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
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
CONSTRUCTION AND WORKING
MIKE: Its converts sound signals into electrical signals.
AMPLIFIER (A): Signals from mike are amplified so that it can drive
INFRARED-LED: It carries signals.
PHOTO TRANSISTOR: The electrical signals are regained from the
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.
CIRCUIT DESCRIPTION OF SWITCH SECTION
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.
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:-
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.
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.
DISPLAYING THE DIALED
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.
DIAGRAM OF IC2 74LS47-DECODER IC FOR SEVEN SEGMENT DISPLAY
AI +5V 16
2 A2 f
4 +5V a
5 +5V b
6 A3 c
7 A0 d
8 GND e
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
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
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
MATERIAL REQUREMENT :-
SOLDERING WIRE FLUX-1
DESOLDERING WICK- 1 Meter
BREAD BOARD- 1
CONNECTING WIRES- ACC. TO
SPEAKER( 8 OHM)-2
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
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.
Optical DATA COMMUNICATION AND CONTROL SYSTEM.
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.
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.