Dan's Data letters #127
Publication date: 7 October 2004.Last modified 03-Dec-2011.
Machine shop nerds
As an avid reader of your website and your obvious knowledge of all-things-knowable. I'd like to ask, do you know how to drive a stepper motor from a PC? I'm attempting to build a small CNC plotter machine as a pet project.
Guy
Answer:
Why yes, I do know.
Well, actually, technically speaking, I don't. But my friend Alan does.
His latest micro micro-stepping controller project's here. He wants to get some boards professionally made, but that means at least a modest quantity of the things, all of which he does not need. So, readers of this page who're interested in the idea, click ye on Alan's e-mail link and help him work out a bulk purchase deal.
HD or not HD?
In Letters #126, regarding large TVs, you provided a link to Sony's KPFS57M31 rear projection TV.
I was looking into buying this TV recently, and was wondering what resolution it can actually display. The Web site states that it has HD input - 1080i/720p/576p, but not what it can actually display. I mean, although this TV accepts a 1080i input, I'm sure it doesn't display 1080 lines of resolution.
I know that plasmas and LCDS quote display resolutions. Is there any way to find what resolution this TV can display?
I have emailed Sony Australia regarding this question, and they said it would display 1080i "effectively", but "we do not measure the physical resolution of this TV".
Chuong
Answer:
Sony don't even own up to what projection technology the KPFS57M31 uses, but I'm 99 point something per cent sure
it's a three-gun CRT projector set.
This introduces some uncertainty in the resolution department, because the resolution of cathode ray tubes of all kinds isn't clearly defined. How many pixels a CRT can display depends on how fuzzy you're happy for your image to be. This explains Sony's weaselly reply to you; there's actually no standardised way to measure the ceiling resolution of a CRT. All you can do is make estimates based on its dot pitch (or stripe pitch, for aperture grille tubes), as I've explained in reviews like this one.
A CRT being fed a particular signal has a definite vertical resolution it's trying to achieve - that's the number of scan lines - but for HDTV applications with TV-type tubes, not high-res computer tubes, the screen may not actually be able to display even 720 (say) lines of data, much less 1080. (Actually, 720p should look better than 1080i, as I discuss here.)
You can, however, expect a basic seven inch gun RPTV to be able to achieve 720p resolution (reference; that page is only talking about NTSC sets, but the resolution issues are the same for HDTV in PAL and NTSC). That's likely to be quite good enough.
Warm swapping
I'm considering buying a WiebeTech ComboDock or SNT ST-2316C. The ST-2316C looks better. But can I run it open so that I can change drives frequently and easily?
I've tried things like ADS Pyro Drives, but it's very difficult to easily unplug drives from those boxes, so I am looking for a way to just pop them in and out without opening and closing cases all the time.
Steve
Answer:
You can't swap drives in any kind of actual external box as easily as you can with the WiebeTech adapter (or the cut-rate
alternative) but yeah, you could do it. Attach the drive to the tray with only one screw
(or put pegs through the screw locations so the drive just sits on them and doesn't slide around), and you'd be OK.
It's also the work of a moment to slide the SNT box's cover on and off when the cover's own two screws aren't done
up, so you can easily protect a drive from damage if you're using it for more than a brief period.
Automotive illumination
I recently purchased a dual stick cold cathode kit with an inverter that can handle both sticks, and I want to use it to add glow to a car interior.
The question is: Can I increase the length of the wire from the inverter to each of the CCFL tubes? If not, Why not? If yes, how long can I go?
Michael
Answer:
Yes, you can make the wires longer. Probably.
The limitation for these things isn't the resistance of the cable - because of the high voltage and low current it's carrying - but the capacitance between the two conductors. If you run the rig you've got and twist the cable up (or just make a fist around it), you'll notice the lamp(s) dimming. That's because the increased capacitance of the two conductors close to each other is letting a significant amount of the high frequency AC leak straight from one conductor to the other.
I haven't conducted any experiments to see what "low capacitance" cable is best for long-ish runs with CCFLs at the other end, or how easy it is to just goose up the output voltage of the inverters (at the risk of blowing 'em up...). But I can tell you right now that putting a CCFL at the end of three metres of figure-8 zip cord (The Teenage Car Modder's Friend) will give you very little light.
Devinylisation
I bought a new Pro-Ject Debut turntable for my birthday and am using it to digitize my LPs. It replaces the old Pioneer that runs through the Pioneer AM/FM Tuner/Amp that I've had since 198x, and which of course plugs into my sound card.
My question is: Would I get any better quality of sound at the sound card if I used a specialist phono pre-amp, either a purchased one or even one of the DIY ones? I'm not unhappy with the Pioneer, but is there any quality benefit in using a pre-amp, for the cost involved?
Deborah
Answer:
Probably not. Some audiophiles might disagree, but as I've pointed out before, cursory
examination of the unexciting noise, distortion and channel separation figures for vinyl indicates that the pre-amp
is very unlikely to be the weak link in the chain, quality-wise.
Your sound card's line in, however, may be significantly noisy, or have other nasty defects; ordinary PC audio hardware commonly picks up noticeable interference from the rest of the computer, for a start. In that case, you may reap quite noticeable benefit from a higher quality line-in device (this one, for instance).
