Electrical Engineering - 2011-03-11

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6:10 AM

New highlighted question!

1

Q: AVR (at90usb1286) sleep and USB

I am using an AVR at90usb1286-based Teensy++ 2.0 to periodically read data from a few sensors. In its final form, my project will act based on the sensor inputs. For now, I log the results to the USB port. Because the measurement interval is relatively long I am placing the microcontroller in po...

Go bug it.

3 hours later…

9:24 AM

Good morning everyone

Sorry it has taken me too long to get on here.

@tyblu, I enjoyed your highlighted question, I look forward to seeing what good work people put in!

2 hours later…

11:51 AM

morning @tina

good evening

or evening @tina

12:19 PM

so, are you big in electronics @tina?

no

my majar is DIP

and for this i need signal prcoessing

and voice recognition

so i joined electronis because i need help in case of signal understanding

12:49 PM

@tina DIP?

Digital image processing?

Sorry, I am bad with majors.

My specialty is Digital signal processing

1 hour later…

1:53 PM

morning @W5VO.

2 hours later…

4:10 PM

Mornin

5:05 PM

ahahn

i have a question

x(t) = cos^2(4pit)

has period of 1/2 sec

how?

@tina, what is DIP?

2 pi is 1 complete rotation

ahan yes

so when t goes from 0 to 1

hm

it goes from 0 to 4pi

and completes 2.

but, cos^2 is a special case.

that has a period of .25 seconds

because of the trig identity

5:07 PM

how

and why

one second, I will show the identity

middle of something

1 sec

you said 2 pi is 1 complete rotation

i agree

o when t goes from 0 to 1

it goes from 0 to 4pi
and completes 2.

i do't understand the above

i mean:

So, if it was cos(4pi*t) that would be true

o when t goes from 0 to 1
it goes from 0 to 4pi
and completes 2.

but cos^2 oscillates twice as fast.

5:10 PM

ahhan

but 4pi means 2 rotation

if it were just cos

pi = 180 degrees

no pi is 180

haha, let me edit

I typoed

ok..:)

noe 4pi = 2 rotation

ok

and the value of cos repeats every 360.

so that is one period

but, cos^2 repeats every 180 degrees.

5:12 PM

no no

if we say cos(2pi) than its 1 rotation means 360

that 1 period

cos(2pi) is a constant, this is a very important point

the reason it has a period is because of the inclusion of a variable, t is normally used for time

yes

as t goes from 0->1 cos(2pi*t) goes from 1 to 1

completing a complete trip around the unit circle

I wanted to make a graph.

but my matlab is not working

you meansc compelte a circle

means 360

so cos2pi =360 have t =1/4 sec origianly

but why fundamental period is to=1/4 sec

why?

here is a graph.

(Wolfram Info)[wolframalpha.com/input/?i=cos^2%28t%29]

hell, link did no go right

damn, take everything in the brackets in paste it in a browser window.

if the problem was the period of cos(2*pi*t) the graph would repeat every second.

if it was cos(4*pi*t) it would repeat every .5 seconds.

cos^2(t) = 1/2 (cos(2*t)+1)

so, by squaring the cos you double the rate at which it repeats.

when looking at the period we only care about terms that affect period.

the cos^2(4*pi*t)=1/2 (cos(2*4*pi*t)+1)

so that means the cos will repeat its value every 1/4 seconds

you just get to a cos or sin

then you take the coefficient of t and divide it out of 2*pi

so 2*pi/(2*4*pi)

1/4

That make some sense @tina?

Sorry it seemed round about, I do not know your background so I had to feel out what you knew.

for these questions the Math SE is very very good.

5:25 PM

ok wait lemme read it

haha, kk

what is a DIP major?

digital image prceossing

how did you say

t was cos(4*pi*t) it would repeat every .5 seconds.

?

5:44 PM

yes, cos(4*pi*t) would repeat every .5

@reemrevnivek, morning

6:07 PM

To sleep I go.

how

was cos(4*pi*t) it would repeat every .5 seconds.

how 5 sec

I said .5

morning @Hans.

your school allows you to major in digital image processing? It seems like that would be a specialization of other things.

Still, I am sure you will enjoy it alot.

hello

6:25 PM

what is spectrum representtaion of a signal

?

a spectrum shows which frequency components a signal contains.

ahhn than what is phasor in signal

you are looking at bode plots?

no

jsut tell me about phasor addition in signals

class.ee.iastate.edu/ee224/Notes/review2.pdf

it's that you combine 2 signals of same frequency that are phase shifted it seems.

6:34 PM

ahhan

what means by amplitude

how large coise signal will eb

thats amplitude

the height of the swing

now frequency will eb repetation of a signal

3 hours later…

9:07 PM

whats happened to the envelope next to our name?

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