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Old 10-06-2009, 12:52 PM   #31
Sergei Steshenko
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Quote:
Originally Posted by pixellany View Post
Vs = supply voltage
R = net series resistance
C = net node capacitance
t = time
e = base of natural log

Vc = Vs (1 - e**(t/RC))

Doesn't look like a differential equation to me.....
Very true, but you still do not need to know differential equations to design circuits. I'll bet you there is more than one circuit designer out there that doesn't even know the formulas------they just know that 0.1uF "works".
Where did you get that formula ? Or, rather, how ? I.e. the formula is correct, but, as I said, to prove it you need to solve a differential equation - otherwise it's a religious belief. I.e. somebody told you and you believed in it.

I'm sorry, but at my high school we were taught about axioms and theorems - axioms are believed in, theorems are proven.

...

Actually, the formula is wrong, it should be

Vc = Vs * (1 - exp(-t / (R * C)))

- pay attention to minus before t (other than the missing minus the formula is OK). Nature is mostly described by decaying (not rising) exponents ...

Last edited by Sergei Steshenko; 10-06-2009 at 01:09 PM.
 
Old 10-06-2009, 01:07 PM   #32
lutusp
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Quote:
Originally Posted by Sergei Steshenko View Post
Where did you get that formula ? Or, rather, how ? I.e. the formula is correct, but, as I said, to prove it you need to solve a differential equation - otherwise it's a religious belief. I.e. somebody told you and you believed in it.

I'm sorry, but at my high school we were taught about axioms and theorems - axioms are believed in, theorems are proven.

...

Actually, the formula is wrong, it should be

Vc = Vs * (1 - exp(-t / (R * C)))

- pay attention to minus before t (other than the missing minus the formula is OK). Nature is mostly described be decaying (not rising) exponents ...
Your position is admirable and I agree completely. Most Americans who learn Calculus learn it as a tool, not a method for analysis. Typically they will know only which equations to apply to which circumstances. But this may change over time -- new, free open-source tools like Sage are making differential equations more accessible and easier to manage:

Sage: Differential Equations

The above tutorial page derives the exact equation you've been discussing (among others).
 
Old 10-06-2009, 01:26 PM   #33
Sergei Steshenko
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Quote:
Originally Posted by lutusp View Post
Your position is admirable and I agree completely. Most Americans who learn Calculus learn it as a tool, not a method for analysis. Typically they will know only which equations to apply to which circumstances. But this may change over time -- new, free open-source tools like Sage are making differential equations more accessible and easier to manage:

Sage: Differential Equations

The above tutorial page derives the exact equation you've been discussing (among others).
Actually, you are opening a can of worms, and it's good. I mean, if a tool solves differential equations numerically, it does not necessarily means it does it correctly - applicability/convergence of numeric methods is the issue.

I was lucky enough to be first taught numeric methods of computations, and only then programming.

Interestingly enough, even the square equation

a * x^2 + b * x + c = 0

should on a computer be solved differently (though equivalently) than in a textbook - I learned this from a book by Niclaus Wirth and the issue, again, is numeric accuracy.

Unfortunately, a lot of modern programmers and engineers have no idea what computer arithmetics are and aren't.
 
Old 10-06-2009, 01:32 PM   #34
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Yeah I have no idea what anyone is talking about.
 
Old 10-06-2009, 02:04 PM   #35
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Quote:
Interestingly enough, even the square equation

a * x^2 + b * x + c = 0

should on a computer be solved differently (though equivalently) than in a textbook - I learned this from a book by Niclaus Wirth and the issue, again, is numeric accuracy.
Using the straight Quadratic Formula is, however, much easier for other people to immediately comprehend. When maintenance is more important than accuracy, like in say, games, you'd better stay with the math textbook. Of course that argument doesn't apply to numerical physics and such where accuracy is much, much, much more important. (then there's things like Gran Turismo which is sort of both, but I won't go there)

Quote:
I'm sorry, but at my high school we were taught about axioms and theorems - axioms are believed in, theorems are proven.
It's interesting you mention axioms and theorems.. Godel's Incompleteness Theorem is quite enlightening on that topic. Axioms aren't simply a belief, but are truths of a particular system of algebra that are inherently unprovable. A conjecture is a truth you can simply believe in, but it's not been proven or proven unprovable.

icecubeflower: Just try everything you feel inclined to try. If you stumble on the right thing, you'll know it. It'll feel completely right for you. As for robotics, the Lego NXT kit is a very good start.
 
