DTMF (Dual-tone multi-frequency )

Dual-tone multi-frequency (DTMF) signaling is used for telephone signaling over the line in the voice-frequency band between telephone handsets and the call switching center. The version of DTMF used for telephone tone dialing is known by the trademarked term Touch-Tone, and is standardized by ITU-T Recommendation Q.23.

There are twelve DTMF signals, each of which is made up of two tones from the following selection: 697 Hz, 770 Hz, 852 Hz, 941 Hz, 1209 Hz, 1336 Hz, 1477Hz,1633Hz, chosen such that it is easy to design filters and to transmit the tones through a telephone line having bandwidth of approximately 3.5 kHz

These tones are divided into two groups (low and high), and each DTMF signal uses one from each group. This prevents any harmonics from being misinterpreted as part of the signal.

The following table shows the frequencies used for each signal:

The signal is encoded as a pair of sinusoidal (sine wave) tones from the table below which are mixed with each other. DTMF is used by most PSTN (public switched telephone networks) systems for number dialling, and is also used for voice-response systems such as telephone banking and sometimes over private radio networks to provide signalling and transferring of small amounts of data.

For example, in order to generate the DTMF tone for "1", we should mix a pure 697Hz signal with a pure 1209 Hz signal

The higher of the two frequencies is normally aloud by 4dB, and this shift is termed as twist. DTMF standard specifies 50ms tones and 600ms duration between two successive tones.

#,*,A,B,C,D Keys:

� These are widely used for vertical service codes such as *67 in the United States and Canada to suppress caller ID.

� Public payphones that accept credit cards use these additional codes to send the information from the magnetic strip.

� The U.S. military also used the letters, relabeled, in their Autovon phone system. Here they were used before dialing the phone in order to give some calls priority, cutting in over existing calls if need be.

� Inbound phone calls are processed using our IVR software and automatic call distribution (ACD) system that answers calls without an operator.

ABCD Tones:

The ABCD tones are simply additional DTMF tones that may be used in any way the standard (0-9) tones are used.

� A � Flash

� B � Flash override priority

� C � Priority communication

� D � Priority override

The A, B, C and D tones are used in amateur radio phone patch and repeater operations to allow, among other uses, control of the repeater while connected to an active phone line.

Some cable television networks and radio networks to signal the local cable company/network station to insert a local advertisement or station identification also use DTMF tones.

At one time it was possible to use the ABCD tones to access a special maintenance mode of the Automatic Call Distributor (ACD) systems used by Directory Assistance operators to connect two callers together.

GENERATING DTMF:

ICs or by using RC networks connected to a microprocessor. MT8880 is an example of a dedicated IC. But getting the latter method work is a bit difficult if high accuracy is needed. The crystal frequency needs to be sacrificed for a non standard cycle length.. Hence this method is used for simple applications DTMF signals can be generated through dedicated. Most often, a PIC micro could be used for the above purpose.

DECODING DTMF:

Detecting DTMF with satisfactory precision is a hard thing. Often, a dedicated IC such as MT8870 is used for this purpose. It uses two 6th order band-pass filters using switched capacitor filters and it suppresses any harmonics. Hence they can produce pretty good sine waves from distorted input. Hence it is preferred. Again microprocessors can also be used, but their application is limited.

The Telephony Application Program Interface (TAPI) provides a way for a program to detect DTMF digits.

Detection of calling Numbers:

An international number consists of a Country Code (CC) and a National (Significant) Number (N(S)N). An example: 46 8 7132920, where CC = 46 and N(S)N = 8 7132920.

A national (significant) number consists of a trunk code (TC) and a subscriber number (SN) e.g. N(S)N=8 7132920, where TC=8 and SN=7132920. An area code consists of a national prefix (0) and the trunk code (TC).

A Start code for a Calling Number (DTMF character �A� )
B Start code for an information code (DTMF character �B� )
C Stop code (DTMF character �C� )
D Start code for a Redirecting Number (DTMF character �D� )
Sn denotes DTMF digits �0� to �9�

TRANSFER OF NUMBER INFORMATION
For an ordinary (non-diverted) call, 1a or 1b shall apply.
For a diverted call, 2a or 2b shall apply.

