1. Introduction

Using this circuit, audio musical notes can be generated and can be heard up to

a distance of 10 meters. The receiver can be placed at a maximum distance of 1 meter

from the transmitter without any considerable noise interference. The circuits of

transmitter and receiver are quite simple and can be placed and carried any where

easily. The small apparatus provided with the infrared communication function is in

many cases operated by a battery incorporated inside so that it is convenient when a

user carries it during movement, and it is preferable that power consumption be

minimized also to lengthen the continuous operation possible time of IR emission is

optimized. Here there is no use of any modulation techniques when working with IR

rays. Hence there is no necessity of carrier generation. This makes the transmitter and

receiver designs much simpler. However the communication distance can be

improved by using Far IR LEDs. The range of communication can be increased to

about 250 meters by using far IR LEDs. In the apparatus provided with a conventional

infrared communication function, however, the infrared light with a constant intensity

is constantly radiated regardless of the communication distance. This project

emphasizes the way by which music is generated and driven by IR rays and gives an

explanation to the one of the methods of receiving IR rays without considerable noise

interference.

.

Fig 1.1 Transmitter Circuit

Fig 1.2 Receiver Circuit

Fig 1.3 Practical model of IR music transmitter

Fig 1.4 Practical model on project board

Fig 1.5 Optimized transmiter circuit that uses a portable music player

to test the circuit

2. Circuit description

The circuit can be divided into two parts: IR music transmitter and receiver.

The IR music transmitter works off a 9V battery, while the IR music receiver works

off regulated 9V to 12V. Fig. 1.1 shows the circuit of the IR music transmitter. It uses

popular melody generator IC UM66 (IC1) that can continuously generate musical

tones. The output of IC1 is fed to the IR driver stage (built across the transistors T1

and T2) to get the maximum range. Here the red LED (LED1) flickers according to

the musical tones generated by UM66 IC, indicating modulation. IR LED2 and LED3

are infrared transmitting LEDs. For maximum sound transmission these should be

oriented towards IR phototransistor L14F1 (T3). The IR music receiver uses popular

op-amp IC μA741 and audio-frequency amplifier IC LM386 along with

phototransistor L14F1 and some discrete components. The melody generated by IC

UM66 is transmitted through IR LEDs, received by phototransistor T3 and fed to pin

2 of IC μA741 (IC2). Its gain can be varied using potential meter VR1. The output of

IC μA741 is fed to IC LM386 (IC3) via capacitor C5 and potential meter VR2.The

melody produced is heard through the receiver’s loudspeaker.

Potential meter VR2 is used to control the volume of loudspeaker LS1 (8-ohm, 1W).

Switching off the power supply stops melody generation.

3. Working

• The electrical signal from your music player is converted into an invisible

infrared light signal by the infrared light emitting diode (IR LED) in the transmitter

circuit.

• To transmit this over a longer distance, a brighter IR LED is needed or an

invisible light is to be focused using lens. The invisible infrared light signal must hit

the photo transistor in the receiver.

• The photo transistor in the receiver converts this invisible infrared light signal

into an electrical signal.

• Then, the amplifier in the receiver circuit takes this electrical signal and makes

it larger using energy from the battery.

• Finally, this larger electrical signal drives the speaker which turns electrical

energy into sound energy.

4. Descriptions of the components used

4.1 Power supply

Fig 4.1 Battery

A nine-volt battery, sometimes referred to as a PP3 battery, is shaped as a

rounded rectangular prism and has a nominal output of nine volts. Its nominal

dimensions are 48 mm × 25 mm × 15 mm (ANSI standard 1604A).

•

4.1.1 Uses

9v batteries are commonly used in smoke detectors, guitar effect units, pocket

radios, and radio-controlled vehicle controllers. They are also utilized as backup

power to keep the time in digital clocks and alarm clocks.

