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IR voice and Data


To Design a circuit of an electronic infrared communication system.
Develop new ideas to implement this circuit purposely.
To study the circuitry and different types of components & DTMF generator, DTMF decoder, op-amp and infrared-LED in the circuit.


For years, infrared LED has been merely a system for piping light around corners and into the inaccessible places to allow the hidden to be lighted. But now, infrared LED has evolved into a system of significantly greater importance and use. Throughout the world, it is now being used to transmit voice, television and data signals as light waves. Its advantages as compared with conventional coaxial cable or twisted wire pairs are manifold. As a result, millions of dollars are being spent to put these light wave communication systems into operation.
One of the most interesting developments in recent years in the field of telecommunication is the use of laser light to carry information over large distances. It has been proved in the past decade that light wave transmission through laser light is superior than that achieved through wires and microwave links. Typically, infrared LED has a much lower transmission loss per unit length (0.15-5db/km) and is not susceptible to electromagnetic interference. Economically also, it serves our purpose. The ever increasing cost and the lack of space available in the congested metropolitan cities asks for advent of a less costly system.
The conventional telephonic systems use copper wires, which easily get oxidized and as such require high maintenance cost. The laser light being made of glass are non-reactive and hence economical. Also, the noise pick up by the copper wire or in electrical signals is quite substantial whereas in laser light, the noise pick up is negligible.

Basic elements of a infrared LED system

(i) Applications for video transmission include high quality video Trunked from studio Transfeter, Broadcast CATV video, Video Trunking within city or between cities, Baasedand Video for closed



MIKE: Its converts sound signals into electrical signals.

AMPLIFIER (A): Signals from mike are amplified so that it can drive to infrared-LED.

INFRARED-LED: It carries signals.

PHOTO TRANSISTOR: The electrical signals are regained from the optical signals.

AMPLIFIER (B): Energy of signals is amplified to drive the speaker.

SPEAKER: Electrical signals which are amplified are reconverted into sound signals at the speaker.

DTMF CODER: It is generates the DTMF signal corresponding to the number entered from the keyboard.

DTMF DECODER : It is fed to DTMF decoder which gives the binary output corresponding to the signal received from the transmitter.

DECODER DRIVER : To drive the 7 segment display.

The main part of Circuit is an amplifier.  This sound signals (even at a distance of 2 meters from the mic) are picked up by the condenser microphone and converted into electrical variation, which are amplified by the op-amp. (Operational amplifier)  IC- 741 is use in the inverting mode with a single supply using divider network of resistor the gain of IC can be set be varying the feed back through R5/6  resistance (can place a 1M variable) here the output of IC is further amplified buy the push-pull amplifier using transistor BC.548/558 pair, in this circuit are R2 is feed back resistance with R1/8 and C1/3 to connected IC-741.  The IC’s pin 2 is connect VR1 (variable resistance) through connect to O/P of T1 (transistor) also use 6volt DC. The microphone should be placed near the circuit with the shield wire to suppress tune. The output of the amplifier is taken from emitter of two transistors, with a filter C5 from speaker.  Same process continues in the second amplifier.


This project was based on photo diodes and photo transistor. Photo diodes had been used as a transmitter and photo transistor as a receiver. This project had been divided in two part, First part transmitter section and second part receiver section. Slide switch selected to voice communication and data.

TRANSMISSIONSECTION :When switch key is pressed, circuit is energised. The output of The transmit IR beams modulated at same frequency 1KHz. The receiver uses infrared module. The IR- signal form the transmitter is sensed by the receiver sensor.

