Miniproject Report On

DTMF Teleswitch

2

CONTENTS

Sl No. Contents Page No

1. Cover Page 2

2. Certificate 3

3. Acknowledgement 4

4. Contents 5

5. Abstract 6

6. Introduction 7

7. Block Diagram 8

8. Circuit Diagram

9. Circuit Description

10. PCB Design & Fabrication

11. PCB Layout

12. Results & Conclusion

13. Reference

14. Data sheets

3

ABSTRACT

Today’s busy world is an assemblage of many communication

networks; some are yet to have their entries. The amazing thing is

that these all are being used for various communication purposes

only, though it is possible to extend their impacts in a variety of

manner by the manifestation of interesting systems where we can

directly have an aid from these. We are coming up with one of such

interesting systems by which we can access even our bedroom

electronic devices even from the most far off places in the world,

provided the network under use has good range everywhere.

Here we are demonstrating a system namely RAN as an

abbreviation for Remote Automation using Networks. In this most

basic demonstration, the transmitter is chosen as a mobile phone and

the decoding receiver as the land phone for convenience. One can

have either two mobile phones or two land phones for the same

purposes. To demonstrate such a system we will control, simply

turning ON and OFF of four LEDs representing the actual devices,

using any mobile phone from anywhere. Here we are designing such

an electronic assemblage which can decode the signals from the

mobile phone and can drive the four LEDs with the help of the BSNL

network and the receiving land phone, representing the receiver

section.

Such a system is really an asset for this busy modern

world, where everything is being sought for automation…………….

4

INTRODUCTION

Here we are restricting our discussion about RAN in

the receiver section alone as the transmitting section is alike the

common communication system with the only change that instead of

a verbal message, a number (or numerical code) representing the

code for a device to be controlled is transmitted. This code is

decoded and used to drive the LED represented by the number using

the receiver section.

The underlying principle mainly relies up on the ability

of DTMF (Double Tune Multi Frequency) ICs to generate DTMF

corresponding to a number or code in the number pad and to detect

the same number or code from its corresponding DTMF. In detail, a

DTMF generator generates two frequencies corresponding to a

number or code in the number pad which will be transmitted through

the communication networks, constituting the transmitter section

which is simply equivalent to a mobile set. In the receiver part, the

DTMF detector IC, for example IC MT 8870 detects the number or

code represented by DTMF back, through the inspection of the two

transmitted frequencies. The DTMF frequencies representing the

number/ codes are shown below.

5

BLOCK DIAGRAM

As mentioned earlier, as the relevance of our

design confines in the receiver section to drive the devices

represented by the LEDs from the DTMF transmitted by the

mobile phones to the land line, we are restricting our whole

discussion therein.

RING DETECTION

RELAY

DECODING SECTION

Input to the

landline

INTERFACE

OUT PUT SECTION

6

CIRCUIT DESCRIPTION

Now let’s have a detailed look into the whole circuit section wisely.

Before getting in to the description, for the sake of easiness, let’s confirm

our aim or let’s predict our expectation regarding its working.

We are supposed to send a code word from the mobile phone, which

is the transmitter and is sending the corresponding DTMF frequencies

along. At the receiver end, i.e. at the land line end we need to detect the

code back using our circuitry and it is to be used for driving the devices,

represented by the LEDs.

RING DETECTION_SECTION

Refer the circuit diagram of this section….Regarding the need of

this section, we want to use this circuitry in the device mode i.e. to control

the device’s turn off and turn on while maintaining the normal functionality

and usage of the land line to make and accept calls. So we must allow

sometime for the land line to get into the off hook mode, also it is

necessary to get the landline from on hook mode to off hook mode to

enable the DTMF reception. If the land line is already in the off hook mode,

then it won’t be able to receive any signal as in the normal speech

communication through networks. So using this section we are aiming to

automatically activate our circuitry after a number of rings are heard from

the landline, while the coupling for automation is done using a relay. Here

we have designed such that the DTMF signals will automatically be coupled

to the

7

Decoding section just after the 6th ring.

Now getting into the detailed analysis, the initial high ring

voltage is coupled to a zener diode circuitry to reduce the voltage level for

protection, at the same time maintaining the enough magnitude for

detection using the opto-coupler. See the details in the circuit diagram.

