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AUTOMATIC NIGHT LIGHT

The circuit will automatically switch on the AC lamp when night falls and the lamp will be automatically switched off after a preset time.

CIRCUIT DIAGRAM:

WORKING:

The working of this night light circuit very simple. An ldr is used as the sensor here. At day time the resistance of the ldr will be low and so do the voltage drop across it, the transistor q1 will be in the conducting mode. When darkness falls the resistance of ldr increases and so do the voltage across it. This makes the transistor q1 off. Base of q2 is connected to the emitter of q1 and so q2 is biased on which in turn powers the ic1. Ne555 is wired as monostable multivibrator that is automatically triggered at power on. This automatic triggering is achieved with the help of capacitor c2. The output of ic1 remains high for a time determined by resistor r5 and capacitor c4. When output of ic1 goes high transistor q3 is switched on which triggers triac t1 and the lamp glows. A 9v battery is included in the circuit in order to power the timer circuit during power failures. Resistor r1, diode d1, capacitor c1 and zener d3 forms the power supply section of the circuit. R7 and r8 are current limiting resistors.

Notes.

1] the circuit can be assembled on a vero board.

2] preset r2 can be used to adjust the sensitivity of the circuit.

3] preset r5 can be used to adjust the on time of the lamp.

4] with r5 @ 4.7m the on time will be around three hours.

5] the wattage of l1 must not exceed 200w.

6] heat sink is recommended for bt136.

COMPONENT USED:

R1=10K

R2=50K

R3=1K

R6=10K

R7=200OHM

R8=150OHM

C1=100uF

C2=0.1uF

C3=.03uF

C4=2200uF

D1,D2=1N40007

D3 =ZENER DIODE

Q1=BC558

Q2=BC558

Q3=BC548

MODIFICATIONS:

As the above circuit is buid by using the 555timer ic now we can buid this circuit by using the LDR and EMOS.

APPLICATIONS:

• HOME APPLIANCES

DANCING LIGHT

Here is a simple dancing light circuit based on ne555 (ic1) & cd4017 (ic2) . The ic1 is wired as an astable multivibrator to provide the clock pulses for the cd4017. For each clock pulse receiving at the clock input (pin14) of ic cd4017, the outputs q0 to q9 (refer pin diagram of cd 4017) becomes high one by one alternatively. The leds connected to these pins glow in the same fashion to give a dancing effect. The speed of the dancing leds depend on the frequency of the clock pulses generated by the ic1.

CIRCUIT DIAGRAM:

COMPONENT USED:

RESISTOR:

R1=10K

R2=100K

R3=1K

R4=1K

R5=1K

R6=1K

R7=1K

R8=1K

R9=1K

555 TIMER

IC CD 4017:

10V POWER SUPPLY

CAPACITORS:

C1=10uF

LED 1-9

MODIFICATIONS:

AS IN THE ABOVE CIRCUIT WE ARE USING 555TIMER AND IC CD4017 ,WE CAN USE THE TWO TRANSISTORS T1 AND T2 (BC 548).

APPLCATIONS:

• HOME APPLIANCES
• DISCO

FM TRANSMITTER:

FM transmitter is a portable device that plugs into the headphone jack of a portable audio or video device, such as a portable media player, CD player, or satellite radio system. The sound is then broadcast through the transmitter, and plays through an FM broadcast band frequency. In this case the frequency of a carrier signal is modulated in accordance with that of frequency of modulating signal.

FM frequency is from 76.0 to 108.0 MHz. FM transmitter have a range of about 30 feet (about 9 meters). A good radio can increase that range to upwards of 75 feet (about 23 meters).

CIRCUIT DIAGRAM:

DESCRIPTION:

This is two transistor FM transmitter circuit. 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.

COMPONENTS USED:

NPN TRANSISTERS Q1 AND Q2

Q1 - BC108

Q2 - 2N2369

POLAR CAPACITER:

                   An electrolytic capacitor is a capacitor that uses an electrolyte(an ionic conducting liquid) as one of its plates to achieve a larger capacitance per unit volume than other types. The large capacitance of electrolytic capacitors makes them particularly suitable for passing or bypassing low-frequency signals and storing large amounts of energy. They are widely used in power supply and interconnecting stages of amplifiers at audio frequencies.