1a) For an ordinary call, the Calling Number shall be transferred as D-S1-S2...Sn-C

1b) For an ordinary call, the Calling Number shall be transferred as A-S1-S2...Sn-C

2a) For a diverted call the Redirecting Number shall be transferred asD-S1-S2...Sn-C

2b) For a diverted call the Calling Number (a) and the Redirecting Number (b) shall be transferred as A-S1-S2...Sn-D-S1-S2...Sn-C


Normal call set-up

(1) The line is in idle state and the user�s terminal equipment is on-hook. Idle polarity at the Z interface shall be 0 V (earth) at a-wire and �48 to �52V DC at b-wire.

When number information shall be sent, the system shall ...

(2) seize the line and perform polarity reversal. The voltage shall be the same as in (1) but the polarity shall be reversed.

(3) send number information according to clause 4 or information codes according to clause 5. The sending of the information shall start not sooner than 200 ms but not later than 1000 ms after the polarity reversal.

(4) perform polarity reversal back to idle polarity as in (1).

(5) send the first ringing signal not sooner than 80 ms after the polarity reversal in (4), but not later than 1000 ms after the end of the stop code �C�.

APPLICATIONS:

DTMF is used in various real-time applications like developing iphone applications, cell-phone operated robots etc..

BY:

SUMAN KUMAR.KONAKALLA

KL UNIVERSITY

sumanksk2006@gmail.com

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DIODES

In real how a diode looks like
its a two terminal device




The circuit symbol for diode is
there are different types of diode....

Diode

Zenerdiode

Every diode leaks (allows a little amount of current to pass through) in the wrong direction, but when there is more then about 60 volts on the diode (in the blocking direction) it will let it all pass, and it often gets defective. This effect is used in zenerdiodes. In a zenerdiode the threshold is much lower, and the diode keeps working. Zenerdiodes are used a lot in power supplies to keep the voltage constant:

LED

LED stands for Light Emitting Diode. This is a very special kind of diode, which produces light. They are available in many different colors: red, green, and yellow. There are also blue and white LEDs, but they are produced in another way, and are much more expensive. LEDs don't act like a normal light bulb, they are still diodes. This is the symbol of a led:



functions of diode
Diodes allow electricity to flow in only one direction. The arrow of the circuit symbol shows the direction in which the current can flow. Diodes are the electrical version of a valve and early diodes were actually called valves.

zener diode

A Zener Diode is a special kind of diode which permits current to flow in the forward direction as normal, but will also allow it to flow in the reverse direction when the voltage is above a certain value - the breakdown voltage known as the Zener voltage.

The Zener voltage of a standard diode is high, but if a reverse current above that value is allowed to pass through it, the diode is permanently damaged. Zener diodes are designed so that their zener voltage is much lower - for example just 2.4 Volts. When a reverse current above the Zener voltage passes through a Zener diode, there is a controlledbreakdown which does not damage the diode. The voltage drop across the Zener diode is equal to the Zener voltage of that diode no matter how high the reverse bias voltage is above the Zener voltage.

The illustration above shows this phenomenon in a Current vs. Voltage graph. With a zener diode connected in theforward direction, it behaves exactly the same as a standard diode - i.e. a small voltage drop of 0.3 to 0.7V with current flowing through pretty much unrestricted. In the reverse direction however there is a very small leakage current between 0V and the Zener voltage - i.e. just a tiny amount of current is able to flow. Then, when the voltage reaches the breakdown voltage (Vz), suddenly current can flow freely through it.

Lighe Emitting Diode(LED)

An LED is an electronic device that emits light when sufficient current flows throughout the object.

