P.V.P.I.T. (Budhgaon)DTMF code generator

2015

DR. V.P.S.S.MS

PADMABHOOSHAN VASANTRAODADA PATIL

INSTITUTE OF TECHNOLOGY, BUDHAGAON (SANGLI)

A

MINI PROJECT REPORT

ON

DTMF code generator using seven segment display

By

Mr. Dnyanesh Umesh Shinde

Mr. Swapnil Kumar Kamble

Ms. Prashant Muralidhar Jadhav

Under the Guidance of

Prof. Kabade R. S.

DEPARTMENT OF ELECTRONICS AND TELECOMMUNICATION ENGINEERING

(2014-2015)

CERTIFICATE

This is to certify that completed this project entitledDTMF code generator using seven segment displayis an original work carried out by Mr. Dnyanesh Shinde Roll no:58, Mr. Swapnil Kamble Roll no:56, Mr. Prashant Jadhav Roll no:55 in the partial fulfillment of degree of bachelor of engineering in Electronics & Telecommunication of PVPIT Budhgaon under Shivaji University , Kolhapur during the year 2014-2015. The project report has been approved as it satisfies the academic requirements in respect of project work prescribed for the bachelor of engineering degree.

Place: Sangli

Date:

Prof.Kabade R. S Prof. Chavan M. S.Dr. SatishchandraV.Joshi

(Project Guide)(H.O.D) (Principal)

ACKNOWLEDGEMENT

We express our deep sense of gratitude to our guide Prof. R.S. KABADEfor his valuable guidance rendered in all phase of project. We are thankful for his wholehearted assistance , advice and expert guidance towards making this project a success.

Our special thanks to honorable Principal Dr. S. V. JOSHI & H. O. D. Prof. M.S. CHAVAN for their keen interest, encouragement and excellent support.

We would also like to thank all the Teaching and Non-Teaching staff members of our college who helped us directly and indirectly during the completion of this report.

Mr. Dnyanesh Umesh Shinde

Mr. Swapnil Kumar Kamble

Mr. Prashant Muralidhar Jadhav

Table of contents

Sr. no.

Title

Page no

Abstract

1

Introduction

1.1

What is DTMF code?

7

1.2

Need of DTMF?

8

2

Diagrams

2.1

Circuit diagram

9

2.2

PCB diagram

10

3

Components used

3.1

Components specifications

11

3.2

Component list

13

4

Description

14

5

Working

14

5.1

Operation of DTMF method

14

5.2

Working of DTMF decoder

15

5.3

DTMF Decoder Application Circuit and Working Procedure

15

5.4

Table showing high and low frequency tones and decoded output

16

5.5

Crystal oscillator

17

6

Pin descriptions

6.1

Pin description of MT 8870

17

6.2

Observation table on MT 8870

19

6.3

Pin description of BC D7447

20

6.4

Observation table of BCD 7447

22

6.5

Common anode seven segment display

23

7

Features

24

8

Advantages

25

9

Disadvantages

26

10

Applications

27

11

Result

28

12

Conclusion

29

13

Reference

30

Table of Figure

Sr.No.

Title

Page no

1.

DTMF code

7

2.

DTMF

8

3.

Circuit diagram

9

4.

PCB layout

10

5.

Table

16

6.

IC MT 8870

17

7.

Observation table on MT 8870

19

8.

BCD 7447

20

9.

Observation table of BCD 7447

22

10.

Seven segment display

23

11.

Result

28

Abstract

Dual-tone Multi-frequency (DTMF) signals are used in touch-tone telephones as wellas many other areas such as interactive control, telephone banking, and pager system. Asanalog telephone lines are converted to digital, researchers became interested in digitalDTMF detectors.

The main aim of our project is to study the DTMF code generation and sven segment display. we use crystal oscillator connected to IC MT8870 which creates a frequency and the binary output is given to the BCD decoder. The BCD decoder decoded the inputs and the decoded digits are displayed on the seven segment display.

This project defines a way for automatic control of any electrical appliances. The switching of any load can be achieved by just pressing a number on the cell phone. A person can dial a number from his/her mobile and this number is redirected to another mobile from where the tones are taken and decoded and the number is used as a command to operate the loads.