4.1.2 Connectors

PP3 actually refers to the type of connection or snap that is on top of the

battery . The PP3 connector (snap) consists of two connectors: one smaller circular

(male) and one larger, typically either hexagonal or octagonal (female). The

connectors on the battery are the same as on the connector itself -- the smaller one

connects to the larger one and vice versa. 6 AAAA batteries may be found inside

when the battery is open. By cutting the 6 metal strips inside found on the bottom and

top, you can use them in a device that uses AAAA batteries. However, not all

manufacturers use AAAA batteries (namely: Rayovac), but stack six small

rectangular batteries for the same effect.

Check each multimeter and 9 V battery by turning the knob of the multimeter

to the 20 V DC setting and touching the probes to the battery terminals. The

multimeter should read more than 8.7 V. If the multimeter reads less than 8.7 V, try a

second meter. If that still reads less than 8.7 V, try a new battery.

4.2 IC 741

4.2.1 Description

A very typical commercial IC op amp circuit is the 741. This IC has been

available for many years, and a number of variations have been developed to help

minimize the errors inherent in its construction and operation. Nevertheless, the

analysis we will perform here using the 741 will apply to any other IC op amp, if this

has been taken into account the actual parameters of the device you are actually using.

Therefore, 741 is used as our example IC op amp.

4.2.2 Circuit Working

Fig 4.2 Circuit using the 741 op amp IC

Above is a circuit using the 741 op amp IC, with the input and feedback resistors that

are required for this circuit to operate properly in an analog computer. Note that there

are actually two inputs to the amplifier, designated "+" and "-" in the figure. This is

because the 741, like all IC op amps of this type, is in fact a differential amplifier.

Thus, the output voltage is determined by the difference between the two input

voltages. The "+," or non-inverting input, is grounded through a resistor as shown.

Thus, its input voltage is always zero. The "-," or inverting input, is the one that is

actively used. Thus, we establish that the inverting input, which is also the junction of

the input and feedback resistors, must operate as a virtual ground in order to keep the

output voltage within bounds.

Now considering the actual voltage gain which can't possibly be infinite, and if it

isn't infinite, there must be some non-zero input voltage to produce a non-zero output

voltage. In fact, the typical open-loop voltage gain for the 741 is 200,000. This does

not mean that every such device has a gain of 200,000, however. It is guaranteed that

the commercial version (the 741C) will have a minimum gain of 20,000. The military

version is more stringently selected, and will have a minimum voltage gain of 50,000.

For the 741C, then, with a maximum output voltage of ±10 volts, the maximum

input voltage required at the inverting input can never be more than ±10/20,000 =

±0.0005 volt, or 0.5 millivolts. Typical measurement accuracy uses three significant

digits, so we would measure voltages from 0.00 volts to ±10.00 volts. The maximum

input voltage is more than an order of magnitude smaller than this, and hence is

insignificant in a typical analog computer.

But what about input bias current? Surely the IC requires at least some small

amount of input current? Well, yes, it does. The 741C requires a typical input bias

current of 80 nA (that's nanoAmperes, where 1 nA = 10-9 A). The maximum input

bias current for the 741C is 500 nA, or 0.5 µA.

This information is used to minimize the errors it could cause into insignificance

Well, let's consider the resistance that would be required for this current to cause a

significant voltage drop. If we keep the voltage error small enough, we can ignore it

as immeasurable. This means we must keep the values of Rin and Rf as small as

possible, consistent with proper operation of the circuit. At the same time, we cannot

make them too small, or the op amp itself will be overloaded. For proper operation,

the total load resistance at the 741 output should not be smaller than 2000 ohms, or

2k. This amounts to a maximum output current of 5 mA at 10 volts output.

This means that the output resistance of the op amp is not the desired zero ohms.

However, too much current can’t be drawn from the output, the use of heavy negative

feedback has an added benefit it makes the op amp behave as if it had zero output

resistance. That is, any internal resistance will simply mean that the op amp must

produce an internal voltage enough higher than the calculated value so that the final

output voltage will be the calculated value.

