As you probably all know by now, I hold an honours degree in Computer 
Science. (Upper-second class, no less.)

As far as I can tell, whoever created this cause was of the opinion that 
"software" is a construct for storing, processing and retreiving 
business data. In other words, you have a UI at the front (possibly 
web-based), a large database at the back, and some complex business 
logic in the middle.

The idea that there might exist "software" which doesn't fit this model 
appears to have not occurred to anybody here. For example:

- Embedded software.
- Device drivers.
- Computer games.
- Mathematical moddeling.
- Signal processing.
- Artificial intelligence.

None of these really fit the world-view described above. Most of them 
don't usually involve any kind of database. Device drivers usually don't 
have a *user* interface of any kind. Computer games might be 3-tier, but 
it's a hell of a lot different to a stock control system! And DSP and AI 
are 90% mathematics.

Given the world-view above, it should come as no surprise that we 
learned about things like project management, object-oriented analysis 
and design, UML, CASE tools, relational databases, SQL, HTML, CSS, Java, 
JavaScript, XSLT, TCP/IP, double-entry book keeping (I'm not making this 
up), a little bit of management theory (Taylor, Maslow, etc.), and 
systems testing.

There were also two modules taught by Mr Apathy. Mr Apathy was tasked 
with teaching us about computer hardware, and later about operating 
systems. In Mr Apathy's opinion, knowing about binary is "pointless" 
because "the computer will do it all for you anyway". He believed that 
"20 years ago it might have been necessary to know this stuff, but in 
the modern world you're really never going to need this information. But 
it *is* in the exam, so I have to teach it to you." I cannot tell you 
what an inspirational motivation for learning this was.

(Basically his idea was that we'd all go out into the world and become 
either computer consultants, or maybe Java programmers, and at that 
level of abstraction, petty details like what addressing modes your CPU 
supports or which IRQ services the serial port are irrelevant because 
your compiler / OS will handle all that for you. I mean, it's not like 
any of us are going to develop device drivers or anything, right?)



During my course, I recall seeing exactly one equation. I forget the 
exact technical term, but it's basically Shannon's formula for 
determining how much data you can theoretically shove down a noisy 
communications channel. (This was during a networking lecture.)

When the lecturer wrote the formula on the whiteboard, everybody freaks 
out and starts going "what the hell does 'log' mean?" And the lecturer 
is all "oh, I'm sorry, I just *assumed* that 3rd year degree students 
would know what a logarithm is". It turns out that actually, only two 
people in the room knew about logarithms.

Obviously, one of them was me. Astonishingly, the other one was the 
loud-mouthed, beer-drinking rugby hooligan from Manchester. O_O (And he 
actually *did* know what he was talking about too.) I remember feeling 
somewhat guilty for assuming the guy was an idiot just because he always 
acted like one...



Actually, I say only one formula... some of the final year optional 
modules I did also had a little more math in them than that.

The first one was Computer Graphics. This certainly involved lots of 
*calculations*, but not all that much mathematics. There was a tiny bit 
of vector and matrix arithmetic (which apparently scared the hell out of 
everybody). I think the word "cosine" might have been mentioned in 
relation to the vector dot product - useful for surface illumination, 
not to mention backface-cull.

Our first CG assignment was to utilise Bresenham's algorithm to draw a 
straight line. (Some people thought the guy was joking when he said 
that!) We also looked at things like low-level clipping and filling 
operations, but for the most part our work was conceptual. Certainly 
there wasn't much exotic mathematics.

It was a nice module though. The guy lecturing it sounded like a 
university professor. He talked very slowly and precisely, but without 
overuse of jargon. He seemed actually good at explaining things in 
simple terms.



The second one was a module entitled "Genetic Algorithms and Artificial 
Neural Networks" (GAANN for short). Actually it seemed to basically 
consist of all things AI-related. The lecturer for this had the weakest 
grasp of English, and his speach was barely intelligable. If somebody 
said they didn't understand something, he would repeat almost exactly 
what he said the first time, but this time shouting. It was *very* 
irritating.

(Also, for some reason his classification problems *always* involved a 
man evaluating potential wives to decide which one to marry - and he 
gave the ladies creepy looks while telling this example. Brrrgh!)

This module did involve some non-trivial math. It was so badly-explained 
that I couldn't possibly tell you how advanced it was. Much of the 
module revolved around feed-forward ANNs trained by back-propogation, 
which is a kind of "grædiɛnt æsɛnt miθæd". For back-propogation to work, 
the transfer function needs to be non-linear. And there was something 
about a "næbl" operator.

IIRC, the part about generic algorithms lasted about an hour.

It's a pitty really, because it seems like a really interesting subject...



So anyway, that's what *I* did during my degree. Anybody out there do 
anything more interesting?



My mum keeps telling me I should do a mathematics course. Personally, 
I'm not sure where the hell I'd get the time or the money from. (It's 
not exactly cheap.) I guess it *is* kind of amazing that I know about 
the Laplace transform, given that I have never at any point in my life 
been "taught" anything beyond simple arithmetic.

Similarly, I know about how to wire logic gates together to make 
interesting devices. And I know about Dijkstra's shunting algorithm. 
(Unfortunately, I'm never sure exactly how to spell the name though!)

Also... I really ought to get a job where all this stuff is useful! I 
wonder if such a thing exists?

Post a reply to this message

Invisible wrote:
> As you probably all know by now, I hold an honours degree in Computer 
> Science. (Upper-second class, no less.)

Yay!

> As far as I can tell, whoever created this cause was of the opinion that 
> "software" is a construct for storing, processing and retreiving 
> business data. In other words, you have a UI at the front (possibly 
> web-based), a large database at the back, and some complex business 
> logic in the middle.

"Welcome to the desert of the real." ;)

> The idea that there might exist "software" which doesn't fit this model 
> appears to have not occurred to anybody here. For example:
> 
> - Embedded software.
> - Device drivers.
> - Computer games.
> - Mathematical moddeling.
> - Signal processing.
> - Artificial intelligence.

You forgot computer graphics. :)

Anyway, those are niches.  90% of IT (which is not the same as compsci) 
is about COBOLs.

> Also... I really ought to get a job where all this stuff is useful! I 
> wonder if such a thing exists?

It only exists within firms providing the infrastructure and research 
everybody else employs to do their things.  I'm talking about Microsoft, 
Adobe, Sun, Autodesk, open source projects etc...

Post a reply to this message

nemesis wrote:

> "Welcome to the desert of the real." ;)

How apt those words suddenly seem...

>> The idea that there might exist "software" which doesn't fit this 
>> model appears to have not occurred to anybody here. For example:
>>
>> - Embedded software.
>> - Device drivers.
>> - Computer games.
>> - Mathematical moddeling.
>> - Signal processing.
>> - Artificial intelligence.
> 
> You forgot computer graphics. :)

I pretty much figured computer games subsumed that - but sure, people 
also use graphics itself for movie special effects and previs, 
scientific visualisation, mathematical modelling, etc.

> Anyway, those are niches.  90% of IT (which is not the same as compsci) 
> is about COBOLs.

Hmm. Between the global telecommunications network (with its custom 
hardware and the recent craze for mobile phones), the 
multi-billion-dollar games industry, the presumably large industry 
making computer components (most of which require drives of some kind), 
the ever-increasing sea of consumer goods that need firmware to 
function, the financial institutions that build and run huge complex 
financial simulations, and the endless array of applications of DSP... 
those look like some pretty ****ing big niches to me! ;-)

I believe it was Djikstra who wrote "The use of COBOL cripples the mind; 
its teaching should therefore be considered a criminal act."

>> Also... I really ought to get a job where all this stuff is useful! I 
>> wonder if such a thing exists?
> 
> It only exists within firms providing the infrastructure and research 
> everybody else employs to do their things.  I'm talking about Microsoft, 
> Adobe, Sun, Autodesk, open source projects etc...

Yeah - maybe I should get said to write open source software?

Oh, wait...

Post a reply to this message

> (Basically his idea was that we'd all go out into the world and become 
> either computer consultants, or maybe Java programmers, and at that level 
> of abstraction, petty details like what addressing modes your CPU supports 
> or which IRQ services the serial port are irrelevant because your compiler 
> / OS will handle all that for you. I mean, it's not like any of us are 
> going to develop device drivers or anything, right?)

