posted
In the spirit of Jon Boy's cool thread about English, and in homage to it, I thought I would open up the floor for questions about something I know a bit about. I've really enjoyed the inside look he's giving into the things he studies and works with. Is it possible anyone would like to know something about mine?
[ April 28, 2004, 11:09 PM: Message edited by: ak ]
Posts: 2843 | Registered: A Long Time Ago!
| IP: Logged |
posted
The bit I never got is: how do the electrons get from the big spinning magnet into the power line? I get the bits before that, I get the bits after that, I don't get that part. Is the electricity around the magnet a field of charged electrons or is it inside the metal?
Now that I'm having to put it into words, I think it's the basics of the big spinning magnet wrapped in copper wire I don't get.
Posts: 2283 | Registered: Dec 2003
| IP: Logged |
posted
I'm sure I've been told how several times, but how do those elevator buttons work? You know, the metal ones that need touch to turn on.
Posts: 1892 | Registered: Mar 2002
| IP: Logged |
posted
AvidReader, the electrons are present all throughout the copper that is in the wires of the whole power grid. It's almost as though there is a sea of electrons there. The thing that makes them move about is a sort of "pressure" called voltage. Electricity always wants to flow away from places with higher voltage towards places with lower voltage.
So with a generator what you are doing is temporarily revving up the voltage in the wires at one point (where you're spinning the rotor), and then you're tapping into that and bleeding it back down at a different point (say, in your computer). The electrons themselves actually have to travel in a big circle. There has to be a return path for current to flow. That's why there are two wires, two prongs to your plug.
So what the generator does is sort of shove hard on the electrons at its place, then far away at your house other electrons feel that impulse as a sort of pressure (not actual pressure but analogous to it) and they respond.
The electrons themselves don't jump the gap from the "spinning magnet" (called the rotor (it rotates)), to the wires wrapped around the surrounding metal (called the stator (it stays still)). What they do is create a field which acts to shove the electrons in the stator around. A little like the way a pump can jack up the air pressure in a tank, the rotor jacks up the voltage in the stator, and from there electrons flow down the wires across the transmission lines and out to your house.
I probably ought to say for completeness that the voltage "pressure" in the circuit is actually switching directions 60 times a second (in most of the Western Hemisphere, and other places like Saudi Arabia), or 50 times a second (in most of Europe, Australia and the far east). This is why it's called AC or alternating current. Thomas Edison despised AC and all his electric systems were DC or direct current, like a battery circuit. Westinghouse went for AC, because that made the voltage easier to change up or down using transformers, and in the end Westinghouse won out.
[ April 28, 2004, 11:00 PM: Message edited by: ak ]
Posts: 2843 | Registered: A Long Time Ago!
| IP: Logged |
posted
Suneun, the elevator buttons work because they constantly measure a quality called capacitance. Capacitance is the ability of something to hold a static charge.
When you touch the button, you suddenly add a lot of capacitance to what the button had by itself. In fact, there is a small charge placed on the button, and though you don't feel it (since it's so minute), a tiny bit of electricity flows from the button over the surface of your body. This tiny surge is what the electronic circuit detects to know that the button has been pressed.
Posts: 2843 | Registered: A Long Time Ago!
| IP: Logged |
posted
I'll open up the topic to how anything works. This is technology 101. What I don't already know I will find out for you.
Posts: 2843 | Registered: A Long Time Ago!
| IP: Logged |
posted
I don't quite understand alternating current. So if the voltage pressure is switching back and forth, does that mean that the electrons are just moving back and forth and not traveling in a loop through the circuit? How does an adapter change something from alternating to direct?
Posts: 9945 | Registered: Sep 2002
| IP: Logged |
posted
I'll answer the second question first. An adaptor, like one of the little black boxy things affectionally known as "wall warts" converts AC to DC in two main stages. First there is a transformer which converts 120 Volts AC to something lower (perhaps 12 Volts or 6 Volts), but still AC or alternating current. Next there is a rectifying diode network which changes the AC to DC, or a smooth direct current.
