Become a fan of Slashdot on Facebook

 



Forgot your password?
typodupeerror

Comment Re:A 'scope is useful when it is. (Score 1) 215

Your approach is a tad wrong. You won't ever know if you need to use it - how would you? You're not an oracle. What you do is you use it first, and only then you have proof that everything is peachy. My bet is that you have very poor idea as to how your circuits really perform. Just because it "works" doesn't mean it's anywhere near being properly engineered. Just look at transition times on modern micro controllers and on the discrete logic chips that you're using. If your scope won't let you see those transition times, it means you have no idea what effect all those transitions have on your circuit as a whole. For all I know your power supply is sagging every time a GPIO pin is switching, and your circuit works just because you got lucky, but it's much closer to not-working. There's a lot of analog design know-how that's needed to properly design "digital-only" electronics.

It took me 15 years to be at a point where I claim I know a bit, and I still consider myself quite dumb when it comes to analog. Well, at least I've got a multi-kW piece of power electronics to pass emissions on the first try, with a whole bunch of cables attached to it - that's kinda hard. It only happened because I was quite conservative in everything, and paid attention to a whole lot of details that don't matter at all in whether "it works". Now of course emissions and susceptibility often go hand-in-hand, so if your circuits ring all over the place, it may also mean that they'll pick up things you don't want them to pick up once someone places a cellphone nearby :)

Yes, I know that if you're on a tight budget, you simply have no option of getting more advanced test gear. If you're in the U.S., I suggest you keep good eye on eBay for used brand-name equipment. Sometimes you can get absolutely exceptional deals. A lot of older analog-style test gear is quite repairable, with free (or very affordable) service manuals available. There's a few exceptional all-transistor, no-custom-IC Tektronix and HP oscilloscopes out there, that go at least to 100MHz. They'd be still considered a baseline kind of an instrument. If you've got room for it, something is to be said for Tek 7603 mainframe. There are mailing lists / discussion groups for every brand of test gear out there, often with folks who used to design the very instruments you now get on the cheap.

Comment Scope is dead? Ha ha ha. (Score 1) 215

If you're serious about your work, you need a scope that gets down to device parasitics. If you're putting together a tiny little app-circuit-based switching power supply that's uses 0402 and 0603 passives with their puny parasitic inductances and capacitances, you better be able to see those effects or else. I'd say that for modern mixed-signal work you need at least 1GHz bandwidth, 10GHz sampling rate oscilloscope (or an analog equivalent, but there's like two to choose from). Anything active that's not bog slow and is sold in tiny surface mount packages (say transistors in ~1mm square packages) can very happily ring at hundreds of MHz. Your 100MHz oscilloscope will very happily lie to you telling "all's peachy boss". I mean, some geniuses back in the day made nice 100MHz+ oscillators in their capacitor-decoupled transistor-using reset circuits. This still happens today, except that your oscillating tank is all made from device parasitics, and quite high-Q.

I keep a couple Tektronix 7000-series oscilloscopes and assorted plugins and probes up and running just because they let me see what's really going on.

Comment Re:Let me guess (Score 1) 294

Maybe in times of Windows 2.x, 3.x and the 3.x-driver-under-95 this could have been true due to device-specific font brouhaha. Once non-device-specific fonts entered the scene (either truetype or bitmap fonts), the device-specific driver wasn't doing any typesetting. You know that, so please, stop with the misinformation. The GDI layer was doing it all, merely consulting the device resolution. Yes, many applications did their rendering such that the device resolution mattered since the fonts were scaled to device pixels. This is still a far cry from "raw typesetting" done by the driver. I don't even know who the heck still uses device fonts. Maybe some braindead label printer people, I don't even know if modern GDI still supports this crap.

Comment Re: External DVD drives (Score 1) 240

This is not quite true. There's this thing called compliance, and your device won't ever get a UL listing (or pass CE compliance testing) if it doesn't provide power limiting on low-voltage outputs. It's braindead to do anyway, as you'll be a ripe target for lawsuits. A USB port should basically protect a 3m 24AWG power wire pair from melting when shorted or otherwise overloaded. In a house, that's what the circuit breakers are for: they protect the wiring from overloads.

Comment Re:Or use what already exists (Score 1) 240

Heck NO! First of all, when measuring current consumption on a port that can deliver a measly 2.5W (5V at 500mA), you won't ever need a 15-20 Watt resistor, even if you used that resistor to short the power wires, much less when you use it in series with one of the wires.

Secondly, you do want as minimum of a dissipation on the current sensing resistor as your measurement amplifier will allow. There are two reasons for that.

The current sensing resistor is in line with the supply, so any voltage developed on it means less voltage to the device. Some devices consume fixed power and are thus negative resistances since they step-up the voltage using a switching converter. In those the more voltage drop your sensor develops, the higher the real current consumption since the load has said negative resistance. You definitely don't want that.