We know that in each diode there is a recombination of electrons and holes. This recombination of electrons and holes releases some energy which is invisible in most of the diodes but in some diodes it is visible in the from of light. When light is emitted on forward biasing of a P N junction than it is known as electroluminance. In this way, the frequency of emitted light from the diode may be in visible spectrum or in invisible spectrum. Emitted light from the diode can be divided into two parts, (i) light which is visible to human and (ii) light which is invisible to human. The frequency range visible to a normal man is 400nm (nenometer) to 700nm (nenometer). Light is generally coloured in this range. The waves of light with wavelength below 400nm (nenometer) are known as ultraviolet and waves of light with length greater than 7(K)nm are known as infra red. Light emitted from LED depends upon two factors,

• On quantity of doping of P and N-type semiconductor material
• On the nature of the added materials. Gallium Phosphide and Gallium Arsenide are such materials which are mostly used in making LEDS. Red and green coloured LEDS are made up of gallium phasphide.

working of diode

zener diode


Zener diode conducts just like a ordinary diode on forward bias. On reverse bias leakage current flows in it. This leakage current increases with the reverse voltage. This leakage current will increase suddenly after a definite reverse voltage. This voltage is known as break down voltage of zener diode or zener voltage and this sudden increase in current is known as zener current. For example, if a 6 volt capacity zener diode is connected in series with the 6 volt battery than the effect of forward and reverse bias will be as follows : There will be current flow in the zener diode in the position shown in the fig. 29A but there will be no flow of current in the zener diode in the position shown in the fig,29B. If now the battery voltage in the position of fig B is raised than there will be leakage current in the zener in the beginning. If reverse voltage are raised in steps than on a definite reverse voltage there will be suddenrise in the current in the zener, In the fig. 29C, the upper position of the graph shows the variations in forward current on forward voltage and lower position shows the effect onreverse current due to reverse voltage.300 ~| | |

light emmiting diode(LED)


The two wires extending below the LED epoxy enclosure, or the "bulb" indicate how the LED should be connected into a circuit. The negative side of an LED lead is indicated in two ways: 1) by the flat side of the bulb, and 2) by the shorter of the two wires extending from the LED. The negative lead should be connected to the negative terminal of a battery. LED's operate at relative low voltages between about 1 and 4 volts, and draw currents between about 10 and 40 mill amperes. Voltages and currents substantially above these values can melt a LED chip.The most important part of a light emitting diode (LED) is the semi-conductor chip located in the center of the bulb as shown at the right. The chip has two regions separated by a junction. The p region is dominated by positive electric charges, and the n region is dominated by negative electric charges. The junction acts as a barrier to the flow of electrons between the p and the n regions. Only when sufficient voltage is applied to the semi-conductor chip, can the current flow, and the electrons cross he junction into the p region.In the absence of a large enough electric potential difference (voltage) across the LED leads, the junction presents an electric potential barrier to the flow of electrons.

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SWITCHES

Function of a Switch

A switch is circuit element that allows or prevents the flow of electricity through a circuit, there are many types of switches they are as follows.

Single pole single throw switch



Circuit symbol

This is the most widely used switch, it can be either closed or open.

Single pole double throw switch


This is an electromagnetic switch also know as a relay, it consists of a coil that acts as an electromagnet and when the coil is powered by a source (Battery) the coil becomes a magnet and attracts the plate and the circuit gets closed and when the source is cut off the coil loses it magnetic property and a spring makes the plate to return to its original position.

Double pole single through switch
Double Pole, Single Throw switches control two circuits simultaneously. Circuits are ON at the same time, OFF at the
same time and may be of different voltages from separate sources.
The main in our house is a DPST switch both the phase and neutral poles are opened or closed at the same time

Double pole double through switch



Double Pole Double Throw switches control four circuits, permitting only two circuits to be energized at a time.

Push to break or Normally close


This switch is normally close and when pressed the circuit becomes open and when released it closes the circuit.

Push to make or Normally open


This switch is normally open and when pressed the circuit becomes closed and when released it opens the circuit.

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BREAD BOARD

A bread board is also known as a project board, It has got itself a place in every electronics hobbyist because of its "User Friendly" Nature, a bread board needs no soldering and already it is connected internally, lets see about it in detail.
This is how a bread board looks

A bread board is available in many shapes and sizes and has a facility to connect many boards as you like.
Connections in a Bread Board



NOTE: In some bread boards the top and bottom are not fully linked only 5 pins are linked.