The transformer is a coolio device which takes advantage of something Faraday noticed, i.e. that when you change the magnetic field inside a coil, it generates voltage. You can try this, in fact. If you shove a bar magnet into the center of a coil of wire, there is a little squirt of voltage in the wire that corresponds to the motion of the magnet. Repeatedly shoving it in and yanking it out will generate a series of pulses of voltage first of one polarity, then the other. (Tries to think of a clever double entendre here and fails.) It works in the other direction too. When you run a current through a coil of wire, any chunk of iron in the center of that coil will be magnetized. This is called an electromagnet. It's like a permanent magnet that you can turn on and off with the flick of a switch.
So the current in a coil is related to the change of the magnetic field inside the coil. This effect is stronger the more loops there are in the coil.
Here's the cool part. You can run this trick in both directions at once. If you wrap one wire around a chunk of iron (called the core) say, 100 times, and another wire around the same core 200 times, then you can run electricity (AC) in the first wire, which changes the magnetization of the core back and forth 60 times a second, and hence generates a voltage in the second wire at double the original voltage! (This is neglecting small losses from inefficiency.) This little device is called a transformer, and it can be used to convert the voltage of AC either up or down. The only thing that determines the voltage change is simply the number of turns of the coils in the input (called the primary) and the output (called the secondary) wires.
That's why we use AC, in fact, because transformers make it very easy to change the voltage to whatever we want, at will.
[ April 29, 2004, 01:49 AM: Message edited by: ak ]
Posts: 2843 | Registered: A Long Time Ago!
| IP: Logged |
posted
The second part of the "wall wart" adaptor is the rectifier, which changes the AC to DC. Next I want to explain how this works.
Diodes are electrical devices that allow current to flow in one direction only. A rectifier bridge is a circuit in which four diodes are connected together in a such a way that whichever way the voltage flipflops on the AC input, it always has the same polarity on the DC output.
I really need to show you a picture. Look there about a third of the way down where it says transformer + rectifier + smoothing. The diamond shaped diagram in the middle is how a rectifier is shown schematically. The little triangles are sort of like arrows pointing in the only direction the electricity can flow. The straight lines at the head of the arrows symbolize the fact that when electricity tries to flow back the other way, it hits a "dam" of sorts, and can't go that way.
When AC (which is a wavy line (sine wave) positive and negative) is hooked up to the left and right corners of the diamond, the diode network makes sure the output connected to the top and bottom corners of the diamond is always positive in the same direction. It's still very bumpy, though, because all it's done is take the part of the sine wave that's underneath and make it positive instead.
So the last stage is a smoothing function, which is usually done by a capacitor. A capacitor stores charge temporarily and squirts it back out. Most of these wall warts will still show a little 60 Hertz ripple in their DC output voltage. As long as it's not too much, it's usually no problem. You wouldn't want to use that in any audio circuits, for instance, or it would give you a rather loud B flat hum.
60 Hertz (cycles a second or Hz), is the note B flat (slightly sharp). If you are a musician and you have relative pitch but not perfect pitch. If you ever want to fake perfect pitch, just stop and listen to the world around you. There will be some refrigerator or pump or flourescent lighting or something in the area which is humming quietly that pervasive B flat.
Rainbow Bright, for those of you who remember her, had this belt that made a strong 60 Hz hum when she energized it. Obviously her technology for colorizing the world and generating rainbows you could travel on used 60 Hz power. Murky and Lurky probably just used DC or something.
[ April 29, 2004, 12:58 AM: Message edited by: ak ]
Posts: 2843 | Registered: A Long Time Ago!
| IP: Logged |
posted
Jon Boy, yes, the individual electrons are just travelling back and forth. However, there must be a continuous loop of metal or other conductor all the way around the circuit for it to work. Think of waves in the sea. Lots of power is traveling from a storm far out at sea to the shore, but hardly any actual water is moving that whole distance. Mostly each bit of water is shoving the water next door, and on and on, until the water near the shore shoves itself up onto the beach.
The energy you use actually comes from the voltage drop across your lightbulb or strip heater or whatever device you have plugged in.