It seemed during my degree (Engineering) that they expected everyone was 
going to go out there and design a finite element analysis software package 
(note I said design, not code), or come up with some new standards for 
building bridges, or use some exotic material for some new purpose.  Nobody 
seemed to imagine that some people might want to actually go and work on 
more mundane things that most Engineers do, hence nobody taught us how to 
make a complete 2D Engineering drawing (either by hand or on the computer), 
or how to use a modern 3D CAD package, or how to use any software to help 
with electronic circuit design.

> During my course, I recall seeing exactly one equation.

Haha, I recall seeing equations in my dreams (or should that be 
nightmares?).  Seriously, I think I did the most theoretical Engineering 
course in existence.

> So anyway, that's what *I* did during my degree. Anybody out there do 
> anything more interesting?

I really enjoyed my University course, for me most subjects were really 
interesting.  The only one I really got bored with was Thermofluid Mechanics 
(all about steam cycles, heat cycles etc, I think we just had a bad 
lecturer).

Here's a list of the 1st and 2nd year courses that everyone had to do: (3rd 
and 4th year you could choose from a much longer list, but basically just 
specialisations of the below subjects)

Kinematics and Dynamics in 2D
Dynamics of Rigid Bodies in 3D
Mechanical Vibrations
Thermofluid Mechanics I & II
Structural Mechanics I & II
Materials I & II
Physical Principles of Electronics and Electromagnetics
Linear Circuits and Devices I & II
Electrical Power
Electromagnetic Fields and Waves
Linear Systems and Control
Comms Fourier Transforms & Signal & Data Analysis
Digital Circuits and Information Processing
Mathematics
Vector Calculus
Linear Algebra
Computing
Dimensional Analysis
Engineering in Society
Product Design
Structural Design Project (ie building a bridge!)

The best part was the robot design project.  We were put into teams of 6 and 
told to make a robot that drove around a track marked by white lines on a 
black board and picked up containers.  The containers would either be empty 
or full, and we had to move the containers to the appropriate bin.  In most 
teams 2 people actually made the robot mechanics, 2 did the electronics 
(motor drive control, interface to PC, etc) and 2 did the software.  Was 
really good fun, especially as the quicker your robot completed the task the 
more points you got.

Post a reply to this message

scott wrote:

> It seemed during my degree (Engineering) that they expected everyone was 
> going to go out there and design a finite element analysis software 
> package (note I said design, not code), or come up with some new 
> standards for building bridges, or use some exotic material for some new 
> purpose.  Nobody seemed to imagine that some people might want to 
> actually go and work on more mundane things that most Engineers do, 
> hence nobody taught us how to make a complete 2D Engineering drawing 
> (either by hand or on the computer), or how to use a modern 3D CAD 
> package, or how to use any software to help with electronic circuit design.

Heh. Well there *are* a lot of people out there working on novel 
materials these days. (Organic semiconductors?! Whatever next!)

>> During my course, I recall seeing exactly one equation.
> 
> Haha, I recall seeing equations in my dreams (or should that be 
> nightmares?).  Seriously, I think I did the most theoretical Engineering 
> course in existence.

Theoretical... engineering... LMAO!

Ah, but did you implement a 9D Hypercardigan? ;-)

> I really enjoyed my University course, for me most subjects were really 
> interesting.  The only one I really got bored with was Thermofluid 
> Mechanics (all about steam cycles, heat cycles etc, I think we just had 
> a bad lecturer).

I mostly enjoyed mine.

9 AM on Monday morning of my very first day at university and we had a 
lecture about Smalltalk. The guy giving the lecture was a seriously 
smart guy. Like, every lecture or lab lession, after everybody had gone 
home, me and him are still standing there arguing about the merits of 
multiple inheritance or something!

OTOH, the whole module on report writing bored the HELL out of me! >_<

> Kinematics and Dynamics in 2D

Kinematics is a word?

> Mechanical Vibrations

That sounds pretty complicated. o_O

Any idea what a "resonant mode" is?

> Thermofluid Mechanics I & II

Ouch. AFAIK, anything involving fluids or gasses = highly complex.

> Materials I & II

Now that *sounds* quite simple... but I bet it isn't.

(I'm presuming this is about elastic vs plastic deformation and so forth.)

> Physical Principles of Electronics and Electromagnetics

...so, Lorenz forces and so on?

> Electrical Power

OK, I have *got* to be missing something here. ;-)

> Comms Fourier Transforms & Signal & Data Analysis

What a title! o_O

> Mathematics

Oh... so that's specific then!

> Vector Calculus
> Linear Algebra

More like it. ;-)

> Computing

Interesting?

> Engineering in Society

Not interesting??

> Structural Design Project (ie building a bridge!)

LOL!

> The best part was the robot design project.  We were put into teams of 6 
> and told to make a robot that drove around a track marked by white lines 
> on a black board and picked up containers.  The containers would either 
> be empty or full, and we had to move the containers to the appropriate 
> bin.  In most teams 2 people actually made the robot mechanics, 2 did 
> the electronics (motor drive control, interface to PC, etc) and 2 did 
> the software.  Was really good fun, especially as the quicker your robot 
> completed the task the more points you got.

That *is* pretty neat.

The... uh... no, I can't remember the name of it. But there *is* a 
programming contest that's a bit like the IRTC. They set a challenge, 
and you have so many days to write a program that solves it. One of them 
was where your program accepts a track description as input, and 
produces a series of driving commands as output. The car that gets round 
the track fastest wins. (But the car simulation part is an external 
program, with limits on acceleration, cornering, etc.)

One day, maybe I will be skilled enough to complete... but I doubt it.

Post a reply to this message

>> Kinematics and Dynamics in 2D
>
> Kinematics is a word?

Yes, it's basically about movements of objects without considering the 
forces that cause the movements.  eg if one part is fixed to move at 5000rpm 
what happens to the rest of the connected system.  Quite a lot of geometry 
and resolving velocities, instantaneous centres of rotation etc.

> Any idea what a "resonant mode" is?

One particular way something can vibrate, that can't be split up further.  A 
bit like splitting a signal into sine waves.  eg take a 30cm ruler, you can 
bend it in the middle, that's the 1st mode.  The 2nd mode is to force it 
into a complete sine wave shape (ie two bends in the length).  Of course in 
3D you get many more modes, like twisting, bending in the other direction 
etc.  It's easier to analyse the system if you can split it down into the 
resonant modes.  Each resonant mode will also have a natural frequency.

> Ouch. AFAIK, anything involving fluids or gasses = highly complex.

Yep this was my worst course, working out the states of steam and water 
vapour as it goes through a cycle, using huge look-up-tables because there 
are no formulae for these highly complex things, etc.  Although learning 
exactly how a jet engine works and calculating the exit speed and 
temperature of the exhaust gases was pretty cool.

>> Materials I & II
>
> Now that *sounds* quite simple... but I bet it isn't.
>
> (I'm presuming this is about elastic vs plastic deformation and so forth.)

Yeh, and how stress and cracks propagate, phase diagrams of mixtures of 
materials, particularly on the iron-carbon one (there are like 100 different 
states of iron depending how quickly it is cooled and what proportion of 
carbon you have in there).  Also hardness of materials, statistical analysis 
of ceramics, that sort of thing.

> ...so, Lorenz forces and so on?

Yep, starting with how semiconductors work (very physicsy) then going on to 
diodes and transistors, the 2nd part of the course did the same for 
magnetics, really a base lecture course for other ones.

>> Electrical Power
>
> OK, I have *got* to be missing something here. ;-)

Well from the previous course we already learnt that resistance is complex, 
so that helps you understand the generators and motors here, then 3-phase 
power, power transmission, transformers, power factor correction, that sort 
of stuff.

>> Comms Fourier Transforms & Signal & Data Analysis
>
> What a title! o_O

Got very hairy at stages with things like cross-correlation and 
auto-correlation, also with things like z-transforms and FIR and IIR filters 
etc.

>> Mathematics
>
> Oh... so that's specific then!

There were 2 courses here, both were optional depending on how much maths 
you had done at A level.  Most people sat the "fast" course just as a 
refresher, just to relearn the basics like how to solve differential 
equations, how matrices work, stuff like that.

>> Computing
> Interesting?

Not really, software life cycle, structured programming, numerical precision 
errors, algorithm complexity, search&sort algorithms, very vague and 
general, clearly aimed at writing some small code block to solve an 
Engineering problem rather than any huge software project.

>> Structural Design Project (ie building a bridge!)
> LOL!

