Using AT Mega8 µc

Introduction This is the robot whose actions can be controlled by a

mobile phone from all over the world using the DTMF

signaling.

Use of mobile phones for robotic controls provide

working range as large as the coverage area of the service

provider and no interference with other controllers.

What is DTMF

DTMF (Dual tone multi frequency) as the name

suggests uses a combination of two sine wave tones to

represent a key dialed on a pushbutton or DTMF

keypad.

These tones are called row and column frequencies as

they correspond to the layout of a telephone keypad.

Hardware Components RequiredA microcontroller (ATMega8)

Transmitter and receiver mobile phones

DTMF decoder IC (MT8870)

DC motor

Motor driver IC (L293D)

Wheels

Power adopter

ATMega8 Development Board

DTMF Keypad Layout A DTMF keypad (generator

or encoder) generates a

sinusoidal tone which is

mixture of the row and

column frequencies.

The row and column frequencies

corresponding to a DTMF keypad

have been indicated in the above

figure.

DTMF tones are able to

represent one of the 16 different states

or symbols on the keypad.

DTMF Decoder IC (MT8870) On pressing any key say key 1, a

combination of frequencies 1209

and 697 Hz will be generated by

keypad which is fed to IC through

sound converter which in turn

produce the output 0001

(Q1, Q2, Q3, Q4).

Following table shows output

of remaining keys.

Motor Driver IC (L293D) It is required to supply sufficient

current to motors as microcontrollers

can’t supply that much current.

It is a dual H-Bridge motor

means it can drive two DC

motors simultaneously in both

clockwise and anticlockwise

direction.

Its input terminals are controlled

by the microcontroller.

It also includes the protection

circuit against back EMF.

Overview Microcontroller

MT8870 DTMF

Decoder IC

IC Output

Audio jack

Boot section

Robot chassis

Wheel

Block Diagram

Description The robot is controlled by a mobile phone that makes call to

the mobile phone attached to the robot and in the course of the

call, if any button is pressed the corresponding DTMF freq.

will be heard at the other end.

DTMF assigns a specific frequency (consisting of two separate

tones) to each key that it can easily be identified by the

electronic circuit. The signal generated by the DTMF encoder

is the direct algebraic submission, in real time of the

amplitudes of two sine(cosine) waves of different frequencies,

for example: pressing key5 will send a tone made by adding

1336hz and 770hz to the other end of the mobile

Conti….. The received tone is processed by the atmega8

microcontroller with the help of DTMF decoder

(MT8870). The decoder decodes the DTMF tone in to

its equivalent binary digit and this binary number is

send to the microcontroller.

The microcontroller is preprogrammed to take a

decision for any given input and outputs its decision

to motor drivers in order to drive the motors for

forward or backward motion or a turn.