DUAL TONE MULTIPLE FREQUENCY

Introduction

Dual Tone Multi Frequency [DTMF] is a technology that can be used to send information through phone lines.

DTMF is also used for signaling between the Telephone network and computer networks.

The DTMF is a popular signaling method between telephones and switching centers.

Uses speech frequency signals.

DTMF signals are the superposition of 2 sine waves with different frequencies

Most mobiles have this technology and by using the right techniques, decoded DTMF signals can be used in robotic microcontrollers to make the robot perform certain actions.

One could use DTMF to create a robot that would navigate its way through a set “arena” or space to a specific location by press of a button on a cell phone.

Components used

DTMF keypadDTMF GenerationDTMF DecoderIR SensorsMicro Controllers

DTMF Keypad

1209Hz 1336Hz 1477Hz 1633Hz

697Hz 1 2 3 A

770Hz 4 5 6 B

852Hz 7 8 9 C

941Hz * 0 # D

Generally, row frequencies are low frequencies and column frequencies are high frequencies.

These frequencies for DTMF are chosen in such a way that they don’t have harmonic relation with the others, so that they will not produce same tones.

The column frequencies are slightly louder than the row frequencies to compensate for the high-frequency roll off of voice audio systems.

Each button pressed in keypad will produce a tone which differs from others.

This DTMF encoder is present in mobile. Output from keypad can be converted into digital form using DTMF decoder IC HT9107B.

The functionality of the keypad determines how thepressed key has to be evaluated. It has to be done intwo steps:

1. Determination of the row of the pressed key - define low nibble of PORTB as output/zero value

- define high nibble of PORTB as input/pull up- low bit in high nibble determines row

2. Determination of the column of the pressed key- define high nibble of PORTB as output/zero value- define low nibble of PORTB as input/pull up- low bit in low nibble determines column

697 Hz

770 Hz

852 Hz

941 Hz

1209 Hz

1336 Hz

1477 Hz

RowSelector

ColumnSelector

+Desired Digit DUAL

TONE+

DTMF Generation

HT9170B IC DECODER

• The HT9170B IC, using digital counting techniques, decodes these two tones to determine the key being pressed.

• The tone from the phone is filtered through the operational filter.

• RT/GT and EST monitor the time taken for the authenticity check of the tone.

• By this process the DTMF decoder can decode 16 different key tones in 4 bit binary code output.

Digit OE D0 D1 D2 D3

1 H 1 0 0 0

2 H 0 1 0 0

3 H 1 1 0 0

4 H 0 0 1 0

5 H 1 0 1 0

6 H 0 1 1 0

7 H 1 1 1 0

8 H 0 0 0 1

9 H 1 0 0 1

0 H 0 1 0 1

FOUR BIT BINARY CODE FOR EACH KEYTONE FOR NUMBER

Frequency Detection

ColumnCalculation

Row Calculation

697 Hz

770 Hz

852 Hz

941 Hz

1209 Hz

1336 Hz

1477 Hz

Digit

Calculation

Calculated DigitX[n]

Pins of Motor Driver

Micro Controller

The microcontroller used in this circuit is an AVR® Atmega 8 built with RISC architecture and 8Kb of self-Programmable flash memory.

It can process 8 bits of data in one clock cycle.

The RISC architecture allows the MCU to process an instruction per second.

IR SENSORTo detect obstacles, an IR sensor will be used in the robot. The IR sensor consists of a Photo-Diode and an LED. The LED emits Infrared radiation. If the surface is reflective it will reflect this light and the reflected light will be absorbed by the photodiode. The Op-Amp in this circuit is set in comparative mode.

The design is flexible to many uses. It can be used in cars when they come from their parking space to their owner. It can be applied to automated trolleys in factories that transport parts around the premises. The sensors are programmed to detect obstacles and so will navigate themselves through pathways by using these obstacles as guides.

Sensor Circuit

Controlling autonomous navigation of a robot using DTMF decoders, sensors and micro-controllers

Advantages

One can control home appliances from anywhere.

It reduces wastage of electricity when we forgot to switch off the lights & fans and gone outside.

It is very low cost compared to other technologies like GSM.

Applications

Cell phone controlled robot can be used in the borders for displaying hidden Land mines

The robot can used for reconnaissance or surveillance

The robot can be used anywhere there is the service provider tower of the connection provided that is mounted on robot.

Robot is small in size so can be used for spying

Limitations

No security. Anyone can control the robot by calling the mobile connected to module.

Number of applications is limited as our mobile can generate only 16 tones.

Conclusion

• By using Ultrasound sensors instead of infrared, one could extend the application of this technology to scenarios in which infrared would be ineffective.

• The simple use of IR technology and Dual Tone Multi Frequency could lead the way to more advances in autonomous vehicles.

Presented by:

K.Srilekha – Y12EC894RVR & JC COLLEGE OF ENGINEERING

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