Here a DTMF decoder is connected to the mobile line such that the when a number is dialed on the phone, the generated tone signals are fed to the DTMF decoder. The decoder decodes these tones to get the original data or the number pressed and feeds this information to the BCD decoder. The BCD decoder , on receiving the input, displays the number on the 7 segment LED display panel.

1.INTRODUCTION

DTMF stands for Dual Tone - Multi Frequency and it is the basis for your telephone system. DTMF is actually the generic term for Touch-Tone (touch-tone is a registered trademark of ATT). Your touch-tone phone is technically a DTMF generator that produces DTMF tones as you press the buttons.

1.1What is DTMF code..??

When any of the key like 1, 2, *, # etc is pressed particular code is transmitted. This code is consist of two frequency among which one is higher frequency and second one is lower frequency. Following table shows the combination of frequency for respected keys.

1

2

3

697 Hz

4

5

6

770 Hz

7

8

9

852 Hz

*

0

#

941 Hz

1209 Hz

1336 Hz

1447 Hz

Fig 1.DTMF code

According to above table 8 is combination of lower frequency of 852 Hz and higher frequency of 1336 Hz and # is of lower frequency of 941 Hz and higher frequency of 1447 Hz. So this is all about DTMF code, now let see about how DTMF code are generated, transmitted and Decoded in mobile phone system. Here i am only talk about GSM system.

1.2What is the Need of DTMF Decoding?

In the premature days, our telephone systems were operated by human operators in a telephone exchange room. The caller will pick up the phone, giving instruction to the operator to connect their line to the destination. It is a kind of manual switching. As more and more people entered in the telephone technology as useful communication gear, manual switching becomes a time consuming tedious task.

As technology established, pulse or dial tone technique were invented for telephone communication switching. It employs electronics and computers to support switching operations. DTMF is the ultimate technique used in any of the Mobile, Telephone communication systems.

Dual Tone Multiple Frequency DTMF

Fig 2.DTMF

Basics of Dual Tone Multiple Frequency DTMF stands for dual tone multiple frequency. DTMF is a term which used in telephone industry. When any key on telephone or mobile phone is pressed one tone is generated and it is audible.

2. Diagrams

2.1CIRCUIT DIAGRAM

Fig 3. Circuit diagram

2.2 PCB layout

Fig 4. PCB diagram

3.Components used

1. DTMF decoder IC (M-8870)

2. Resistors (100k (2); 330k;100)

3. Capacitors (0.1Fx 2)

4. Crystal oscillator (3.579545MHz)

5. BCD decoder 7447

6. 7 Segment

3.1Component specification

COMPONENTS

FIGURE

SPECIFICATION

USE

IC

DTMFdecoder IC (M-8870)

Which decodes tone generated by the keypad of cell phone.

Resistors

100k (2), 330k ,100

It opposes the flow of the current.

Capacitors

0.1F,10F

For the removal of ripple.

Oscillator

Crystal oscillator (3.579545MHz)

It create an electrical signal with a very precise frequency.

IC

BCD decoder 7447

Generates their complements internally and decodes

the data

7 segment

Display

To display numbers, letters and characters in a digital system.

3.2 Component list

Component name

Quantity

Specifications

DTMF decoder

1

IC M-8870

Resistors

4

330 k, 100 k, 100 k, 100

capacitor

2

0.1F,10F

Crystal oscillator

1

3.579545MHz

Bcd decoder

1

IC 7447

7 segment display

1

Common anode

Chasis

1

Wooden chasis

General purpose PCB

1

IC base

2

Aux cable

1

Total cost of project in Rs : 300/-

4. DESCRIPTION

In this project, which based on DTMF decoder Ic M8870, we showing the output of M8870 ic in 7 segment. The 4 bit data output of M8870 ic further connected with LS7447 decoder which is BCD decoder to 7 segment display unit.

Input tone from mobile gives to M8870 ic which further connected to BCD decoder LS7447 ic and then 7 segment.