If we make our input and feedback resistors about 10k each then the current

demand on the output is only 1 mA at 10 volts, leaving plenty of capacity for

additional inputs. And the voltage caused by the input bias current won't exceed

10,000 × 0.5 × 10-6 = 0.005 volt. This is half of the least significant digit of our

measurement capability, which is not as good as expected, but will do. Also, this is

the absolute worst-case situation; most practical applications won't see an error this

big.

In addition, the input bias current applies equally to both inputs. This is the reason

for the resistor connecting the "+" input to ground. If this resistor is close in value to

the parallel combination of Rin and Rf, the same voltage error will be generated at the

two inputs, and will therefore be cancelled out, or very nearly. Thus, this problem can

be relegated to true insignificance by means of correct circuit design and careful

choice of component values.

The 741 does also have two error characteristics, called input offset voltage and

input offset current, which define the inherent errors which may exist between the two

inputs to the IC. However, the 741 also has the means for balancing these variations

out, so the actual errors are minimized or eliminated, thus once again removing them

from significance.

A problem with any op amp is a limited frequency response. The higher the gain of

the complete circuit, the lower the working frequency response. This is one reason an

overall gain of 20 is a practical limit. (Another reason is that the input and feedback

resistors become too different from each other.) Also, the standard 741 has a slew rate

of 0.5 v/µs. This means that the output voltage cannot change any faster than this. The

newer generation of op amps, such as the 741S, has a slew rate more like 5 v/µs, and

hence can operate over the entire audio range of frequencies without serious

problems.

4.3 Zener diode

Fig 4.3 Zener diode

Fig 4.4 Zener diode schematic symbol

4.3.1 Introduction

A Zener diode is a type of diode that permits current in the forward direction like a

normal diode, but also in the reverse direction if the voltage is larger than the

breakdown voltage known as "Zener knee voltage" or "Zener voltage". The device

was named after Clarence Zener, who discovered this electrical property.

A conventional solid-state diode will not allow significant current if it is reverse-

biased below its reverse breakdown voltage. When the reverse bias breakdown

voltage is exceeded, a conventional diode is subject to high current due to avalanche

breakdown. Unless this current is limited by external circuitry, the diode will be

permanently damaged. In case of large forward bias (current in the direction of the

arrow), the diode exhibits a voltage drop due to its junction built-in voltage and

internal resistance. The amount of the voltage drop depends on the semiconductor

material and the doping concentrations.

4.3.2 Working

A Zener diode exhibits almost the same properties, except the device is specially

designed so as to have a greatly reduced breakdown voltage, the so-called Zener

voltage. A Zener diode contains a heavily doped p-n junction allowing electrons to

tunnel from the valence band of the p-type material to the conduction band of the n-

type material. In the atomic scale, this tunneling corresponds to the transport of

valence band electrons into the empty conduction band states; as a result of the

reduced barrier between these bands and high electric fields that are induced due to

the relatively high levels of dopings on both sides. A reverse-biased Zener diode will

exhibit a controlled breakdown and allow the current to keep the voltage across the

Zener diode at the Zener voltage. For example, a diode with a Zener breakdown

voltage of 3.2 V will exhibit a voltage drop of 3.2 V if reverse bias voltage applied

across it is more than its Zener voltage. However, the current is not unlimited, so the

Zener diode is typically used to generate a reference voltage for an amplifier stage, or

as a voltage stabilizer for low-current applications.

The breakdown voltage can be controlled quite accurately in the doping process.

While tolerances within 0.05% are available, the most widely used tolerances are 5%

and 10%.

Another mechanism that produces a similar effect is the avalanche effect as in the

avalanche diode. The two types of diode are in fact constructed the same way and

both effects are present in diodes of this type. In silicon diodes up to about 5.6 volts,

the Zener effect is the predominant effect and shows a marked negative temperature

coefficient. Above 5.6 volts, the avalanche effect becomes predominant and exhibits a

positive temperature coefficient.