Another way you can think of it is like a small waterfall where you get energy from the water dropping over a dam. Picture a very strange dam built in the middle of a lake which is sloshing back and forth so that the water level on each side keeps reversing. Whichever side is higher, you can still get energy from letting water drop across from the high side to the low side.
Posts: 2843 | Registered: A Long Time Ago!
| IP: Logged |
Sorry to impose on this tech thread. I was wondering if you might have any poetry to go along with this topic, or not. I would dearly like to read some.
posted
I don't have any electricity poetry, sorry.
But I do have this one that's quite old. Maybe I should do an astronomy thread someday.
Skygazer
Stars like clotted dust across the sky, You fit the Barlow, focus, squint your eye, While gleaming planets swim into your view, I watch the night, the telescope, and you.
Exploding starsurf winds, galactic seas Across the aeons spins in mysteries Of long ago, of here, the never now, The deeping cold, the whistling void, and thou.
Posts: 2843 | Registered: A Long Time Ago!
| IP: Logged |
posted
I'll use this thread to make a techie's confession: no matter how much I stare at the diagrams on howstuffworks, I can't picture an engine in my head. Especially if it's DOHC, all those valves somehow reciprocating in time... I blame all those 3D paradox posters, of which I've been able to "see" precisely zero.
Posts: 1839 | Registered: May 1999
| IP: Logged |
posted
Richard, you should maybe rebuild one, or go take a long look at one being rebuilt. There are really 4 dimensions you have to see something like that in (3 spatial plus time), and it's very hard to depict with diagrams.
Another thing you can do is look at simpler versions and understand them completely first. The first widely available internal combustion engines were single cylinder and sold to run farm equipment with belts. A retired engineer I know collects them, refurbishes them, and shows them. He's fanatical about it. There are other like minded people who share his passion, and they have get togethers to which they all bring their toys and have demonstrations. They're the most incredible infernal contraptions you can imagine. They make a ludicrous noise like something in a mad scientist's laboratory. Absolutely delightful! Posts: 2843 | Registered: A Long Time Ago!
| IP: Logged |
posted
ak, while I don't have a question at the moment, I would like to thank you for starting this thread. I've always been fascinated by technology and how it works.
Oh, wait, I just thought of a question. How does a camera flash work? Does it have a capacitor in it? I'm referring to a stand a lone flash unit as opposed to the ones that are built into point and shoot cameras.
I have a 35mm camera and a detachable flash unit. I'd love to know how it works. Thanks.
Posts: 4569 | Registered: Dec 2003
| IP: Logged |
posted
A flash unit for a camera is like a very bright neon light (only using xenon gas instead of neon). The light from them comes from the ionization of the gas inside. The electrons in the gas jump into higher orbits in the presence of a strong electric field, then emit photons when they fall back into their normal orbits. Since neon lights need high voltage, and because a camera flash must be powered from a battery which supplies low voltage, a number of other electronic components are needed to make up the total flash package.
First of all, there is an oscillator which changes the DC to AC. This is basically a switch that turns on and off very rapidly. The high pitched whine that you may hear while the system is charging comes from this switch.
Secondly, there is a transformer to change the AC electricity from low voltage to high voltage. It does this by way of turns of wire around an iron core, similar to the description for the "wall wart" adaptor, above, but this time with a whole lot more turns of wire on the output coil (or secondary) than on the input (primary). That way we can take, for instance, 1.5 Volts in (a typical battery voltage) and get out the 500 Volts or more that are needed for the very bright light.
Next, there has to be a capacitor to store the charge that's building up, because a small battery can provide energy rather slowly, and we need an awful lot of energy in a short time to make our flash very bright. Capacitors are essentially metal foil sheets which are close together but not allowed to touch. The two sheets of foil are sandwiched together with a third sheet between them (the dielectric), which keeps them from touching and discharging. The whole sandwich is typically rolled up into a little cylinder. When you apply a voltage across a capacitor, it can store energy, similar to a battery, but with much shorter charge and discharge times, since no chemical reaction is taking place as it is in a battery.
