There’s been a hull breach from a refrating pulse torpedo, and we’re all out of nanobots. Never fear though, because Dan Rutter’s donning an astro stripper and the might super wrench to fix it himself. Personally. Tautology at its finest, yes, but not as fine as the Logitech MX500 optical mouse, or Dan’s super wrench.
IOOTM: CRT conundrums
I: CRTs are damn strange.
As I understand it, you have your electron beam firing onto little triads of phosphor dots -- red, blue and green ones. These dots are painted onto the inside of your screen and light up in various levels of brightness depending on how many electrons hit them.
If they're physically painted onto the screen, does that mean all CRTs have a "native resolution" similar to the way LCD monitors do? And if the dots are fixed, why doesn't the image quality degrade when you increase resolutions above this native res? And why can you have resolutions that aren't whole multiples or factors of the native resolution without the electron beam hitting the wrong triad, or dot, and making the colours come out all screwy?
This has been bugging me and my mates for a while.
Samuel Robert West
O: CRTs do not have a 'hard' number of pixels, like LCDs, because their phosphor dots are not arranged in a rectangular matrix. The standard arrangement of dots on a conventional shadow mask CRT is hexagonal.
While CRTs don't have a "native resolution", they do have limits; practically all CRTs can display resolutions that are too high for the number of actual phosphor dots available on the screen. When you display too high a resolution – 1,600 by 1,200 on a 17in CRT, for instance -- you get a fuzzy image.
The general rule of thumb for shadow mask monitors is that you need about 1.25 dot triads (adjacent sets of one red, one green and one blue dot) per pixel.
The screen in the above picture doesn't look hideously blurry when viewed normally, because the phosphor dots are too small for the human eye to resolve. You can just see them, as a hexagonal grain pattern, if your eyesight's ok, and your nose is pretty much touching the screen. They become clear if you use a magnifying glass or jeweller's loupe, but that's not the usual monitor viewing technique.
As you can't see the individual dots, you perceive all-dots-bright as white, and all-dots-dark as black, and edges look pretty sharp. They won't at higher resolutions, but there are enough dot triads per pixel to carry it off at 1,280 by 960.
There's no distinct correlation between pixels and dots. The pixels just fall as they will, as the monitor does its best to paint however many pixels you've asked for on the phosphor dots available.
The reason why changing the resolution doesn't screw up the colour is because there isn't just one electron beam; there's one each for red, green and blue. The beams come from different spots at the back of the tube, and the shadow mask -- or aperture grille, in Trinitron/Diamondtron monitors -- stands between each gun and every phosphor dot that that gun is not meant to be able to illuminate. You can temporarily misalign the mask, and significantly misalign an aperture grille, by whacking the monitor; I don't recommend you do that, but if you do, you'll notice colour changes while the mask or grille vibrates, and its shadow moves around. Drop a monitor hard enough and you can permanently misalign the mask or grille, which will give you trippy colour forever.
Etch the oceans!
I: I have just been reading in the April issue of Atomic about etching PCBs for the Aural Decipher. Something that has been preventing me having a go at etching PCBs is what to do with the etchant after use -- how to neutralise it, and whether it is then safe to simply dispose of down a drain. I'm guessing that the etchant would be a fairly strong acid (it is removing a layer of copper after all).
Nowhere I have looked seems to have any directions of what to do after etching is complete. They leave it up to you to figure out what to do with it.
Matthew Ruth
O: The kinds of PCB etchant used by hobbyists aren't actually acidic; they're alkaline. But they are, as you say, not good to tip down the drain. Copper is poisonous, for a start, and it goes into the solution in the course of etching the board.
You can pour all sorts of horrible acids and bases down the drain with sufficient dilution (caustic soda drain cleaner, for instance, is ghastly stuff when concentrated, but goes into the sewer by definition), but no amount of dilution makes it okay to dump toxic metals. This doesn't mean that lots of hobbyists don't dump used etchant down the drain, mind you, but they shouldn't.
The most popular hobbyist PCB etchant is ferrous trichloride, which is cheap but dirty. Ammonium or sodium persulfate is cleaner and more elegant, but needs to be heated to work.
You can neutralise used persulfate etchant by mixing it with used PCB developer solution, but there'll still be copper in there. To make the result safe to dispose of yourself, you can mix it with cement; that locks up the copper effectively, and leaves you with the makings of a lovely rockery.
If you don't feel up to that, you should be able to unload the stuff at your local Waste Management Centre, or whatever it's called in your state or territory.
There's a good PCB making FAQ here, by the way: www.ping.be/~ping0751/thepcb.htm
CPU on a wire
I: Dear l337 Atomic Hax0r gUrU
I was wondering: are their any socket extensions you can plug into your CPU socket to extend it, just like an extension cord? Then you could cool your CPU outside of your case, where there is cooler air. Think of all the possibilities -- you can seal your CPU off and have a direct contact water cooling set up! No more Artic Silver!
Steven Xue
O: Can't be done, I'm afraid.
The high bus speeds of modern CPUs -- heck, even of very [i]old[/i] CPUs -- mean that if you unsoldered the socket and attached it to the motherboard with a bunch of lengths of hookup wire, you'd get horrible noise and crosstalk problems between the wires carrying signals. Shield all the wires and capacitance and inductance will eat the signal. Jacking up a socket a few millimetres would be doable, but that wouldn't achieve much; a real extension cord would be a very difficult proposition indeed.
Assuming you managed to magically solve the signal degradation problems, you'd also find you needed pretty hefty wire, because even if you boosted the supply voltage so that the CPU still got enough volts through the extra resistance of the wires, you'd burn up thin wires. A 60-watt CPU running from 1.5V is drawing a total 40 amps through its various supply wires. Even if you managed to squeeze 20AWG hookup wire into the socket, you'd still only have a current rating of about 3.3 amps per strand!
Alas, poor hard drive. . .
I: I was in the process of creating a server, and required a hard drive that was in my main PC. My brother was playing a game at the time, and asked if I could remove the hard drive without him having to shutdown, as the drive wasn't plugged in. This seemed logical, but about three seconds after unscrewing and removing the drive I noticed his game cease movement. I had accidentally pulled the IDE cable out of my main drive.
I shut down, plugged it back in and restarted, but nothing happened.
Is my hard drive completely dead, or is there some way of reviving it? Should I start saving for a new drive?
Damien
O: The drive's mechanical components, and the data on the platters, are all probably perfectly fine. There mi
Issue: 137 | June, 2012