They applied prices to each bit of metal you could use, then you had a 
budget to build a bridge to span a certain gap (about 1 metre) and support a 
certain weight (about 150kg).  Of course the cheapest one that could 
withstand 150kg won.  Mine buckled and collapsed spectacularly at about 70kg 
due to me not actually putting it together very squarely.  I still have this 
twisted lump of rusting metal in the attic at home!

> The... uh... no, I can't remember the name of it. But there *is* a 
> programming contest that's a bit like the IRTC. They set a challenge, and 
> you have so many days to write a program that solves it. One of them was 
> where your program accepts a track description as input, and produces a 
> series of driving commands as output. The car that gets round the track 
> fastest wins. (But the car simulation part is an external program, with 
> limits on acceleration, cornering, etc.)

Oh that sounds cool, one of our practicals was a bit like that, we had to 
write a program to control some factory that was producing several different 
parts according to demand.  It got quite complex and remember writing a 6 or 
8 dimensional optimisation algorithm to see when was best to switch 
production lines from one product to another!

Post a reply to this message

scott wrote:
>>> Kinematics and Dynamics in 2D
>>
>> Kinematics is a word?
> 
> Yes, it's basically about movements of objects without considering the 
> forces that cause the movements.  eg if one part is fixed to move at 
> 5000rpm what happens to the rest of the connected system.  Quite a lot 
> of geometry and resolving velocities, instantaneous centres of rotation 
> etc.

So if you wanted to describe the motion of a complex arrangement of 
rigid components (e.g., a car gearbox), you'd use kinematics?

>> Any idea what a "resonant mode" is?
> 
> One particular way something can vibrate, that can't be split up 
> further.  A bit like splitting a signal into sine waves.  eg take a 30cm 
> ruler, you can bend it in the middle, that's the 1st mode.  The 2nd mode 
> is to force it into a complete sine wave shape (ie two bends in the 
> length).  Of course in 3D you get many more modes, like twisting, 
> bending in the other direction etc.  It's easier to analyse the system 
> if you can split it down into the resonant modes.  Each resonant mode 
> will also have a natural frequency.

So... the resonant modes of a effectively 1D system (a string, a 
gas-filled pipe, etc.) would just be harmonics of the main resonant 
frequency?

>> Ouch. AFAIK, anything involving fluids or gasses = highly complex.
> 
> Yep this was my worst course, working out the states of steam and water 
> vapour as it goes through a cycle, using huge look-up-tables because 
> there are no formulae for these highly complex things, etc.  Although 
> learning exactly how a jet engine works and calculating the exit speed 
> and temperature of the exhaust gases was pretty cool.

Heh. So you know how an ideal gas is different from a real gas then? ;-)

>>> Materials I & II
>>
>> Now that *sounds* quite simple... but I bet it isn't.
>>
>> (I'm presuming this is about elastic vs plastic deformation and so 
>> forth.)
> 
> Yeh, and how stress and cracks propagate, phase diagrams of mixtures of 
> materials, particularly on the iron-carbon one (there are like 100 
> different states of iron depending how quickly it is cooled and what 
> proportion of carbon you have in there).  Also hardness of materials, 
> statistical analysis of ceramics, that sort of thing.

Perhaps you could explain something to me then:

If I take a piece of paper and hold it horisontal, it flops under its 
own weight. But if I fold it down the middle, now it *can* stand up 
under its own weight. (But only if you hold it the right way.)

At the same time, a straight metal rod is very strong, but once bent it 
becomes drastically weaker, and it seems that nothing will restore it to 
its original condition.

>>> Comms Fourier Transforms & Signal & Data Analysis
>>
>> What a title! o_O
> 
> Got very hairy at stages with things like cross-correlation and 
> auto-correlation, also with things like z-transforms and FIR and IIR 
> filters etc.

Now that really does sound interesting! Heh.

I still have trouble getting the fine technical details of DSP straight 
in my head. The basic principles are quite simple - once somebody 
explains them properly - but minor details can make all the difference. 
(Is this a normalised or an un-normalised sinc function?)

>>> Mathematics
>>
>> Oh... so that's specific then!
> 
> There were 2 courses here, both were optional depending on how much 
> maths you had done at A level.  Most people sat the "fast" course just 
> as a refresher, just to relearn the basics like how to solve 
> differential equations, how matrices work, stuff like that.

Wait - there's a way to *solve* differential equations?? o_O

I thought you just guess formulas at random until you happen upon one 
that has the desired properties - or more likely, use numerical 
simulation instead.

>>> Computing
>> Interesting?
> 
> Not really, software life cycle, structured programming, numerical 
> precision errors, algorithm complexity, search&sort algorithms, very 
> vague and general, clearly aimed at writing some small code block to 
> solve an Engineering problem rather than any huge software project.

Floating-point arithmetic is a non-associative algebra. Isn't that sad? :'(

>>> Structural Design Project (ie building a bridge!)
>> LOL!
> 
> They applied prices to each bit of metal you could use, then you had a 
> budget to build a bridge to span a certain gap (about 1 metre) and 
> support a certain weight (about 150kg).  Of course the cheapest one that 
> could withstand 150kg won.  Mine buckled and collapsed spectacularly at 
> about 70kg due to me not actually putting it together very squarely.  I 
> still have this twisted lump of rusting metal in the attic at home!

Niiiice...

I wonder - can I find it on YouTube? Hold on a sec...

...yep, I found it:

http://uk.youtube.com/watch?v=-fE5ZE4Pj5w

PROPPER JOB!!

OMG, the first time I watched this on TV, I killed myself laughing. All 
those hours to build, and it ****ed itself to pieces in seconds! :-D

>> The... uh... no, I can't remember the name of it. But there *is* a 
>> programming contest that's a bit like the IRTC. They set a challenge, 
>> and you have so many days to write a program that solves it. One of 
>> them was where your program accepts a track description as input, and 
>> produces a series of driving commands as output. The car that gets 
>> round the track fastest wins. (But the car simulation part is an 
>> external program, with limits on acceleration, cornering, etc.)
> 
> Oh that sounds cool, one of our practicals was a bit like that, we had 
> to write a program to control some factory that was producing several 
> different parts according to demand.  It got quite complex and remember 
> writing a 6 or 8 dimensional optimisation algorithm to see when was best 
> to switch production lines from one product to another!

...I DID THE WRONG DEGREE! >_<

AND I'M IN THE WRONG JOB NOW... :'{

By the way... how much of the stuff you learnt do you actually *use* now 
anyway? ;-)

Post a reply to this message

Invisible wrote:

> When the lecturer wrote the formula on the whiteboard, everybody freaks 
> out and starts going "what the hell does 'log' mean?" And the lecturer 
> is all "oh, I'm sorry, I just *assumed* that 3rd year degree students 
> would know what a logarithm is". It turns out that actually, only two 
> people in the room knew about logarithms.

log is kind of a neat function.

One cool trick is ln(x)/ln(n) will compute the base n log of x. Then you 
can use it to solve x in 2^x = 128 ;)

Its sort of the inverse of exponentiation.


Anyway .... you have all this CS background and are not a programmer... 
get out there and get a programming job already! :)

My last job had me using a ton of trig, vector and matrix arithmetic. 
This one, not so much, I'm basically basically n-tier hell. But, it pays 
the bills.

-- 
~Mike

Post a reply to this message

Mike Raiford wrote:

> log is kind of a neat function.

It's certainly a very useful thing.

Logarithmic decay, the complex-valued log and antilog functions (Euler's 
relation and all that), the discrete logarithm problem...

> Its sort of the inverse of exponentiation.

Indeed - although I think "antilogarithm" sounds so much cooler than 
"exponent". ;-)

> Anyway .... you have all this CS background and are not a programmer... 
> get out there and get a programming job already! :)

Apparently there's a global economic crisis of some kind happening... I 
don't really pay much attention... But apparently this is a bad time to 
get hired.

FWIW, I applied to about 7 jobs on Saturday. (Before I got dragged to 
Watford and made to dance in public.) The soul-destroying thing is, you 
apply to all these jobs AND NEVER GET A REPLY. x_x

> My last job had me using a ton of trig, vector and matrix arithmetic. 
> This one, not so much, I'm basically basically n-tier hell. But, it pays 
> the bills.

Basically basically?

So that's, what, tier-2?

Post a reply to this message

Invisible wrote:

> 
> Basically basically?
> 
> So that's, what, tier-2?