Then finally, of course there is a trigger switch, which is wired in with the camera's shutter, so that the flash will correspond exactly with the time the shutter is opened.
When you press the button to ready the flash, the oscillator turns DC from the battery to AC, which then goes through the transformer to be jacked up to a higher voltage and stored in the capacitor. Once the capacitor is sufficiently charged, the indicator light will light. Then when the camera shutter is opened, the trigger fires and lets all this stored energy light up the xenon in the little tube.
[ April 29, 2004, 01:37 PM: Message edited by: ak ]
Posts: 2843 | Registered: A Long Time Ago!
| IP: Logged |
quote: The electrons themselves actually have to travel in a big circle. There has to be a return path for current to flow. That's why there are two wires, two prongs to your plug….
I probably ought to say for completeness that the voltage "pressure" in the circuit is actually switching directions 60 times a second
I was under the impression that the alternating current itself took the place of the return circuit. When wiring our basement, the hot lead was a single strand, and the neutral and ground wires both went back to a ground, not the wire coming into the house. So there isn’t a return circuit to the generator, just to the main switch panel in the house. Like this:
DC: Positive pole ------Appliance --------- Negative Pole, where positive pole and negative pole are both part of the battery.
In other words, I thought DC created current by setting up pressure differentials between two poles of the battery (which would require a complete circuit back to the source) while AC acted more like a wave generator in a stream, where as long as the water is connected to a big enough pool of water, the waves will pull water out and push water into that pool as needed.
But this is just the image I came up with based on wiring the basement.
posted
There is no distinction between AC and DC in this regard. Part of the return circuit can actually always be the ground, if you like. It's common practice (and required by code) to ground one side of house power at the place where it enters the building from the power company's transformer. This is done by hammering a long rod usually six or so feet into the earth. It requires a good solid connection, since dirt isn't all that great of a conductor, and because you want lightning strikes, and other large surges of current, to bleed off to ground as quickly as possible keeping the voltage spike as low as possible.
In an AC circuit, the grounded side is called the neutral wire. In your house it is the one with white insulation. (This is the Western Hemisphere I'm talking about here. These color conventions are different in Europe, Australia, and the rest of the world.) The other side is the hot wire. In your house it's colored black. The third wire is the ground wire and it's colored green. (Green with a yellow stripe in Europe.)
Every place you see one of those big old cylinders up on a power pole in your neighborhood, that's a transformer. (They can also be boxy things about the size of a washing machine mounted on a little concrete pad on the ground.) There is usually one for every two or three houses. The power for your house (for grounding purposes) is isolated at that transformer. There are typically three leads that come from that transformer, which has a split winding on the secondary. (Two independent coils of wire on the output side.) One side (we'll call it the center side) of each of the two coils is connected together and thence to ground. That's one of the three leads. The other two leads are 60 cycle AC but of opposite polarity. So picture the squiggly sine wave of voltage vs. time on each side, varying back and forth 60 times a second, only when one wire is positive, the other is negative, and vice versa. In this way you can have 120 volts AC between either side and Neutral, or you can have 240 Volts AC from one leg to the other. Your dryer and other large appliances will often use 240 Volts.
Because the output side (secondary) of this transformer is grounded like that, you can be sure the potential with respect to ground in those other two legs is always +120V and -120V (though they reverse back and forth 60 times a second). If you didn't ground the secondary of that transformer, then the voltage would be allowed to float, and there is no telling what it would be with respect to ground. Because various devices can only take so much voltage difference across them before they fry, it's a good thing always to fix one side of your voltage source by grounding the Neutral.
Voltage is sort of like height. You always measure it with respect to something else. It is a potential difference between two things. The convention we use for "zero" voltage is the potential of the ground. Ground is like the "sea level" of voltage.
At each place in a power circuit where you have a transformer, the output side is completely isolated from the input side. Therefore you need to ground each side separately. So your house power's neutral is grounded at your house, at the place where it enters from the power company's transformer (called the "service entrance").