Working
The heart of the solder-less breadboard is a small metal clip that looks like this:



The clip is made of nickel silver material which is reasonably conductive, reasonably springy, and reasonably corrosion resistant. Because each of the pairs of fingers is independent we can insert the end of a wire between any pair without reducing the tension in any of the other fingers. Hence each pair can hold a wire with maximum tension.
Using a Bread Board

1. Before building a circuit, connect power to the red terminal. For a battery pack, connect the positive (+) from the battery pack to the red screw terminal. Since ground is a reference voltage, connect the negative (-) from the battery pack to the black screw.
2. Unscrew the terminals and connect the battery pack, as described above. Screw the wire down firmly so that it doesn't move, but not so firmly that the wire is cut.
3. If you are using a power supply, simply connect power to the red terminal on the breadboard with a banana plug to a banana plug cable. There will be a ground connection on the power supply that can be connected to the ground terminal.
4. Once power and ground have been connected to the board, connect a wire, also known as a jumper wire, from the red terminal to the power bus (the red highlighted row). The wire should be just long enough to span the distance between the terminal and the bus.
5. Take the wire and strip off � inch of insulation from both ends. Connect the ground to the blue highlighted bus. Make sure the wire is just long enough to span the distance between the black terminal and the bus.
6. Strip off � inch from both ends and connect the ground bus to the black terminal. The breadboard is now ready to have a circuit built upon it.

Example Connection


This shows how a 380 ohm resistor and an LED are setup on a breadboard. When a 9 volt battery is attached the LED lights. Try replacing the resistor with a higher value such as a 680 ohm resistor. The resistance will be greater and the LED should shine less bright.

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LIGHT DEPENDENT RESISTORS(LDR)

A Light Dependent Resistor (aka LDR, photoconductor, or photocell) is a device which has a resistance which varies according to the amount of light falling on its surface.

Symbol for LDR

Light sensor circuit

Opposite is a simple light/ dark sensor. This can be connected as an input or switch to another circuit. The sensors has three green wires (1, 2 and 3). Wire 2 should always be connected to one of the inputs. If wire 1 is also connected then the sensor acts as a dark sensor. If wires 2 and 3 are connected to the inputs then sensor operates as a light sensor.

Functions of LDR...

An LDR and a normal resistor wired in series across a voltage, say 5V DC, can be used to develop a signal. Depending on which is tied to the 5V and which to 0V, the voltage at the point between them, call it the sensor node, will either rise or fall with increasing light. If the LDR is the component tied directly to the 5V, the sensor node will increase in voltage with increasing light. It doesn't really matter which way (rise or fall) because the designer has a choice of several simple circuits to invert the signal as needed for whatever function is to be performed.

This voltage at the sensor node (between the components) will vary gradually with the light level. To use for security light control, it's desired to develop a signal that switches level from one extreme to the other suddenly as light level goes from light to darker and darker. This result could be called a binary signal, a signal with two states (perhaps about 4V and 0.5V), indicating yes/no or 1/0. To develop this, the sensor node voltage can be compared, by an electronic circuit, with some threshold voltage to determine whether the light level is more or less than the threshold. The result of the comparison would give a "DARK? yes/no" determination.

Working of LDR:-

Typically, photocells only operate at low current, so you don't want to use them to directly drive a load, they're more for sensors. However, if you connect a positive voltage source in series with the photocell and then connect the other end to the gate of a transistor, you can use the transistor to drive the load, such as an LED. That way, if you shine a light on the photocell, the LED will turn on. In the sources is a good graphical representation and explanation of this.

Applications

Photoconductive cells are used in many different types of circuits and
applications.

Analog Applications

� Camera Exposure Control
� Auto Slide Focus - dual cell
� Photocopy Machines - density of toner
� Colorimetric Test Equipment
� Densitometer
� Electronic Scales - dual cell
� Automatic Gain Control � modulated light
source
� Automated Rear View Mirror

Digital Applications

� Automatic Headlight Dimmer
� Night Light Control
� Oil Burner Flame Out
� Street Light Control
� Absence / Presence (beam breaker)
� Position Sensor

Formula:

This formula is responsible for calculating the output power of LDR

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