Whoops, missed that must have duped the word when editing my post :/


-- 
~Mike

Post a reply to this message

Mike Raiford wrote:

> Whoops, missed that must have duped the word when editing my post :/

I know how it happens: You start writing. You briefly do something else. 
You come back to finish writing, and don't realise how much you've written.

Annoying, isn't it? :-P

Post a reply to this message

Invisible wrote:
> As you probably all know by now, I hold an honours degree in Computer 
> Science. (Upper-second class, no less.)
> 
> As far as I can tell, whoever created this cause was of the opinion that 
> "software" is a construct for storing, processing and retreiving 
> business data. In other words, you have a UI at the front (possibly 
> web-based), a large database at the back, and some complex business 
> logic in the middle.
> 
> The idea that there might exist "software" which doesn't fit this model 
> appears to have not occurred to anybody here. For example:
> 
> - Embedded software.
> - Device drivers.
> - Computer games.
> - Mathematical moddeling.
> - Signal processing.
> - Artificial intelligence.
> 
> None of these really fit the world-view described above. Most of them 
> don't usually involve any kind of database. Device drivers usually don't 
> have a *user* interface of any kind. Computer games might be 3-tier, but 
> it's a hell of a lot different to a stock control system! And DSP and AI 
> are 90% mathematics.
> 
> Given the world-view above, it should come as no surprise that we 
> learned about things like project management, object-oriented analysis 
> and design, UML, CASE tools, relational databases, SQL, HTML, CSS, Java, 
> JavaScript, XSLT, TCP/IP, double-entry book keeping (I'm not making this 
> up), a little bit of management theory (Taylor, Maslow, etc.), and 
> systems testing.
> 

IMHO, for computer science that sounds right.  You learn about 
programming at a higher level.  You are taught the tools to write 
programs typically for the end user.  Business is a very large area that 
uses this type of talent - and programming in that environment typically 
involves data storage.


You are right, the areas that you list also use software, and you have 
been taught a lot of the logic and thinking to be able to program in 
those areas.  But a lot of those areas also require specialized 
instruction - hence degrees in electrical engineering, computer 
engineering, math.

The areas you listed do require programming, but usually from other 
areas of expertise - computer engineering, electrical engineering, math, 
etc...




> There were also two modules taught by Mr Apathy. Mr Apathy was tasked 
> with teaching us about computer hardware, and later about operating 
> systems. In Mr Apathy's opinion, knowing about binary is "pointless" 
> because "the computer will do it all for you anyway". He believed that 
> "20 years ago it might have been necessary to know this stuff, but in 
> the modern world you're really never going to need this information. But 
> it *is* in the exam, so I have to teach it to you." I cannot tell you 
> what an inspirational motivation for learning this was.
> 

To a point he is right - programming in upper level languages does not 
require a knowledge of the very low level happenings.  That's part of 
why they are there - you can program faster without having to worry 
about as much as it is taken care of for you (e.g. garbage collection)

In a sense it would be like teaching you about electron flow in a diode 
and FET so that you can type the word 'print' better.

At level do you stop digressing?

He decided that binary is not really necessary.
He could have presented his case better so that it wasn't so discouraging.

> 
> Actually, I say only one formula... some of the final year optional 
> modules I did also had a little more math in them than that.
> 
> 
> This module did involve some non-trivial math. It was so badly-explained 
> that I couldn't possibly tell you how advanced it was. Much of the 
> module revolved around feed-forward ANNs trained by back-propogation, 
> which is a kind of "grædiɛnt æsɛnt miθæd". For back-propogation to work, 
> the transfer function needs to be non-linear. And there was something 
> about a "næbl" operator.
> 
> IIRC, the part about generic algorithms lasted about an hour.
> 
> It's a pitty really, because it seems like a really interesting subject...
> 
> 

Computer Science is not about math, it's about laying down code, user 
interface, and bringing it together.
The thought is that if you need math, someone will show what they need.




> 
> So anyway, that's what *I* did during my degree. Anybody out there do 
> anything more interesting?
> 

To heck with my course work.
Built and raced 2 solar powered racing cars.
Think 70mph and 'for highway use'.


> 
> 
> My mum keeps telling me I should do a mathematics course. Personally, 
> I'm not sure where the hell I'd get the time or the money from. (It's 
> not exactly cheap.) I guess it *is* kind of amazing that I know about 
> the Laplace transform, given that I have never at any point in my life 
> been "taught" anything beyond simple arithmetic.
> 
> Similarly, I know about how to wire logic gates together to make 
> interesting devices. And I know about Dijkstra's shunting algorithm. 
> (Unfortunately, I'm never sure exactly how to spell the name though!)

It sounds like you think very technically.  What is you interest level 
in electronics.  There's plenty of heavy lifting math there ;-)

Have you ever wanted to build your own 'light blinker' (a device that 
does something that you made it do it)?  This can be done without lots 
of heavy lifting math.



Later... Tom

Post a reply to this message

Invisible wrote:

> Annoying, isn't it? :-P

Yup :)

-- 
~Mike

Post a reply to this message

> So if you wanted to describe the motion of a complex arrangement of rigid 
> components (e.g., a car gearbox), you'd use kinematics?

Yes, for analysis of how fast each bit spins, but that part is actually very 
simple and well known about gearboxes.  Kinematics would be more useful to 
design the windscreen wiper mechanism for instance, where it is assumed that 
the motor can generate enough torque to maintain a constant speed.  What the 
designer must consider is how the constant angular velocity of the electric 
motor is converted to that movement you see the wiper blades making.

> So... the resonant modes of a effectively 1D system (a string, a 
> gas-filled pipe, etc.) would just be harmonics of the main resonant 
> frequency?

Haha I should have known this had something to do with organ pipes!  Yes 
pretty much.

> Heh. So you know how an ideal gas is different from a real gas then? ;-)

From what I recall, ideal gasses are ones that follow the PV=nRT equation 
and a host of other equations.  Which works pretty well for most "normal" 
gasses at "normal" temperature and pressure.  IIRC it doesn't work for steam 
though, which is why we needed hideous fold-out tables and charts.

> If I take a piece of paper and hold it horisontal, it flops under its own 
> weight. But if I fold it down the middle, now it *can* stand up under its 
> own weight. (But only if you hold it the right way.)

You can do that without folding it too, along the edge that you are holding 
it, just push down in the middle with your thumb above the paper with two 
fingers underneath either side.  By introducing that slight curvature in the 
paper you are making it very difficult to bend downwards without stretching 
or ripping the paper, so of course then the paper does not have enough 
weight to do that by itself.  I don't know what category this would come 
under, dynamics or thin bodies or something ;-)

> At the same time, a straight metal rod is very strong, but once bent it 
> becomes drastically weaker,

Actually it usually becomes stronger after the 1st bend because you have 
work hardened it at that point.

> and it seems that nothing will restore it to its original condition.

Because when you try to bend it back, it just wants to bend at a different 
point rather than where the original bend was, because that point is now 
stronger!  Eventually of course if you repeatedly bend it enough fatigue 
will set in and it will break.

> Wait - there's a way to *solve* differential equations?? o_O

Use Laplace transforms, makes things way easier for non-trivial differential 
equations.

> OMG, the first time I watched this on TV, I killed myself laughing. All 
> those hours to build, and it ****ed itself to pieces in seconds! :-D

Hehe yeh I love that program.  Our robot almost did the same, when I 
disconnected the control interface to the PC while the motor that lifted the 
arm was still running.  Of course it was in software that the motor is 
stopped when it hits the switch at the end of the arm's travel, so with no 
more control input the motor continued to wind up and start bending the 
metal arm before I could pull the power :-)  The mechanics guys weren't 
pleased that they had to rebuilt it.

> By the way... how much of the stuff you learnt do you actually *use* now 
> anyway? ;-)

Around 10% probably, but I would imagine every job would have a slightly 
different 10% so I certainly don't regret doing such a wide range of 
subjects within Engineering.

Post a reply to this message

Tom Austin wrote:

>> There were also two modules taught by Mr Apathy. Mr Apathy was tasked 
>> with teaching us about computer hardware, and later about operating 
>> systems. In Mr Apathy's opinion, knowing about binary is "pointless" 
>> because "the computer will do it all for you anyway". He believed that 
>> "20 years ago it might have been necessary to know this stuff, but in 
>> the modern world you're really never going to need this information. 
>> But it *is* in the exam, so I have to teach it to you." I cannot tell 
>> you what an inspirational motivation for learning this was.
> 
> To a point he is right - programming in upper level languages does not 
> require a knowledge of the very low level happenings.  That's part of 
> why they are there - you can program faster without having to worry 
> about as much as it is taken care of for you (e.g. garbage collection)
> 
> In a sense it would be like teaching you about electron flow in a diode 
> and FET so that you can type the word 'print' better.
> 
> At level do you stop digressing?