However, the opposite side of that transformer coming from the power company, actually originates from a transformer further up the line, at one of those yard-sized fenced in places full of electrical equipment that you've seen in your neighborhood, called a substation. From there it is isolated by another transformer that steps down the voltage from the higher voltage used for the transmission lines, and so on back to the generator. There will typically be many transformers between the actual generator and your house, each one isolating the power from the other side, and each one independently grounded.
Grounding is very interesting and subtle. There are completely different grounding issues for low voltage electronic sort of signals and things than for power circuits. Here the main concern is trying to get rid of electromagnetic noise in the circuit.
[ April 29, 2004, 01:40 PM: Message edited by: ak ]
Posts: 2843 | Registered: A Long Time Ago!
| IP: Logged |
posted
I wish we had a hatrack chalk board, so I could draw diagrams of this stuff. Spent some time searching the web for a good one but didn't come up with what I need.
Anyway, there always is a complete circuit of wires in our power grids, only they are grounded on one side to fix the voltage with respect to ground. That way you don't shock people and fry things by accident.
The ground is never part of the return path of the electricity, not deliberately anyway. When it is, there is a fault (called a ground fault) and there are special ground fault breakers that sense this condition and trip to keep from frying people or starting fires.
Long ago this wasn't necessarily true, and for instance they used to use the frame of the car as the return path for electricity in automotive design. I've seen old electrical components for cars that only have one wire, (the hot).
In DC also (as in your car), by the way, one side of the power supply will always be grounded. The black terminal on your car battery (the one marked with a minus sign) will be grounded to the frame of the car. Inside equipment, the ground is to the metal frame. This is in turn usually grounded to the earth (the third prong of your 3 prong plug.)
Oh, and Europeans call it "earth" instead of ground. They talk about earthing things where we say we are grounding them.
Posts: 2843 | Registered: A Long Time Ago!
| IP: Logged |
Does an AC circuit really move the electrons through the "loop" (if I were to put a coloured tag on a particular electron, would I be able to watch it run a lap?), or does it just move them from a higher to a lower potential (like "the wave" at a sports game)?
This whole back-and-forth thing with AC always messes with my head. I always understood the "DC = water hose" analogy much better. (Voltage = Pressure, Current = Flow)
posted
ssywak, the actual electrons are moving only as far as they need to move, back and forth, in AC.
It's like ocean waves at the shore. You can get lots of power out of a storm far out to sea delivered to the shore. But the water molecules involved don't have to move hundreds of miles. The energy is carried by the waves. Each bit of water just shoves on its neighbor, and so on, all the way to shore.
So any individual electron (to the extent that it makes sense to say that (for the moment we can take a classical view and think of electrons as particles)) doesn't have to travel the whole route from the transformer to your light bulb and back to the transformer. But each one shoves its neighbor and so on down the line, and the resulting cascade of electrons back and forth across the filament is what heats it up and makes it glow white hot.
However, just as there must be water the whole way from the storm to the shore for the waves to travel to land, so there must be copper or some other conductor around the whole circuit from the transformer to your light bulb for the energy to be carried there.
[ April 29, 2004, 02:09 PM: Message edited by: ak ]
Posts: 2843 | Registered: A Long Time Ago!
| IP: Logged |
posted
Dagonee, yes, although as you realized, the white wire is connected to ground at the service entrance to your house.
Posts: 2843 | Registered: A Long Time Ago!
| IP: Logged |
posted
Wow, kat! Great question. You want the underlying reason these things work as they do? You cut to the heart of the matter, don't you?
I think this is what you are asking. You may be asking a much easier question which is where is the energy put into the system that we take out when we use electricity in our houses. The answer to that is simple, it's at the generator. Some engine is running, or turbine turning, converting something we get for free, like wind or waterfalls or the chemical energy inside a lump of coal into electrical impulses.
But I think the real question you are asking is the deep one. Why do electrical charges behave the way they do? What is charge? Why are there such things as electrical fields? This is really the same question you can ask for gravity or any other feature of the universe. Why is there gravity? Why do the laws of physics work the way they do? And the answer to that one is extremely cool and interesting.
