IR-Based Voice Transmitter And Receiver

IR-Based Voice Transmitter And Receiver
     Using this circuit you can communicate with your neighbours wirelessly. Infrared signals are used as the carrier in the circuit. The infrared signals can transmit up to a distance of about 5 meters. The phototransistor of the receiver must be accurately oriented towards the IR beam. If there is any obstruction in the path of the IR beam, no sound will be heard from the receiver.

     IR-BASED VOICE TRANSMITTER AND RECEIVER, the aim of the project is to communicate wirelessly. In this project we are using various transistors, LED, op-amp etc. and we made a detailed study on this so as to effectively use them in our project.

     When ever you want to transmit information from one person to another our equipment i.e. transmitter and receiver is very much useful.
     You may also think a mobile does the same work, but it charges for every second you talk, our system just works like a walky-talky. As a mobile, you need not press the number whom u need to call, if the other person had this equipment, by just pressing a key you will get connected.

     Using this circuit you can communicate with your neighbours wirelessly. The IR led can transmit light up to a distance of about 5 meters. The phototransistor of the receiver must be accurately oriented towards the IR beam. If there is any obstruction in the path of the laser beam, no sound will be heard from the receiver. The transmitter circuit (Fig. 1) comprises condenser microphone transistor amplifier BC548 (T1) followed by an opamp stage built around μA741 (IC1). The gain of the op-amp can be controlled with the help of 1-mega-ohm pot.meter VR1.The AF output from IC1 is coupled to the base of transistor BD139 (T2), which, in turn, modulates the laser beam.
     The transmitter uses 9V power supply. The receiver circuit (Fig. 2) uses an npn phototransistor as the light sensor that is followed by a two-stage transistor preamplifier and LM386-based audio power amplifier. The receiver does not need any complicated alignment. Just keep the phototransistor oriented towards the remote transmitter’s laser point and adjust the volume control for a clear sound. To avoid 50Hz hum noise in the speaker, keep the phototransistor away from AC light sources such as bulbs. The reflected sunlight, however, does not cause any problem. But the sensor should not directly face the sun.

     A Resistor is a two-terminal electronic component designed to oppose an electric current by producing a voltage drop between its terminals in proportion to the current, that is, in accordance with Ohm's law:
V = IR
     Resistors are used as part of electrical networks and electronic circuits. They are extremely commonplace in most electronic equipment. Practical resistors can be made of various compounds and films, as well as resistance wire (wire made of a high-resistivity alloy, such as nickel/chrome).
     The primary characteristics of resistors are their resistance and the power they can dissipate. Other characteristics include temperature coefficient, noise, and inductance. Less well-known is critical resistance, the value below which power dissipation limits the maximum permitted current flow, and above which the limit is applied voltage. Critical resistance depends upon the materials constituting the resistor as well as its physical dimensions; it's determined by design.
     Resistors can be integrated into hybrid and printed circuits, as well as integrated circuits. Size, and position of leads (or terminals) are relevant to equipment designers; resistors must be physically large enough not to overheat when dissipating their power.

Fixed and Variable Resistors
     There are two kinds of resistors, FIXED and VARIABLE. The fixed resistor will have one value and will never change (other than through temperature, age, etc.). The resistors shown in A and B of figure 1-29are classed as fixed resistors. The tapped resistor illustrated in B has several fixed taps and makes more than one resistance value available. The sliding contact resistor shown in C has an adjustable collar that can be moved to tap off any resistance within the ohmic value range of the resistor.
     There are two types of variable resistors, one called a POTENTIOMETER and the other a RHEOSTAT (see views D and E of fig. 1-29.)An example of the potentiometer is the volume control on your radio, and an example of the rheostat is the dimmer control for the dash lights in an automobile. There is a slight difference between them. Rheostats usually have two connections, one fixed and the other moveable. Any variable resistor can properly be called a rheostat. The potentiometer always has three connections, two fixed and one moveable. Generally, the rheostat has a limited range of values and a high current-handling capability. The potentiometer has a wide range of values, but it usually has a limited current-handling capability. Potentiometers are always connected as voltage dividers.

     Capacitors store electric charge. They are used with resistors in timing circuits because it takes time for a capacitor to fill with charge. They are used to smooth varying DC supplies by acting as a reservoir of charge. They are also used in filter circuits because capacitors easily pass AC (changing) signals but they block DC (constant) signals.

     This is a measure of a capacitor's ability to store charge. A large capacitance means that more charge can be stored. Capacitance is measured in farads, symbol F. However 1F is very large, so prefixes are used to show the smaller values.
Three prefixes (multipliers) are used, µ (micro), n (nano) and p (pico):
· µ means 10-6 (millionth), so 1000000µF = 1F
· n means 10-9 (thousand-millionth), so 1000nF = 1µF
· p means 10-12 (million-millionth), so 1000pF = 1nF
     Capacitor values can be very difficult to find because there are many types of capacitor with different labeling systems!
     There are many types of capacitor but they can be split into two groups, polarised and unpolarised. Each group has its own circuit symbol.
Polarised capacitors (large values, 1µF +)
     Electrolytic capacitors are polarised and they must be connected the correct way round, at least one of their leads will be marked + or -. They are not damaged by heat when soldering.
     There are two designs of electrolytic capacitors; axial where the leads are attached to each end (220µF in picture) and radial where both leads are at the same end (10µF in picture). Radial capacitors tend to be a little smaller and they stand upright on the circuit board.
     It is easy to find the value of electrolytic capacitors because they are clearly printed with their capacitance and voltage rating. The voltage rating can be quite low (6V for example) and it should always be checked when selecting an electrolytic capacitor. If the project parts list does not specify a voltage, choose a capacitor with a rating which is greater than the project's power supply voltage. 25V is a sensible minimum most battery circuits.