Well now, it all depends on what you're trying to do.

How many times have you seen a program that behaves strangely given a 
large enough number as input? Many people seem confused that large 
positive numbers come out negative. But this is a simple and obvious 
consequence of 2s complement arithmetic. I don't care what language 
you're programming in, you need to have a basic high-level understanding 
of this stuff.

(As to whether you need to know exactly how many bits are assigned to 
the mantissa of an IEEE double-precision float, or the exact bit 
patterns for demonals... er, no, most people will never actually need to 
know that.)

The stuff about how hardware interrupts work is fairly irrelevant to 
most programming exercises, but if you were doing something slightly 
more specialised it would become highly relevant.

In the end, what it boils down to is that low-level hardware details 
interest me, whereas Mr Apathy did has absolute level best to discourage 
anybody from even *attempting* to put any effort into learning this stuff.

(FWIW, this is the same guy who told us that the rebuilding of Colossus 
was "pointless" because "it will never be the same machine as the 
original".)

> Computer Science is not about math, it's about laying down code, user 
> interface, and bringing it together.
> The thought is that if you need math, someone will show what they need.

Actually, "Information Technology" is about applying computers to solve 
real-world problems. "Computer Science" is the abstract study of 
theoretical models of computation, which results are actually 
computable, computer algorithms, and so forth.

> It sounds like you think very technically.  What is you interest level 
> in electronics.  There's plenty of heavy lifting math there ;-)

My *interest level* is moderately high. My *knowledge level* is very low.

(As in, I know how it's *supposed* to work. It just doesn't work that 
way when *I* do it.)

Post a reply to this message

scott wrote:
>> So if you wanted to describe the motion of a complex arrangement of 
>> rigid components (e.g., a car gearbox), you'd use kinematics?
> 
> Yes, for analysis of how fast each bit spins, but that part is actually 
> very simple and well known about gearboxes.  Kinematics would be more 
> useful to design the windscreen wiper mechanism for instance, where it 
> is assumed that the motor can generate enough torque to maintain a 
> constant speed.  What the designer must consider is how the constant 
> angular velocity of the electric motor is converted to that movement you 
> see the wiper blades making.

So things like cams and eccentrics then?

>> So... the resonant modes of a effectively 1D system (a string, a 
>> gas-filled pipe, etc.) would just be harmonics of the main resonant 
>> frequency?
> 
> Haha I should have known this had something to do with organ pipes!  Yes 
> pretty much.

Well, it was a simple example of something I've already looked at a fair 
bit.

Where I actually heard it mentioned was in relation to "the resonant 
modes of [the air in] this room".

Presumably a 2D surface like a drum head would have quite a lot of 
possible resonant modes?

How is all this related to standing waves?

>> Heh. So you know how an ideal gas is different from a real gas then? ;-)
> 
>  From what I recall, ideal gasses are ones that follow the PV=nRT 
> equation and a host of other equations.  Which works pretty well for 
> most "normal" gasses at "normal" temperature and pressure.  IIRC it 
> doesn't work for steam though, which is why we needed hideous fold-out 
> tables and charts.

...because steam can condense? (Or at least is likely to under typical 
conditions, whereas air isn't.)

>> If I take a piece of paper and hold it horisontal, it flops under its 
>> own weight. But if I fold it down the middle, now it *can* stand up 
>> under its own weight. (But only if you hold it the right way.)
> 
> You can do that without folding it too, along the edge that you are 
> holding it, just push down in the middle with your thumb above the paper 
> with two fingers underneath either side.  By introducing that slight 
> curvature in the paper you are making it very difficult to bend 
> downwards without stretching or ripping the paper, so of course then the 
> paper does not have enough weight to do that by itself.  I don't know 
> what category this would come under, dynamics or thin bodies or 
> something ;-)

Ah yes - just curving the paper makes it behave quite differently. (See 
corrigated sheet metal.) But why, I wonder?

Similarly, a hollow tube responds differently to a solid rod. And again, 
a tear tends to propogate along a sheet, but if you put a hole in the 
sheet, it actually stops the tear. WTF?

>> At the same time, a straight metal rod is very strong, but once bent 
>> it becomes drastically weaker,
> 
> Actually it usually becomes stronger after the 1st bend because you have 
> work hardened it at that point.
> 
>> and it seems that nothing will restore it to its original condition.
> 
> Because when you try to bend it back, it just wants to bend at a 
> different point rather than where the original bend was, because that 
> point is now stronger!  Eventually of course if you repeatedly bend it 
> enough fatigue will set in and it will break.

Really? OK, well that's even weirder!

Presumably there's some molecular-level *reason* for all of this?

>> Wait - there's a way to *solve* differential equations?? o_O
> 
> Use Laplace transforms, makes things way easier for non-trivial 
> differential equations.

...because the Laplace transform turns differential equations into 
algebraic equations?

Presumably there are still equations which can't be "solved" in this way 
though? (It seems quite easy to come up with a set of equations which 
yield absurdly complicated behaviour...)

>> OMG, the first time I watched this on TV, I killed myself laughing. 
>> All those hours to build, and it ****ed itself to pieces in seconds! :-D
> 
> Hehe yeh I love that program.

Did you see Scrappy Races, where the same guy tried to "tune" a 6 L 
diesel engine, and the govener fell off? (I don't know what a govener 
is, but it sounds important...)

> Our robot almost did the same, when I 
> disconnected the control interface to the PC while the motor that lifted 
> the arm was still running.  Of course it was in software that the motor 
> is stopped when it hits the switch at the end of the arm's travel, so 
> with no more control input the motor continued to wind up and start 
> bending the metal arm before I could pull the power :-)  The mechanics 
> guys weren't pleased that they had to rebuilt it.

Niiiice! :-D

>> By the way... how much of the stuff you learnt do you actually *use* 
>> now anyway? ;-)
> 
> Around 10% probably, but I would imagine every job would have a slightly 
> different 10% so I certainly don't regret doing such a wide range of 
> subjects within Engineering.

Mmm, true...

Post a reply to this message

scott wrote:

> The best part was the robot design project.  We were put into teams of 6 
> and told to make a robot that drove around a track marked by white lines 
> on a black board and picked up containers.  The containers would either 
> be empty or full, and we had to move the containers to the appropriate 
> bin.  In most teams 2 people actually made the robot mechanics, 2 did 
> the electronics (motor drive control, interface to PC, etc) and 2 did 
> the software.  Was really good fun, especially as the quicker your robot 
> completed the task the more points you got.

We did a "software development project". This is where a team of (IIRC) 
6 of us got together to plan, design, build and test a "large" piece of 
software, and exhibit it at a show.

Of course, of the 6 people in the group, I was the only one who knew how 
to program. So this "project" consisted of the following:

- We all sat round a table, and we're like "OK, so what are we gonna make?"
- After a while, we decide what to build, and generate a few design 
ideas. "Do you think you can do that, Andrew?" "Yeah, probably." "OK 
mate, sounds like a plan."
- I sit in a corner by myself, building and testing the program. Every 
now and then another team member will casually ask me how it's going. I 
tell them it's going OK. They smile and nodd, and wander off.

Fortunately, for this particular module, most of the marks are for 
producing all the pretty GANT charts and all the project-management 
garbage, and not for actually producing a working product.

[The urge to insert something about software consultants here is 
overwhelming!]

Which is just as well - my "product" was a trivial job searching engine 
that would have taken about 3 seconds if I had used a real database 
engine rather than manually full-scanning flat files held entirely in 
RAM. >_<

Can you spell "not scalable", "lost update problem" and "security"?

Post a reply to this message

> So things like cams and eccentrics then?

Yep, or just plain linkages of rods and stuff, some of them can get quite 
complex.  On my old Peugeot 206 it had some pretty funky wiper blade 
mechanism to that it would cover much more of the window than a simple arc.

> How is all this related to standing waves?

A standing wave is just a wave that stays in position, ie it's frequency and 
spatial phase remain constant.  If you see a resonant mode by itself, it 
will look like a standing wave and you can easily identify the stationary 
points that remain at rest.