5. WORKING

When we press any key from mobile (mobile keypad tone should be on) the tone goes to decoder ic which receiver certain key frequency and then converts to 4 bit data which further given to BCD decoder and then 7 segment connected to BCD decoder show that number which key pressed on mobile.

It can remotely operate when someone calls to that mobile (which is connected to circuit) and remotely press any dial number which can be received and circuit can show dial pressed number of caller .

5.1 The operation of DTMF method are as follows:

Caller generates a dial tone consisting of two frequencies. It is transmitted via the telephone line (communication media).

Telephone exchange consists of a DTMF decoder, which decodes the frequencies in to digital code.

These codes are the address of destination subscriber; it is read and processed by a computer which connects caller to the destination subscriber.

5.2 Working of DTMF decoder circuit

DTMF keypads are employed in almost all landline and mobile handsets. Thus this technology is used in the telephone switching centers to identify the number dialed by the caller.

The decoder distinguishes the DTMF tones and produces the binary sequence equivalent to key pressed in a DTMF (Dual Tone Multi Frequency) keypad.

The circuit uses M-8870 DTMF decoder IC which decodes tone generated by the keypad of cell phone.

DTMF signals can be tapped directly from the microphone pin of cell phone device. Cut the microphone wire and you will get two wires red and green. The red wire is the DTMF input to the circuit.

The signals from the microphone wire are processed by the DTMF decoder IC which generates an equivalent binary sequence as a parallel output like Q1, Q2, Q3, and Q4

5.3 DTMF Decoder Application Circuit and Working Procedure

DTMF keypad is placed out on a 4 cross 4 matrices, in which each row represents low frequency, each column represents high frequency, with DTMF, each key passed on a phone generates two tones of the specific frequencies one tone is generated from a high frequency tones and low frequency tone. These tones are converted to digital form using DTMF decoder circuit. These codes are the address of the destination which is read and preceded by the computer that connects the caller to the destination. The DTMF decoder circuit used in many electronics projects for better connectivity to control the applications.

5.4 Table showing DTMF Low and High frequency tones and decoded output

5.5 Crystal Oscillator

The internal clock circuit is completed with the addition of an external 3.579545 MHz crystal and is normallyconnected as shown in fig However, it is possible to configure several MT8870D/MT8870D-1 devicesemploying only a single oscillator crystal. The oscillator output of the first device in the chain is coupledthrough a 30 pF capacitor to the oscillator input (OSC1) of the next device. Subsequent devices areconnected in a similar fashion. The problems associated with unbalanced loading are not a concern with thearrangement shown, i.e., precision balancing capacitors are not required.

6. Pin Descriptions6.1 Pin description of MT8870

Fig 5.pin diagram of MT 8870

1 IN+ :This pin is input to the non-inverting terminal of internal op-amp.

2 IN-: This pin is input to the inverting terminal of internal op-amp. Input signal from the mobile is applied to this pin using 3.5mm connector pairs and aux cable.

3 GS : Gain selector, This pin provides feedback to the op-ampcircuitry. Feedback resistor of appropriate value is connected between this pin and input signal. Value of resistor decides the gain of amplification.

4 Vref : Reference Voltage, This is output pin. Op-amp is configured in differential amplifier mode and both the inputs are bias in mid-rail range so for that generally Vcc/2 voltage is apply to non-inverting terminal hence Vref is connected to IN+ i.e. pin no 1.

5 INH : Inhibit, This is active high input pin. If you dont want to decode A,B,C,D then connect this pin to Vcc and if you want to decode them then connect it to ground, internally it is pulled down.

6 PD : Power down, This is also active high input pin. Vcc supply (High) at this pin enables the power down mode and in power down mode oscillator and internal filters stops functioning and IC goes to stand by mode.

11 to 14 Q1 to Q4 : four output bits, When TOE is connected to Vcc this will represents the DTMF code as per valid DTMF tone and when TOE is connected to ground this pins are remain in high impedance state.