C1 - 1uF
C2 - 1uF
C3 - 2.2nF
C4 - 4.7nF
C5 - 10pF
C6 - 10pF
C7 - 100pF
C8 - 2.2nF




RESISTERS:
R1 - 86K
R2 - 10K
R3 - 3.3K
R4 - 2.2K
R5 - 100ohm


POWER SUPPLY : 9VOLT



Antenna can be a 1m copper wire
MODIFICATIONS:
As the above FM transmitter is made up of the two transistor were as we can made the FM transmitter from one transistor, so given below the circuit diagram of the FM transmitter using only one transistor.
CIRCUIT DIAGRAM:

COMPONENTS USED:

Q1 - Transistor- 2N3904
Capacitors - 4.7pF, 20pF, 0.001uF, 22nF
Resistors - 4.7 kilo Ohm, 470 Ohm
Inductor - 0.1uF.
Antenna: Use 15cm to 1 meter long wire for antenna. If you have a long antenna, the
signal transmission will be better.

APPLICATIONS:

• In home
• In car
• In stations

Night security light-Security Alarm System

Here is a simple circuit switches on a light around 2 hours after midnight, the time at which most of the robberies taking place.This simple circuit is build around a cmos ic 4024 to obtain the required timing. During day time the ldr has low resistance and keeps the pin 12 of the ic1 high, preventing the ic1 from oscillating. When it is dark the ldr resistance becomes high and the pin 12 of ic1 becomes low and the ic starts oscillating, which indicated by the flashing of led d3.The Values of the timing components r1, r2, c4 are so selected that the out put pin3 of ic1 goes high after 8 hours. That means the high output drives the triac to switch on the lamp around 2’o clock. At morning, the ldr resistance drops and the pin 12 of ic1 goes high and stops the oscillation, making the lamp off. The switch s1 can be used to manually on the lamp. The capacitor c2 prevents false triggering.

Circuit diagram with Parts list:

COMPONENTS USED:

The LDR can be general purpose LDR.

The light sensitivity can be adjusted using the preset R6.

• RESISTOR:It is a passive component and mainly employed in the circuit to direct the flow of current in the circuit. Resistors are broadly classified as fixed type and variable type.
• R5-Thermistor is a kind of temperature dependent resistor and its resistance varies depending on the temperature in its vicinity.
• R1=120k
• R2=1M
• R3=1000ohm
• R4=1000ohm
• R6=-100k
• C1 (1000uf) – Capacitors are mainly employed in the circuit to store the charges. A dielectric medium flows in it which is used to separate the two conducting plates inside it.
• c2=100uF
• C3=.1uF
• C5=1uF
• 4024 IC
• FULL WAVE RECTIFIER
• 1 TO 1 TRANSFORMER
• POWER SUPPLY OF 12 VOLT.

MODIFICATIONS:

THIS CIRCUIT CAN BE MODIFIED BY USING THE 555TIMER IC.

APPLCATIONS:

• HOME SECURITY

PARK AID MODIFICATION






PURPOSE:This model is designed for parking purposes, instead of looking at the LED display,we are using the audio for parking which make easier the parking operation.




CIRCUIT DIAGRAM:

COMPONENT USED:
R15 ---- 3K3 1/4W Resistor

      R16           ----   330K   1/4W Resistor
      R17           ----   470K   1/4W Resistor
      R18           ----   150K   1/4W Resistor

    C6              ----   1µF  63V Electrolytic or Polyester Capacitor
    D8,D9,D10----   1N4148  75V 150mA Diodes
    IC4            ---     555  Timer IC
    BZ1          ----Piezo sounder (incorporating 3KHz oscillator)

CIRCUIT WORKING:
In this model the input pins of IC2B, IC2C and IC2D are reversed. LED’s D5, D6 and D7, as also resistors R12, R13 and R14 are omitted. IC2B, IC2C and IC2 outputs drive resistors R15, R16 and R17 through D8, D9 and D10 respectively, in order to change the time constant of a low frequency oscillator based on the 555 timer IC4.
This allows the Piezo sounder to start beeping at about 2 times per second when bumper-wall distance is about 20 cm., then to increase the beeps to about 3 per second when bumper-wall distance is about 10 cm. and finally to increase further the beeps frequency to more than 4 beeps per second when the distance is about 6 cm. or less.

