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A REPORT ON SIMPLE F.M. TRANSMITTER CIRCUIT

INTRODUCTION: A FM transmitter circuit is one which is used to transmit signals which are frequency modulated. This is a simple two transistor FM transmitter circuit. The frequency depends on the value of capacitor and inductors.

WORKING:The first stage of the circuit is a preamplifier stage based on transistor Q1. This is a collector to base biased amplifier stage where resistor R2 sets the collector current and R1 provided the necessary collector to base bias. C1 is the input DC decoupling capacitor which couples the input audio signal to the Q1 base. C8 is the power supply by-pass capacitor. Next stage is the oscillator cum modulator stage built around transistor Q2. Electrolytic capacitor C2 couples the output of the first stage to the second stage. R3 and R4 are the biasing resistors of Q2. R5 is the emitter resistor of Q2. Inductor L1 and trimmer capacitor C5 forms the tank circuit which is necessary for creating oscillations. The modulated FM signal is available at the collector of Q2 and it is coupled to the antenna using capacitor C9.

REQUIREMENTS:

1. Resistors
2. Capacitors
3. Antenna
4. Transistor
5. Inductor
6. Power supply

CIRCUIT DIAGRAM:

    

MODIFICATION: Can use different values of capacitor and inductor to increase and decrease the frequency of the transmitter.

APPLICATIONS: It can be widely used in wireless communication and also for wireless data transmission.

A REPORT ON SELECTIVE TIMER ALARM

INRTODUCTION: A selective timer alarm is a device which is used to ring the alarm after a selective period of time. This types of alarms system are mainly used by people as their sleeping alarms and also as remainders. The timing of the alarm can be set manually by the user of the alarm. The alarm also consist of a indicator (led) which emit light until we manually switch off it.

COMPONENTS REQUIRED:

1. The display which is used to set the the alarm time.
2. A delay IC.
3. LED
4. Switches
5. Buzzer
6. Power supply

WORKING: First we have to set the alarm then only we can only ring the alarm. We can also reset the alarm using the reset button. When the ringing time of the alarm occur the IC get the input and transfer it to the alarm indicator and buzzer as a result of this the alarm sounds till we don’t close it or switch off it.

CIRCUIT DIAGRAM:

                              

APPLICATION :This circuit consist of a lower number number of component so it is less costly and also small in size. Can be used as alarm systems in houses and industry.

A REPORT ON 12VOLT DC TO 120 V AC INVERTER

INTRODUCTION: This device will convert 12v DC supply to 120v AC supply.

REQUIREMENT:

1. resistances
2. capacitors
3. transformer
4. transistors

WORKING:Q1 and Q2, as well as T1, determine how much wattage the inverter can supply. With Q1,Q2=2N3055 and T1= 15 A, the inverter can supply about 300 watts. Larger transformers and more powerful transistors can be substituted for T1, Q1 and Q2 for more power. Since this circuit produces 120 V AC.

CIRCUIT DIAGRAM:

MODIFICATION: The IC 4047 can also be used for this purpose.

APPLICATION: Use in industry ,houses,offices and etc.

A REPORT ON BATTERY CHARGER CIRCUIT

USING LM317

INTRODUCTION: The battery charger circuit can be used to charge batteries. The circuit is quite small and cheap. The circuit can be used to charge 12Vlead acid batteries. IC LM 317 ,which is an adjustable voltage regulator IC.

WORKING: The pin 1 of the IC is the control pin which is used to control the charging voltage. The pin 2 is the output pin. Pin 3 is the input pin to which the regulated DC supply is given.
The charging voltage and current is controlled by the Transistor Q1,resistor R1. When the battery is first connected to the charging terminals ,the current through R1 increases. This in turn increases the current and voltage from LM 317. When the battery get charged the charger reduces the charging. The capacitor are used for filtering operation and also they do not allow the AC to pass though it which finally got ground. The require DC is used at the output of the charger to charge the batteries.