Half way there
I've just come across a brand new pair of Sennheiser HD 600 headphones (still haven't solved the plural issue) and have just started listening to them in the comfort of my living room chair and couch, obviously after the obligatory one night of breaking them in (by the way, is that really necessary?). First impression: they sound amazing, compared to my medium class living room speakers.
However, I've discovered that with these 'phones there are quite some quality differences between the various headphone outputs on my equipment. My el cheapo Sony CD player plays adequately, no discernable hiss or other things my ears can pick up. But its output only has one sound level (LOUD!) so it is not really suitable for comfortable listening. My not so el cheapo Denon receiver, however, has quite some hiss, but has volume control. And last, my Sony DVD player has volume control and no hiss, so it is the preferred source for the moment.
Do I need to upgrade to a dedicated headphone amp in order to experience the abundance of quality that the HD 600's have? Your HeadRoom gear reviews have led me to believe that there are some serious gains to be had by moving to a dedicated amp, but you have only covered the computer/portable ones in your reviews.
Remco
Answer:
On the subject of break-in: Yes, it's conceivable that it does have some effect, for some headphones. The dramatic
break-in differences reported by many users, however, pretty much have to be imaginary, particularly when you consider
the similarly dramatic improvements reported by people who "break in" things like cables. Including digital cables.
Regarding the headphone amp: Yes, it's probably worth getting one.
Generally, most lower impedance headphones can be driven quite well by various devices, even including higher quality portable players. The HD 600s, though, have a quite high 300 ohm nominal impedance, which means you need to wind the volume knob well up to get respectable loudness out of them. Many of the headphone amps integrated into audio components don't expect to have to drive anything with an impedance much above 120 ohms, and may, as you say, have noise and harshness problems when cranked up further. Or may just be lousy at all volumes; it's common for "blackgoods" manufacturers to keep costs down by giving hi-fi components really lousy headphone outputs, because few customers ever use them.
Some high-end headphones are really difficult to drive to decent volume; 600 ohm impedance and not-too-great efficiency. The HD 600s at least have decent efficiency, and only medium-high impedance, but you're still likely to see considerable benefit from an amplifier of some kind.
This doesn't, of course, mean you need to go nuts and buy an amp that costs five times as much as the headphones did. A CMoy-based amp running from a mains power adapter would pretty much solve your problem by itself, for instance.
Juice boxes
I'm looking for a digital camera battery that won't run out of gas so frequently.
My camera came with a Canon NB-2L 7.4 volt 570mAh battery.
I read somewhere to get more power, you need more mAh. I can't seem to find anything more than 570 mAh in the electronic stores in the Chicago area, though. They all seem to stock Digipower or Maxell. Also, I cannot see on the packages whether their batteries are NiMH.
My camera is only 18 months old; I've probably taken about 30 pictures per month. I use the LCD screen on all shots.
Any hints on where I can find a longer lasting battery?
Connie
Answer:
You won't be able to fit a bigger battery into your camera. There may be some slightly higher capacity batteries in
that size, though I doubt it; usually, "higher capacity" off-brand lithium ion batteries are just misleadingly marked.
Lithium ion batteries generally need to be bigger to have higher capacity, and the only devices that can use larger
batteries are camcorders that wear their battery on the side or back, not in an enclosed bay.
All of the batteries that can fit in your camera will be lithium ion. Your camera can't use an internal NiMH battery.
There is a solution, though, if you're willing to use an external pack that plugs into the AC adapter socket. There are pre-made packs in various shapes and sizes (this one, for instance), to save you from rolling your own.
LANs For The Puzzled
I'm an Australian who's about to get ADSL, and wondered if there is there a good site that explains home network setup and Internet sharing simply? I have looked around, but there is one thing I do not understand. If I have an ADSL modem coming into a router, and two PCs are connected to the router, does the router enable me to "see" the other PC, or is it for Net connectivity only?
I would like to both share a Net connection (preferably without having to have one PC on all the time in order for the other to use ICS), and network to one other PC.
Does this make sense?
Russell
Answer:
You might like to check out Practically Networked. If all I'd done
for the last four years was expand my old networking guide, then my site would probably
look like Practically Networked by now.
A home DSL router should work as a basic network switch as well, so yes, it'll give you a LAN as well as a shared Internet connection.
You can use most cheap "plastic box" connection sharing Internet appliances with most DSL providers these days, but those ISPs that require something odd for login (like iiNet's setup, where by default, with my DSL adapter at least, you have to use the adapter's HTTP interface and click buttons to connect) won't necessarily work. If you pick any vaguely popular Aussie ISP, though, there should be a recommendation about what sharer box to use on the Whirlpool forums.
The ISP itself may have a sharer box they'd like you to buy, too. That's likely to be a great way to spend $AU100 or so more than you have to.
But does the fridge taste better?
It was nice of those lovely Wine Clip people to send you the world's strongest fridge magnet!
Brad
Answer:
Actually, I'm using the giant truncated square pyramid magnet from this review as a fridge
magnet at the moment. If you stick it on the fridge pointy end first, it's possible to grab it and yank it off, or
just tilt it so you can stick a pile of mail under it, or something; its strength is still a bit frightening, but
it works very well.
I once absent-mindedly grabbed that magnet when I had an ATM card in my hand, though. Well, so much for that magstripe.
