Learning electronics: Release the Magic Blue Smoke

The Something Awful Forums > Discussion > Hobbies, Crafts, & Houses > Learning electronics: Release the Magic Blue Smoke

Jdohyeah: Apr 15, 2006; You... accuse... me?

Jairbrekr posted:

Alright, heres one. Its pretty lame because I'm just not that angry and venomous anymore....

ACHTUALLY

allaboutcircuits.com posted:

When Benjamin Franklin made his conjecture regarding the direction of charge flow (from the smooth wax to the rough wool), he set a precedent for electrical notation that exists to this day, despite the fact that we know electrons are the constituent units of charge, and that they are displaced from the wool to the wax -- not from the wax to the wool -- when those two substances are rubbed together. This is why electrons are said to have a negative charge: because Franklin assumed electric charge moved in the opposite direction that it actually does, and so objects he called "negative" (representing a deficiency of charge) actually have a surplus of electrons.

By the time the true direction of electron flow was discovered, the nomenclature of "positive" and "negative" had already been so well established in the scientific community that no effort was made to change it, although calling electrons "positive" would make more sense in referring to "excess" charge. You see, the terms "positive" and "negative" are human inventions, and as such have no absolute meaning beyond our own conventions of language and scientific description. Franklin could have just as easily referred to a surplus of charge as "black" and a deficiency as "white," in which case scientists would speak of electrons having a "white" charge (assuming the same incorrect conjecture of charge position between wax and wool).

However, because we tend to associate the word "positive" with "surplus" and "negative" with "deficiency," the standard label for electron charge does seem backward. Because of this, many engineers decided to retain the old concept of electricity with "positive" referring to a surplus of charge, and label charge flow (current) accordingly. This became known as conventional flow notation.

I can't believe I haven't seen this thread before!

# ¿ Feb 8, 2008 02:39

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Jdohyeah: Apr 15, 2006; You... accuse... me?

scholzie posted:

I don't understand what you're trying to say here. Jarbrekr made an image of exactly what you just posted... he just left Franklin out of the discussion.

Well he implied current was intentionally labeled to match hole flow, when it was just because of a wrong guess. Taught different things I suppose, I've actually never seen current flow represented as holes in anything but semiconductors.

Jdohyeah fucked around with this message at 03:48 on Feb 8, 2008

# ¿ Feb 8, 2008 03:46

Jdohyeah: Apr 15, 2006; You... accuse... me?

iamlark posted:

...

cool

# ¿ Feb 19, 2008 11:41

Jdohyeah: Apr 15, 2006; You... accuse... me?

18V LEDs? Do you mean 1.8V?

# ¿ Mar 15, 2008 04:06

Jdohyeah: Apr 15, 2006; You... accuse... me?

Delta-Wye posted:

Sorry to say, but it's impossible to directly power 18V LEDs with 3V batteries.

EDIT:

Can you not subtract and divide? (Vbatt - Vforward) / I = R. Ohm's law yo. Don't act like a retard and people won't treat you like one.

Of course, given your information, I get (3 - 18) / 20mA = -750 ohms. Good luck finding that component!

Don't be so condescending man, he made a typo. Your reds, ambers and yellows are generally 1.8 - 2.4V, it's pretty obvious what he meant

# ¿ Mar 19, 2008 00:32

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Jdohyeah: Apr 15, 2006; You... accuse... me?

jovial_cynic posted:

I've successfully made the Little Gem amp, since plans were readily available on various websites, and the circuitry was pretty simple. The main part of the circuit was the LM386, which is an audio amplifier.

Here's the little gem site:
http://www.runoffgroove.com/littlegem.html

Now, while I can follow instructions fairly well, and I have a novice understanding of how to read datasheets, I don't quite get why the little gem works.

The reason why I'm asking is because I've been scavenging parts from some broken audio equipment, and one of the ICs I pulled was a KA4558 -- a dual op-amp.

I get the wiring -- I see where the audio input connects, and where the power connects, and where to ground the chip. But wiring nothing but the chip, the power, a speaker, and the input-jack for a guitar just makes the speaker buzz when I play through it. I know that I need capacitors and resistors somewhere in the circuit, and I could try to mimic what I see in the LM386 circuit, but that won't help me understand what's going on.

Any explanation would be helpful. I'd like to see what I can do with this KA4558, just for the sake of experimentation.

With opamps, it's all about the transfer function - that is, how the voltage out relates to the voltage in and is expressed as a formula. Opamps do nothing really by themselves, you've got to use resistors and caps to adjust voltages around the opamp which generates a gain. It's hard to describe without getting into math, have a look at the first page of this document for some examples:

http://www.national.com/an/AN/AN-31.pdf

Looking at the non-inverting amplifier there, if you wanted the output voltage to be 20 times the input voltage, you'd let (R1 + R2)/R1 = 20, pick one resistor value and solve for the other. That's probably the most basic example you'll find. Once you start introducing caps and inductors you'll get differential equations and imaginary numbers, better to just believe that they work unless you want to teach yourself a bunch of math

# ¿ Mar 19, 2008 08:04

The Something Awful Forums > Discussion > Hobbies, Crafts, & Houses > Learning electronics: Release the Magic Blue Smoke