REQUIREMENT:

1. IC LM 317
2. Resistors
3. Capacitors
4. Transistor

CIRCUIT DIAGRAM:

                                     

MODIFICATION: -LM117,LM317A can also be used to instead of LM317.

APPLICATION: This types of battery chargers are used for charging the electronic devices having batteries, also this circuit can also be implemented as charging circuit for other devices according to the requirement of output device to be charged.

A REPORT ON BATTERY OPERATED HEATER

INTRODUCTION: The heater is a device which emit heat when current passes through the coils so connected. It works on the heating effect of the current. Here in the circuit heater that can be operated from a 12V battery.

WORKING: The first part of the circuit is an astable multivibrator consisting of two transistors Q1 and Q2 .The ON time of transistor Q1 and Q2 is set different. The output pulses at the collector of Q2 is used to drive the Darlington power transistor Q3. The transistor Q3 drives the heating elements L1 to L3.The net heat produced can be varied by selecting the desired combination of heating elements at the output. The net heat can be also varied by varying the duty cycle of the triggering pulse using potentiometer. The heat can also controlled by using the switches S1 and S2.

REQUIREMENT:

1. Transistors
2. Capacitors
3. Resistors
4. Potentiometer
5. LED
6. Inductors
7. Power supply

CIRCUIT DIAGRAM:

                                          

MODIFICATION: Instead of astable we can use other configuration which result in different output power or variable output power.

APPLICATIONS: As the name suggest it can be used in houses, cars ,buses Etc due to its compatibility and small size.

A REPORT ON FIRE ALARM SYSTEM

USING THERMISTOR AND NE555

INTRODUCTION: The fire alarm system is device which is used for security purpose when the fire take place. This device consist of a heat sensitive component thermistor which conduct heat very quickly and make the whole path conductible, as a result the alarm get start to sound.

WORKING: The IC1 NE555 is configured as a free running oscillator at audio frequency. The transistors T1 and T2 drive IC1. The output (pin 3) of IC1 is couples to base of transistor T3, which drives the speaker to generate alarm sound. The frequency of NE555 depends on the values of resistances R5 and R6 and capacitance C2. When thermistor becomes hot, it gives a low-resistance path for the positive voltage to the base of transistor T1 through diode D1 and resistance R2. Capacitor C1 charges up to the positive supply voltage and increases the the time for which the alarm is ON. The larger the value of C1, the larger the positive bias applied to the base of transistor T1. As the collector of T1 is coupled to the base of transistor T2, the transistor T2 provides a positive voltage to pin 4 (reset) of IC1. Resistor R4 is selected so that NE555 keeps inactive in the absence of the positive voltage. Diode D1 stops discharging of capacitor C1 when the thermistor is in connection with the positive supply voltage cools out and provides a high resistance path.

REQUIREMENT:

1. Transistors
2. Capacitors
3. LED
4. Thermistor
5. IC NE555
6. Speaker
7. Resistors

CIRCUIT DIAGRAM:

                                                       

MODIFICATION: We can use another timer IC such as TDA2822.

APPLICATIONS: Can be used in banks,airports,houses,malls and etc

A REPORT ON INTUDER ALARM SYSTEM

INTRODUCTION: The shadow of an intruder passing few meters nearby the circuit is enough to trigger the alarm. This types of alarm system are used for security purpose.

WORKING: The IC2 A 741 is wired as a sensitive comparator ,whose set point is set by R6 &R7. The voltage divide by LDR and R9 is given at non inverting pin of IC2. At standby mode these two voltages are set equal by adjusting R9. Now the output (pin6) of comparator will be high. Transistor Q1 will be off. The voltage at trigger pin of IC1 will be positive and there will be no alarm. When there is an intruder near the LDR the shadow causes its resistance to increase. Now the voltages at the inputs of comparator will be different and the out put of IC2 will be low. This makes Q1 on. This makes a negative going pulse to trigger the IC1 which is wired as a monostable multivibrator. The output of IC1 will be amplified by Q2 to produce alarm.

