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 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.
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Fig 1.1 Transmitter Circuit
Fig 1.2 Receiver Circuit
Fig 1.3 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 pin2 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 milli volts. 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 ntype 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 doping 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 5.6V 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 semiconducting 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
Ø Peak Wavelength 940 nm
Ø Spectral Bandwidth 45 nm
Ø Half Angle Beam Width +/- 30 degrees (60 degrees total)
Ø Package T1-3/4 (5mm)
Ø Max Current: 100 mA
Ø Breakdown Voltage 5V
Ø Forward Voltage 1.4V-1.5V
Ø Power Dissipation 150 mW
Fig 4.7 IR Led
Fig 4.8 Circuit Showing Typical 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
Ø Battery operation
Ø Minimum external parts
Ø Wide supply voltage range: 4V–12V or 5V–18V
Ø Low quiescent current drain: 4mA
Ø Voltage gains from 20 to 200
Ø Ground referenced input
Ø Self-centering output quiescent voltage
Ø Low distortion: 0.2% (AV = 20, VS = 6V, RL = 8, PO =125mW, f = 1kHz)
Ø Available in 8 pin MSOP package
4.8.3 Applications
Ø AM-FM radio amplifiers
Ø Portable tape player amplifiers
Ø Intercoms
Ø TV sound systems
Ø Line drivers
Ø Ultrasonic drivers
Ø Small servo driver
Ø 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
| component | Pin1 | Pin2 | Pin3 |
| IC UM 666 | output | +Vcc | -Vcc |
| BC548b | emitter | base | collector |
Table 4.1 Pin Description
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 its 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 = s . IB amperes pass between C et E (fig. 3). In this case, s 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
Ø Never connect the IC in reverse supply connection.
Ø The music depends on the part number of the IC.
Ø The transistor are should be connected in proper pin configuration.
Ø The recommended power supply is battery of 3 volt.
Ø 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.
8. 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.
9. References
1. G-QRP Club Circuit Handbook
2. WIA Book
3. ARRL/RSGB Handbooks
4. www.electronics4ru.com
5. www.techxite.pratt.duke.edu
6. www.electrotechonline.com