In a 5.6 V diode, the two effects occur together and their temperature coefficients

neatly cancel each other out, thus the 5.6 V diode is the component of choice in

temperature-critical applications.

Modern manufacturing techniques have produced devices with voltages lower than

5.6 V with negligible temperature coefficients, but as higher voltage devices are

encountered, the temperature coefficient rises dramatically. A 75 V diode has 10

times the coefficient of a 12 V diode. All such diodes, regardless of breakdown

voltage, are usually marketed under the umbrella term of "Zener diode".

4.3.3 Uses

Zener diodes are widely used to regulate the voltage across a circuit. When

connected in parallel with a variable voltage source so that it is reverse biased, a

Zener diode conducts when the voltage reaches the diode's reverse breakdown

voltage. From that point it keeps the voltage at that value.

4.4 Light-emitting diode LED

Fig 4.5 LED

Blue, green, and red LEDs; these can be combined to produce most perceptible colors,

including white. Infrared and ultraviolet (UVA) LEDs are also available.

Fig 4.6 LED schematic symbol

.

4.4.1 Introduction

A light-emitting-diode (LED) is a semiconductor diode that emits light when

an electric current is applied in the forward direction of the device, as in the simple

LED circuit. The effect is a form of electroluminescence where incoherent and

narrow-spectrum light is emitted from the p-n junction in a solid state material.

4.4.2 Uses

LEDs are widely used as indicator lights on electronic devices and

increasingly in higher power applications such as flashlights and area lighting. An

LED is usually a small area (less than 1 mm2) light source, often with optics added

directly on top of the chip to shape its radiation pattern and assist in reflection. The

color of the emitted light depends on the composition and condition of the semi

conducting material used, and can be infrared, visible, or ultraviolet. Besides lighting,

interesting applications include using UV-LEDs for sterilization of water and

disinfection of devices, and as a grow light to enhance photosynthesis in plants.

4.5. Infrared LED Emitter

4.5.1 Introduction

The infrared LED emitter is a high power (150 mW) infrared LED that is

commonly used in a wide variety of remote control and communications projects. It's

wide 60 degree beam width and high output power make it a great infrared

transmitter. Combined with the PNA4602M IR receiver and you have the makings for

a solid IR communications or control link (See the related products section for the

PNA4602).

4.5.2 Specifications

• Peak Wavelength 940 nm

• Spectral Bandwidth 45 nm

• Half Angle Beam Width +/- 30 degrees (60 degrees total)

• Package T1-3/4 (5mm)

• Max Current: 100 mA

• Breakdown Voltage 5V

• Forward Voltage 1.4V-1.5V

• Power Dissipation 150 mW

Fig 4.7 IR Led

Fig 4.8 Circuit ShowingTypical Usage of LED

4.6 Use of Infrared Detectors Basics

Fig 4.9 Detector and Emitter

Fig 4.10 IR Phototransistor

4.6.1 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.

4.6.2 Working

As shown in the diagram below, the phototransistor is wired in a similar

configuration to the voltage divider. The variable current traveling through the resistor

causes a voltage drop in the pull-up resistor. This voltage is measured as the output of

the device.

Fig 4.11 Circuits of IR emitter and IR Phototransistor

Fig 4.12 Circuit diagram of an infrared reflectance sensor

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 ambient 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.

Fig 4.13 Schematic Diagram for a Single Pair of Infrared Transmitter

and Receiver

4.7 Loudspeaker Basics

Fig 4.14 Loudspeaker

4.7.1 Introduction

A loudspeaker (or "speaker") is an electro acoustical transducer that converts

an electrical signal to sound. The speaker pushes the air in accordance with the

variations of an electrical signal and causes sound waves to propagate.

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.

If a good loudspeaker is chosen from a reputable manufacturer and paid a

good price for it, then it will be presumed that good sounds can be reproduction from

it. But it is not without a good enclosure. The enclosure is an essential part of sound

production because of the following problems with a direct radiating loudspeaker:

Fig 4.15 Loudspeaker Details

4.7.2 Construction

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.