REQUIREMENT:

1. Resistors
2. Capacitor
3. LED
4. LDR
5. Buzzer
6. Transistors
7. IC 741 and IC 555

CIRCUIT DIAGRAM:

MODIFICATION: Can use other timer IC another than 555 which provide better timing.

APPLICATIONS: Can be used as safety and security purpose in buildings,malls,airports,houses and etc.

A REPORT ON SINGLE CHIP METAL DETECTOR

INTRODUCTION: A metal detector is a device which detect the metals and magnets when it comes under it range. The metal detector are very effective for security purpose, so they are widely used in railway,airport,hall,malls and etc. Their are different types of metal detectors having different functionality one of the metal detector is explained here which is quite cheap and easy to design.

REQUIREMENTS:

1. Resistor 47k
2. Capacitors 2.2uf
3. Inductor 10mh
4. 555 timer
5. Buzzer
6. Power supply

WORKING: The metal detector detect metal. When a piece of metal is brought close to the inductor the output frequency changes and you can hear sound from the buzzer. The distance of detector detection can be increased by increasing the value of inductor. The output is taken across the pin 3 of the 555 timer and it is connected to the positive end of the buzzer. The supply of 5 to 12 V can be given to start the circuit. The pin 2 is used as input or to trigger the input in the 555 timer.

CIRCUIT DIAGRAM:

                                          

ALTERNATIVES AND APPLICATION: . The other IC TDA 0161 can also be used. Can be used for security system in various levels.

A REPORT ON POCKET HEADPHONE

INTRODUCTION: The headphones are the sound devices ,which are used for hearing aids, here the circuit of powerful headphone amplifier using OPA134 is discuss as follow. In addition to the IC OPA134, the circuit uses only few passive components and can easily generate a lot of sound from even the most inefficient headphones and there will be no compromise for the quality.

REQUIREMENTS:

1. Resistors
2. Capacitors
3. LED
4. Battery
5. OPA-135

WORKING: OPA134 is low noise, low distortion operational amplifier .The FET based input stage provides the IC with high input impedance and it makes the circuit very flexible in terms of the audio source. You can plug almost all types of sound sources like, mp3 players, i Pods, mobile phones etc to the circuit.

In the circuit IC OPA134 is wired as a non-inverting amplifier. LED which indicates power ON. Switch S1 can be used as a ON/OFF switch .Resistor R2 and capacitor C1 forms a high pass filter with corner frequency around 15KHz. R1 can be used as a volume controller. The load resistor R5 will stabilize the virtual ground and prevents any noise or distortion in the output, but the output will be DC coupled.

CIRCUIT DIAGRAM:

                                   

MODIFICATION: The op-amp can be replaced by other high performance op-amp and also we can use the cascade configuration for more power and amplification.

APPLICATIONS: You can plug almost all types of sound sources like, mp3 players, i Pods, mobile phones etc.

A REPORT ON MICROPHONE CIRCUIT

INTRODUCTION: Microphones are a type of transducer (a device which converts energy from one form to another). Microphones convert acoustical energy (sound waves) into electrical energy.

REQUIREMENT:

1. Resistors
2. Capacitors
3. Transistors
4. Power supply
5. Mic

WORKING: Here is the circuit diagram of a simple dynamic microphone amplifier using two transistors. The amplification factor of this circuit is around 150 and can handle signals from 50Hz to 100Khz.These features make it ideal for audio applications. The audio signal from the microphone is coupled to the base of Q1 via the capacitor C1 and resistor R3. Q1 works as a preamplifier here. The preamplifier signal will be coupled to the base of Q2 for further amplification. Resistor network comprising of R4, R5 and R6 provides the necessary negative feedback. Final output signal will be available at the emitter of Q2.

CIRCUIT DIAGRAM:

                                          

MODIFICATION: The modification can be done by changing the values of the capacitors and also the transistors so that the high amplification can be achieved.

APPLICATIONS: Used in public hearing , telephones and hearing aids etc.