ALTERNATIVE COMPONENTS :
Here is this model we are using 555 IC which is used to generate the high stable time delay or oscillations so instead of this IC we can use IC 4060 which is an excellent integrated circuit for timing applications. Its ten active high outputs can give time delay from few seconds to hours. With a few components, it is easy to construct a simple but reliable time delay circuit.

PHONE DETECTOR

A cell phone typically transmits and receives signals in the frequency range of 0.9 to 3GHz. This simple circuit is used to detect the presence of an activated cell phone by detecting these signals.




CIRCUIT DIAGRAM:

DESCRIPTION:

The basic principle behind this circuit is the idea of using a schottky diode to detect the cell phone signal. Mobile phone signal is in the frequency range of 0.9 to 3ghz.Schottky Diodes have a unique property of being able to rectify low frequency signals, with low noise rate. When an inductor is placed near the RF signal source, it receives the signal through mutual induction. This signal is rectified by the schottky diode. This low power signal can be amplified and used to power any indicator like an led in this case.

WORKING:

In normal condition, when there is no RF signal, the voltage across the diode will be negligible. Even though this voltage is amplified by the transistor amplifier, yet the output voltage is less than the reference voltage, which is applied to the inverting terminal of the comparator. Since the voltage at non inverting terminal of the OPAMP is less than the voltage at the inverting terminal, the output of the OPAMP is low logic signal.

Now when a mobile phone is present near the signal, a voltage is induced in the choke and the signal is demodulated by the diode. This input voltage is amplified by the common emitter transistor. The output voltage is such that it is more than the reference output voltage. The output of the OPAMP is thus a logic high signal and the LED starts glowing, to indicate the presence of a mobile phone. The circuit has to be placed centimeters away from the object to be detected.

COMPONENTS USED:

• V1 = 12V
• L1 = 1uH
• R1 = 100Ohms
• C1 = 100nF
• R2 = 100K
• R3 = 3K
• Q1 = BC547
• R4 = 200 Ohms
• R5 = 100 Ohms
• IC1= LM339
• R6 = 10 Ohms

LED = Blue LED

CIRCUIT MODIFICATION:

As in the above diagram we are using only transistors and op-amp 741IC so we can modify the circuit by using the 555timer ic as well as the CA3130IC.

APPLICATIONS:

1. This circuit can be used at examination halls, meetings to detect presence of mobile phones and prevent the use of cell phones.
2. It can be used for detecting mobile phones used for spying and unauthorized transmission of audio and video.
3. 3.It can be used to detect stolen mobile phones.

POLARITY CUM COUNTINUITY CIRCUIT

The polarity of lots of components viz diodes, led comprises zener diode as well as infrared led can be tested with the help of polarity cum continuity tester. With the help of this circuit, we can also identify that whether the components we are using in our circuit are good or bad before mounting them on the PCB. Although it happens many times that people are not being able to discovered the polarity of any component and mount them wrong in the circuit which leads to damage of the component or may damage the entire circuit. The content of any circuit can also be tested with the help of this circuit.

DESCRIPTION:

Firstly connects the component which you want to test with test probe. Glowing of any led in this circuit is the indicator of cathode terminal. Both the led in the circuit will start glowing when you first start the circuit. Now across the probe provide for testing connect the component. If led1 start glowing it means that the cathode side of the component is coupled to the probe 1 and if led2 start glowing it implies that the cathode side of the component is coupled with probe 2.

The circuit is finished with the aid of two transistors and both the transistors in the circuit are connected as an astable multivibrator. The circuit output which we get from the both transistors are not in phase with one another, it implies that if we get high output from the first transistor then the other transistor output will be low or if the output of the second transistor is higher than the output from the first transistor will be low. Led 1 will start glowing when t1 transistor is in “on” state and t2 transistor is in “off” state. In the same manner led 2 will be glowing when the t1 transistor is in the “off” state while t2 transistor is in “on” state.

When the component like diode or led which you want to test is put between the probes provided for testing it bypasses to any one of the led based on the polarity. In Place of the bypass led the test current will start flowing via a component in the circuit. Series grouping of led as well as diodes are connected in the circuit with the t1 and t2 transistor at the collector terminal so that it can raise the forward voltage drop. This Will make sure that the voltage drop across any one of the led is bigger as compared with the forward drop of the component being examined.

The result of the test when the component is connected.

