Confused about electronics/electricity

[LiquidCyanide]

High school physics class is a horrible place to learn electronics, sure you are taught Ohm's law and other rhetoric, but how does it apply to real electronics. I saw some people in here saying that a 330 Ohm resistor is proper for the amount of V and current drop you want to drive an LED, but why? If you have a 50mA LED on 5 V how exactly do you calculate what resistor and such to put on. Also, the use of diodes for slight voltage drops, how can you calculate that?

Thanks

Also, if anyone has some good, fairly technical, books to recommend to me, or web sites, please do. I also have never seen anything accurately explain logic to me, OR, XOR, AND, etc etc

 

[blahblah99]

LEDs are nothing more than Light Emitting Diodes, and diodes, in general, have about 0.7V drop across it. If the led requires 50mA to light up properly and you have a 5V supply source, the voltage across the resistor is 5 - 0.7 = 4.3V. V=I*R, you know V, you know I. Use that to find R.


If you want to find the exact voltage drop across the diode, you need to look up its characteristics.. I believe the general equation for diodes is I = Is*e^(V/Vt) or something like that... where Is is the saturation current (determined by physical properties of the diode), and Vt is ~26mV.

Anyways, electronics is something you can't really learn by just reading books. You need to play with them and do problems consistently to learn the basics. I'd check out
this web site for a start and a book called "The Art of Electronics".

 

[jeremy806]

Sedra and Smith - I forget the title, it's a college level electronics book.

jeremy806

 

[pm]

"The Art of Electronics" (Horowitz and Hill) and "Microelectronic Circuits" (Sedra and Smith) are both very good books for circuit theory, and
general electronics. I particularly like "The Art of Electronics".

For an intro to logic design check out this place.

 

[Demon-Xanth]

LEDs rarely have a 0.7V drop. Typically they're closer to 1.5V.

To caclulate the drop required for a diode:
Vcc-Vdiode==Vcurrent limiter
Vcurrent limiter/Irequired=R


Or easier put:
Subtract the drop across the diode from the source voltage and divide by the current required for the desired brightness.

It'll vary a bit by LED, 330Ohms gives about 10-15mA of current which is usually a good amount of current.

 

[CTho9305]

nice link. that adder they build is a ripple adder, right?

 

[Elledan]

<< "The Art of Electronics" (Horowitz and Hill) and "Microelectronic Circuits" (Sedra and Smith) are both very good books for circuit theory, and
general electronics. I particularly like "The Art of Electronics".

For an intro to logic design check out this place. >>

I own both books ("The Art of Electronics" analog & digital electronics). Pretty good stuff 🙂

 

[Danzilla]

Yeah. I still have my copy of Sedra&Smith. They changed editions during my semesters. :| "The Art of Electronics" was only suggested reading sooooo.... 🙂


<< Also, if anyone has some good, fairly technical, books to recommend to me, or web sites, please do. I also have never seen anything accurately explain logic to me, OR, XOR, AND, etc etc >>

Pretty much any fundamental book on digital logic will explain the basics of boolean algebra (Not, Or, And, Nor,..., etc. and their interaction). From what I remember, you don't even need that much of a background in electronics before you can jump in. It's basically a branch of mathematics all by itself. Understanding the physical aspects of digital logic (ie. design of logic gates from basic component) is something else and requires a foundation in digital electronics (sedra&smith).

D.

 

[LiquidCyanide]

cool, thanks guys

 

[blahblah99]

I have the Sedra and Smith book Microelectronic Circuits. Its an excellent book and provides a lot of insight on the fundamentals of circuit designs. If you go through this book (its like a dictionary) and really understand how to do the problems, you will be ready for a $80,000 job 🙂

 

[Mday]

ironically, i am in EE in school now. I have no idea how to do anything, except solve problems on paper =\

at least i know that much, which is not much, since I have mostly done passive devices only =(((

sigh... poor me.

--

anywho... you'll learn more in shops, should you go to school, than in lectures. cuz being electricuted is a very good learning tool ;-)

 

[Bluga]

i'm learning digital logic and electronics now but i'm confused about the difference. What's the difference between logic circuit(logic gate....etc) and regular circuit (resistors, transistors...etc)? How are they related?

 

[blahblah99]

In logic, you deal with boolean algrebra, 0s and 1s, and gates (not, or, nor, and, nand, xor, xnor) and each of those gates are made up of transistors.... for example, a NOT gate is just an NMOS and a PMOS with their gates and sources tied together with the input at the gate and the output at the source.