why do we use these

How long is a piece of string ?

Perhaps you'd like to put these in some context ?

Graham

--
Examples of devices called out in homework questions?

I believe that is the correct answer, since I was thinking of posting an almost identical reply.

Michael

1. Composite signal generators are used in those applications where all-metal ones would be too heavy.
2. Zero crossing detectors are used when it is important to recognize and/or count the number of zeroes which cross one's path. In many cultures, having your path crossed by a zero is analogous to our beliefs regarding a black cat crossing your path.
3. "Comparator" is a term which derives from the same Latin root as the word "compose," i.e., it is a device which puts stuff together, as opposed to a "separator," which of course takes stuff apart.

Best of luck on the homework!

Bob M.

This is important in some areas because zeroes are slippery and can wiggle through where a one can not. The ones may get stuck in the bit grate, whereas the zeros can slither through. Counting these is important in defining the efficacy of a bit grate (measured, of course, in it's duty cycle).

Cheers

PeteS

. PeteS wrote:

You guys slay me. 8-) These rate with some of my favorite respones to homework trolls:

*-Fields+textbook+*-megohms *-*-*-unwilling-to-do-*-homework-*-*+remember-*+try-posting-to-*-*-*+zz-zz+your-teacher-*-*-*+qq-qq+*-*-exist *.*.*.*.*.*+some.managers+Hire-engineers-that-did-their-own-homework-in-college

A previous one from Pete:

*-job-function-*-*-*-*+*-*-english-*-*+*-platitudes-*+*-*-*-dangerous+*-*-what-you-really-mean+insert-task-here+*-having-to-think . .

Now that the accounting industry has oversight,

it appears the lazy, corner-cutters are trying to find other fields.

*-*-*-to-get-answers-to-homework-questions+*-*-*-*-*-*-explanation-of-why-most-people-won't-*-*-*+*-*-*-*-meant-to-reinforce-*-*-*-*-class+*-no-real-education-*-*-*+not.the.place+textbooks+context+reading

*-Fields+textbook+*-megohms

*-*-*-unwilling-to-do-*-homework-*-*+remember-*+try-posting-to-*-*-*+zz-zz+your-teacher-*-*-*+qq-qq+*-*-exist

*.*.*.*.*.*+some.managers+Hire-engineers-that-did-their-own-homework-in-college

*-job-function-*-*-*-*+*-*-english-*-*+*-platitudes-*+*-*-*-dangerous+*-*-what-you-really-mean+insert-task-here+*-having-to-think

I had been considering writing an authoritive guide on 'How to post your homework questions to s.e.b and s.e.d', but I never got past the first paragraph as I kept snorting my wine on the keyboard.

Now there is the possibility I could write such a thing while not drinking wine, but that would remove any real point ;)

Cheers

PeteS

*-Fields+textbook+*-megohms

*-*-*-unwilling-to-do-*-homework-*-*+remember-*+try-posting-to-*-*-*+zz-zz+your-teacher-*-*-*+qq-qq+*-*-exist

*.*.*.*.*.*+some.managers+Hire-engineers-that-did-their-own-homework-in-college

*-job-function-*-*-*-*+*-*-english-*-*+*-platitudes-*+*-*-*-dangerous+*-*-what-you-really-mean+insert-task-here+*-having-to-think

We need a real, nice "Homework helper FAQ" for the sci.electronics.* newsgroups. Maybe we could all use up lots of puns before they go stale? ;-)

--
Service to my country? Been there, Done that, and I\'ve got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

a zero crossing detect circuit is used to indicat when and AC voltage is crossing the 0V line or within a window of a few volts either way. You know that AC voltages swing to a positive voltage and then a negative and this repeats continuously right?

If you are switch something on, at the point the current starts flowing, it can make "noise" both electrically and within the radio spectrum (you may have seen this as lines of interference on your TV when someone has gone past on a motorbike or similar - the Radio interference from the ignition circuit is temporarily swamping the TV signal and being displayed as rubbish on the screen). So, if you turn on an AC device, you generally don't have any idea where in the swing cycle the voltage is and if it is significantly in, current will "rush" in to the device - with the same effect as the motorbike. Dimmer switches on lighting that don't use resistors use a triac to switch to the voltage on and off rapidly - because the bulb take a while to reach full brightness, if you switch off the power before it gets there it will appear to be dim constantly, but if you do this without a zero crossing trigger of some sorts it will play merry hell with your electrics and TV. A zero crossing detect will tell when it's safe to switch the power on... because you are at zero voltage, there is no current flowing (actually there will be a bit because 0v lasts for a fraction of a second) so you allow the curretn to build up nicely with the voltage. You can turn the power off anywhere in the cycle with minimum interference.

So to recap, ZCD lets you know (in this application) when to switch the power on to eliminate electrical and RF noise (also stops overheating)

--

A comparator lets you compare two voltages. One is usually a reference
and the output of the comparator will be at 0v so long as the input
voltage remains less than the reference. as soon as it is more, the
output will go "high" (to the positive supply voltage). A window
comparator will have two references and the output will go high only
when the input voltage is in between those - you could make a ZCD out
of a window comparator - if you set the lower reference to same -0.5v
and the upper to +0.5v, the output would go high breifly for the time
the imput voltage was between these two levels (right around 0v)

but this is a "basics" NG

. feebo wrote:

When you subsidize a behavior, you get more of it. If the OP is too lazy to pay attention in class or to learn to use Google, a failing grade is apt. Please don't feed the homework trolls.

It is obviously a homework assignment. The answers are readily available--probably in the OP's textbook.

Perhaps you should consider changing to the

*Teach a man to fish* school of thought.

I hear what you are saying Jeff, and while I do agree that this is probably someones homework I chose to give the benefit of the doubt. Certainly if this had been posted anywhere but SEB I would have ignored it.

I'll try to be a bit more discerning in the future but I remember what a mystery it all was (and a lot still is) all those years ago - I couldn't even find someone to tell me how the pins on a transistor related to the connections inside the circle (which was the emitter) ! so much water under the bridge since then :o)

I was thinking on the lines of a non-FAQ (mild sarcasm mode) thus:

Title: The title of your question is all important. To get the attention of the people who can answer your question, you need to make it stand out. Known methods of doing this:

1. USE ALL CAPS
2. Reference a current political problem
3. Ensure it is indecipherably vague.
4. Use 733t 5p34k, or txt spk

Examples:

WHY DOES THIS IC RESET ALL THE TIME? Are Republicans to blame for my project? Confubulator fries? Cn U Hlp wth prblm?

and so forth ;)

and then perhaps a serious (well, mildly serious) one afterwards that gives real guidance. Make it through the first part and one is rewarded :)

Cheers

PeteS

I think what JeffM (and myself) are saying is we help those who have tried to help themselves :)

I will definitely help with homework *provided the OP has tried to solve the problem already* and is perhaps stuck on phraseologu or perhaps a somewhat murky chapter in a text.

To paraphrase, _We help those who help themselves_

Cheers

PeteS

Just make sure that they learn to ask, "Doyahal want fries with that?" ;-)

--
Service to my country? Been there, Done that, and I\'ve got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

All the others are to proceed to the closest fast food place to apply for their job in their lifelong career in the food service industry. ;-)

--
Service to my country? Been there, Done that, and I\'ve got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

Snort

I know we all agree, but many an OP doesn't seem to realise that if you don't do your own work, you really won't learn anything. There are some professions where this may, in fact, be desirable. Engineering (especially design engineering) isn't one of them ;)

Cheers

PeteS