Whenever a ring occurs a sufficient amount of ring voltage is established

across the inputs of the opto-coupler which causes the internal transistor to

conduct and effectively the output 5th and 4th pin to get short. This results

in an effective coupling of input ring voltage to pass through. Now we will

exploit this signal to use it as a clock signal for the decade counter IC 4017,

which will produce a high logic level at its Q5 pin upon reception of the 6th

ring, which was changed into a quality clock signal. The diode-resistor-

capacitor network along with the NAND gates of the IC 4093 is used to

shape up the irregular voltage signal obtained at the output of the opto-

coupler into a quality clock pulse for the IC 4017. Because of this, as

mentioned earlier, just after the 6th ring the counter 4017 will produce a

high level at the Q5 pin till the next clock occurs. This logic 1 level of Q5 pin

is then used to drive the monostable multivibrator using 555 timer IC

through BC 547 transistor coupling. The monostable multivibrator is

designed for a period of about 60 seconds which is the allotted time for the

operator to control the device using the palm device he has. Thus the

monostable multivibrator will produce logic 1 level for a period of about 60

seconds at its output which is used to drive a relay as shown through

transistor coupling, which will couple a low resistance in between the RING

and the TIP terminals of the landline, resulting in the manifestation of a DC

loop driving the landline from ON HOOK to OFF HOOK preparing the

decoding section for the reliable reception of the signal transmitted from

the mobile phone.

8

Now, we have to contend with a problem arising from the

past counting of the IC 4017. Suppose a fellow called to our landline and cut

the phone at the 4th or 5th ring. After this if somebody calls again then right

at the first ring the landline will get into the OFF HOOK mode contrary to

our expectation at the 6th ring. How can we avoid this error? To solve this,

what we have with us is only the RESET pin of IC 4017. So the solution is

that we must reset the IC 4017 every time just after once the 6th ring has

occurred or the decoding section is coupled for decoding. So for this we use

the retrigerrable monostable multivibrator using IC 74LS123 commonly

called as the MISS-PULSE-DETECTOR. For this we supply the same clock

pulse of 4017 to the IC74123, which has been designed for a period of more

than twice as long as the duration of a single ring signal, which is about 5

seconds. The out put from the 4th pin of IC 74123, which is the TOGGLED Q

output, is then supplied to the active high RESET pin of IC 4017. Thus this

arrangement will avoid the past counting nature of IC 4017 by resetting it

just after the completion of the 6th ring and the consequent coupling of the

decoding section.

Now that we have effectively coupled the signals from the palm device

to the decoding section, let’s see how the decoding section performs the

decoding function.

DECODING_ SECTION

Refer the circuit diagram of this section….when the 1k resistor is

brought across the RING and TIP terminals the landline also brought to OFF

HOOK mode so that the decoding section is now connected to the

transmitted signal and can receive it.

9

The input capacitor-zener-resistor network is meant for both the

protection of the DTMF decoder IC 8870 from comparatively higher ring

voltage and the coupling of the signal to the same IC. Based on the

reference DTMF frequencies the DTMF decoder IC 8870 decodes the binary

equivalent of the keys or numbers in the number pad of the transmitting

mobile phones. The decoding scenario of the IC 8870 can be consolidated

as given below.

KEYS Q4 Q3 Q2 Q1

1 Off Off Off On

2 Off Off On Off

3 Off Off On On

4 Off On Off Off

5 Off On Off On

6 Off On On Off

7 Off On On On

8 On Off Off Off

9 On Off Off On

0 On Off On Off

* On Off On On

# On On Off On

10

A On On Off On

B On On On Off

C On On On On

D Off Off Off Off

The output of the DTMF decoder IC 8870 is binary code, which is then fed

to the binary to decimal decoder IC 74HC154 retrieving the original

transmitted key or number. But the IC 74HC154 has active low output pins.

So these active low outputs are converted to active high ones by passing

them through NOT gates. Note that here we are using only five outputs of

IC 74HC154 to control four devices represented by LEDs as an instance.

Specifically the pins we are using are the 13th pin which produces an active

low corresponding to the code *, the 2nd pin which produces an active low

corresponding to the code 1, the 3rd one for the code 2, the 4th one for the

code 3 and finally the 5th one for the code 4. Thus in the decoding section

we retrieve back the same number or code transmitted from the mobile

phone.

