Atomic I/O letters column #34

Originally published in Atomic: Maximum Power Computing
Reprinted here June 2004.
Last modified 16-Jan-2015.

 

Cable conundrum

I have recently built my new computer and, because I live with uni mates and we have no Xbox or PS2, the PC currently resides in the lounge room. I was wondering about running some cables under the floor so the computer can live in my room. I have measured the length of wire needed - 17 metres.

I wanted to run shielded A/V leads (for the TV and sound) and USB wire for a USB hub (game controllers, keyboard and mouse) to the lounge room.

It seems to do this I might need to boost the USB signal, as theoretically USB can only go 5m without a repeater. I also need advice on how the A/V signal will degrade over this distance.

I hope this is possible without too much outlay, because I'm probably not the only one who could make use of this setup.

Josh

Answer:
Sometimes people can get surprisingly long USB leads to work, but "work" in this case usually means "run one, and only one, full speed device that's highly tolerant of data flow interruptions, like a printer". Low speed devices (mouse, keyboard, joystick...) only have a three metre cable length limit, so your keyboard and mouse are actually even less likely to work at that distance.

These length limits are because of timing issues, not mere signal attenuation, so you can't just swap in better cable. Classically, you're meant to have to daisy-chain USB repeaters (USB hubs are repeaters, and so are powered USB extension cables, which can be thought of as single port hubs) to get a long USB cable. The awkwardness of this should tip you off to the fact that you're not meant to be doing it.

There's a workaround, though - "USB extender" gadgets. These look, physically, like USB Ethernet adapters - USB cable on one side, RJ45 socket on the other. They let you spool out as much as 50 metres of Ethernet cable between them, and as far as USB devices are concerned, the extender setup is just a short USB cable with a hub on the end. Expect to pay around $150 for a basic USB extender (including the two end units, but not the Ethernet cable). Here in Australia, MicroGram Computers has one. A more common kind of extender, by the way, pipes VGA video (of moderate resolution...) and PS/2 mouse and keyboard signals down Ethernet cable.

And then there's the A/V leads. There are two ways in which they could be a problem.

First, there's attenuation - signal loss over the length of the cable. Audio cables around 20 metres in length just require more gain at the end; tweak up the volume control and 20-odd metres of wire should be fine, provided it's not running next to a power conduit all the way or otherwise picking up noise.

The video cable (whether composite or S-Video) is also likely to be all right, as far as attenuation goes. Video attenuation manifests as darkening of the image, which for very long leads is likely to be unacceptable but which shouldn't be too bad at 20 metres.

For the video cables in particular, you'll want high quality cable, preferably with no joins in the middle - one 20 metre lead is better than a 10m plus a 5m plus a 2m, despite having more wire in it. Leads this long aren't easy to find in stores; get someone who can assemble cables to knock one up for you, if you don't feel up to crimping and/or soldering it yourself.

The other way in which long leads can bite you is if you end up with an earth loop, which is quite common if you connect shielded cables between devices in different parts of the house. If you hear a hum over the audio, that's probably why. You can read all about this in Jaycar Electronics' handy PDF-format primer, here.

If the earth loop problem is only caused by an RCA-cable connection, then you'll be able to deal with it with a simple isolation transformer box, like this one.

 

Post-OCing Stress Disorder

I own an Athlon XP 2500+ with the Barton core. Recently I overclocked it to around 1950MHz, but it was running around 70 degrees C with the stock cooler, so I reset it back to standard settings. But now my CPU temperature sits around 60 degrees while I'm not doing anything!

I even set the FSB to 100MHz, so the CPU was running at 1100MHz, but it still idles at 46 degrees! Is this normal?

Kristopher

Answer:
Motherboard temperature readings, even if they're based on modern CPUs' internal sensors, are unreliable. They're good enough for comparison with other readings from the same mobo, but comparing readings across different computers is often a waste of time.

My basic rule about this stuff applies: If your computer ain't crashin', then your CPU ain't too hot.