Also, whatever power the resistor is dissipating will necessarily heat it up, changing its resistance. Unless you measure that resistance (or the temperature of the resistor), you're facing an uncorrected error.

Alas, for USB use, you don't even need a discrete resistor. The resistance of the traces on your board (or a section of the cable) should be sufficient - 10mOhms is all you'd need, as it gives you a rather respectable 5mV at 0.5A. If you know your analog electronics, you should have no problem working with even 0.5mV at 0.5A, so just 1 mOhm is all you'd need. Even at 10A, such a "resistor" would dissipate a measly 0.1W, so with the currents seen in USB use, you're completely OK.

Comment Re:Nine Years? (Score 2) 294

This was a planned process and it took time for a reason. They did this slowly but surely. That's the only way to do it without blowing your budget many times over. I hope you recall that big software rewrites almost universally fail. This is a big infrastructure rewrite, it'd fail too if it were done in a "let's just rip it all at once" fashion. It's the same reason you need to be wary of many a company that grows too fast - usually it's internals can't keep up, and it'll eventually fail. Many companies failed just for not artificially limiting their growth. Southwest Airlines is a shining example that sometimes just artificially clipping your growth at 8% annually is a good thing to do :)

Comment Re:Let me guess (Score 2) 294

Word itself, like many other GUI apps that handle formatted text delegates a lot of the raw typesetting to the video card and the selected printer driver.

It's amusing that you speak about it with such conviction yet it's all a fantasy, no less. Man, where did you get this "insight" from? Lest anyone be confused about it: fuck no .

Comment Re:How about it uses much more fuel (Score 1) 567

The major contributors to "waste" when flooring it, that I know of, are (in no particular order):

1. Engine friction,
2. Rich mixture,
3. Torque converter losses,
4. Drivetrain friction.

Torque converter losses eventually go up with applied torque, even though they may be "funky" at lower torques. Engine friction is an issue at high RPMs, but you get better efficiency at high RPMs as well, so it really depends on a particular engine. Rich mixture is a factor as well, especially if you're not using premium gasoline. Drivetrain friction on gear pairs simply goes up with torque, so if everything else were constant, you'd want to minimize the torque, but of course everything else is quite complex so this has an effect, except when it doesn't ;)

What I've noticed is that using regular gas I get worse mileage with jackrabbit starts, compared to premium gas. It's easy for me to test, since 99% of my driving is on the same road every workday. We do groceries and errands in my wife's car. For freeway driving that I do very occasionally, and is mostly on cruise control, there's no benefit to premium gasoline, other than slightly quieter engine operation (the difference is measurable, but is really meh otherwise). In my city driving, it's actually cheaper for me to use premium gas.

So, if you're using regular gasoline, you probably shouldn't be flooring it, but on my particular car there seems to be no big difference in gas consumption between aggressive starts and less-aggressive ones if I use premium gas. The biggest impact to me, it seems, is from slight "hypermiling" - letting off the accelerator way ahead of stopped traffic, coasting longer. When I do that, jackrabbit starts on premium gas seem not to matter at all.

Comment Re:What about the US empire? (Score 3, Informative) 243

LOL, Genghis Khan has way more up his sleeve than you give him credit for. Show me a U.S. president that had about a thousand 1st-generation descendants. 800 years later - today - Genghis has about 15 million descendants. This is based on hard science genetic testing, not historic record, by the way. An average male person living 800 years ago has a bit above 500 descendants living today.

Comment Re:after all these years (Score 3, Informative) 243

We may not be able to identify his tomb, but sure as heck we can identify his ancestors! It so happens that this guy had about half a thousand children that have descendants that survive today. Rape and pillage he did, allrighty. There's more than ten million of those descendants alive today, by the way. Genetics for the win, I say.

Comment Re: Security 101 (Score 1) 332

So, obviously if one of them dies in a random accident, you've lost your investment, right? That's why one can't use a word investment here. It simply doesn't work, unless you're literally putting a dollar value on human life, happiness and whatnot. Not every cool thing you do is an investment, nor can it be thought of as being one, even if it costs you real money.

Going back to your dad: to support his position, one'd need to support a zero-sum stance where one says "either I support your low-risk lifestyle in college, or I get to pay some other kid, or maybe even myself". I think that's going full-retard.

Comment Re:That's a shame (Score 1) 332

I have 10 ton jackstands, and for the life of me I wouldn't know how they could be unreliable. When the car is up on four of those jackstands, there's no reasonable way to tip the jackstands by merely interacting with the car. I've had two people try to push the car in various directions as hard as they could - nothing happened. It wouldn't budge, heck it seemed as if it was comparably glued to the ground. When the car is supported by the suspension, there's a lot of "give" and you can get it moving a bit. On the jackstands it's quite different.

Sure, if you have crappy jackstands then it may not be quite safe.

Slashdot Top Deals

They are called computers simply because computation is the only significant job that has so far been given to them.

Working...