OUT PUT_ SECTION

Refer the circuit diagram of this section….using the converted

active high outputs of the decoding section we are now supposed to

control the TURN OFF and TURN ON of four LEDs. The output

11

corresponding to the code * from the decoding section is used to trigger a

monostable circuitry in the output section, which is designed to produce a

high pulse at it’s output for a period of about 5 seconds. This high pulse

with the duration of 5 seconds is used to activate the four tristate buffers

i.e. the ICs 74LS126 enabling the coupling of the respective inputs of the

buffers to their respective outputs. Now with in this 5 second duration we

can have our control signals to pass through the buffers and can be used to

control the D flip flops i.e. the ICs 74LS74, which has been set in the

latching mode to get its output toggled upon receiving consequent clock

pulses, thus triggering the turn ON and turn OFF of the devices once the

same code is transmitted for a second time. In a nutshell, the latching mode

operation of D flip flops causes a device to get turn on from off state or vice

versa on reception of the code word. The IC 74LS74 is a positive edge

triggered IC. One of the practical limitation we face here is to create a

positive edge at the clock input of the D flip flop IC, using the isolated pulse

coming through the buffer to its output. If we directly apply the pulse to

the D flip flop to work in the latching mode it won’t work due to the lack of

establishment of the positive edge to its clock input, resulting from the

occurrence of logic 1 level at the clock input of D flip flop right at the time

of biasing or when connected to the power supply. For this purpose to

create a positive edge going from logic 0 level to logic 1 level we pass the

pulse coming out of the buffer through another NOT gate as shown.

Finally, we need to find out a code which we have to

transmit from the mobile phone so that we can establish a well shaped

pulse as clock pulse at the clock input pin of the D flip flop for it to work in

latching mode i.e. to get the LEDs turned on if they were in the off state

and vice versa.

12

First of all we must activate the buffer in the output section

for the predetermined time by triggering the monostable circuitry there in.

So the first symbol in the code word should be *. Now, we need to transmit

a high level through the activated buffer using another symbol specific to

each of the device represented. From the circuit diagram we can see it can

be 1 for the 1st device, 2 for the second one and so on. Thus by sending

*(ordinal number of the device) we can create a low to high transition at

the out of the buffer. But it’s not yet been a well defined pulse with both

trailing and falling edge. So to get a falling edge we should now send a

symbol other than ordinal number of the device. Let it also be * to have a

convenient code. Now, as we know we use * for triggering the monostable

circuitry in the output section we must not end our code word with *.

Other wise, it will cause the triggering input of the monostable

multivibrator to continue in the logic 1 level even after the specified 5

seconds which in turn forces it not to get triggered for a second time on

pressing * as there lacks the transition from low to high level at it’s

triggering input. Hence we must end our code word with a symbol other

than both * and ordinal number of the device. Let it be 0. Thus, we got the

code word that is to be send for our expected control as * ordinal number

of the device*0. For example, to change the state of first device we have to

send a code-*1*0, for the 2nd one *2*0 etc…

By following the similar logic, it is possible to find some other

formats of code words. For example, the code word * ordinal number of

the device 0 is also seeming to be worthy of.

Thus the whole control procedure can be consolidated as first of

all we need to make a call to the land line, just after the 6th ring it will

automatically get on to the OFF HOOK mode for about 1minutes, during

this time we can control the required devices with code words of specified

format with in the installments of 5 seconds.

20V

1N41

4810

K

4N25

1uF

BC547

74LS

123N

4017N

NE555

20V

100K

1K 1N4148

BC547

1M

4093N 4093N

100u

F

100K

1K

1K

10K

1K 1K

560K

100uF

1K

GND

+5V

GND

GND

+5V

1N41

48GND

0.47uF (250V)0.

1uF

0.1uF

+5V GND

M01

PTH

+5V GND

+5V GND

+5V GND

ZEN

ER

D2

R1

1

2

6

4

5

OPTO

C2

T1

A1

B2

CLR

3Q

4

Q13

C14

R/C

15

IC1A

816 IC1P

GNDVCC

Q5 1

Q1 2Q0 3

Q2 4

Q6 5

Q7 6

Q3 7

Q8 9

Q4 10

Q9 11

CO 12

ENA13

CLK14

RES15

IC3

816 IC3PVDD VSS

TRE6

OUT 3DIS7

TRI2

VCC+ 8

GND 1CON 5

/RES 4

IC4

ZEN

ER

.

R2

R3 D4

T2

R4

1

23

IC5A 5

64

IC5B

714 IC5PVDD VSS

C3R5

R6

R7

R8

R9

R10 R11

C5

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112

K1_DPDT56

3

K1_DPDT

87

10

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D5

C1C

7

C8

1 2

JP1

1

U$1

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JP2

1234JP

3

1 2RJ1

1

RING TIP

+12V

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8

23

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1

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D2

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C2

T1

IC1

IC3

IC4

ZEN

ER

.