Old 10-06-2009, 02:19 PM   #36
Sergei Steshenko
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Quote:
Originally Posted by tuxdev View Post
...
Axioms aren't simply a belief, but are truths of a particular system of algebra that are inherently unprovable.
...
Unprovable truth is a belief - isn't it ? Otherwise it would have been proven. Or, as I recently read elsewhere "a truth is a set of mutually agreed upon lies" .

If we want to be more practical/physical on the set of observed facts, we choose the set of axioms which fits the facts - until we observe a fact that doesn't fit what logically comes out from the set of chosen axioms.

As someone (a well known physicist) said - science is a cemetery of buried theories - or something like that.

...

To the OP - my programming education is not very formal, and in programming I am mostly self-taught. Still, if I understand it correctly, programming is based on so called discrete mathematics, so to formally fill the gaps one needs to study it.
 
Old 10-06-2009, 02:20 PM   #37
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OK, I fixed my stupid typo.......

Actually, I think you can prove the capacitor equation with a lab experiment---assuming that you first calibrate all the components and the voltmeter.

(Showing my age) I will now confess to have taken a class in ANALOG computers. I'm not kidding: big heavy boxes full of precision capacitors, resistors, voltage and current sources, etc.----change the jumpers to simulate a math problem.

Now for a brief quiz:
Take two identical capacitors. Charge one to 10 volts, and fully discharge the other. Now connect them and wait for the voltage to stabilize. To first order, you will find that the total stored energy is 1/2 of the original.
Where did the other half go?
Repeat with ideal capacitors in a circuit with no resistance. Now where did the missing energy go?

extra credit if you do with differential equations......
 
Old 10-06-2009, 02:31 PM   #38
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Guys can you start a different thread for the circuit math debate? I don't know that stuff.

If I was 20 again I'd probably go to school and pick computer engineering and get straight A's and learn circuits and all that stuff. But I'm not a kid, I'm 31. Everybody tells kids how important it is to get an education and get a job they like and they're right. But kids already know that. It was other stuff that I didn't know back then and I was too lost to make it in college.

Anyway I'm not going to school. I have a high school education and I know how to program and my skills are comparable to Comp Sci graduates. (certain Comp Sci graduates) I just wanted to know if I should stick with machine shops and just program for fun or if it was possible for someone like me to make a buck writing software.

I mean circuits and robotics and all this stuff, it's above my head. I mean I have no idea if I could teach myself that stuff on my own or where to start. That's intimidating stuff.
 
Old 10-06-2009, 02:46 PM   #39
pixellany
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Sorry---I will immediately cease the off-topic stuff. But you did start it----sort of.....

Seriously, the best advice I can add to what's been posted here is: Stop talking about what you CANNOT do, learn, etc. Focus on what you WANT to do---or where you want to be---and then do, learn, etc. what is required.
 
Old 10-06-2009, 03:04 PM   #40
Sergei Steshenko
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Quote:
Originally Posted by icecubeflower View Post
Guys can you start a different thread for the circuit math debate? I don't know that stuff.

If I was 20 again I'd probably go to school and pick computer engineering and get straight A's and learn circuits and all that stuff. But I'm not a kid, I'm 31. Everybody tells kids how important it is to get an education and get a job they like and they're right. But kids already know that. It was other stuff that I didn't know back then and I was too lost to make it in college.

Anyway I'm not going to school. I have a high school education and I know how to program and my skills are comparable to Comp Sci graduates. (certain Comp Sci graduates) I just wanted to know if I should stick with machine shops and just program for fun or if it was possible for someone like me to make a buck writing software.

I mean circuits and robotics and all this stuff, it's above my head. I mean I have no idea if I could teach myself that stuff on my own or where to start. That's intimidating stuff.
There are tutorials on electronics, there are prototype boards, there are oscilloscopes and there are electronic components - all this can be bought and is not that expensive - a used, but quite decent oscilloscope can be bought for $100 .. $200 on eBay. There are also computer driven ADC cards with USB interface which serve as a good oscilloscope and more - their program package typically has stuff like FFT built in.

All this enables one to have a pretty decent electronics lab at home.

Actually, a modern soundcard can serve as a pretty decent oscilloscope HW for audio (and above - up to sometimes 192kHz) range frequencies, and is quite sufficient for initial electronic studies (well, in AC, not in DC).
 
Old 10-06-2009, 03:22 PM   #41
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Yeah I get that. But there's so much stuff that I don't know. I guess I'm just looking for some kind of roadmap. I mean getting myself a robotics kit and teaching myself circuits and Diff EQ in my apartment after work and then getting a job making robots, is that something I should seriously consider or is that just a pipe-dream?

