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Voice communication

Data communication

Controlling devices





Components required:-

Ic 741 Op Amp

IC 7805 Voltage Regulator

Diode 4004 Pn diodes

IC 91214 DTMF encoder

IC 7447- Seven Segment Display driver IC

Seven Segment Dispaly

Ic8870  DTMF decoder

9 v Transformer 50mA

IR Singal mode

Resistances- 10k,1k,4.7k,220k

Capacitors- 0.1microfarad,00.1 microfarad,1000f,470f

Cupper clad board

Fecl3 for PCB design

Software Required:-

Window os


MS word







In this project we will learn about how to use IR for communication purpose. IR need not to introduce. Everybody although he/she may be from any field know about Optical. IR as we know a reliable, low cost, flexible, large bandwidth communication medium. In this communication system we will use condenser mic for txer . Condenser mic is most sensitive mic. Its generally available and low cost.

In this circuit voltage amplifier will amplify the mic signal then signal will be amplified by power amplified.LED will transmit the rxed voice signal via IR. On rxer side detector will detect the signal then it will transfer the signal to special amplifier then the signal will be input for speaker. We will use DPDT switch for selecting voice and data signal

In data transmission we will transfer the data using DTMF technology. DTMF is dual tone multi frequency technology. In this we will use dtmf encoder with keyboard for data generation purpose. On the receiver side we will use dtmf decoder IC 8870 for it. Output of it will be the input od seven segment display driver IC. Output of Seven segment decoder IC will be the input of Seven segment display. We will common anode seven segment display. Seven will show the no entered with kryboard. When we will give signal on mic then speaker will give voice signal output. We will make +5v power supply for encoder & decoder ICs & +9v for amplifier circuits.  In this project will study about voice and data transmission.




In this project we will learn about how to use IR for communication purpose. IR need not to introduce. Everybody although he/she may be from any field know about Optical. IR as we know a reliable, low cost, flexible, large bandwidth communication medium.

In this project we can control any electrical appliances through DTMF dialing circuit for remote purpose .  When we want to control any electrical appliances through DTMF dialing circuit. Now again we press the switch on/off code to on/off any electrical appliances. With the help of this code unit is on and base unit give a acknowledge pulse for on and off separately.

DTMF Encoder Circuit:- in this circuit we will use IC91214 for no of devices. We will add keyboard with this IC. Ethis IC have option to generate 16 different pulses with different frequencies. These dual tone multi frequencies can be decoded at receiver side with IC8870 . these IC are esily available in market. We will use LASER for data transmission.

1.                 DTMF DECODER

In dtmf decoder circuit we use ic 8870 ic. IC 8870 is a dtmf decoder ic. IC 8870  converts the dual tones to corresponding binary outputs.


DTMF SIGNALLING. Ac register signaling is used in dtmf telephones, here tones rather than make/break pulse are used fro dialing, each dialed digit is uniquely represented by a pair of sine waves tones. These tones ( one from low group for row and another from high group fro column) are sent to the exchange when a digit is dialed by pushing the key, these tone lies within the speech band of 300 to 3400 hz, and are chosen so as to minimize the possibility of any valid frequency pair existing in normal speech simultaneously. Actually, this minimisator is made possible by forming pairs with one tone from the higher group and the other from the lower of frequencies. A valid dtmf signal is the sum of two tones, one from a lower  group ( 697-940 Hz) and the other from a a higher group ( 1209-1663 Hz). Each group contains four individual tones.  This scheme allows 10 unique combinations. Ten of these code represent digits 1  through 9 and 0. . tones in DTMF dialing  are so chose that none of the tones is harmonic of  are other tone. Therefore  is no change of distortion caused by harmonics. Each tone is sent as along as the key remains pressed. The dtmf signal contains only one component from each  of the high and low group. This significaly simplifies decoding because the composite dtmf signal may be separated with band pass filters into single frequency components, each of which may be handled individually.