The temperature readings you report are not remarkable. Again, no crashes mean no problem - and even if the system does crash, it's not necessarily CPU heat that's the cause.

It's possible, though, that your overclocking experiment has mildly barbecued the thermal compound between the CPU and its cooler. Cheap thermal compound may not deal well with high temperatures.

The way to be scientific about this is to establish a baseline idle temperature for the computer - X many degrees above ambient - and then do your overclocking experiments, and then go back to stock speed and see if the PC idles warmer now (remembering to correct for ambient temperature - yes, that means you need a separate thermometer).

If the PC does now run warmer, then it's possible you've got some dry and powdery thermal goop in there. You should replace it with some fancy "premium" goop, the only really advantageous feature of which is that it's unlikely to dry out.

If you haven't established a baseline, though, there's nothing for it but to lift the CPU cooler and see what's up!

 

Precious metal (oxide)

At the moment I have a Thermaltake Volcano 9 HSF and the copper base isn't really smooth. I want to lap the base, but wouldn't lapping a copper heat sink remove the protective layer that stops copper from oxidising?

My temp now is 54C for a Thoroughbred 1800+, which is somewhat horrifying. Any help would be appreciated.

Steven

Shiny sinks!
They might not work any better, but shiny heat sinks sure do look cool!

Answer:
The protective layer that stops copper from oxidising is... copper oxide. Different metals corrode in different ways - iron rust is porous and flaky, and keeps allowing more fresh metal to be exposed to water and air, but copper and aluminium oxide forms an impermeable layer that prevents the corrosion from going any further.

Hence: Don't sweat it. Whip out the ultra-fine wet-and-dry paper and piece of plate glass and lap to your heart's content.

As mentioned above, though, note that you shouldn't be alarmed about this CPU temperature reading.

 

Well worth what he paid

My mother has recently purchased a new laptop for herself, so I did the only fair thing and claimed the old one - a Toshiba 435CDS with a 120MHz Pentium processor.

Now me and my Athlon have a beautiful relationship, I know every nook and cranny, but I have found that info on my new toy is pretty light on the ground. I only really plan to use it as a word processor for uni next year, but I would like to know how far I can work this little sucker (let's face it, 16 megs of RAM really isn't the best, well it's inhuman actually!).

Also (and I feel like a bit of a tool for asking), is it possible to upgrade mobos in laptops?

Nathan

Answer:
It's hard to find info on the 435CDS online, but you'll be able to dig up more if you search for the 430CDS. Like a lot of other Toshiba laptops with model numbers ending in "5", the only difference between your machine and the "0" version is the software it came with, and possibly the way it was sold (mail order versus retail). All of this is ancient history now, of course; this computer's an easy six years old by now.

That said: There's not much you can do to upgrade this machine. More RAM would be the obvious thing; a 120MHz Pentium can run Win98 OK if it's got at least 128Mb of RAM. But the 430s can only accept 48Mb total, and that's in funny EDO modules that are hard to find these days.

Regrettably, the memory is highly upgradeable, compared with the rest of the machine! As you suspected, a motherboard upgrade is not an option.

So, what to do with it besides run a DOS word processor (which, by the way, is a perfectly sensible if very boring option)?

Install Linux, of course!

 

What's that, sonny?

I've got some annoying problems regarding my sound. After getting a new PC (I kept my speakers) I found that my sound is really soft. This happens with everything I play on my PC - music, movies etc. Even when I turn the main and Wave settings to max in Volume Control it's still really soft.

I'm using onboard sound with a Shuttle MV43N mobo. Any help would be appreciated, as this is really peeing me off.

Duffy

Answer:
If your speakers don't have their own power supply, that might explain it. If your old computer had an old-style sound card with an amplified output, then it would have given reasonable volume with un-powered speakers, but modern audio adapters don't have amplified outputs. Modern audio adapters have enough output power to be fine with headphones, but you must use amplified speakers if you want more than whisper-volume.

 

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