R2

R3

D4T2

R4

IC5

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R5

R6

R7

R8

R9

R10 R

11C

5

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DP

DT

D5

C1

C7

C8

U$1

JP2

JP3

RJ1

120

V

1N41

4810

K

4N25

1uF

BC

547

74LS123N

4017

N

NE555

20V

100K

1K1N4148

BC

547

1M

4093N

100uF

100K

1K

1K

10K

1K 1K 560K

100u

F

1K

1N41

48

0.47

uF (2

50V

)

0.1uF

0.1u

F

M01PTH

29

30

3.57MHz

74HC154N

74HCT04N

74HCT04N

74HCT04N

74HCT04N

74HCT04N

56K

47K

68K

56K

56K

56K

0.1uF(250V)

0.1uF(250V)

150K

5.6V

5.6V

GND

+5V

+5V

+5V

GND

GND

CM8870CP

330K

1N4148

100K

0.1uF

+5V

10K

GNDGND

1K

M01PTH

M01PTH

M01PTH

M01PTH

M01PTH

21Q1

01

12

23

34

45

56

67

78

89

910

1011

1113

1214

1315

1416

1517

G1

18G2

19

D20

C21

B22

A23

1224

IC1P

GND

VCC

12 IC2A

34 IC2B

56 IC2C

98 IC2D

1110

IC2E

714

IC2P

GND

VCC

R2

R3

R4

R5

R6

R7

C2

C3

R8

ZENER.

ZENER

1 2

JP1

1 2

JP2

1 2 3 4 5

JP3

IN+1

IN-2

GS3

OSC17

OSC28

VREF4

ST/GT 17

EST 16

STD 15

TOE 10

Q1 11

Q2 12

Q3 13

Q4 14

INH 5

VDD18

VSS9

IC3

VSS6

R11D1

R12

C1

R13

R1

1234JP5

JP4

JP6

1234

JP7

JP8

JP9

JP10

1234JP11

9

JP4

M01PTHJP6

M01PTH

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JP9

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IC1

IC2

R2

R3

R4

R5

R6

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C2

C3

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ZENER.

ZENER

JP1

JP2

JP3

IC3

R11

D1

R12

C1

R13

R1

JP5

JP7

JP11

3.57MHz

74HC154N

74HCT04N

56K

47K

68K

56K

56K

56K

0.1uF(250V)

0.1uF(250V)

150K

5.6V

5.6V

CM8870CP

330K

1N4148

100K

0.1uF

10K

1K

31

32

74LS126N

74LS126N

74LS126N

74LS126N

74HC04N

74HC04N

74HC04N

74HC04N

74LS74N

74LS74N

74LS74N

74LS74N

4.7K

4.7K

4.7K

4.7K

BC547

BC547

BC547

BC547

47uF(35V)

NE555

BC547

1K

0.1uF1K

0.1uF

1K

1K10K

100K

GND

GND VCC

GND+5V

+5V

+5V

1

23 IC1A

45

6 IC1B

10

98 IC1C

13

1211 IC1D

12 IC2A

34 IC2B

56 IC2C

98 IC2D

CLR

1

D2

CLK

3

PRE

4Q

5

Q6

IC3A

CLR

13

D12

CLK

11

PRE

10Q

9

Q8

IC3B

CLR

1

D2

CLK

3

PRE

4Q

5

Q6

IC4A

CLR

13

D12

CLK

11

PRE

10Q

9

Q8

IC4B

R1

R2

R3

R4

T1 T2 T3 T4

LED1

LED2

LED3

LED4

C1

TRE6

OUT 3DIS7

TRI2

VCC+ 8

GND 1CON 5

/RES 4

IC5

T5

R5

C2

R6

C3

R7

R8

R9

R10

1 2 3 4 5

JP1

1 2

JP2

1234JP3

10

23 1 23 1 23 1 23 1

23

1

IC1

IC2

IC3

IC4

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R2

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R4

T1T2

T3T4

LED1 LED2 LED3 LED4

C1

IC5

T5R5

C2

R6

C3

R7

R8

R9

R10

JP1 JP2

JP3

74LS126N

74HC04N

74LS74N 74LS74N

4.7K

4.7K

4.7K

4.7K

BC547 BC547

BC547

BC547

47uF(35V)

NE555

BC547

1K

0.1uF

1K

0.1uF

1K

1K10K

100K

33

34

230-12VAC

1N4004

1N4004

1N4004

1N4004

0.1uF470uF

M01PTH

GND

M01PTH

78L05Z

GND

1

23

4

TR1

D1

D2

D3

D4

C1C21 2

JP1

JP2

1 2

JP3

1 2

JP4

1 2

JP5

JP6

VI 3

2

VO1

IC2

GND

PRI

SEC +

11

P1

S1

VP31

JP2M01PTH

JP6

M01PTH

TR1

D1

D2

D3

D4

C1C2

JP1JP3 JP4JP5

IC2

35

36

13

RESULTS AND CONCLUSIONS

The Remote Automation using Networks

[RAN] on test performed exceptionally well to its

capability and accuracy. All the inherent parts of the

circuit performed consistently. It helped us to come out

with good judgment. With the features what it inherits, it

seems to be advantageous to the present era.

14

Final Implementation