First ic of this section is ic 74154. IC 74154 is  bcd to decimal decoder. 74154 is active low ic. Pin no 20,21,22,23 is connected to dtmf decoder ic.

Pin no 18 and 19 of this ic is connected to the collector of one npn transistor Base of the npn transistor is connected to the pin no 15 of the ic 8870. When dtmf decoder decode the signal at that time pin no 15 is on for a time and acknowledge the signal. This signal is fed to the  base of NPN transistor through 1 kohm resistor. When this signal is coming then 74154 is on and gives a output.


Then output of 74154 is active low. We will use IC 74ls 74  or transistors to invert the active low output. After that we will use flip flop & SCRs or relays to control & to give 220v Ac to devices for switching purposes.

             8             9            10           11            12                                 












IC 74154 is a BCD to Decimal converter. This IC is a 24 pin IC. Pin no.20,21, 22,23 are the BCD input pins of this IC,pin no. 2,3,4,5,6,7,8,9,10,11, are the output pins, pin no.24 is connected to the positive 5 volt supply  and pin no.12 is the negative supply pin. Pin no. 18 and pin no. 19 of this IC is enable pin. If the data available on the pin no. 19 is negative then output is negative for a time. The negative pulse is given by the NPN transistor collector point. IC 74154 is a special package may be used to provide a 1 low output out of 16 outputs or may be used to send input data to one selected output of 16, the remaining 15 staying high.


Substitute IC: No other substitute easily available









IC 4049 is a hex inverter IC. Pin no. is connected to the positive supply. Pin no. 7 is connected to negative supply. Pin no. 3,5,7,9,11 are the inputs of the IC and pin no. 2,4,6,10,12 are the input pins of this IC. Since the output of IC 74154 are low hence IC 4049 is used to invert the output of IC 74154, ie ,  to convert the low output of the decoder IC into high output


Substitute IC:  7404


   IC 8870      








In this stage   student  select the topic of the project of the project. Its the main stage of project work.its the area where talented students shows their innovative ideas.  Innovative students make project with a new idea then others. We selected this project because we want to do something in with our own hands. We use main electronics components uded in the industry. First of  all we selected the GSM based project. Then we drop idea because there was little bit practical electronics to learn and mobile companies already providing those facility.


In this section we collected the study material. We searches about our project on google.com,www.yahoo.com,www.msn.com


TESTING OF MAIN CIRCUIT- Then we collect the components  of project. It was not a easy task. Because no shop in our area have all the components. Then after collection of components we test the circuit on bread board - step by step. Because we want to sure about the circuit. We checked it in different steps beacuuse it was a big project and  was not possible to check it in a single step.

  1. PCB DESIGNING - After Testing of circuite sure about the circuit.

First of all we designed the layout of PCB .

Then we made a screen .

After that we mark the layout on clad board with the help of paint and screen.

Then we  dip that painted PCB in Ferric chloride solution.

After that we drill holes in PCB.

Then we washed PCB with Isopropyl solution.

  1. COMPONENT MOUNTING- We kept the hole size from 0.8mm yo 1 mm for leads of components. Then we insert components according ton their pitches.
  2. SODERING- Afgter mounting components we solder the components ane by one. We kept the temperature of iron at 250 degree to 400 degree. Because above this temperature it can damage to component. We used general iron available in the market of siron company. Its temperature was nearly 350 degree acc to company specifications.  We used soldering wire of 22 gauge with flux inbuilt.
  3. FINAL TESTING- After that  we test the circuit step by step . and insert the ICs after testing the one portion of the circuit an then after other step by step. Its was tough work  we tested voltage across the compents with erepect to ground. And current in series.
  4. TROUBLSHOOTING- Then we tried to troubleshoot the errors in the project.

reduce the  ripple factor  of power supply.




Notes by

Innovative project solutions

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            For Medical machines- used as a sensing device

            For lightening purpose in decoration