Use of Infrared Detectors Basics
IR emitter and IR phototransistor
     An infrared emitter is an LED made from gallium arsenide, which emits near-infrared energy at about 880nm.
     The infrared phototransistor acts as a transistor with the base voltage determined by the amount of light hitting the transistor.
     Hence it acts as a variable current source. Greater amount of IR light cause greater currents to flow through the collector-emitter leads.
     IR reflectance sensors contain a matched infrared transmitter and infrared receiver pair.
These devices work by measuring the amount of light that is reflected into the receiver.
Because the receiver also responds to ambient light, the device works best when well shielded from abient light, and when the distance between the sensor and the reflective surface is small(less than 5mm).
     IR reflectance sensors are often used to detect white and black surfaces. White surfaces generally reflect well, while black surfaces reflect poorly. One of such applications is the line follower of a robot.

 Condenser Microphones
     Condenser means capacitor, an electronic component which stores energy in the form of an electrostatic field. The term condenser is actually obsolete but has stuck as the name for this type of microphone, which uses a capacitor to convert acoustical energy into electrical energy.
     Condenser microphones require power from a battery or external source. The resulting audio signal is stronger signal than that from a dynamic. Condensers also tend to be more sensitive and responsive than dynamics, making them well-suited to capturing subtle nuances in a sound. They are not ideal for high-volume work, as their sensitivity makes them prone to distort.

How Condenser Microphones Work:
     A capacitor has two plates with a voltage between them. In the condenser mic, one of these plates is made of very light material and acts as the diaphragm. The diaphragm vibrates when struck by sound waves, changing the distance between the two plates and therefore changing the capacitance. Specifically, when the plates are closer together, capacitance increases and a charge current occurs. When the plates are further apart, capacitance decreases and a discharge current occurs.

The Electret Condenser Microphone
     The electret condenser mic uses a special type of capacitor which has a permanent voltage built in during manufacture. This is somewhat like a permanent magnet, in that it doesn't require any external power for operation. However good electret condenders mics usually include a pre-amplifier which does still require power. Other than this difference, you can think of an electret condenser microphone as being the same as a normal condenser.

Loudspeaker Basics
The loudspeakers are almost always the limiting element on the fidelity of a reproduced sound in either home or theater. The other stages in sound reproduction are mostly electronic, and the electronic components are highly developed. The loudspeaker involves electromechanical processes where the amplified audio signal must move a cone or other mechanical device to produce sound like the original sound wave. This process involves many difficulties, and usually is the most imperfect of the steps in sound reproduction. Choose your speakers carefully. Some basic ideas about speaker enclosures might help with perspective. Once you have chosen a good loudspeaker from a reputable manufacturer and paid a good price for it, you might presume that you would get good sound reproduction from it. But you won't --- not without a good enclosure. The enclosure is an essential part of sound production because of the following problems with a direct radiating loudspeaker:

Loudspeaker Details
     An enormous amount of engineering work has gone into the design of today's dynamic loudspeaker. A light voice coil is mounted so that it can move freely inside the magnetic field of a strong permanent magnet. The speaker cone is attached to the voice coil and attached with a flexible mounting to the outer ring of the speaker support. Because there is a definite "home" or equilibrium position for the speaker cone and there is elasticity of the mounting structure, there is inevitably a free cone resonant frequency like that of a mass on a spring. The frequency can be determined by adjusting the mass and stiffness of the cone and voice coil, and it can be damped and broadened by the nature of the construction, but that natural mechanical frequency of vibration is always there and enhances the frequencies in the frequency range near resonance. Part of the role of a good enclosure is to minimize the impact of this resonant frequency.

 IC LM386:-
     It’s a low voltage Audio power amplifier. The gain is internally set to 20 to keep external part count low, but the addition of an external capacitor and resistor between pins 1 and 8 will increase the gain to any value from 20 to 200.
     The inputs are ground referred while the output automatically biases to one-half the supply voltage. The quiscent power drain is only 24milliwatts when operating froma a 6volts supply, making the LM386 ideal for battery operation.

· Wide supply voltage range: 4v-12v or 5v-18v
· Low quiscent current drain: 4mA
· Voltage drains from 20 to 200
· Ground referred input
· Self-centering output quiscent voltage
· Low distortion: 0.2%
· Available in 8 pin MSOP package

· AM-FM radio amplifiers
· Portable tape player amplifiers
· TV sound systems
· Line drivers
· Ultra sonic drivers
· Small servo drivers
· Power converters

     Hence we conclude that by using our equipment there is easy transmission and receiving of information for a short range of distance. The distance can be increased by using lasers instead of IR devices. More over we got to have a practical overview of what we studied so far in our curriculum.

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