A REPORT ON RAIN ALARM CIRCUIT

INTRODUCTION: This circuit produce an alarm when its sensor is wet ted by water. That's why it is known as rain alarm.

REQUIREMENT:

1. Battery
2. 555 timer IC
3. Resistors
4. Capacitors
5. Speaker
6. Water sensor

WORKING: It is placed making an angle of about 30 - 45 degrees to the ground. This makes the rain water to flow through it to the ground and prevents the alarm. The metal used to make the sensor has to be aluminum and not copper. This is because copper forms a blue oxide on its layer on prolonged exposure to moisture and has to be cleaned regularly. The 555 astable multivibrator is used here which gives a tone of about 1kHz upon detecting water. In this way the output from the pin number 3 goes to the alarm system or speaker and the speaker sounds.

CIRCUIT DIAGRAM:

                                              

MODIFICATION: Other timer devices can be used instead of 555 timer for a higher level of sensitivity and performance. Sound devices such as buzzer can also be used.

APPLICATION: It can be used as an alarm device in greenhouses, plant nurseries and etc.

A REPORT ON SAWTOOTH WAVE GERNATOR

INTRODUCTION: Sawtooth waveform is a type of linear non sinusoidal waveform with a triangular shape in which the rise time and fall time are different. A pure triangular waveform is is also linear, non sinusoidal and have a triangular shape but it has equal rise and fall times. The sawtooth waveform can also be called an asymmetric triangular wave. The graphical representation of a triangular and sawtooth waveform are shown in the figure

REQUIREMENT:

1. Capacitors
2. Resistors
3. 555 timer IC
4. Op-amp IC 741

WORKING:Here the IC NE555 is wired as an astable multivibrator with unequal ON and OFF times. The the resistor R1, R2 and capacitor C2 sets the ON and OFF time periods. The value of these components are so selected that the OFF time is less than 10% of the ON times. The asymmetric square wave is available at pin 3 of the IC. The working of the astable multivibrator is given below.

When the power supply is switched ON, capacitor C1 starts charging through resistors R1 and R2. When the voltage across C1 is above 2/3Vcc the upper comparator inside the NE555 swings to positive saturation and this triggers the internal flip-flop. This makes the output (pin 3) of the timer low. Now the capacitor C1 starts to discharge through resistor R2 into pin 7 of the IC. When the voltage across capacitor C1 becomes less than 1/3Vcc, the lower comparator inside the IC switches to positive saturation and this again triggers the internal flip-flop. As a result the output of the timer( pin 3) goes low. This action is repeated and the result will be a square wave at pin 3 of the NE555. The charging time period (ON time) is given by the equation T1= 0.69(R1+R2)C1 and the discharging time period (OFF time) is given by the equation T2=0.69R2C1.

CIRCUIT DIAGRAM:

MODIFICATION: As in the above circuit we are using 555timer ,but we can also use two 741 IC to generate sawtooth waves.

APPLICATION: Can be used in most of the practical application such as for the generation of ramp signal it is also they are widely used in the music for creating sound. 

A REPORT ON SHADOW DETECTOR ALARAM

INTRODUCTION:Shadow sensors are widely used to detect the movement of a person in a confined area. This is also known as Sun up alarm, in this type of circuit you can set the LDR’s sensitivity by 100k potentiometer, you can set it with the help of any lamp around your room (tube light, bulb, LED etc) by varying the 100k potentiometer. We can also control the buzzer time by 1M potentiometer. As u enter in the room the lights gets ON of their own.

REQUIREMENT:

1. resistors
2. potentiometer
3. capacitors
4. transistor
5. power supply
6. buzzer
7. 555 timer IC

WORKING: The circuit uses the light sensing property of the Photo diode. The p-n junction of the photo diode gives light current when it is forward biased. IC 555 get a input through the photo diode at pin number 2 and it provide the output at the pin number 3 , the pin get high voltage due to this the buzzer so connected sounds. The LDR’s sensitivity by 100k potentiometer, you can set it with the help of any lamp around your room (tube light, bulb, LED etc) by varying the 100k potentiometer. We can also control the buzzer time by 1M potentiometer. As u enter in the room the lights gets ON of their own.

