, but it's not good enough for 3D gamers who play with a very high mouse speed setting and want accurate aim for sniping. Then, the granularity of a 400dpi mouse's response is too large, and an 800dpi mouse (like a current-model Logitech optical) will probably be better.

The same can apply for people like you using graphics software, if you use a pretty high mouse speed and/or run a pretty high screen resolution, which isn't hard to do. 1280 by 960 at 400dpi mouse sensitivity requires 3.2 by 2.4 inches of mouse mat, and most experienced computer users with reasonable manual dexterity prefer something closer to 2 by 1.5 inches of mouse movement to cover the whole screen.

The high imaging rate of the third generation Microsoft mouses means they won't skip even if you move them very quickly; this is another feature that's more interesting to gamers than it is to the rest of the world. The current Logitechs have a higher imaging rate than the current Microsofts, too, but the Microsoft sensor's 6000 images per second is quite fast enough already, so that doesn't matter.

 

Small PC, smaller screen

I have a Shuttle SS51G... cute little cube of a computer. It does what I want it to do (basically, be something that can run my Radeon 9800 Pro and Windows games well). It also has a unused 3.5" floppy drive bay that could be used for nifty things that are not floppy drives.

Have you, in your travels, chanced upon a Vacuum Fluorescent Display that can hook into a serial or USB port that can actually fit in this 1 inch by 5 inch space?

Ed

Answer:
I didn't know of one, so I appealed to my readers to suggest one. Hey presto; someone told me about this one. The smallest of these could be an option, too.

There are plenty of other LCDs and VFDs whose readout isn't bigger than a 3.5 inch bay's panel hole (as you probably already know), but finding one that doesn't have a board behind it that's too big for a single 3.5 inch bay isn't so easy (as you also probably already know). Two stacked 3.5 inch bays will accommodate various Matrix Orbital boards and similar products; one won't.

You could hack one of the larger displays in if you've got some room above and below the bay (or if you install it on a side panel, or something...), but there's not much air space in most SFF cases, and you're not necessarily itching to break out the Dremel anyway. So, thus far, this one looks favourite.

 

Baby-cam shopping

Something was not quite clear in your reviews on the Aiptek pocket cameras. The picture sample of your "special object" thingy looked much better taken by the Pocket DV2 than it did when you photographed it with the Pocket DV3100. Was this an unusual, case or should I count on fairly demonstrably inferior pictures with the "updated" DV3100?

All the Aiptek pictures seemed superior to the Digitrex DSC-2100 (which I think we can buy in the US as the Umax AstraPix 540 - I am not sure where I would order it and it is not in our stores). If the landscape pictures come out as poorly as your picture of the seaside scene, would you buy this camera for indoor use?

Peter

Answer:
To some extent, the GrandVision CoolDV 350 (AKA the Aiptek Pocket DV3100) is inferior to the older Pocket DV2; its higher resolution sensor wants more light.

The difference isn't as big as the indoor shots I took suggest, though, because the DV2 shot...

Pocket DV II demo shot

...was more brightly lit. I took it in a small room with a low ceiling illuminated by a 500 watt floodlight, probably giving about twice the light level I got when I used the same flood to illuminate the ceiling of the bigger room in which I photographed the same subject...

CoolDV close-up sample

...with the CoolDV 350. There were downlights shining on the subject for the CoolDV 350 shot, but even they didn't push the illumination up to the same level.

Note that I also didn't actually review the Aiptek Pocket DV3100; I believe it's exactly the same as the GrandVision CoolDV 350, but it may behave differently. Later production cameras may also be different from earlier ones, though this doesn't generally affect image quality much, if at all - just things like firmware bugs.

The Digitrex camera takes crummy landscape pictures largely because of its fixed focus lens. Fixed focus cameras always give fuzzy results on distant subjects, unless their focus distance is set far enough away that they give fuzzy results for indoor shots.

If you leave the Aiptek/GrandVision cameras set to close focus and take landscape shots, they'll suck too.

 

Your Tiny Head Is Frozen

I recently bought a Petzl LED headlamp for use when hiking - mainly for around campsite use. It takes three AAA batteries which sit behind the light.

However, I have limited/no knowledge on batteries or power sources. What I want is a battery which will help my light burn longer, preferably brighter and work in cold conditions (down to -10 degrees Celsius).