4.8 LM386

4.8.1 General Description

The LM386 is a power amplifier designed for use in low voltage consumer

applications. The gain is internally set to 20 to keep external part count low, but the

addition of an external resistor and capacitor between pins 1 and 8 will increase the

gain to any value from 20 to 200. The inputs are ground referenced while the output

automatically biases to one-half the supply voltage. The quiescent power drain is only

24 mill watts when operating from a 6 volt supply, making the LM386 ideal for

battery operation.

4.8.2 Features

• Battery operation

• Minimum external parts

• Wide supply voltage range: 4V–12V or 5V–18V

• Low quiescent current drain: 4mA

• Voltage gains from 20 to 200

• Ground referenced input

• Self-centering output quiescent voltage

• Low distortion: 0.2% (AV = 20, VS = 6V, RL = 8 , PO =125mW, f = 1kHz)

• Available in 8 pin MSOP package

4.8.3 Applications

• AM-FM radio amplifiers

• Portable tape player amplifiers

• Intercoms

• TV sound systems

• Line drivers

• Ultrasonic drivers

• Small servo driver

• Power converters

4.8.4 IC LM 386

In a previous article building audio amplifiers using discrete transistors are

discussed. While it is possible to build good audio amplifiers from discrete transistors,

they are no match for the many audio amps IC are available to us. IC’s offer many

advantages including high efficiency, high gain, low standby current, low component

count, small size and of course, low cost. It is little wonder that audio amp IC’s have

replaced discrete transistors in most consumer electronic devices. While many

experimenters have stayed away from these little black mysteries, I am going to

uncover some of their secrets and demonstrate how easy they are to use. Here an

LM386 IC will be used. The LM386 comes in 3 flavors now; LM386-1, LM386-2,

LM386-3 with output power levels of 300, 500 and 700 mille watts respectively. The

type sold by Radio Shack is the LM386-1 and is the one we used in this circuit.

Perhaps the most unique feature is that it is available at any Radio Shack and can

operate at voltages as low as 5 volts. Just like regular op amps, audio amp IC’s have

an inverting and non- inverting input. Input signals are normally fed to the non-

inverting input while the inverting input is normally tied to ground. Because of the

high gain of IC audio amps, it is highly recommended to isolate them from the power

supply to prevent oscillations. In this circuit, R1 and C1 accomplish this task very

well. Resistor R3 controls the gain and Capacitor C3 couples the output to the

speaker. Output capacitor coupling is mandatory in just about all IC audio amp

designs.

The LM386 IC is unique in that the gain can be modified by changing Resistor

R2 and Capacitor C2. This configuration will give us a gain of 20. By removing R2

and connecting C2 across pins 1 and 8, we can increase the gain to 200. It is important

to understand that increasing the gain does not increase the output power. The

increased gain is only used when a very low input signal is to be amplified. Our next

IC is the LM380 and it also comes in two flavors; LM380-8 and LM380 with output

powers of 700 mille-watts and 2 watts respectively. Figure depicts the LM380-8 and

Figure 3 depicts the LM380. The LM380-8 comes in an 8 pin package and its basic

circuit is virtually identical to the LM380 except for the different pin out. The LM380

comes in a 14 pin package and pins 3,4,5,10,11 and 13 are connected to ground to act

as a heat sink. Experience has shown the LM380 should be soldered directly to the

circuit board (no IC socket) if it is going to be operated at its full rated 2 watt output.

This IC can become quite warm and it’s important to get rid of excess heat through

the pins. The primary advantages of the LM380 series IC’s are higher output power,

very low distortion and low external parts count.

4.9 Melody Generator using IC UM66

4.9.1 Introduction

This is the simplest ever musical calling bell that can be easily built. It uses the

musical 3 pin IC UM66 and a popularly known Transistor BC548b. The circuit can be

made even without soldering and the ideal for the first electronic project for newbie’s.

