scott wrote:
>> But this has basically been my experience in every group project I've 
>> ever worked on. I've never met any other students who can actually 
>> program / do advanced math / comprehend complicated logic / etc. 
>> Basically I'm always the only guy in the group with any kind of 
>> technical skill.
> 
> Maybe you should have gone to a better University with more people at 
> your level?  I can't remember exactly how old you are, did you have to 
> go through the whole University application thingy where you supply your 
> predicted A-level grades and get made offers from different places?  DId 
> you choose somewhere that offered you really low grades or what?  You 
> seem to have been quite mismatched with the course.

Just for the record: I have never taken any A-levels. I only took 3 
GCSEs. I got a B and two Cs. This are unprecidentedly high grades for 
the school I went to. (Remember, I went to a school for mentally 
retarded people.)

I went to DeMontfort simply because it's the only university in the city 
of Milton Keynes. (Gotta love the way they shut down the year I 
graduated though! Apparently some folks had to transfer to some other 
random city to actually finish their courses...)

When I mentioned this to some guy in the local LUG, he goes "What? 
DeMontfort? That's not a university, it's an old polytechnic that 
*thinks* it's a university now." I have no idea what he's talking about 
- presumably some kind of cultural thing that would be over my head...

FWIW, my statements above were about college too. The class I was in 
contained a bunch of "lads" who were more interested in getting drunk 
and arguing about Cast vs Blur than actually learning stuff. Bunch of 
losers they were! I still remember the weekly paper fights. Oh, and the 
C'paddy races. (The objective being to say the word "c'paddy" the most 
times in 60 seconds.) Like, WTF?

> I think some people are just destined not to program, we had a 4x2 hour 
> time slot to do some C++ practical, which anyone who had ever made a 
> simple program with a few functions could have done easily in the first 
> 2 hours. Yet there were 1 or 2 people who were still there right at the 
> end struggling with the whole concept.

Yes. A lecturer once told me that grades for programming assignments 
show a curios bimodel distribution. There are people who "get it", and 
find the assignments ridiculously easy. They walk away with A-stars and 
better. And there are people who do not "get it". They struggly to write 
anything.

For reasons beyond my comprehension, during my entire degree I kept 
having random Asian people come up to me and beg me to "fix" their 
programs. Quite how they knew my name is beyond me...

Just once, I did in fact take a look at one guy's Java program. Except 
that... it wasn't Java. It had Java keywords in it, and the syntax was 
sort-of reminiscent of Java. But it was gibberish. COMPLETE GIBBERISH. I 
couldn't even take a wild guess at what it was *supposed* to do! The guy 
claimed he just needed me to make "a few small fixes" - but this text 
file was quite clearly not removely compilable, never mind runnable.

Clearly, the only way to "fix" this code would begin with deleting all 
the currently existing code.

I am unsure as to whether the guy in question was so clueless that he 
honestly believed that it wouldn't take much to fix this, or whether he 
was just trying to sweet-talk me. How the HELL he expected the person 
marking the work to believe that he wrote it is beyond me - unless he 
really did think he had it almost right to start with...

Seriously. What. The. Hell.

But it seems that to some people, Java is just words on a page. Only a 
few people can see beyond that and comprehend the conceptual constructs 
that those words denote.

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> How many resistors can you see? Because I count NONE!

Sure, but that circuit does not show how you generate the inputs A,B,Cin or 
how to connect the output to an LED.

Both of which require some basic knowledge of analogue electronics.

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> Just for the record: I have never taken any A-levels. I only took 3 GCSEs. 
> I got a B and two Cs. This are unprecidentedly high grades for the school 
> I went to. (Remember, I went to a school for mentally retarded people.)

OOC why did you go to that school, you don't seem mentally retarded!

> FWIW, my statements above were about college too. The class I was in 
> contained a bunch of "lads" who were more interested in getting drunk and 
> arguing about Cast vs Blur than actually learning stuff.

That mostly stops when you get to A-levels, because it's optional you only 
get people there who actually want to be there.

> I am unsure as to whether the guy in question was so clueless that he 
> honestly believed that it wouldn't take much to fix this, or whether he 
> was just trying to sweet-talk me. How the HELL he expected the person 
> marking the work to believe that he wrote it is beyond me - unless he 
> really did think he had it almost right to start with...
>
> Seriously. What. The. Hell.

Aww, would have been better if you had some hot girls in your group, then 
I'm sure you wouldn't have minded completely rewriting their code from 
scratch :-)

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scott wrote:
>> How many resistors can you see? Because I count NONE!
> 
> Sure, but that circuit does not show how you generate the inputs A,B,Cin 
> or how to connect the output to an LED.
> 
> Both of which require some basic knowledge of analogue electronics.

