unclejed613

"I'm going to blow up the earth, it obstructs my view of Venus......"

quite often there are posts i see, that remind me of this classic cartoon line. common subjects are EMP generators, lasers (in the Megawatt or Gigawatt range), and other devices in the "infernal machines" class. usually the interest in these devices is from some type of annoyance factor ("my neighbor plays his stereo too loud", etc...)... in fact i've been known to dabble in the "infernal machine" category myself from time to time (once built a Tesla coil that blanketed the 4-story apartment building i lived in with wall-to wall RFI, and burned out every CMOS chip within 50 feet). my interest was just plain curiosity, i wanted to build one just to see it work. while i have no problem with experimenters trying stuff out to see it work, i do have a problem with annoyance driven projects whose purpose is to intimidate or exact retribution. grow up, and tell your neighbor...

it would be nice to be able to measure impedance of an AC circuit as easily as measuring DC resistance, wouldn't it? there are many times in the audio business, when i would like to find out what the impedance of something is at a particular frequency, and i usually have to resort to some indirect method. an impedance bridge is a piece of test equipment that measures impedance, but such a beast is expensive, and is an indirect method, and a bit more complicated than putting a pair of test leads across a device and reading a number. i would like to be able to put a pair of test leads across a device and know it's impedance as a direct measurement. of course there would be one added step, dialing in the frequency i want to measure at, but i can live with that one extra step. so how to go about it?

a DC DMM ohmmeter circuit is a simple device. you have a digital voltmeter across a pair of probes, and a DC current source set to a known current. if the current were for instance...

everybody should know what this means...... if not here's a linux page with a description of this command and it's usage.........
http://www.wlug.org.nz/rtfm(1)



ok, if after you read that, and you're still not sure, it means Read The Fine Manual, Read the Fun Manual, or another version not suitable for polite conversation.

working for a large service center, i see a lot of equipment that comes in for repair which, frankly, wouldn't have to if people pulled out that mysterious book that comes with your shiny new home theater system, sat down and read it cover to cover just once. and those who should read the manual are not only the consumer, but the sales staffers who guide the consumer in their purchasing decisions. two examples of this are from actual pieces of equipment that came in for repair recently one of them is from a consumer, one is from a home theater sales "tech". the first one (from a consumer adding an additional...

actually, not me, since i work for a warranty service center, but i saw the t-shirt and had to post a picture of it. it says "I void warranties" and has a picture of many common screwdriver bits used in consumer electronics. if it's broke and it's still under warranty, get it fixed for free, don't open it to poke around. if it's out of warranty, and you don't have a service plan you paid for, go ahead, poke around all you like, it's already broken and you will a) find something simple like a bad solder connection, b) figure out what component has failed, c) take it to get fixed COD (take my word for it, the repair will cost less if everything is back where it belongs), or d) give up on it and toss it and buy a new one.

there may be no such thing as a free lunch, but a free repair on a warrantied item (or maybe the manufacturer can't figure it out and gives you a new one anyway) is a pretty good deal if you can resist the urge to see what made the thing tick before...

i see (and answer) a lot of posts both here and elsewhere about 1kW inverters. my immediate answer is usually something along the lines of "there's no such thing as a free lunch". first of all do the math. 1000W/12V=83A. assuming about 15% in losses, that's pretty close to 100A. not only are we talking "heavy iron" here for a transformer, we're talking heavy copper too, since the wire used in the primary circuit needs to have negligible copper losses at 100A. you also need about 20 MOSFETs per side (of a split winding on the transformer) assuming 10A devices, and a safety factor of 2:1. that also makes for a very large heat sink. so basically we're looking for a "welding" transformer with a 12Vct @100A winding, 00ga wire (or at the very very least 2ga kept very very short) 40 MOSFETs, and a very big heat sink.

like i said above, there are 1000W inverters that can be had for free, but it takes a bit of looking to find one that works from 12V....