Here the musical IC UM66 generates the music when it receives supply and drives a

small speaker through a class c amplifier using silicon transistor BC548b.

Fig 4.16 Connection Diagram

The battery supply should be kept in a battery container to ensure the

connection. The volume of the sound of this circuit is so much that it can be used as a

calling bell. To reduce the volume of the circuit then a resistance is inserted in place

of the blue line connection. In this circuit please don't give the supply beyond 3 volt

without modification as the IC may get damaged. It is better that you should not run

this circuit in Eliminator as most of the available eliminator don't have a good filter

built in and have no precision over voltage protection.

The circuit should not be run in Rechargeable battery also if the Speaker resistance is

less than 8 Ohm and may burn the Transistor.

4.9.2 Component Description

Fig 4.17 Pin configuration

Table 4.1 Pin Description

Component Pin1 Pin2 Pin3

ICUM66 Output +Vcc -Vcc

BC548b Emitter Base Collector

Fig 4.18 Music generator using UM66 IC

UM66 is a pleasing music generator IC which works on a supply voltage of

3V. The required 3V supply is given through a zener regulator it’s output is taken

from the pin no1 and is given to a push pull amplifier to drive the low impedance loud

speaker. A class A amplifier before push pull amplifier can be used to decrease the

noise and improve output. UM66 is a 3 pin IC package just looks like a BC 547

transistor.

4.10 Rheostat

Fig 4.19 Rheostat

4.10.1 Introduction

The most common way to vary the resistance in a circuit is to use a variable

resistor or a rheostat. A rheostat is a two-terminal variable resistor. Often these are

designed to handle much higher voltage and current. Typically these are constructed

as a resistive wire wrapped to form a toroid coil with the wiper moving over the upper

surface of the toroid, sliding from one turn of the wire to the next. Sometimes a

rheostat is made from resistance wire wound on a heat-resisting cylinder with the

slider made from a number of metal fingers that grip lightly onto a small portion of

the turns of resistance wire. The 'fingers' can be moved along the coil of resistance

wire by a sliding knob thus changing the 'tapping' point. They are usually used as

variable resistors rather than variable potential dividers. Any three-terminal

potentiometer can be used as a two-terminal variable resistor, by not connecting to the

third terminal. It is common practice to connect the wiper terminal to the unused end

of the resistance track to reduce the amount of resistance variation caused by dirt on

the track.

4.10.2 Rheostat Construction

Most rheostats are the wire-wound type that has a long length of conductive

wire coiled into a tight spiral. The linear type has a straight coil while the rotary type

has the coil curved into a torus to save space. The coil and contacts are sealed inside

the case to protect them from dirt which can cause an open circuit, and from moisture

which can cause a short circuit. Rheostats can be made from other materials such as

carbon disks, metal ribbons, and even certain fluids. As long as a material has a

significant resistance change over a short length, it can probably be used to make a

rheostat.

4.10.3 Working

The basic principle used by rheostats is Ohm's law, which state that current is

inversely proportional to resistance for a given voltage. This means the current

decreases as the resistance increases, or it increases as the resistance decreases.

Current enters the rheostat through one of its terminals, flows through the wire coil

and contact, and exits through the other terminal. Rheostats do not have polarity and

operate the same when the terminals are reversed. Three-terminal potentiometers can

be used as rheostats by connecting the unused third terminal to the contact terminal.

4.10.4 Applications

Some light dimmers use rheostats to limit the current passing through the light

bulbs in order to change their brightness. The greater the resistance of the rheostat, the

lower the brightness of the light bulbs. Some lights cannot use dimmers, such as

fluorescents and gas-discharge lamps. These lights have large resistance loads, called

ballasts that maintain a constant current through them. Rheostats have no effect on

their brightness and can even damage them.

Motor controller also uses rheostats to control the speed of a motor by limiting

the flow of current through them. They are used in many small appliances such as

blenders, mixers, fans, and power tools. Rheostats are also used as test instruments to

provide an accurate resistance value. While rheostats can be used to control electric

ovens and cook tops, thermostats are preferred because they have additional parts

which automatically adjust the current flow to maintain a constant temperature.