NNOOOOOOOOOO!!!! X_X



Well anyway, FWIW, the IC managed to drive the LED just fine. (I bought 
special 5V LEDs; apparently normal ones take roughly 3V.) It's just that 
I couldn't get the right truth table out of it. :-(

You think using a 2-pole switch with the poles connected to each of the 
power rails will do it?

Post a reply to this message

scott wrote:
>> Just for the record: I have never taken any A-levels. I only took 3 
>> GCSEs. I got a B and two Cs. This are unprecidentedly high grades for 
>> the school I went to. (Remember, I went to a school for mentally 
>> retarded people.)
> 
> OOC why did you go to that school, you don't seem mentally retarded!

Have you heard my voice? I certainly *sound* retarded! (I talk waaaaay 
tooo sloooowllllyyyy...)

Well anyway, the first school I went to was a rough school. Kids could 
beat up other kids just for entertainment. Whoever the weakest kid was, 
he or she got beat the most. Wanna guess who the weakest kid in my class 
was?

Anyway, when I reached the age of 9, I still couldn't read or write. At 
all. I mean, I spent every day at school in a state of absolute terror, 
I wasn't even paying attention to *lessons*! And the school repeatedly 
refused to lift a finger to stop the kids bullying me.

I can vividly remember being chased across the playground screaming blue 
murder begging for somebody to save me. But the staff just stood there 
smoking, not really paying attention. Afterwards I asked one of them 
"why didn't you save me?!" The disinterested individual casually 
responded "uw, I thought they woz just playin widja". Yeah, thanks for that.

So then I got moved to this school for weird kids. And my god, were they 
weird! Some of them couldn't even speak properly, or at all. Almost all 
of them were very obviously strange.

On the plus side, I learned to read and write. (Although it seems some 
people here have nothing better to do than point out my spelling 
mistakes.) On the minus side... I spent 7 years without being able to 
interact with normal humans, and without being able to interact with 
*girls*. As absurd as it seems, I was 21 years old the first time I had 
a real conversation with a girl my age who wasn't my sister.

(Actually, this turned out to be the first time I *touched* a real girl 
too. After weeks of pestering, she did eventually let me kiss her. Most. 
Terrifying. Thing. EVER! But DAMN she was ****ing good at it!! *sigh* 
She's married now. I can't even contact her any more...)

Originally I assumed that I went to this school because I couldn't read 
or write. But now, looking back, it has gradually become clear to me 
that *I* am not normal either. I do things that normal people don't do. 
There clearly *is* something wrong with me. And I know it's incurable. I 
find this extremely upsetting.

>> FWIW, my statements above were about college too. The class I was in 
>> contained a bunch of "lads" who were more interested in getting drunk 
>> and arguing about Cast vs Blur than actually learning stuff.
> 
> That mostly stops when you get to A-levels, because it's optional you 
> only get people there who actually want to be there.

Well, going to college is optional too. People told me it would be 
"different" at college. But from what I can tell, the guys who were 
there were too hopeless to get actual jobs, so they went to college 
instead. Wuh?! o_O

At least at uni the people weren't so *completely* stupid...

> Aww, would have been better if you had some hot girls in your group, 
> then I'm sure you wouldn't have minded completely rewriting their code 
> from scratch :-)

Girls? In a computing course...?

Which part of the world do *you* live in?? o_O

(Actually, in fairness, the full class was 80 people, and IIRC about 6 
of them were female. And 2 of them were my age. The other 4 were married 
with children. The two my age held a deep fascination for me... although 
obviously I was terrified of them. And, apparently, they were both 
spoken for anyway...)

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> Well anyway, FWIW, the IC managed to drive the LED just fine. (I bought 
> special 5V LEDs; apparently normal ones take roughly 3V.)

"normal" ones work at all sorts of voltages, it even varies from piece to 
piece quite significantly.  But you never drive an LED directly by applying 
a fixed voltage, you always drive it by regulating the current to a fixed 
amount (like 20 mA or whatever).  Adding a series resistor to a raw LED is a 
quick and crude method of fixing the operating current.

> You think using a 2-pole switch with the poles connected to each of the 
> power rails will do it?

Yup, or just connect a high value resistor (eg 10 or 100K) between the input 
and the other power rail - so you have your switch arranged like this:

http://www.seattlerobotics.org/encoder/mar97/basics4.gif

That way, when the switch is open, the input is connected to 0V, and when 
it's closed it is connected to V+.