CIRCUIT DIAGRAM:

                                         

MODIFICATION: Insted of 555 timer we can also used op-amp IC 741.

APPLICATION: It can be used as a security device.

A REPORT ON SIMPLE UPS

INTRODUCTION: Simple UPS that can deliver 12V unregulated and 5V regulated DC. This can be done by using the rectifier circuit and a voltage regulator.

REQUIREMENT:

1. voltage regulator
2. LED
3. transformer
4. diodes
5. capacitors
6. resistances

WORKING:The transformer T1 steps down the mains voltage to 12V AC and then the bridge rectifies it. The rectified signal is smoothed by the capacitor C1.When the mains supply is available the battery will be charged through diode D3 and the regulator IC gets supply via diode D5. 12V and 5V DC will be available at the output terminals. When mains supply is not available the battery supplies current to the regulator IC and to the 12V DC terminal through diode D4.Also, the diode D3 blocks reverse flow of current during battery mode. Capacitors C2 and C3 acts as filters.

CIRCUIT DIAGRAM:

                                                  

MODIFICATION: We can modify it by using the IC 4047B that provide constant voltage and better efficiency.

APPLICATION: It is used as the electricity provider in houses, malls, offices and etc during the power breakdown. 

A REPORT ON SQUARE WAVE GERNATOR CIRCUIT

INTRODUCTION: Square waves belongs to a wide range of frequencies and duty cycle can be generated using the uA741 op-amp. The circuit diagram of a typical square wave oscillator using uA741 is discussed as follow.

REQUIREMENT:

1. IC ua741
2. resistors
3. potentiometer
4. capacitors

WORKING:Initially the voltage across the capacitor C1 will be zero and the output of the op-amp will be high. As a result the capacitor C1 starts charging to positive voltage through potentiometer R1. When the C1 is charged to a level so that the voltage at the inverting terminal of the op-amp is above the voltage at the non-inverting terminal, the output of the op-amp swings to negative. The capacitor quickly discharges through R1 and then starts charging to negative voltage. When the C1 is charged to a negative voltage so that the voltage at the inverting input more negative than that of the non-inverting pin, the output of the op-amp swings back to positive voltage. Now the capacitor quickly discharges the negative voltage through R1 and starts charging to positive voltage. This cycle is repeated endlessly and the result will a continuous square wave swinging between +Vcc and -Vcc at the output.

CIRCUIT DIAGRAM:

                                           

MODIFICATION: Instead of op-amp we can use UJT (ultra junction transistor)to produce square wave.

APPLICATION: Its higher order circuit can be used for digital communication purpose and practicality uses in labs for reading their behavior for other waves. 

A REPORT ON ZERO CROSS DETECTOR CIRCUIT

INTRODUCTION:The zero crossing detector circuit is an important application of the OP-AMP comparator circuit. It can also be called as the sine to square wave converter. Anyone of the inverting or non-inverting comparators can be used as a zero-crossing detector. The only change to be brought in is the reference voltage with which the input voltage is to be compared, must be made zero (Vref = 0V).

REQUIREMENT:

1. op-amp IC741
2. resistor
3. diode
4. power supply

WORKING:An input sine wave is given as Vin. For a reference voltage 0V, when the input sine wave passes through zero and goes in positive direction, the output voltage Vout is driven into negative saturation. Similarly, when the input voltage passes through zero and goes in the negative direction, the output voltage is driven to positive saturation. The diodes D1 and D2 are also called clamp diodes. They are used to protect the op-amp from damage due to increase in input voltage. They clamp the differential input voltages to either +0.7V or -0.7V.

CIRCUIT DIAGRAM:

                                      

MODIFICATION:Basic zero crossing detector can be designed using DS3486 .

APPLICATION: It can be used in electronics, mathematics, sound, and image processing.