The rheostat is still a common and fundamental electronic component used to

control the flow of current in a circuit. However, it has largely been replaced by the

triac, a solid-state device also known as a silicon controlled rectifier (SCR). A triac do

not waste as much power as a rheostat and has better reliability due to the absence of

mechanical parts. Rheostats commonly fail because their contacts become dirty or the

coil wire corrodes and breaks.

4.11 Transistor

4.11.1 Introduction

The transistor is a component with 3 electric wires coming out of it. They are named

B (base), C (collector), and E (emitter).

This is a drawing of the BC 547 transistor, four times bigger:

Fig 4.20 Pin configuration

Such a transistor costs $0.3 in electric components stores.

Here is a classic drawing for a transistor inside electronic diagrams:

Fig 4.21 Symbol of BC 547

4.11.2 Working

• If one connects a tension source between the wires C and E, the transistor will

not let any current trough.

• But between B and E there is a shortcut. If one wants to make a given current

go through B and E, one must use a tension source and a resistor (fig. 2).

• If one sends a current of IB amperes between B and E, then the resistor will

allow a current of IC = ß . IB amperes pass between C et E (fig. 3). In this case,

ß is about 100.

The electronic diagrams corresponding to figures 1, 2 and 3 are figures 4, 5 and 6:

Note: For those who would like to try out these diagrams, one sole battery of 9 Volts

can replace the two batteries

4.12 Capacitors

Fig 4.22 Capacitors

4.12.1 Function

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.

4.12.2 Capacitance

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, polarized

and unpolarized. Each group has its own circuit symbol.

Polarized capacitors (large values, 1µF +)

Examples:

Fig 4.23 Schematic of Polarised and unpolarised Capacitors

4.12.3 Electrolytic Capacitors

Fig 4.24 Electrolytic Capacitor

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.

4.12.4 Variable capacitors

Variable capacitors are mostly used in radio tuning circuits and they are sometimes

called 'tuning capacitors'. They have very small capacitance values, typically between

100pF and 500pF (100pF = 0.0001µF). The type illustrated usually has trimmers built

in (for making small adjustments - see below) as well as the main variable capacitor.

Many variable capacitors have very short spindles which are not suitable for the

standard knobs used for variable resistors and rotary switches. It would be wise to

check that a suitable knob is available before ordering a variable capacitor.

Variable capacitors are not normally used in timing circuits because their

capacitance is too small to be practical and the range of values available is very

limited. Instead timing circuits use a fixed capacitor and a variable resistor if it is

necessary to vary the time period.

Fig 4.25 Variable Capacitor Symbol

fig 4.26 Variable Capacitor

4.13 Resistors

Fig 4.27 Resistors

A resistor is a two-terminal electronic component that produces a voltage across its

terminals that is proportional to the electric current through it in accordance with

Ohm's law:

V = IR

Resistors are elements of electrical networks and electronic circuits and are

ubiquitous 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 a resistor are the resistance, the tolerance, maximum

working voltage and the power rating. 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.

5. Points of importance

• Never connect the IC in reverse supply connection.

• The music depends on the part number of the IC.

• The transistor are should be connected in proper pin configuration.

• The recommended power supply is battery of 3 volt.

• The speaker and resistance have no terminal polarity and connection can be

interchanged.

6. Modifications

6.1 For supply voltage difference

The IC positive point should be biased with potential divider such that the

voltage at the positive in should not exceed 2.5 volt. For example it should be 68k and

10k and the terminal voltage will be 1.82 volt. Sometimes the IC is supplied only

through a very high value series resistance like 220k from 12 volt, but the output bias

current of the IC will not be sufficient then to drive and works as a signal and can

only be driven through preamplifier or using Darlington pair/Zhikli pair as buffer.

