DTMF BASED MOBILE CONTROLLED ROBOT PROJECT REVIEW TEAM 1-SRISRUTHI.S,SUSMITHA ROS,NITIN BHARATTWAJ, VISHAL KUMAR.P.M

DTMF SIGNALLING DTMF – ( double tone multiple frequency ) is a group of signalling methods that use a mixture of two pure tone sounds. Uses a set of 8 audio frequencies transmitted in pairs to represent 16 signals. Applications – Widely used in telecommunication systems, robotics, home automation.

BLOCK DIAGRAM

MT8870 DECODER IC PIN OUT DIAGRAM

DECODER CHECKS THE INCOMING SIGNAL FOR STANDARD DTMF FREQUENCIES. AN AVERAGING ALGORITHM PROTECTS AGAINST FREQUENCY GENERATION FROM EXTRANEOUS SOURCES. ONCE THE HIGH AND LOW FREQUENCIES ARE DETECTED, THE EARLY STEERING OUTPUT(EST) GOES TO A HIGH STATE.

CIRCUIT DIAGRAM

STEERING CIRCUIT CHECKS FOR VALID SIGNAL DURATION USING THE EXTRERNAL TIME CONSTANT R AND C DRIVEN BY EST. THE LOGIC HIGH ON EST CAUSES VC TO INCREASE AS THE CAPACITOR DISCHARGES PROVIDED EST REMAINS HIGH FOR THE VALIDATION PERIOD TGP, AND VC ATTAINS THRESHOLD VTS TO REGISTER THE TONE PAIR.

THE GT OUTPUT DRIVES VC TO VDD AS LONG AS EST REMAINS HIGH AND AFTER A SHORT DELAY FOR OUTPUT LATCH TO SETTLE, THE STD DELAYED STEERING OUTPUT FLAG GOES HIGH INDICATING THE ARRIVAL OF INPUT TONE. ON THE ARRIVAL OF INPUT, THE 4 BIT OUTPUT IS MADE AVAILABLE ON PINS 11,12,13,14 WHEN THE TOE LOGIC GOES HIGH, FAILING WHICH THE TOE GETS GROUNDED AND THE OUPUT PINS ARE ON HIGH IMPEDANCE STATE.

WHY ARE PINS 1 AND 4 SHORTED? PINS 1 AND 2 ARE THE NON INVERTING AND INVERTING TERMINALS OF AN OPAMP IN DIFFERENTIAL MODE. OPAMP TERMINALS REQUIRE BIASING IN MID RAIL RANGE. THE NON INVERTING TERMINAL IS BIASED WITH A VOLTAGE VDD/2. INTERNALLY A VREF BUFFER PROVIDES A VOLTAGE OF VDD/2. THUS THE TWO PINS ARE SHORTED.

ATMEGA 16 PIN DIAGRAM

MICROCONTROLLER It is a high performance – low powered microprocessor (operating between 4.5 – 5V) with a inbuilt clock of 1MHZ Consists of 40pins out of which 32 are I/O lines divided into 4 sections – PORTA, PORTB, PORTC, PORTD. It has various in-built peripherals like USART, ADC, Analog Comparator, SPI, JTAG etc.

Acts as a decision making device. Output of the DTMF decoder is given as input to the controller. Output pins - Q4,Q3,Q2,Q1 of the decoder are connected to PB0,PB1,PB2,PB3 of the input section(PORT B-INPUT). Output pins of microcontrollers – PD3,PD4,PD5,PD6 are given to the motor driver.(PORT D-OUTPUT)

MOTOR DRIVER: (IC L293D) Amplifies the current required to drive the motors. 16pin IC, used to support 2 motors simultaneously & enable them to move in forward and backward direction. When input pin is high, output gets internally connected to VSS. When input pin is low, output gets internally connected to the ground (0V). When one input is high and the other is low, the motor rotates either in forward or backward direction.

L293D PIN DIAGRAM

ADVANTAGES Eliminates the use of conventional RF circuits which have the drawbacks of limited working range, limited frequency range and control. Provides robust control, working range as large as the coverage area of the service provider Does not require the construction of receiver and transmitter units. Reduction in interference noise.

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