> Presumably a 2D surface like a drum head would have quite a lot of 
> possible resonant modes?

Yep, see these photos that show the stationary points, try to imagine how 
the non-stationary parts would bend up and down.

http://www.meta-synthesis.com/webbook/34_qn/2d_waves.jpg

> Ah yes - just curving the paper makes it behave quite differently. (See 
> corrigated sheet metal.) But why, I wonder?

To curve a flat sheet of paper all you need to do physically is to stretch 
the top half of the thickness by a tiny amount and compress the bottom half 
by an equally tiny amount.  Once you start curving it in other directions as 
well the amount of stretching and squashing you need to perform becomes 
orders of magnitudes higher.  You can see this just by looking at the 
geometry of a curved piece of paper and thinking about how it must deform in 
order to curve it in the other direction.

> Similarly, a hollow tube responds differently to a solid rod.

For a hollow tube and a rod of the same weight, the tube will always be 
stronger and stiffer because it will have a higher 2nd moment of area. 
Actually the I-beam is pretty much the best useful shape you can have, which 
is why they are so common (tubes are not so easy to join together and funny 
angles).

> And again, a tear tends to propogate along a sheet, but if you put a hole 
> in the sheet, it actually stops the tear. WTF?

It's to do with the radius at the tip of the tear (very small) compared to 
the radius of the hole (much bigger).  It's why the windows in aeroplanes 
are round and not square (they had some square ones to start with but they 
got cracks at the corners once the pressure difference went up).

> Presumably there's some molecular-level *reason* for all of this?

Yeh, something to do with dislocations in the crystal lattice from what I 
remember.

> ...because the Laplace transform turns differential equations into 
> algebraic equations?

Yup.

> Did you see Scrappy Races, where the same guy tried to "tune" a 6 L diesel 
> engine, and the govener fell off? (I don't know what a govener is, but it 
> sounds important...)

No I didn't see that one, the governer stops the engine going too fast if 
there is no load.  Diesel engines are quite capable of self-destruction if 
you try to run them flat out with no load.

Post a reply to this message

scott wrote:
>> How is all this related to standing waves?
> 
> A standing wave is just a wave that stays in position, ie it's frequency 
> and spatial phase remain constant.  If you see a resonant mode by 
> itself, it will look like a standing wave and you can easily identify 
> the stationary points that remain at rest.

I see... So the resonant modes of something are all possible standing 
waves that can be created in that space?

>> Presumably a 2D surface like a drum head would have quite a lot of 
>> possible resonant modes?
> 
> Yep, see these photos that show the stationary points, try to imagine 
> how the non-stationary parts would bend up and down.
> 
> http://www.meta-synthesis.com/webbook/34_qn/2d_waves.jpg

Ooo... so there are both concentric and radial modes, and combinations 
thereof?

Presumably for a square surface it would be different though.

>> Ah yes - just curving the paper makes it behave quite differently. 
>> (See corrigated sheet metal.) But why, I wonder?
> 
> To curve a flat sheet of paper all you need to do physically is to 
> stretch the top half of the thickness by a tiny amount and compress the 
> bottom half by an equally tiny amount.  Once you start curving it in 
> other directions as well the amount of stretching and squashing you need 
> to perform becomes orders of magnitudes higher.  You can see this just 
> by looking at the geometry of a curved piece of paper and thinking about 
> how it must deform in order to curve it in the other direction.

So it happens due to the infintesimal but finite thickness of the sheet? 
Interesting....

>> Similarly, a hollow tube responds differently to a solid rod.
> 
> For a hollow tube and a rod of the same weight, the tube will always be 
> stronger and stiffer because it will have a higher 2nd moment of area. 
> Actually the I-beam is pretty much the best useful shape you can have, 
> which is why they are so common (tubes are not so easy to join together 
> and funny angles).

"2nd moment of area"? ._.

Well anyway, it strikes me that a hollow tube of the same weight would 
be very much larger, and hence obviously stronger.

The reason I mention this is that apparently trees that have rotted 
hollow tend to survive storms better. Thus, the fungi that rot trees 
actually *prolong* their life, not shorten it. (It's amazing what you 
can find out from wildlife books!)

>> And again, a tear tends to propogate along a sheet, but if you put a 
>> hole in the sheet, it actually stops the tear. WTF?
> 
> It's to do with the radius at the tip of the tear (very small) compared 
> to the radius of the hole (much bigger).  It's why the windows in 
> aeroplanes are round and not square (they had some square ones to start 
> with but they got cracks at the corners once the pressure difference 
> went up).

How interesting...

>> Presumably there's some molecular-level *reason* for all of this?
> 
> Yeh, something to do with dislocations in the crystal lattice from what 
> I remember.

Ouch. "Doctor, I've got a dislocated crystal in my lattice. It hurts 
when I bend over..."

>> ...because the Laplace transform turns differential equations into 
>> algebraic equations?
> 
> Yup.

I see...

>> Did you see Scrappy Races, where the same guy tried to "tune" a 6 L 
>> diesel engine, and the govener fell off? (I don't know what a govener 
>> is, but it sounds important...)
> 
> No I didn't see that one, the governer stops the engine going too fast 
> if there is no load.  Diesel engines are quite capable of 
> self-destruction if you try to run them flat out with no load.

Guy was tinkering with this fuel-injected diesel engine. (The engine is 
about the size of a small bath tub.) Obviously the camera crew weren't 
paying too much attention. (This was during build time.) Suddenly we got 
a shot of the machine in the distance with ****-off black Clouds Of Doom 
spewing out of the exhaust pipes, and the team of hill-billies running 
for their lives in every direction like startled rats.

Apparently the governer just fell off, and the engine is now running at 
full tilt in neutral with the fuel injection system at non-default settings.

A few moments later the team run back to the machine. One of them is 
trying to stuff his shirt into the air intake. Another is trying to 
physically rip the leads off the battery. (Uh, how does that help?) 
Another is trying to squeeze the fuel lines with his hands. I don't know 
quite what happened, but after a few moments the machine fell silent.

Cut to a scene 20 minutes later, and they've taken the head block off 
the engine, and the team captin is holding up bits of pistol rods, and 
other items which look like they really ought to be *attached* to 
something, but clearly aren't...

Post a reply to this message

> I see... So the resonant modes of something are all possible standing 
> waves that can be created in that space?

Yes I guess so.

> "2nd moment of area"? ._.

Determines the geometric stiffness of a cross-section.  Basically the more 
"material" further away from the axis of bending the stiffer it will be.  So 
if you have an area budget of 10cm^2, better to put it all as far as 
possible away from the centre (ie a circle), or if it only needs to bend in 
one direction, then two parallel plates (usually connected though, so that 
will be an I-beam then).

> Apparently the governer just fell off, and the engine is now running at 
> full tilt in neutral with the fuel injection system at non-default 
> settings.

I had a similar thing happen to my radio controlled car, the throttle fell 
off, literally the bit that regulates the air-flow into the engine fell out 
of the air intake.  Of course then the car is going full throttle in a 
street full of parked cars and all I can control is the steering!  Finally I 
think it got wedged underneath a real car and not too much damage.  I found 
the throttle too and put it back in, with some loctite this time!

> Cut to a scene 20 minutes later, and they've taken the head block off the 
> engine, and the team captin is holding up bits of pistol rods, and other 
> items which look like they really ought to be *attached* to something, but 
> clearly aren't...

Try running a lawn mower with no oil, part way through cutting the grass it 
stopped, not like the running out fuel stopped, but instant stop from 200rpm 
or whatever to silence.  Took the head off, a big bit of wood and a big 
hammer freed up the piston from the side of the cylinder, then a good dose 
of oil and it was working again!

Post a reply to this message

Invisible wrote:
> - I sit in a corner by myself, building and testing the program. Every 
> now and then another team member will casually ask me how it's going. I 
> tell them it's going OK. They smile and nodd, and wander off.

I had one of those. The funny part was when the partners came back three 
weeks later for the next project and said "You wanna work together 
again?"   Noooo...

-- 
Darren New / San Diego, CA, USA (PST)

Post a reply to this message

Mike Raiford wrote:
> This one, not so much, I'm basically basically n-tier hell. 