6.2 To limit speaker current/reduce volume

The speaker current can be limited using series resistance in blue line such that

the base current as well as collector current (i. e. Speaker current also). The formula is

R={(Vcc-Vee)-.05}*[ratio of potential divider if used]*b/Ispk. Ispk=Speaker Current,

b= hFE of the transistor

6.3 To Increase volume/Protection of Transistor

The current carrying capacity can be increased using Darlington pair with

Power transistor to increase volume.

7. Applications

Today everyone is looking for portability of electronic gadgets. The IR rays

communication can play a crucial role in developing such wireless gadgets. Here are a

few gadgets that can be built using IR transmission and reception systems.

7.1 Wireless music systems

The principle used in above circuits can be used in wireless music systems.

The speakers that we use today in our desktop computers can be made wireless by

using infrared ray transmission. This increases the portability of the audio systems

and in fact a desktop computer can be used as disc-man in our room.

7.2 Mobile gadgets

The same principle of IR audio Transmission can be used in cord less

earphones which can be very useful especially when you are driving.

Fig 7.1 Wireless Infrared earphones

7.3 CC Cameras

IR ray transmission can be employed in microphones that can be used in cc

cameras. This reduces the complexity to a great extent. The audio systems that are

employed today for security purposes in cc cameras can be replaced with IR

transmission systems which are quite simple and easy to handle.

Fig 7.2 Latest Infrared CC Camera

7.4 RF-Link AVS-5811 5.8 GHz Wireless PAL Audio/Video

Transmitter and Receiver System - Built-in IR Remote Extender

The RF-Link AVS-5811 5.8GHz wireless PAL video/audio sender consists of one

transmitter and one receiver. This device transmits wirelessly vivid video and hi-fi

stereo sound from a VCR, TV set, LD, DVD, and VCD, Satellite Receiver or cable set

top box to any TV or monitor. It can also be used in conjunction with a camcorder or

CCD camera and turns into a wireless security monitoring system. As to the

transmission capability, the signal can go up to 300 feet clear light-of-sight and even

penetrate wall. With the built-in IR remote extender, it allows the user to remotely

control the audio/video sources in the other rooms. In addition, four user selectable

channels allow multiple transmitters to multiple receivers operation in the same area.

All these advanced features will make your home life with amazing convenience and

joy.

• Avoid the interference from crowded 2.4GHz ISM band applications such as Video

Sender, 802.11b Wireless LAN, Bluetooth, Cordless Phone, Microwave Oven, etc.

• 5.8 GHz wireless transmitter and receiver with 4 selectable channels.

• Transmitting and receiving of crisp video and hi-fi stereo even through walls.

• Long transmission range up to 300 feet clear line-of-sight. PAL video format.

Fig 7.3 Wireless PAL Audio/video Transmitter and Receiver system

7.5 X-10 Powermid Receivers and Transmitter IR Remote Control

Extender

Fig 7.4 powermid Receiver and Transmitter IR Remote Control Extender

7.5.1 Description

Easily change channels from any room in your home! The Wireless Remote

SENDER is the missing link in your home. Have you ever wished your infrared

remote control could transmit through walls? Now it can. Simply place the transmitter

in another room and place the receiver anywhere in the room where the equipment

you want to control is located. The transmitter receives the infrared (IR) signals from

your remote control and converts them into a radio frequency signal. This signal

penetrates walls and is picked up by the Receiver. The receiver then converts the

signal back into an IR signal and sends the command to the equipment being

controlled.

Conclusion

IR ray communication is very easy to understand and simple to implement. It

finds various applications in short distance field of communications. It is one of the

best ways of building wireless gadgets. In future there is scope of building virtual

environment using the principles of IR ray transmission and reception. Virtual gaming

which also employs IR reception techniques is still in research process which is soon

going to rule the world of gaming.

References

1. G-QRP Club Circuit Handbook

2. WIA Book

3. ARRL/RSGB Handbooks

4. www.electronicsfo ru.com

5. www.techxcite.pratt.duke.edu

6. www.electrotechonline.com