>> MOST companies need salesmen. Not all of them, but most of them.
> 
> Every company needs at least one salesman. Sometimes that person is also 
> (say) the inventor, president, and CEO, tho. :-)

OK, I rephrase: Some companies need far fewer salesmen that others. It 
depends what they do.

>>> 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.
> 
> That is definitely a stumbling block.  Another kind of thing you learn 
> at school...

The only thing *I* learned at _school_ is that people are terrifying 
things to be avoided at any cost.

Fortunately I have now unlearned that one. Unfortunately, I now have no 
starting point.

>> SOME people want somebody who can definitely do the job RIGHT NOW. 
> 
> Yes. And not infrequently, those are exactly the companies you don't 
> want to work for.

Yeah, I gathered. ;-)

>> (E.g., I suspect if you applied to work for Google,
> 
> Not if their interview process is anything to go on.

O RLY?

You know something about this then?

(All I know is that all the "interesting" companies like Google, NI, 
etc. seem to be in other countries. Not this one.)

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>> Yeah, it does - just not particularly often. ;-)
> 
> Tell that to all of those employees here or at RedHat who get paid.
> 
> But there is an added advantage to working on OSS projects - helps build 
> a resume and people can see your work.

I'm not disputing that getting paid for OSS is a good idea - I'm just 
saying it's highly nontrivial to achieve this.

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Nicolas Alvarez wrote:
> scott wrote:
>>> Well, I had a diagram for a circuit where you connect a lamp to the
>>> battery through a linear potentiometer. The brightness of the lamp
>>> varies roughly linearly. But the brightness of an LED... does not.
>> LED brightness is proportional to current not voltage!
> 
> Also, are *human eyes* linear? Would you notice when brightness is changing
> perfectly linearly? :)

Probably not. But when the light stays off, and then suddenly turns full 
on, with nothing in between, I'm fairly sure that's non-linear. ;-)

Post a reply to this message

"Invisible" <voi### [at] devnull> wrote in message 
news:491bf342$1@news.povray.org...
>>
>> Not if their interview process is anything to go on.
>
> O RLY?
>
> You know something about this then?

Google for google interviews. Quite a bit has been written about their 
interview process.

> (All I know is that all the "interesting" companies like Google, NI, etc. 
> seem to be in other countries. Not this one.)

Google's EU headquarters are in Ireland (though that is another country)

http://www.google.co.uk/intl/en/jobs/index.html
They seem to have a lot of openings. Won't suit you though, they're in that 
horrible, terrible place that no one want to go (London)

Post a reply to this message

Gail wrote:

> Google for google interviews. Quite a bit has been written about their 
> interview process.

...the irony...

> Google's EU headquarters are in Ireland (though that is another country)
> 
> http://www.google.co.uk/intl/en/jobs/index.html
> They seem to have a lot of openings. Won't suit you though, they're in 
> that horrible, terrible place that no one want to go (London)

Sadly it seems that 80% of all UK jobs are in London. Regardless of 
which industry.

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"Invisible" <voi### [at] devnull> wrote in message 
news:491bf7ae@news.povray.org...
> Gail wrote:
>>
>> http://www.google.co.uk/intl/en/jobs/index.html
>> They seem to have a lot of openings. Won't suit you though, they're in 
>> that horrible, terrible place that no one want to go (London)
>
> Sadly it seems that 80% of all UK jobs are in London. Regardless of which 
> industry.

Well, yes. It's the capital city and (iirc) the largest city in the UK. 
Hence most things will be there

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>> Sadly it seems that 80% of all UK jobs are in London. Regardless of 
>> which industry.
> 
> Well, yes. It's the capital city and (iirc) the largest city in the UK. 
> Hence most things will be there

This is not surprising.

What *is* surprising (to me at least) is that lots of things happen in 
cities near to MK, but very little happens in MK itself. I'm not sure 
why that would be...

(I'm thinking more of social events - I'm not really sure what the jobs 
markets are like.)

Also... the UK has plenty of other large cities besides London. Yet not 
many of these seem to have huge quantities of work available. I'm not 
really sure why.

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Invisible wrote:
>> "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.
> 


Sorry I've been away and missed the fun.


I hook up a LED this way:

A LED will always drop or *consume* a fixed voltage - again, that's 
voltage not current.
A LED is NOT a resistor - in the most basic sense it generally will not 
prevent current from flowing through it once it starts flowing - it 
starts flowing at it's rated voltage drop.

The typical voltage drop for a basic red LED is 1.7 volts.
For most LEDs you can use this number for calculations.
Be aware, that different colors may have a higher voltage drop.
A LED will generally not light up unless your voltage across its leads 
goes above it's drop.

