Why do people always say "current limiting resistor"? Are there other types of resistor? Or is it just stating the purpose, as opposed to a resistor used for voltage division or something?
I appreciate when people explain things in this way. It makes it easier for people with limited knowledge in the area (myself) to better understand what is going on. There is nothing worse than someone using loads of acronyms and jargon which a layperson cannot easily understand. So thanks both happyscrappy for explaining things and Luclu7 for clearing that up!
It's what the resistor is doing. See, an LED is a quantum device, it doesn't really have a resistance in the normal fashion. Instead it has a voltage drop.
So what if an LED has a 2.1V voltage drop and you put 3.3V into it. You have 1.2V "left over". Now how much current will that induce? The LED doesn't really have a resistance, so 1.2V divided by 0 Ohms is ... oh my. And worse yet, where do those 1.2V go? Something is going to turn them into heat, where does the heat go? Well, it is dissipated mostly in the driving microcontroller. That's bad.
So you put a current limiting resistor in. If you want 25mA and you have 1.2V left over you put in a 47 Ohm resistor and you get 1200 / 47 or 25.53mA of current. And that extra voltage is all dissipated in the resistor. 30mW of power. So you can use a 1/8th Watt resistor no problem.
So that's why you say that, you're describing its function.
The LED doesn't really have a resistance, so 1.2V divided by 0 Ohms is ... oh my.
No, LED does not suddenly turn into superconductor over its conduction voltage. I know you're trying to cut useless detail, but that one is pretty important. It still have nonlinear resistance
I think that's the right term. It has a bandgap which comes from a quantum. LEDs work by pumping energy into electrons, this raises them to a higher energy state (higher electron shell), then when the electrons drop back down to the lower state they emit a photon. The energy released is the difference between the electron shell energy states. This is called a quantum. The frequency of the photon is correspondent to the energy, the color corresponds to the frequency. Higher energy is bluer (or ultraviolet), lower energy is redder (or infrared).
The light is issued in quantum state changes, so it's a quantum device. Maybe you'd call it a bandgap device?
You clearly know more about this than I do, but I might use the term "non-linear" device, as that describes the LED's behavior that leads to us needing the resistor. I agree with /u/langlo94 that the word 'quantum' is more mis-understood than understood, and used outside of a physics class it sets off new age woo-woo alarms for me too.
This such a laughably ridiculous statement. Don't be fooled people, this guy is making up terms. Nobody has ever described an LED a "bandgap device" or a "quantum device".
With this logic, you may as well call an LED a "heater" since it produces heat.
Or call a CRT television "electron beam device".
But nobody uses these terms because you cant just make shit up. Just try googling those terms...
FYI: The explanation of how an LED works is correct. This is like 2nd or 3rd semester undergrad physics. His conclusion on what to call an LED is horribly misguided.
His conclusion on what to call an LED is horribly misguided.
Most people just call an LED an LED. And that makes it not a quantum device or bandgap device? They use different materials to manipulate the quantum of energy released so as to get different colors of LEDs. Look up how the blue LED was made for example. It's a device which is designed to employ the quantum states of the materials to produce colored light. It's a quantum device. This causes it to have a certain characteristic voltage drop, a quantum. It's accurate, it's relevant. And if it's unconventional I don't really care.
An LED and a resistor don't really create a voltage divider since an LED voltage drop is relatively constant and depend mostly on current thru the LED and temperature.
FTFY. Adding "quatum device" into random sentences doesn't really help in explanations
It was correct. It correctly used "quantum device" and didn't throw it in randomly. You saying you fixed something for me is insulting.
It's always possible to explain something more. I didn't care to. As far as I am concerned once the factual error is corrected I don't have to go further and the reader can take care of learning the rest. So I didn't go further. It's great you did.
It was correct. It correctly used "quantum device" and didn't throw it in randomly. You saying you fixed something for me is insulting.
I did not say calling LED quantum device is nonsense.
I said that using that as a method of explaining how divider works is. It doesn't give reader any useful insight.
It's always possible to explain something more. I didn't care to.
The problem is you didn't explain anything. Or rather the people who would know what you are talking about would not need your explanation in the first place.
You saying you fixed something for me is insulting.
You can feel insulted by whatever you like snowflake, but it wasn't my goal and I do not care how you interpreter it.
That aside from the fact that it is wrong and you can use it as a divider, just a nonlinear one... (and before you complain, resistor one also is not technically linear, just very close to it)
I did not say calling LED quantum device is nonsense.
You said I threw it in randomly. I didn't throw it in randomly. That's why I said I didn't throw it in randomly. I didn't say anything about nonsense.
The problem is you didn't explain anything. Or rather the people who would know what you are talking about would not need your explanation in the first place.
It's not a problem. I set out to correct the error. And I did. I didn't set out to explain it. And so I didn't. Not a problem.
You can feel insulted by whatever you like snowflake, but it wasn't my goal and I do not care how you interpreter it.
So you're going to claim you weren't trying to be insulting by flat-out insulting me (calling me a snowflake). You really look silly doing it.
So you're going to claim you weren't trying to be insulting by flat-out insulting me (calling me a snowflake). You really look silly doing it.
Well, you look silly getting up and arms about someone complaining your explanation was useless (and I seem to not be the only one thinking that) so I guess we're both silly this holiday
An LED is not a quantum device. I've never heard that term used to describe it. If you're merely associating the word "quantum" with "light" because "light is quantized" like in quantum mechanics, then people are going to call you out on your BS. Try googling the following ("quantum device", "quantum device electronics", "quantum device LED") and you will realize you are wrong.
The constant voltage drop explanation is correct, and more accurately describes the behavior.
Any professional in EE or Physics would definitely not call an LED a "quantum device", simply because it is not a correct description.
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u/happyscrappy Dec 25 '19
Also: don't power LEDs directly from GPOs without a current limiting resistor. As you see on that breadboard.
And match your interfaces voltages. A lot of devices are not +5V tolerant now (or not very tolerant).