<< Chapter < Page Chapter >> Page >

Front Panel of a DTFT and DFT Transformation System: Periodic Signal

[link] and [link] illustrates the front panel of the above transformation system. It shows the Analog signal and Discrete signal in the time and frequency domains using two waveform graphs. The transformation type is also shown in the front panel for both of the signals.

Telephone signal

Now let us examine a DFT application. In a touch-tone dialing system, the pressing of each button generates a unique set of two-tone signals, called dual-tone multi-frequency (DTMF) signals. A telephone central office processes these signals to identify the number a user presses. The tone frequency assignments for touch-tone dialing are shown in [link] .

Frequency Assignments for Touch-Tone Dialing

The sound heard when a key is pressed is a signal composed of two sine waves. That is

x ( t ) = sin ( 2πf 1 t ) + sin ( 2πf 2 t ) size 12{x \( t \) ="sin" \( 2πf rSub { size 8{1} } t \) +"sin" \( 2πf rSub { size 8{2} } t \) } {}

For example, when a caller presses 1, the corresponding signal is

x 1 ( t ) = sin ( 697 t ) + sin ( 1209 t ) size 12{x rSub { size 8{1} } \( t \) ="sin" \( 2π"697"t \) +"sin" \( 2π"1209"t \) } {}

Other than touch-tone signals, modern telephone systems use DTMF event signals for dial tone, busy tone and ringing tone. Table 1 lists the frequency and timing for standard DTMF event signals.

DTMF Event Signals
Tone type Frequency Timing
Dial tone 350 and 440 Hz Continuous
Ringing tone 480 and 620 Hz Repeating cycles of 2 s on, 4 s off
Busy tone 480 and 620 Hz 0.5 s on, 0.5 s off

In this application, let us examine the touch-tone dialing system of a digital telephone. Ten input variables ( k 0 , k 1 , . . . . . , k 9 ) size 12{ \( k rSub { size 8{0} } ,k rSub { size 8{1} } , "." "." "." "." "." ,k rSub { size 8{9} } \) } {} are assigned to the telephone keys ( 0,1, . . . . . , 9 ) size 12{ \( 0,1, "." "." "." "." "." ,9 \) } {} . Each input is connected to a Boolean control. Different types of Boolean controls can be created on the front panel. For this application, use OK Buttons (Controls Modern Boolean OK) , each of which is marked with a number from 0 to 9. The selected operation properties of an OK Button is “Switch until released,” as shown in [link] . This ensures that the corresponding signal gets generated when a key is pressed and gets back into its initial position when the key is released.

Operation Properties of an OK Button

Use another input variable, k 10 size 12{k rSub { size 8{"10"} } } {} , to act as a counter to count the number of times the keys are pressed. At the beginning, when no key is pressed, the value of k 10 size 12{k rSub { size 8{"10"} } } {} is zero and the system returns the dial tone (350 and 440 Hz continuous tone). When the value of k 10 size 12{k rSub { size 8{"10"} } } {} is equal to 10, meaning that the keys were pressed for a total of 10 times, the system assumes that a valid phone number is dialed and returns the busy tone or ringing tone. Connect all the Boolean inputs ( k 0 , k 1 , . . . . . , k 9 ) size 12{ \( k rSub { size 8{0} } ,k rSub { size 8{1} } , "." "." "." "." "." ,k rSub { size 8{9} } \) } {} to a Compound Arithmatic function (Functions Programming Boolean Compound Arithmatic) and select the OR mode. The output of this function becomes true(1) if any number key is pressed. The result is connected to the Case selector input of a case structure. The input variableis also connected to the case structure. For true case, k 10 size 12{k rSub { size 8{"10"} } } {} is connected to an Increment function (Functions Programming Numeric Increment) and for the false case, it is kept unchanged. The entire system is wrapped inside a W hile L oop (Functions Programming Structures While Loop) . The output of the case structure is then connected to a Greater or Equal function (Functions Programming Comparison Greater or Equal) to ensure that the program exits from the while loop whenis greater than or equal to 10. The system shows the ringing tone or busy tone in the graph and plays the waveform. [link] shows the completed block diagram of the touch-tone telephone system.

Questions & Answers

where we get a research paper on Nano chemistry....?
Maira Reply
nanopartical of organic/inorganic / physical chemistry , pdf / thesis / review
what are the products of Nano chemistry?
Maira Reply
There are lots of products of nano chemistry... Like nano coatings.....carbon fiber.. And lots of others..
Even nanotechnology is pretty much all about chemistry... Its the chemistry on quantum or atomic level
no nanotechnology is also a part of physics and maths it requires angle formulas and some pressure regarding concepts
Preparation and Applications of Nanomaterial for Drug Delivery
Hafiz Reply
Application of nanotechnology in medicine
what is variations in raman spectra for nanomaterials
Jyoti Reply
ya I also want to know the raman spectra
I only see partial conversation and what's the question here!
Crow Reply
what about nanotechnology for water purification
RAW Reply
please someone correct me if I'm wrong but I think one can use nanoparticles, specially silver nanoparticles for water treatment.
yes that's correct
I think
Nasa has use it in the 60's, copper as water purification in the moon travel.
nanocopper obvius
what is the stm
Brian Reply
is there industrial application of fullrenes. What is the method to prepare fullrene on large scale.?
industrial application...? mmm I think on the medical side as drug carrier, but you should go deeper on your research, I may be wrong
How we are making nano material?
what is a peer
What is meant by 'nano scale'?
What is STMs full form?
scanning tunneling microscope
how nano science is used for hydrophobicity
Do u think that Graphene and Fullrene fiber can be used to make Air Plane body structure the lightest and strongest. Rafiq
what is differents between GO and RGO?
what is simplest way to understand the applications of nano robots used to detect the cancer affected cell of human body.? How this robot is carried to required site of body cell.? what will be the carrier material and how can be detected that correct delivery of drug is done Rafiq
analytical skills graphene is prepared to kill any type viruses .
Any one who tell me about Preparation and application of Nanomaterial for drug Delivery
what is Nano technology ?
Bob Reply
write examples of Nano molecule?
The nanotechnology is as new science, to scale nanometric
nanotechnology is the study, desing, synthesis, manipulation and application of materials and functional systems through control of matter at nanoscale
Is there any normative that regulates the use of silver nanoparticles?
Damian Reply
what king of growth are you checking .?
What fields keep nano created devices from performing or assimulating ? Magnetic fields ? Are do they assimilate ?
Stoney Reply
why we need to study biomolecules, molecular biology in nanotechnology?
Adin Reply
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
what school?
biomolecules are e building blocks of every organics and inorganic materials.
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
Privacy Information Security Software Version 1.1a
Got questions? Join the online conversation and get instant answers!
Jobilize.com Reply

Get Jobilize Job Search Mobile App in your pocket Now!

Get it on Google Play

Source:  OpenStax, An interactive approach to signals and systems laboratory. OpenStax CNX. Sep 06, 2012 Download for free at http://cnx.org/content/col10667/1.14
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'An interactive approach to signals and systems laboratory' conversation and receive update notifications?