A LED likes to have between 10mA and 20mA - to be safe you can use 10mA 
in calculations.  The current will affect brightness, but too much 
current will cause it to burn out.  You are better off to select a 
*bright* LED with a high light output rating than try to get more light 
by putting more current through it.


So some easy calculations:

lets say 5v power source
1.7v LED
10mA current

the LED drops 1.7v so the rest of the circuit will drop 3.3v
(5v)-(1.7v)=(3.3v)

If don't put a resistor in then the current through the circuit will be:
I=V/R   from V=IR

I=(5v)/(0 ohm)
not good  too much current - things get hot
	(note:  LEDs should not get hot)

we want the current (I) to be about 10mA
so R=V/I   again from V=IR

R=(3.3v)/(10mA)
R=330 ohm


330 ohm happens to be a common resistor value
so put one in

if your source is 12v then you need a 1,030 ohm resistor - not a common 
value.  But 1,000 ohm is - so use it instead.

Typical resistor values are only +-10% anyway - so a 330 ohm resistor 
could be as low as 300 or as high as 360 and you don't know it.

So picking something slightly off from the *calculated* value is OK.
After all, you are just trying to make a LED light up - not try to 
maximize it's brightness.



Tom




















Different LEDs drop different voltages, but you can usually safely bet 
on 1.5V and still be safe.

Then there is the current rating of the LED - usually 10mA to 20mA - you 
can pick 15mA and be pretty safe.

Post a reply to this message

Orchid XP v8 wrote:
> Darren New wrote:
>> Invisible wrote:
>>> How many resistors can you see? Because I count NONE!
>>
>> I look at an Intel chip stuck to my motherboard, and I don't see any 
>> transitors, either.  The gate-level logic is working with bits, not 
>> voltages. You're not going to see the analog stuff that makes the bits 
>> work there.
> 
> ....which is why I'd rather work at the gate-level. ;-)
> 

The problem is that digital electronics are based on analog circuits.  A 
lot of digital circuits can be wired up with out knowing anything about 
analog, but when something doesn't work as you expect, you might quickly 
get lost.


And as you have found out with LEDs, even when you think you are only 
dealing with digital, you are dealing with analog as well.

You don't have to understand breakdown voltages and the like to 
successfully work with LEDs, you just have to understand some of their 
base characteristics.

Even something as simple as a button or switch can cause problems.
When you close the contact there are literally thousands of connections 
made and broken in the very short time before the contact is completely 
closed.  If you have a counter, it might count 4 or 5 on each button 
press, not just one.  That's what debounce circuits are for, but they 
can be analog - go figure.



Electronics can be deceptively simple, but insanely complex.


I think you have the capacity to really work well in electronics - but 
you just don't have the background in how it all comes together.  That 
comes mostly with experience.

Books will tell you how to calculate you need a 524 ohm resistor - 
that's insane.
Experience will tell you that 470 ohm (a typical value) is OK.

Don't get discouraged when things don't work as you think they should.
Pretend that you don't know anything about what is not working and go 
research it.  You will learn loads and loads.
If a LED doesn't light, go learn how it works.
The same goes for most anything else.

Don't try to build a rocket ship - build something simple.
Get a book that doesn't just say hook this wire here and there, but that 
actually goes through how it all works.
The CMOS Cookbook I pointed out earlier is a good book in that reguard.




Tom

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>> ....which is why I'd rather work at the gate-level. ;-)
>>
> 
> The problem is that digital electronics are based on analog circuits.  A 
> lot of digital circuits can be wired up with out knowing anything about 
> analog, but when something doesn't work as you expect, you might quickly 
> get lost.

Yeah, this is the thing. I had assumed that the digital devices you buy 
in the shop are carefully designed to behave in a simple, predictable 
mannar, even though their internal construction is a tangle on analogue 
devices. I thought you could just treat a 7400 as a black box. 
Apparently not...

> And as you have found out with LEDs, even when you think you are only 
> dealing with digital, you are dealing with analog as well.

The LEDs actually worked just fine. It's the gate driving them that 
didn't do what it was ment to.

> Even something as simple as a button or switch can cause problems.
> When you close the contact there are literally thousands of connections 
> made and broken in the very short time before the contact is completely 
> closed.  If you have a counter, it might count 4 or 5 on each button 
> press, not just one.

I wouldn't find this surprising. Rather, to be expected.

> That's what debounce circuits are for, but they 
> can be analog - go figure.

Presumably a debounce circuit is merely a low-pass filter?

> Don't try to build a rocket ship - build something simple.

Heh. I got stuck just trying to get a truth table out of a logic gate. :-S

> Get a book that doesn't just say hook this wire here and there, but that 
> actually goes through how it all works.
> The CMOS Cookbook I pointed out earlier is a good book in that reguard.

...does it matter that I'm using TTL?

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