That can be fun on a sufficiently large project.  You know, like the 
stuff google does. :-)

-- 
Darren New / San Diego, CA, USA (PST)

Post a reply to this message

Invisible wrote:
>> It sounds like you think very technically.  What is you interest level 
>> in electronics.  There's plenty of heavy lifting math there ;-)
> 
> My *interest level* is moderately high. My *knowledge level* is very low.
> 
> (As in, I know how it's *supposed* to work. It just doesn't work that 
> way when *I* do it.)

I bet that if you dedicate yourself to learning electronics the same way 
that you dedicated yourself to playing the church organ and uploading 
the file to youtube you could likely have something working.

Parts of digital electronics can be very simple - join wire a to wire b.
Some of it can get tricky, but most of the work has been done for you 
and is packaged into nice chips.

Analog can get a bit more tricky.  You have to calculate resistor values 
and capacitor values to make things work.  Then the parts you can 
actually use have a tolerance of +-10% - but i calculated I needed a 
2045 ohm resistor.....


Take a look at
http://www.amazon.com/Cmos-Cookbook-Donald-E-Lancaster/dp/0750699434

It's a pretty good book that gives some basics and provides enough 
information to get started hooking thing up.  I own it myself.

If you want to *program* something, then you need a microcontroller or 
the like.  BasicStamp is a good place to start that does not cost too 
much to get started.  You could look at their SX lineup that involves 
raw assembly programming.

You can hook all of these up on a breadboard pretty easily - no 
soldering needed.  Start small - don't try to build a antonymous robot 
the first time you light up a circuit.

There are a bunch of guys in here in Pr.O.T that know how this stuff 
works - you can always ask questions.


Tom

Post a reply to this message

Darren New wrote:
> Invisible wrote:
>> - I sit in a corner by myself, building and testing the program. Every 
>> now and then another team member will casually ask me how it's going. 
>> I tell them it's going OK. They smile and nodd, and wander off.
> 
> I had one of those. The funny part was when the partners came back three 
> weeks later for the next project and said "You wanna work together 
> again?"   Noooo...

Well, I mean, let's be honest about this. Only I have the skill required 
to write programs beyond Hello World that actually compile, much less 
execute in a way resembling the designer's intensions. So I did all the 
coding. The guys were perfectly nice about it; they just lacked the 
skills required to help me in any meaningful way.

What they *did* do is write all the GANT charts and other baloney that 
we actually got marked on. So, in a way, it's actually *me* that got the 
good deal! ;-)

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.

(Although saying that... I *did* give some guy on my college course the 
code to my Mandelbrot generator. Actually I didn't *give* him the code, 
I just sat next to him and told him what to write. He seemed to be a 
half-competent programmer. That is, I didn't have to tell him character 
by character what to type, and he made lots of alterations after I went 
away which didn't break the code...)

-- 
http://blog.orphi.me.uk/
http://www.zazzle.com/MathematicalOrchid*

Post a reply to this message

Tom Austin wrote:
> Invisible wrote:
>>> It sounds like you think very technically.  What is you interest 
>>> level in electronics.  There's plenty of heavy lifting math there ;-)
>>
>> My *interest level* is moderately high. My *knowledge level* is very low.
>>
>> (As in, I know how it's *supposed* to work. It just doesn't work that 
>> way when *I* do it.)
> 
> I bet that if you dedicate yourself to learning electronics the same way 
> that you dedicated yourself to playing the church organ and uploading 
> the file to youtube you could likely have something working.
> 
> Parts of digital electronics can be very simple - join wire a to wire b.
> Some of it can get tricky, but most of the work has been done for you 
> and is packaged into nice chips.
> 
> Analog can get a bit more tricky.  You have to calculate resistor values 
> and capacitor values to make things work.  Then the parts you can 
> actually use have a tolerance of +-10% - but i calculated I needed a 
> 2045 ohm resistor.....

I actually have some breadboard and a stack of 7400s *somewhere*. (I 
seem to have misplaced them currently.) I was going to try to build a 
CPU... but I never actually got round to it.

(Actually, I got as far as not being able to get the chips to give me 
the truth table I was expecting...)

-- 
http://blog.orphi.me.uk/
http://www.zazzle.com/MathematicalOrchid*

Post a reply to this message

Invisible escreveu:
> nemesis wrote:

> Hmm. Between the global telecommunications network (with its custom 
> hardware and the recent craze for mobile phones), the 
> multi-billion-dollar games industry, the presumably large industry 
> making computer components (most of which require drives of some kind), 
> the ever-increasing sea of consumer goods that need firmware to 
> function, the financial institutions that build and run huge complex 
> financial simulations, and the endless array of applications of DSP... 
> those look like some pretty ****ing big niches to me! ;-)

Videogames sell a lot, but don't employ nearly as much as such huge an 
industry should.  Beat a game and read the credits listing:  one or two 
lead programmers, some main game and level designers, many beta testers 
and one musician or band and many artists specialiazed in textures, 
modelling and such.

Telecoms are mostly about networks and hardware, but, yes, hardware is 
becoming more and more general purpose mobile computers and so, 
programming should increase as well.  But firmware writing is still a 
niche for very few people.

I don't know, I have a feeling such huge niches do not employ people by 
advertising jobs through conventional channels.  I mostly never hear of 
them.  Either that or some fake "Senior Manager needed" ad will actually 
get you as lead programmer of a firmware division... :P

>> It only exists within firms providing the infrastructure and research 
>> everybody else employs to do their things.  I'm talking about 
>> Microsoft, Adobe, Sun, Autodesk, open source projects etc...
> 
> Yeah - maybe I should get said to write open source software?
> 
> Oh, wait...

You could try submitting your resumé to Novell, RedHat and the likes. ;)

Post a reply to this message

>> those look like some pretty ****ing big niches to me! ;-)
> 
> Videogames sell a lot, but don't employ nearly as much as such huge an 
> industry should.

Well, yeah, I guess that's true.

Games are a fairly high-risk industry; gotta plough in a crapload of 
money, and at the end of it you might not even sell many units if the 
game isn't that great.

More to the point, once the game exists, you can just keep selling and 
selling it for basically no cost. (Think I'm joking? Valve are yelling 
that I can buy Quake 2 for $10 or something now. How many years ago was 
Quake 2??) Those programmers were only hired once, but a huge industry 
is powered by the profits.

> I don't know, I have a feeling such huge niches do not employ people by 
> advertising jobs through conventional channels.

Now *that* I won't disagree with at all.

I have no idea where these jobs are, but *I* can't find them...

>> Yeah - maybe I should get said to write open source software?
>>
>> Oh, wait...
> 
> You could try submitting your resumé to Novell, RedHat and the likes. ;)

...are either of those companies still going? I thought Novell went 
under years ago, and RedHat vanished off the face of the earth once they 
realised that trying to sell Linux services isn't profitable.

I did look into a few companies such as IBM, HP, Nokia, etc. But they're 
all based either in London or in other remote areas of the country.

-- 
http://blog.orphi.me.uk/
http://www.zazzle.com/MathematicalOrchid*

Post a reply to this message

nemesis wrote:
> Videogames sell a lot, but don't employ nearly as much as such huge an 
> industry should. 

It's really not that huge an industry. Even software in general is 
"niche" compared to, for example, construction or banking.

> I don't know, I have a feeling such huge niches do not employ people by 
> advertising jobs through conventional channels. 

Most jobs requiring competence don't advertise. It's mostly 
word-of-mouth. And since it's not technically a profession (unlike, for 
example, medicine or law), there's no minimum requirements where you can 
hire anyone with the right certification and assume you're getting 
someone at least minimally competent to do the job.

Plus, it seems most software places are utterly uninterested in someone 
who could learn to do the job quickly but who don't already know all the 
skills required. I haven't quite figured that out.  "We need someone who 
knows Java 1.5.7.  You only list Java 1.5.4 on your resume."

-- 
Darren New / San Diego, CA, USA (PST)

Post a reply to this message

Orchid XP v8 wrote:
> 
> I actually have some breadboard and a stack of 7400s *somewhere*. (I 
> seem to have misplaced them currently.) I was going to try to build a 
> CPU... but I never actually got round to it.
> 
> (Actually, I got as far as not being able to get the chips to give me 
> the truth table I was expecting...)
> 

When beginning, don't think that big - making your own CPU is cool, but 
is very involved.

Think - "I want to make a counter" and wire up the chips to count.


A device like this can be very practicable - I use a BCD counter to 
count windings on electromagnets that I make.  3 chips and a bunch of 
breadboard wire.  No computer or programmer required.  Tho with a basic 
stamp you could hook up something similar and do the counting in program 
code.