Richard Feynman, one of my greatest heroes, addressed that question in a book he wrote called The Character of Physical Law. The laws of physics are just equations. Matter is knots in the fields, and fields are numbers in space. We can describe perfectly HOW the laws of physics work, but there is no WHY that we can discern in our instruments. There is no underlying nuts and bolts mechanical explanation of everything.
For gravity the equation (classically) is F = GmM/R^2. The force between two masses is directly proportional to the product of their masses and inversely proportional to the square of the distance between them. In electrostatics there is a similar equation with charges instead of masses (and the added twist that there can be both positive and negative charges).
Feynman would say to his classes "In the middle ages they thought the planets traveled around in circles due to angels flying along behind them pushing with their wings. Now we have a different theory. Now the angels push inward."
Posts: 2843 | Registered: A Long Time Ago!
| IP: Logged |
quote:transformers make it very easy to change the voltage to whatever we want
I think it's important to note that transformers have a constant input and output power. That is, when you use a step-up transformer to increase voltage from the primary to secondary windings, you don't get that increase for free; it comes at the expense of current (voltage is approximately how hard each electron is being pushed, current is how many electrons are moving past a point per unit time). Power (energy per time) is equal to current times voltage, so if you are increasing voltage and decreasing current, it makes sense that power stays constant.
Posts: 4534 | Registered: Jan 2003
| IP: Logged |
posted
Dagonee, yeah, you want the green wire to connect to the white at a single point at the service entrance and nowhere else. White is for the actual return path of the current. Green is to prevent shocks. Its purpose is to provide a better path for any short circuit currents to travel than someone's body. If you connect green and white together willy nilly you are defeating the safety features of having an independent green wire. The appliance will still work, but it will also (if ever there's a short) be more likely to electrocute someone someday.
[ April 29, 2004, 02:49 PM: Message edited by: ak ]
Posts: 2843 | Registered: A Long Time Ago!
| IP: Logged |
quote:Feynman would say to his classes "In the middle ages they thought the planets traveled around in circles due to angels flying along behind them pushing with their wings. Now we have a different theory. Now the angels push inward."
Yes!! Yes, that's exactly the question I was asking.
posted
saxon75, yeah, I was hoping someone would ask me that question about transformers; how come you can jack the voltage up as high as you like for free.
No they are not perpetual motion machines. Every time it doubles the voltage, it halves the current. Transformers are definitely magic, but not quite so magical as that. Posts: 2843 | Registered: A Long Time Ago!
| IP: Logged |
posted
If only I was smart enough for this thread, think of the things I'd be learning!
Instead, I'm reading it, eating cheetos, and drooling cheese powder on my shirt. But I remembered to wear a bib this time, so I'm already learning.
Posts: 7600 | Registered: Jan 2001
| IP: Logged |
posted
Ralphie, people who have wired up things, or played with electricity all their lives, will be asking questions at a different level than someone who hasn't.
I'd love to get questions from people who haven't, too. Think of a question. I'll do my best.
I am curious for my part how people who aren't technological geeks see the world, too. When you use the myriad devices and systems you use every day, how are you thinking about them? How are they modeled in your mind? What is electricity like, to you? Maybe it's just not something you think about much at all. Sort of like me with social dynamics or taxes? Or maybe you know more or less what behavior to expect from different devices and leave it at that?
[ April 29, 2004, 03:07 PM: Message edited by: ak ]
Posts: 2843 | Registered: A Long Time Ago!
| IP: Logged |
posted
I keep trying to come up with a good "stump the expert" question (which I know is insufferably rude, not to mention a bit unfair since ak and I are in the same line of work [granted, she has more experience than I do]), but the only one I really care about is why my stupid card keeps making the stupid system crash on what seems to be a totally nondeterministic time frame.
--------------------------------
quote:Or maybe you know more or less what behavior to expect from different devices and leave it at that?