10 TOE : Three state output enable, This is active high input pin. +Vcc at this pin will allow output Q1, Q2, Q3 and Q4 to latch data from internal latch circuitry. When this pin is connected to ground output Q1 to Q4 will not latch decoded DTMF code. This pin also pulled up internally .

15 StD : Delayed steering, This is output pin. When DTMF tone received, decoded and latched by the output pins Q1 to Q4 then Std will goes high and when voltage on pin no 17 i.e St/Gt falls below threshold voltage Vtst then Std again fall down to low.

16 ESt : Early steering, This is output pin. If valid DTMF tone is received then this pin goes high and remains high till any loss of signal occurs however Loss of signal make this pin to go logic low.

17 St/Gt : This is dual purpose pin and performed bidirectional operation i.e St Steering input as input and Gt Guard time as output. When voltage greater Vtst appears at St, it causes latch to register new output data. GT is used to configure time constant of Est pin.

6.2 Observation Tableof MT 8870

Pin No

Pin Name

voltage

1.

IN+

0.01V

2.

IN -

0.01V

3.

GS

0.01V

4.

VRef

O.O1V

5.

INH

0V

6.

PD

0V

7.

OSC1

0.01

8.

OSC2

0.01

9.

VSS

0V

10.

TOE

0.01V

11.

Q1

0.01V

12.

Q2

0.01V

13.

Q3

0.01V

14.

Q4

0.01V

15.

StD

0V

16.

ESt

0V

17.

St/Gt

0V

18.

VDD

0.01

6.3Pin connection ofBCD decoder 7447

Fig 6 pin diagram of 7447

Pin No

Function

Name

1

BCD Input 2

A1

2

BCD Input 3

A2

3

Display test; Active low

LT

4

Ripple blanking output; Active low

RBO

5

Ripple blanking input; Active low

RBI

6

BCD Input 4

A3

7

BCD Input 1

A0

8

Ground (0V)

Ground

9

Segment outputs; Active low

e

10

d

11

c

12

b

13

a

14

g

15

f

16

Supply voltage; 5V (4.75V 5.25V)

Vcc

6.4 Observation table of BCD decoder 7447Pin no.Pin namevoltage1. A10.01V2. A20.01V3. LT0.01V4. RB00.01V5. RB10.01V6. A30.01V7. A00.01V8. GND0V9. E0.01V10. D0.01V11. C0.01V12. B0.01V13. A0.01V14. G0.01V15. F0.01V16. VCC0.01V6.5 Common Anode 7-segment Display

Fig 7.common anode seven segment display

In general, common anode displays are more popular as many logic circuits can sink more current than they can source. Also note that a common cathode display is not a direct replacement in a circuit for a common anode display and vice versa, as it is the same as connecting the LEDs in reverse, and hence light emission will not take place.

Depending upon the decimal digit to be displayed, the particular set of LEDs is forward biased. For instance, to display the numerical digit 0, we will need to light up six of the LED segments corresponding to a, b, c, d, e and f. Then the various digits from 0 through 9 can be displayed using a 7-segment display as shown.

7. Featuresof DTMF decoder

1. Complete DTMF Receiver

2. Low power consumption

3. Internal gain setting amplifier

4. Adjustable guard time

5. Central office quality

6. Power-down mode

7. Inhibit mode

8. Backward compatible with MT8870C and MT8870C-1

8.Advantages:

1. Effective control of home appliances. 2. Home automation using mobile phone. 3. Increases power efficiency. 4. Increases appliances lifetime. 5. Power wastage is reduced.

9. Disadvantages

1. External reset circuit is required.

2. We can supply on 5v to the circuit otherwise the IC will damage.

10. Applications

1. Paging systems

2. Repeater systems/mobile radio

3. Credit card systems

4. Remote control

5. Personal computers

6. Telephone answering machine

11. Result

Fig 8. Result

12. Conclusion

In our project we studied the DTMF code generator and seven segment display. We get to know the frequency of each dialed number on the cell phone which is decoded and displayed on the seven segment display.

13. References

www.circuitsgallery.com

www.genave.com

www.edgefxkits.com

www.electronicshub.com

www.wikipedia.com

Department of Electronics & telecommunication Page 10