I mean it's scary, you know? What if I came home after work every day and worked my way through a book on circuits and did all the problems. Suppose I hated it the whole time. And then I try getting a job and the employer laughs at me and it turns out I just wasted all that time.

So if I'm supposed to be more positive then what I do know how to do is program and make data structures. Basically if there's anything you want a computer to do I can think of a way to make it happen off of the top of my head. And then usually I can research it and find out better ways to do it and make it happen more efficiently.

I think I should keep my day job and be prepared to be stuck there for the rest of my life. I think I should finish my computer game. (Which honestly I've only been working on maybe 1 out of 12 weeks so I guess I should get more focused.) And then I should learn more about design patterns, SQL, and Java. And I should learn that list of stuff I got from orgcadman's post. And then try to get into web design or Database administration or something.

I'd like to start from scratch and go to college and learn all that Computer Engineering stuff you guys were debating but it's too late. I'd rather just stick with what I know. And then just tell my kids, yeah if I would have just stuck it out and gotten straight A's, even when I felt lost and didn't like it, then it would have made my life a lot easier. Life is so freaking backwards.
 
Old 10-06-2009, 03:24 PM   #42
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Last post was to Pixellany.

I just read Sergei's post. Hey thanks. That stuff does sound interesting and that is the advice I was looking for as far as robotics and stuff goes. I might look into it. I don't know. Probably not. I mean that's something you only hear about the Nikolai Teslas and John Carmacks of the world doing on their own. I don't think I could do it without any structure and lab partners and stuff.

Actually I could do it. But it would have be completely laid out, like an online teach yourself Computer Engineering tutorial. Where it tells you what books to read and what problems to do. Then it tells you what experiments to do. But at the level I'm at right now and without a clear guide like that I just feel way too lost to take that path.

Last edited by icecubeflower; 10-06-2009 at 03:35 PM.
 
Old 10-06-2009, 03:54 PM   #43
Sergei Steshenko
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Quote:
Originally Posted by icecubeflower View Post
Last post was to Pixellany.

I just read Sergei's post. Hey thanks. That stuff does sound interesting and that is the advice I was looking for as far as robotics and stuff goes. I might look into it. I don't know. Probably not. I mean that's something you only hear about the Nikolai Teslas and John Carmacks of the world doing on their own. I don't think I could do it without any structure and lab partners and stuff.

Actually I could do it. But it would have be completely laid out, like an online teach yourself Computer Engineering tutorial. Where it tells you what books to read and what problems to do. Then it tells you what experiments to do. But at the level I'm at right now and without a clear guide like that I just feel way too lost to take that path.
Well, it again feels that your aim is little details and not big picture.

The first 3 years at the university were not easy and required an effort, but after that life suddenly became easier - I started finding repeated application of base knowledge to particular subject - be it holography or lasers or waveguides or radar.

So, it's up to you to decide whether to try to grab "small" stuff like Java and SQL or whether to finally complete the basis.

I know some academic stuff looks boring and unnecessary, but if/when you realize what it's needed for, interest in learning the stuff shows up.

Robotics, I think, will require some HW/circuit stuff (and mechanical one, and electric motors - studied the latter at the university).

For pure programming, as I said, try discrete mathematics to begin with.

...

I had somebody I was trying to help with programming stuff, but the person was of younger generation. I was astonished how the person was trying to grab C++, Java, Perl, you name it not having basic understanding what computing/programming was about, not caring about O(N^2) algorithms, etc.

The person's goal was to grab as many certificates as possible thus hoping to get a better paying job. It was hopeless to explain the person that the root cause of difficulties was lack of proper basic knowledge/understanding.
 
Old 10-06-2009, 03:59 PM   #44
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I mean circuits and robotics and all this stuff, it's above my head. I mean I have no idea if I could teach myself that stuff on my own or where to start. That's intimidating stuff.
In America, you are what you want to be. If you believe that it is above your head, then it is. Because you say so.

As for learning being for kids (you didn't quite say that but it was a definite subtext), I'm 53. I'm still learning new skills; I hope to never stop. When it comes to learning, nothing intimidates me, though at times I do have to decide whether this particular thing is worth spending time on.
 
Old 10-06-2009, 04:05 PM   #45
icecubeflower
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I just mean I'm not going to college. I'll learn anything on my own if I know where it's going. I just don't know how to go about learning computer engineering without some kind of syllabus or tutorial or roadmap or something.

I'm not just trying to learn all the small stuff. I'm working my way through CLRS right now. I know about big O notation and algorithms and stuff.
 
  


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