Post a reply to this message

scott wrote:
>> Well anyway, FWIW, the IC managed to drive the LED just fine. (I 
>> bought special 5V LEDs; apparently normal ones take roughly 3V.)
> 
> "normal" ones work at all sorts of voltages, it even varies from piece 
> to piece quite significantly.  But you never drive an LED directly by 
> applying a fixed voltage, you always drive it by regulating the current 
> to a fixed amount (like 20 mA or whatever).  Adding a series resistor to 
> a raw LED is a quick and crude method of fixing the operating current.

This doesn't make sense to me.

Presumably the resistence of the LED is finite and fixed. How does 
adding another resistor help? There are several schematics in my 
electronics kit that involve LEDs and no resistors at all.

>> You think using a 2-pole switch with the poles connected to each of 
>> the power rails will do it?
> 
> Yup, or just connect a high value resistor (eg 10 or 100K) between the 
> input and the other power rail - so you have your switch arranged like 
> this:
> 
> http://www.seattlerobotics.org/encoder/mar97/basics4.gif
> 
> That way, when the switch is open, the input is connected to 0V, and 
> when it's closed it is connected to V+.

Now, see, I've never been able to comprehend stuff like this. To me, 
this diagram just looks like when you close the switch, all the current 
will flow straight from one rail to the other, shorting out the battery 
and not providing any current at all to the input of the gate.

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> Presumably the resistence of the LED is finite and fixed.

No.  Here's a graph of voltage against current for a typical LED:

http://www.cq.cx/pics/int-led-vi.png

Note that for a fixed value resistor this would be a straight line starting 
at the origin.

Say you want to operate the LED at 20 mA (brightness/lifetime etc of LEDs is 
all related to current, not voltage).  That means you need to drive it at 
exactly 2.0 V.  You need to add a resistor in series to connect it to eg a 
5V supply.  So you need 3V across the resistor with 20 mA flowing through 
it, R=V/I=3.0/0.02= 150 ohms.

Of course there are more complex LED driving circuits that actively keep the 
current constant over a wide range of operating conditions, some can even 
drive chains of LEDs in series and flag up when there are failures etc.

> Now, see, I've never been able to comprehend stuff like this. To me, this 
> diagram just looks like when you close the switch, all the current will 
> flow straight from one rail to the other, shorting out the battery and not 
> providing any current at all to the input of the gate.

Yes, *some* current will flow from one rail to the other, which is why it is 
important to use a *high* value resistor.  If you use a 10kOhm resistor 
across 5 Volts, that's I=V/R=0.5mA which is hardly going to cause a problem. 
But the important thing is, that point in the middle that is directly 
connected to the input will be at 5V when the switch is closed.

Post a reply to this message

scott wrote:
>> Presumably the resistence of the LED is finite and fixed.
> 
> No.  Here's a graph of voltage against current for a typical LED:
> 
> http://www.cq.cx/pics/int-led-vi.png

Where do you *find* this stuff??

> Note that for a fixed value resistor this would be a straight line 
> starting at the origin.

OK, now I'm confused. A graph of current against voltage? But current is 
completely *determined by* voltage! o_O

>> Now, see, I've never been able to comprehend stuff like this. To me, 
>> this diagram just looks like when you close the switch, all the 
>> current will flow straight from one rail to the other, shorting out 
>> the battery and not providing any current at all to the input of the 
>> gate.
> 
> Yes, *some* current will flow from one rail to the other, which is why 
> it is important to use a *high* value resistor.  If you use a 10kOhm 
> resistor across 5 Volts, that's I=V/R=0.5mA which is hardly going to 
> cause a problem. But the important thing is, that point in the middle 
> that is directly connected to the input will be at 5V when the switch is 
> closed.

OK... so... why not an open circuit then? That would have infinite 
resistence?

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>> http://www.cq.cx/pics/int-led-vi.png
>
> Where do you *find* this stuff??

I did a google image search for "LED VI graph" IIRC.  Easier than trying to 
explain it.

>> Note that for a fixed value resistor this would be a straight line 
>> starting at the origin.
>
> OK, now I'm confused. A graph of current against voltage? But current is 
> completely *determined by* voltage! o_O

Of course it is determined, but it's only a linear relationship (V=IR) for 
resistors.  LEDs are diodes and are certainly not linear, so you need a 
graph.  You could draw a graph for a resistor if you wanted like I said, but 
it would be a bit pointless because we know V=IR for a resistor.

> OK... so... why not an open circuit then? That would have infinite 
> resistence?

Then the input would be equally connected to 0V and V+ with near infinite 
resistances, that's called a "floating" input, because it can be persuaded 
very easily to either go to 0V or V+, depending on the exact details inside 
the IC (and maybe some state of the other inputs, who knows?!).  Best to 
ensure you have at most around 100K of resistance to one of the rails to fix 
the input reliably.

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