RECEIVER SECTION:- This section is worked as a Flip-flop (Bistable). IC-3 is decade counter, its Pin No.14 is input and Pin No. 2 output. The output of frequency detector stage is used, via a flip-flop, to switch ‘ON’ or switch ‘OFF’ a LED alternately. The receiver uses infrared modules IR-signal from the transmitter is sensed by the sensor through and its output PIN 1 goes low and switched LED. IC-3 is worked on clock pulse which receives to infrared modules at Pin No. 14. Its output at Pin No 2 throughes high.
The output of IC-2 is also used for lighting LED-1 indicating presence of signal. When no signal is available output of sensor module goes high and transistor LED is switched ‘OFF’. When another signal arrives, LED is switched ‘ON’ and through clock pulse at Pin No. 14 of IC-3. This makes the LED to switch ‘ON’ the appliance at first pulse and ‘OFF’ the appliance at its Second pulse arrived at its sensor. Transmitter circuits works satisfactorily with 6-9V DC. Battery but receiver circuits needs 6V regulated supply. The CAMD CM8870/70C provides full DTMF receiver capability by integrating both the band-split filter and digital decoder functions into a single 18-pin DIP, SOIC,or 20-pin PLCC package. The CM8870/70C is manufactured using state-of-the-art CMOS process technology for low power consumption (35mW, MAX) and precise data handling. The filter section uses a switched capacitor technique for both high and low group filters and dial tone rejection. The CM8870/70C decoder uses digital counting techniques for the detection and decoding of all 16 DTMF tone pairs into a 4-bit code. This DTMF receiver minimizes external component count by providing an on-chip differential input amplifier, clock generator, and a latched three-state interface bus. The on-chip clock generator requires only a low cost TV crystal or ceramic resonator as an external component.
1. dBm = decibels above or below a reference power
of 1mW into a 600. load.
2. Digit sequence consists of all 16 DTMF tones.
3. Tone duration = 40ms. Tone pause = 40ms.
4. Nominal DTMF frequencies are used.
5. Both tones in the composite signal have
an equal amplitude.
6. Bandwidth limited (0 to 3KHz) Gaussian Noise.
7. The precise dial tone frequencies are
(350Hz and 440Hz) ±2%.
8. For an error rate of better than 1 in 10,000
9. Referenced to lowest level frequency component
in DTMF signal.
10. Minimum signal acceptance level is measured with
specified maximum frequency deviation.
11. Input pins defined as IN+, IN–, and TOE.
12. External voltage source used to bias VREF.
13. This parameter also applies to a third tone injected onto
the power supply.




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





IC 8870 is a DTMF (dual tone multiple frequency) decoder .It converts dtmf pulse into the equivalent BCD signal. Pin no. 18 and 10 of this IC are connected to the positive supply. This positive supply is from the 5 volt regulator circuit. Pin no. 9,5,6 are connected to the negative supply. Signal from the telephone line is in the form of dtmf pulse is applied to pin no. 2 of this IC through 2.2k ohm resistor and .1mfd capacitor. This signal is also connected to pin no. 3 through 100k ohm resistor. Pin no. 7 and 8 are connected to a crystal of frequency 3.7945 mh. Pin no. 16 and 17 of this IC is reset pin. Pin no. 11,12,13,14 are the BCD output of this IC.


Substitute ICs:  9170, 3170







The binary output of the decoder is connected to 7-segment display decoder/driver 74LS47 (IC2). The 7-segment decoder driver decodes the binary output of the DTMF decoder to drive a 7-segment LED. This display indicates the dialed number.





                        1   AI                         +5V   16



                              2   A2                           f      15


                              3   +5V                          g      14


                              4  +5V                         a      13


                              5    +5V                       b      12


                              6    A3                         c      11


                              7    A0                        d        10


                              8     GND                    e        9   



IN this circuit we use two  circuit one is dtmf generator and second is operational amplifier. In the dtmf generator circuit we use ic um 91214 as a dtmf generator. Working voltage of this ic is 3.3 volt dc. So that we use one 3.3 volt zener diode as a regulator and provide a regulated power supply to this circuit. Output signal is available on the pin no 7 . this output signal is coupled to the input of the amplifier through selector switch. One 3.58 mhtz crystal is connected to the pin no 3 and 4 to give a carrier frequency to the circuit. IN this mode we use 3.58 mhtz crystal  as a main carrier source of the dtmf generator.


All the switches are connected to the input of the dtmf generator to provide a multiple signals. All the switches are connected in four rows and three coloum. When we press any key then one row and one coloum is activate automatically.