Tom

Post a reply to this message

Tom Austin wrote:
> Orchid XP v8 wrote:
>>
>> I actually have some breadboard and a stack of 7400s *somewhere*. (I 
>> seem to have misplaced them currently.) I was going to try to build a 
>> CPU... but I never actually got round to it.
>>
>> (Actually, I got as far as not being able to get the chips to give me 
>> the truth table I was expecting...)
>>
> 
> When beginning, don't think that big - making your own CPU is cool, but 
> is very involved.
> 
> Think - "I want to make a counter" and wire up the chips to count.

Well, as I say, I started by wiring up one NAND gate, a pair of switches 
and an LED. What *should* have happened is that the LED lights up unless 
you simultaneously press both switches. What *actually* happened was 
completely different. :-/

-- 
http://blog.orphi.me.uk/
http://www.zazzle.com/MathematicalOrchid*

Post a reply to this message

Orchid XP v8 wrote:
> What *actually* happened was completely different. :-/

Hey, I followed instructions to make a Xenon flash strobe light back in 
high school.  I was picking glass out of the carpet for weeks.

-- 
Darren New / San Diego, CA, USA (PST)

Post a reply to this message

Orchid XP v8 wrote:
> ...are either of those companies still going? I thought Novell went
> under years ago, and RedHat vanished off the face of the earth once they
> realised that trying to sell Linux services isn't profitable.

...

I don't even know how to reply to that.

Post a reply to this message

On Tue, 11 Nov 2008 11:37:03 +0000, Invisible wrote:

>> It only exists within firms providing the infrastructure and research
>> everybody else employs to do their things.  I'm talking about
>> Microsoft, Adobe, Sun, Autodesk, open source projects etc...
> 
> Yeah - maybe I should get said to write open source software?
> 
> Oh, wait...

http://www.novell.com/careers

Getting paid for developing open source does happen.  Novell, RedHat, 
Canonical - even Microsoft - all pay pretty well for open source 
development.

Jim

Post a reply to this message

On Tue, 11 Nov 2008 20:39:06 +0000, Orchid XP v8 wrote:

>> You could try submitting your resumé to Novell, RedHat and the likes.
> 
> ...are either of those companies still going? I thought Novell went
> under years ago, and RedHat vanished off the face of the earth once they
> realised that trying to sell Linux services isn't profitable.

Who do I work for again? ;-)

And RedHat is currently selling more Linux than Novell.  Turns out 
customers *want* service contracts for things their business depends on.

Jim

Post a reply to this message

> 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.

> (Although saying that... I *did* give some guy on my college course the 
> code to my Mandelbrot generator. Actually I didn't *give* him the code, I 
> just sat next to him and told him what to write. He seemed to be a 
> half-competent programmer. That is, I didn't have to tell him character by 
> character what to type, and he made lots of alterations after I went away 
> which didn't break the code...)

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.

Post a reply to this message

> Well, as I say, I started by wiring up one NAND gate, a pair of switches 
> and an LED. What *should* have happened is that the LED lights up unless 
> you simultaneously press both switches. What *actually* happened was 
> completely different. :-/

How did you wire up the switches to the inputs? You can't just use a 
connect/disconnect switch to the V+ line, because when it is disconnected 
the input will be "floating" and probably float high.  You need to either 
add a pull-down resistor or wire up a switch to connect between 0V and V+ 
alternately.

How did you wire up the LED? LEDs operate depending on current, not voltage, 
so you usually need a resistor in series to fix the current.  Did you also 
check that the IC could source/sink enough current to drive the LED?

Post a reply to this message

Jim Henderson wrote:
> On Tue, 11 Nov 2008 20:39:06 +0000, Orchid XP v8 wrote:
> 
>>> You could try submitting your resumé to Novell, RedHat and the likes.
>> ...are either of those companies still going? I thought Novell went
>> under years ago, and RedHat vanished off the face of the earth once they
>> realised that trying to sell Linux services isn't profitable.
> 
> Who do I work for again? ;-)

Uh... you tell me?

> And RedHat is currently selling more Linux than Novell.  Turns out 
> customers *want* service contracts for things their business depends on.

OK. So why have I not heard anything about RedHat for several years? 
Have they gone into some kind of specialised market or something? Once 
upon a time you used to hear of them quite a bit, and now they seem 
awful quiet...

Post a reply to this message

>> Yeah - maybe I should get said to write open source software?
>>
>> Oh, wait...
> 
> http://www.novell.com/careers
> 
> Getting paid for developing open source does happen.

Yeah, it does - just not particularly often. ;-)

Post a reply to this message

>> Videogames sell a lot, but don't employ nearly as much as such huge an 
>> industry should. 
> 
> It's really not that huge an industry. Even software in general is 
> "niche" compared to, for example, construction or banking.

My sister is an accountant. (Not even a fully-qualified accountant yet.)

One week, they tell her on Monday "oh, by the way, we don't need you any 
more. Goodbye."

That Friday, she's all moaning because she has FIVE FIRM JOB OFFERS and 
SHE CAN'T DECIDE which one to pick! o_O

As in, it took her less than 3 business days to find (presumably more 
than) 5 jobs, apply to them, go to (at least) 5 interviews, actually get 
accepted and get 5 firm job offers.

WTF? I've been trying to get a new job for, like, 2 years, and so far 
I've been to *one* job interview.

On the other hand... every company on Earth needs at least one 
accountant. (This is a legal requirement. IIRC, it's something like if 
you employ more than 6 people, one of them must be an accountant.) Big 
companies need them. Small companies need them. Companies in every 
sector of commerce need them. EVERYBODY needs accountants. If you're an 
accountant, you can work for anybody, in principle.

MOST companies need salesmen. Not all of them, but most of them.

Almost no companies need programmers. MOST companies need computers and 
need software, but MOST companies buy software rather than making it. If 
you're a programmer, you can ONLY work for companies that write 
software, or companies that are large enough to have an internal 
department that writes software.

That's a pretty small market. And obviously, I'm just some random 
computer nerd. There are people out there with actual *talent*. Why is 
some company gonna hire me when they could hire one of the talented guys?

Also, apparently there's some kind of global recession thing happening 
at the moment, so people are currently firing rather than hiring...

>> I don't know, I have a feeling such huge niches do not employ people 
>> by advertising jobs through conventional channels. 
> 
> Most jobs requiring competence don't advertise. It's mostly 
> word-of-mouth.

...and since I don't know anybody, it's not going to be me.

> Plus, it seems most software places are utterly uninterested in someone 
> who could learn to do the job quickly but who don't already know all the 
> skills required. I haven't quite figured that out.  "We need someone who 
> knows Java 1.5.7.  You only list Java 1.5.4 on your resume."

Depends.

SOME people want somebody who can definitely do the job RIGHT NOW. They 
are only interested in what technologies you know (or claim to know) 
right now, and won't look at anything beyond that.

SOME people want somebody who can learn stuff. Some of them are 
explicitly not interested in what you know now, they just want somebody 
who can learn. (E.g., I suspect if you applied to work for Google, what 
they'd be most interested in is that you can learn Crazy New Gizmo X 
really quickly next time they roll out something new.)

Unfortunately, at the moment I'm having trouble finding either kind of 
employer... :-(

Post a reply to this message

scott wrote:
>> Well, as I say, I started by wiring up one NAND gate, a pair of 
>> switches and an LED. What *should* have happened is that the LED 
>> lights up unless you simultaneously press both switches. What 
>> *actually* happened was completely different. :-/
> 
> How did you wire up the switches to the inputs? You can't just use a 
> connect/disconnect switch to the V+ line, because when it is 
> disconnected the input will be "floating" and probably float high.  You 
> need to either add a pull-down resistor or wire up a switch to connect 
> between 0V and V+ alternately.
> 
> How did you wire up the LED? LEDs operate depending on current, not 
> voltage, so you usually need a resistor in series to fix the current.  
> Did you also check that the IC could source/sink enough current to drive 
> the LED?

.......see, now, I went into digital electronics to precisely to *avoid* 
this kind of craziness! >_<

Take a look at a diagram such as this:

http://upload.wikimedia.org/wikipedia/commons/a/a9/Full-adder.svg

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

Post a reply to this message

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.

Post a reply to this message

> 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.

Post a reply to this message

> 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 :-)

Post a reply to this message

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...)

Post a reply to this message

> 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.

Post a reply to this message

> 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.

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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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