What would you suggest? What should I stay clear of for below freezing use?

Brent

Answer:
Use nickel metal hydride (NiMH) rechargeables. Alkalines suck at low temperatures; you'll only get about 65% capacity from alkalines at zero Celsius, and they slide rapidly below that, down to practical uselessness at -20C. Lithium batteries work well at low temperatures, but you can't get them in the AAA form factor. So NiMH it is; both NiMH and lithium should deliver rather better than half of their rated capacity at -10C.

Note that you mustn't charge NiMH cells when they're at or below zero Celsius; they have to be warmer than freezing to avoid damage.

Also, if you're going to be spending a lot of time in the freezing dark, consider a headlamp with a separate cabled battery pack that you can keep in a pocket, strap to your body, or whatever. This lets you use whatever kind of batteries you like. It's not terribly difficult to hack such a battery pack onto a regular headlamp, either.

 

I can see the music!

If you put a Petri dish of ferrofluid on top of a small, rare-earth speaker, would it dance in time to the music? What about the magnetic viewing film, say if you stuck it over the speaker cone and back-lit it? How much does the magnetic field change?

Bennett

Answer:
Nothing perceptible would happen, in either case.

The external field from the voice coil of a speaker is almost zero. Unshielded speaker drivers have a pretty large constant external field, but that's all "wasted" magnetism from the big permanent magnet on the back of them; the voice coil itself is quite weak, and its field is much smaller.

If you ripped the voice coil out of a speaker, though - or just made your own coil with appropriate impedance to be driven by an amplifier - then you could put it right next to the viewing film or ferrofluid, and get more action, for bass frequencies at least. Ferrofluid is much too gooey to respond to high frequency audio, especially at sub-ferrite-magnet field strengths, and viewing film has a response time, too. You couldn't see high frequency oscillation, anyway.

A coil outside a speaker could be more easily cooled, too. You could drive it really hard, if you put it in a hose and ran water over it.

If you put a coil in a hose and connect the whole contraption to the mains for good old degaussing-wand 50Hz fun, though, and anyone asks, I never said any of this.

 

Track tracking

I'm a bit puzzled by your Tamiya Sherman review. In the review you talked about the Sherman having metal tracks - fair enough, but I can't find any 1/16 Tamiya R/C Shermans which have metal tracks. They all have "pre-assembled plastic tracks" (which to be frank are very substandard, and snap the first time you turn the tank on any surface that has some degree of grip).

I was wondering whether you could tell me where you got your tank from? Or did you buy the tracks separately?

Neil

Answer:
I got my Sherman from an ordinary hobby shop. That was long enough ago, though, that they still came with the steel tracks.

The current 56014 Sherman kit is of the light-and-sound type, with turret motors and engine and weapon sounds and light-up guns, but it comes with pre-assembled plastic-pad tracks similar to those that came with my light-and-sound Pershing. I found the Pershing's tracks to be quite tough, by the way; perhaps the plastic-pad Sherman tracks are lousier.

Anyway, that's what you get, these days. Tamiya no longer make any tanks with all-steel tracks.

My old kit is a 56005, with no light-and-sound gear, but with the you-build-'em steel tracks. I don't know whether the old-style tracks will work on the new-style tanks; someone at a good hobby shop might. Tamiya ought to know as well, of course, but their support outside Japan is often lousy (apparently their support people in Japan are amazing).

Assuming the steel tracks will work on the new tanks, you'd just have to buy the parts to build a set. The parts list for the 56005 is in PDF format here.

If you can get the 9415498 "Track Bag", that'd be perfect. Otherwise, you'd have to buy two each of the four items listed above it. Don't expect your local hobby shop to have the parts in stock, and don't expect them to be cheap to order in.

Tamiya have, by the way, made previous steel-track Sherman models. Their first Sherman used one motor and twin-clutch drive, and was sold back in the 70s. If the tracks from a 56005 will work on your tank, the tracks from one of those original tanks ought to as well. Old broken Tamiya tanks show up on the auction sites (and in garage sales...) from time to time for good prices.

(Old working Tamiya tanks, in contrast, cost an absolute fortune.)

If you want to ask me a question, feel free - but please read this and this first.

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