Data from the dtmgf generator is further connected to the pin no 2 of the ic 741 through capacitor .04 micro farad. Here capacitor block the dc voltage and pass only signal to the amplifier circuit. Pin no 6 is the output pin no of the ic 741. Pin no 3 is connected to zero voltage through voltage divider circuit. Here we use two 10 k ohm resistor as a voltage divider components. Two 10 k ohm resistor provide a zero reference voltage to the pin no 3 of the ic 741. Output of the ic 741 is further amplify by the two transistor circuit. Here we use one is npn and second is pnp transistor . Collector of the npn transistor is connected to the positive voltage and collector of the pnp transistor is connected to the negative voltage. Output of the transistor is available on the emitter point and this output voltage is connected to the laser diode through one current limiting resistor and one zener diode.


Analogue signal from condenser mike is also feeded to the input of the op-amplifier using selector switch. Condenser mike convert the sound signal into electrical singal and this signal is  coupled to the pin no 2 of the ic 741 through .04 microfarad capacitor. Resistor 10 k ohm provide a dc voltage to the condenser mike.


Gain of the amplifier or ap-amp is depend on the feedback connec mmmmted to the circuit. In this project we use one 10 k ohm resistor in series with the  100 k ohm variable resistor. With the help of this variable resistor we control the gain of the op-amplifier.


Now whatever we speak or  press the switch this data is  superimposed on the light of the laser. Laser respond this signal and then this signal is focus on the photodiode  in the line of sight.




In the receiver circuit we use one photodiode as a main sensor. Photodiode receive the  data in the light and then converted into electrical signal. This electrical signal is coupled to the pin no 2 of the ic 741 amplifier through .04 microcfarad capacitor. Pin no 3 is connected to the zero voltage. For zero voltage we connect two resistance one from the positive line and second from the negative line to the pin no 3 for a zero reference voltage. Output is available on the pin no 6 . Output signal which is available on the output pin is further amplify by the transistor circuit and then this signal is . Now signal  is connected to  speaker  through  capacitor in series circuit.

Now when we apply a dtmf data from the keyboard then this data is again receive on the photodiode and then again pass through the op-amp circuit and then  decode by the dtmf decoder ic. Here we use 8870 as a dtmf decoder circuit.




1.      IR sensor



4.      DESOLDERING WICK- 1 Meter

5.      BREAD BOARD- 1


7.      IC 741(2)

8.      L.E.D’S-1



11.  SPEAKER( 8 OHM)-2

12.  RESISTANCES(10 K,4.7K,220K,110K,1K)

13.  P.C.B


15.  LASER

16.  SUPPLY- 9V


18.  IC 91214

19.  IC 8870

20.  IC 74154

21.  ZENER 3.3V

22.  IC 7805

23.  DIODES(4007)



Software Required:-

Window os


MS word


output of the ic 8870 is a bcd output. Pin no 10 and 18 is connected to the positive supply. Pin ni 5,6,9 is connected to the ground pin. Input data is available on the pin no 2 and 3. One crystal is connected to the pin no 7 and 8 to demodulate the  carrier frequency. Output signal available is bcd output. This BCD signal is further  decoded by the seven segment decoder and  seven segment decoder display the bcd code into seven segment display. Pin no 15 od the 8870 is ack pin output of  bcd signal. When signal is available on this pin then  it means that  ic 8870 decode the signal and


Working voltage of the  circuit is 9 volt dc.  Op-amp is working on the  9 volt dc and  8870 and 7447 is working on the 5 volt Dc. We use one regulator circuit with 9 volt power supply to reduce the voltage from 9 volt dc to 5 volt dc.




By using this portion with optical commnication, we can control different electrical or electronics equipments with the help of the  control signal. In communication circuit we use one dtmf decoder circuit. In that dtmf decoder circuit we use ic 8870 as a dtmf decoder circuit and one ic 7447 as a bcd to seven segment decoder.


We use one another dtmf decoder circuit, ic 8870 decoder and sense the output in the form of the bcd signal from the  dtmf decoder circuit.