You know, it's been my experience that non-tech people generally think like this. On the spectrum of (electrical) tech geekness (on which major points are [in descending order]: design engineer, field technician, computer hobbyist, Trekker, average netizen, theater major, Amish) the further from the nerd side you get, the less deeply people tend to probe and speculate about different devices.
Posts: 4534 | Registered: Jan 2003
| IP: Logged |
quote: design engineer, field technician, computer hobbyist, Trekker, average netizen, theater major, Amish
That's brilliant.
I'm somewhere between Trekker and computer hobbyist. I'm secretly fascinated by technical stuff, but fear it's beyond my ability to comprehend. And, honestly, I think it comes down to math, which I've never excelled at simply because I'd forget to carry an integer, or misplace a decimal point, or something else equally as stupid. I like mess about with technical things in my hand, but if I have to figure out WHY something does something, and if it includes math, I go back to drooling cheeze-dust on my kitchy Rainbow Brite shirt.
Posts: 7600 | Registered: Jan 2001
| IP: Logged |
posted
saxon75, stump the chump is a GREAT game! I LOVE the hard ones. I particularly love the ones that are hard because you've never ever thought of it that way before.
Anything I don't know I will look up. Or I will consult the tea leaves, halibut bones, and the pig entrails. I will scan the heavens for a sign. I will use dice and other arcane instruments of my craft.
Your card is making your system crash in a non-repeatable way because ... <pauses while eyes roll back in head> ... the card is flaky. Try another one, if easily available. Otherwise reread the entire documentation on the card, check that all installation instructions were followed, dip switches are set correctly, and so on, test your power supply and check all your inputs, and the reason will eventually become clear. If none of that works, reorient the cabinet with respect to the surface of the earth using your foot or other source of kinetic energy. Posts: 2843 | Registered: A Long Time Ago!
| IP: Logged |
Unfortunately it is my job to understand why it is flaky.
quote:Try another one, if easily available.
No such luck; it's a prototype.
quote:Otherwise reread the entire documentation on the card,
::sigh:: Unfortunately documentation is the first thing to fall by the wayside when a program is impacted, as I'm sure you know. Almost all of the documentation on this card was written by yours truly after I inherited it fourth-hand from the actual designers, many of whom are now retired.
quote:If none of that works, reorient the cabinet with respect to the surface of the earth using your foot or other source of kinetic energy.
Oh, how happy that would make me... I think I'll just go take my lunch break now instead, though. Posts: 4534 | Registered: Jan 2003
| IP: Logged |
posted
Ralphie, I'm also one who makes stupid math mistakes. I have to double and triple check all my calculations because of that. Unlike on tests, at work you have plenty of time for that.
Minus signs, decimal places, arithmetic. I screw up those all the time. I can't add 2 and 5 reliably without my trusty HP calculator with Reverse Polish notation (I call it my prosthetic brain).
Understanding how things work is what counts in my job. Math mistakes are easy to take care of by double- and triple-checking.
Posts: 2843 | Registered: A Long Time Ago!
| IP: Logged |
quote:One day, years ago, when I was at the beach with Peg & the kids, we met a group of friends (not our friends; they were their own friends, though) struggling to start their car. When they saw me "chirp" my car alarm, they must have figured I knew about car alarms (not really, but let us continue) and came over to us.
Apparently, they also had one of those self-installed car alarms, with a siren and with a starter cut-off. But their "key fob" thingie was dead. They had unlocked and opened the car anyway, and had clipped the wire to the siren to keep from going insane. But the starter cut-off was working as designed, and they could not start their car (I do still hope it was their car...).
Being the geek that you all know me to be, and having either a pen-knife or Leatherman pliers with me, I was able to unscrew the back of their key fob remote. As I had assumed, the battery was dead--the contacts were visibly corroded. I removed the battery and noticed that it was about the same diameter and one-third the length of a AAA battery--and, it was a 12 volt battery!
Now, as you know (if you don't, then you really shouldn't be answering questions like this), cars have a 12 volt battery also. But the battery in a car is about the size of your head, typically larger. This key fob battery was smaller than your pinky.
Apologies, of course, to people who may have been born without pinkies, or who may have lost their pinkies later in life. Or their heads.
