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Author Topic: Everything you've always wanted to know about Electricity or other technology
HollowEarth
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I've always like that its called annihilation when a hole meets an electron.
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Samuel Bush
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Howdy, ak. Great thread.

I once met a guy who had a wooden box with a metal handle on top and a metal crank on the side. I asked him what it was and he said to go ahead and turn the crank. So I did and got a big surprise. And the harder I cranked the more my arm muscles convulsed.

It was way cool!

(And the box had sign on it. "Warning. Do Not Crank Handle" which I thought was a nice touch.)

So when the guy stopped laughing, he told me there was a magneto inside. So my question is:

Can a magneto like that generate enough 'lectricity to kill a person? (Assuming that person doesn't have a pacemaker or weak heart.)

Oh yes, and another question I have is: where can I get a working magneto really cheap? Ever since then I've wanted to make one of those boxes. And I have some sons who are one up on me on the practical joke tally sheet. (hey, it's a guy thing) [Evil Laugh]

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ak
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Oh, I have been quite remiss in my duties as resident mad scientist! I must beg all of your forgiveness and try to remediate this deficit very soon. My only excuse is that I have been very busy with my researches in the laboratory, and am on the cusp of a great new discovery involving feline mediated neurological torture mechanisms. Details to follow.
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suntranafs
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bumpity bump just for kicks
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WheatPuppet
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quote:

An AND gate is an electronic component which behaves in such a way that the output will be high (there will be voltage present on the output wire (the dash)) if and only if there is voltage on both input signals (the legs of the equals sign).

I know that. I went through several classes where we started with simple logic gates, and continued up through 16-bit adders (that was a bitch to build), and finished with doing something with ISA ports (that I've since forgotten). I wanted to know how a logic gate is built, what kind of little hardware bits go into it to make it do a certain thing. I know it's a little bit of doped semiconductor and some wire, but not much beyond that.

Someone asked about op-amps...
An op-amp is an operational amplifier. It can be used in a bunch of different ways, but is used a lot in communications for making frequency filters . A radio is basically a controlled varying op-amp that filters out all but a certain range of frequencies to pick up a frequency-modulated (FM) station. My memory on it is a bit hazy, though.

Here's a general-purpose question:

I'm thinking about cramming a Mini-ITX motherboard into a heavy plastic ammo case for a Bradley Fighting Vehicle that I picked up from an Army-Navy store. My issue is that it would be a lot easier to make the housing frame for the electrical bits out of wood or acrylic rather than metal, but I know some computers take it personally if they aren't seated on a metal plate for grounding purposes. What I want to know is if all motherboards want to be housed on a metal groundplate, or if it's just certain kinds. I havn't spent much time researching it because I'm not planning on doing anything until the end of the summer, so if someone has an easy answer...

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saxon75
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quote:
I wanted to know how a logic gate is built
Logic gates are built out of transistors, typically out of MOSFETs (Metal Oxide Semiconductor Field Effect Transistors). The math behind FETs is a bit more difficult than the math behind BJTs (which are the type of transistors that we've been discussing in this thread), but conceptually they're a bit easier, I think.

I think the easiest way to explain the MOSFET is to do a quick little diagram:
code:
     S       G        D
| _____|______ |
| | ins | |
----------------------------
| P | | P |
|-----| |-----|
N

----------------------------

You have a big well of N-type semiconductor with two smaller wells of P-type semiconductor. Each well of P-type semiconductor has an electrode attached directly to it; one is called the "source" and one is the "drain" (I have labeled them S and D, respectively). Between the source and drain there is a region of N-type semiconductor that is called the "channel." Above the channel is another electrode called the "gate." However, the gate is separated from the channel by a thin piece of insulating material. Normally, the channel does not conduct electricity. However, if a voltage is applied to the gate, a conductive region in the channel is formed. The larger the voltage, the more conductive. So basically, you have a structure that acts like a switch; with no voltage on the gate the switch is off and with a positive voltage on the gate the switch is on.

The transistor that I drew above is called an N-channel MOSFET, or "nMOS" for short. You can also make a P-channel MOSFET, or "pMOS" which is similar except that it is normally "on" and by applying a voltage you turn it "off." An nMOS transistor has a symbol that looks like this (when used in digital applications) and a pMOS is represented by this symbol.

Logic gates are made by using both types of MOSFETs, a technique called "CMOS," which stands for "Complementary Metal Oxide Semiconductor." The simplest gate is the NOT gate, also called an inverter. Here's a diagram of an inverter. You have one nMOS transistor and one pMOS transistor with the drains tied together. The source of the pMOS is tied to a +5 volt source and the source of the nMOS is tied to ground. Let's say that +5 V represents a logical 1 and that ground represents a logical 0. When the input, labeled "A", is 1, then the nMOS transistor is "on" and the pMOS transistor is "off" and the output, labeled "B" will be electrically connected to ground so the voltage at B will be zero. When A is 0, then the nMOS is "off" and the pMOS is "on," so the output will be connected to the +5 V source and the voltage at B will be 5 V. Thus, the output is always the logical inverse of the input.

A more complicated gate is the AND gate. It involves four transistors. As you can see, if both inputs are 0, then both nMOS transistors will be "off" and both pMOS transistors will be "on," making the output become 0. If either one of the inputs is 0, but not both, then one of the nMOS will still be "off" and one of the pMOS will still be "on," so the output is still 0. Finally, if both inputs are 1, then both pMOS will be "off" and both nMOS will be "on," so the output is 1. And there you have it.

Edit: You can also build gates out of BJTs, vacuum tubes or even relays. The important thing is that you have something that acts like an electrically-controlled switch.

[ June 02, 2004, 01:29 PM: Message edited by: saxon75 ]

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