But, to continue. I also had a set of jumper cables in the back of my car.
Here's your question: Can you really jump start a 1 inch square by 1/4 inch thick key fob with a battery big enough to jump start a 2000 pound automobile? Or did it just blow the hell up in my hands? Explain your answer.
(You know you spend too much time on the Internet when you Google yourself just to find something you posted 5 months ago, so you don't have to retype it now)
Posts: 1862 | Registered: Mar 2000
| IP: Logged |
That's REALLY fun! In that case test everything you can test, whether it would seem relevant or not. Check all your assumptions about everything. Try different screwy things just to see how it behaves. First play around with it trying to get it to work, then play around with it trying to get it to not work. Pay attention to dreams and fortune cookies that you get during this phase of discovery. Sooner or later, some datum that you shake loose in this way will give you the aha that you need. There's no telling how long it will take, though. Good luck!
Posts: 2843 | Registered: A Long Time Ago!
| IP: Logged |
posted
If I make a stripline using dielectric materials with different dielectric constant of say, 4.2 and 2.6 above and below the signal line, will the transmission be Transverse electric and magnetic (TEM), quasi-TEM, or something else? Will there be any effect on group delay? Posts: 4548 | Registered: May 2001
| IP: Logged |
posted
Stump the chump question 1 answer. The voltage is all that matters. If the thing is in good shape apart from a dead battery, and if you are careful not to short anything out when you apply the 12V from the car battery to the device, then it should work just fine. The current will be limited by the resistance in the device.
However, it's possible the battery is dead because something shorted out inside the key fob and drained it, too. Or it's possible the dead battery had corroded and spilled acid all over the key fob and now it's ruined. But assuming neither of these is true, then it could certainly work.
[ April 29, 2004, 03:57 PM: Message edited by: ak ]
Posts: 2843 | Registered: A Long Time Ago!
| IP: Logged |
How might I go about designing and building high power energy weapons (Charged particle projectors, plasma based weapons, high intensity lasers, and so on) in the comfort of my own home?
I promise to use them only for good, never for evil.
Posts: 5383 | Registered: Dec 1999
| IP: Logged |
Correct. I will tell you, though. When you've got those jumper cables in your hands, you definitely think twice about applying them to that tiny little key fob. And the guys who owned the car looked at me as if I were crazy to try such a thing.
Puzzler #2:
quote:You take a regular helium-filled balloon, and you put it in the (otherwise empty) passenger area of your Dodge Caravan. You're stopped at a traffic light, your windows are closed, and your climate control fan is off. The light turns green, and you gently press on the accelerator pedal. Since it is a Dodge Caravan, it hesitates about 20-30 seconds before it decides that it should really engage the transmission, and then it takes off like a bat out of hell.
posted
This just might be the thread where I get an answer to something that's been bugging me since I was five years old (that's a lot of time).
Our driveway had a depression which served as a collector for water and debris carried along with the water. One summer day, I was walking past the puddle that had been sitting there in the sun, and noticed a penny sitting in the puddle, on top of a bunch of (probably) decomposing leaves.
I reached for it. When my finger hit the water, a weird sensation spread up my finger, like my finger was vibrating - very unpleasant. The sensation stopped at the knuckle joint. After a couple tried (I catch on slowly), I left the penny alone.
Years later, I realized what the sensation was when I accidentally hit an electrified cattle fence with a soda can - twice (like I said, I catch on slowly). The sensation was the same, except the one from the cattle fence was much stronger, with the sensation terminating at the elbow joint.
Questions: Is this feasible or am I really as whacked out as the few adults I told this to when I was a kid thought I was?
If it's feasible, what's the mechanism involved here?
You can solve a mystery that has been bugging me for over four decades!
Posts: 4344 | Registered: Mar 2003
| IP: Logged |
Printer-friendly view of this topic
![[Kiss]](graemlins/kiss.gif)
![[Smile]](smile.gif)
![[Taunt]](graemlins/taunt.gif)
![[Mad]](mad.gif)