1. If LED 1 starts glowing this implies that at probe 1 of the tester cathode is coupled while at probe 2 of the tester anode is coupled.
2. If LED2 starts glowing it implies that at probe 1 of the tester anode is coupled while cathode of the component is coupled with probe 2.
3. If any of the LED will not glow it implies that the component coupled to the circuit is short circuit and due to that stable multivibrator of the circuit stop oscillating.
4. If the components open circuit than both the LED in the circuit will start glowing.

If you want to check the continuity of the circuit coupled the circuit with the polarity cum continuity tester circuit with the help of probe C1 and C2 provided in the circuit. A sound of the buzzer will start when both the probes are attached to each other it means that your circuit is in proper working condition. When probe C1 and C2 are not connected with each other than at that time transistor T3 is closed and there is no base current. At this moment voltage level of transistor T3 at the emitter and base are of the same level. Transistor gotten open at the time when you start the continuity test and as compared with the emitter base of the transistor is at a higher level so the sound started from the buzzer connected with it.

CIRCUIT DIAGRAM:

COMPONENTS USED:

• RESISTOR:it is a passive component and mainly employed in the circuit to direct the flow of current in the circuit. Resistors are broadly classified as fixed type and variable type.
• R1, R4 (820e) – 2
• R2, R3 (33k) – 2
• R5 (270e) – 1
• R6 (1m) – 1
• D1, D2 (1n4148) – It is a semiconductor device and it permit the current to flow merely in forward direction and block the current in backward direction.
• LED1, LED2 – LED is a semiconductor device and generally work as an indicator in any circuit and works on low voltage and current.
• C1, C2 (1uf) – Capacitors are mainly employed in the circuit to store the charges. A dielectric medium flows in it which is used to separate the two conducting plates inside it.
• T1,T2,T3 (BC547) – Transistor is a semiconductor device mainly used to amplify the current.
• BUZZER – also known as beeper and is an audio signal device.
• POWER SUPPLY OF 5 VOLT .

APPLICATIONS:

• Cables and PCB can be checked with the help of this circuit.
  
• Polarity of components.

BAND PASS FILTER:

A device that passes frequency within a certain range,and reject the frequency outside the range. This filter can be made by combining the low pass filter with the high pass filter. An ideal bandpass filter would have a completely flat pass band (e.g. with no gain/attenuation throughout) and would completely attenuate all frequencies outside the pass band. In practice, no bandpass filter is ideal .The bandwidth of the filter is simply the difference between the upper and lower cutoff frequencies.

one of its type is R.L.C band pass filter .

Here in the above circuit we are using the resister ,capacitor and inductor in series. Sin wave data is connected with having frecuency10kHz.

Resister - 8k
capacitor - 1uF
inductor - 1uH

Resonance Frequency:- AT which the simple driving force will produce large amplitude oscillation.

WO =2piFO

Q-factor:-A band-pass filter can be characterized by its q-factor higher q-factor narrow the pass band.

Q= WOL
R

WAVEFORM OF R.L.C BAND PASS FILTER:

Applications:

1. A very frequent use of these circuits is in the tuning circuits of analogue radios.

Adjustable tuning is commonly achieved with a parallel plate capacitor which allows the value of
to be changed and tune to stations on
different frequencies. For the IF stage in the radio where the tuning is preset in the
factory the more usual solution is an adjustable core in the inductor to adjust L.
2. Oscillators
3. Voltage multiplier
4. Pulse discharge circuit

BAND PASS FILTER:

A device that passes frequency within a certain range,and reject the frequency outside the range. This filter can be made by combining the low pass filter with the high pass filter. An ideal bandpass filter would have a completely flat pass band (e.g. with no gain/attenuation throughout) and would completely attenuate all frequencies outside the pass band. In practice, no bandpass filter is ideal .The bandwidth of the filter is simply the difference between the upper and lower cutoff frequencies.

one of its type is R.L.C band pass filter .

Here in the above circuit we are using the resister ,capacitor and inductor in series. Sin wave data is connected with having frecuency10kHz.

Resister - 8k
capacitor - 1uF
inductor - 1uH

Resonance Frequency:- AT which the simple driving force will produce large amplitude oscillation.

WO =2piFO

Q-factor:-A band-pass filter can be characterized by its q-factor higher q-factor narrow the pass band.

Q= WOL
R

WAVEFORM OF R.L.C BAND PASS FILTER:

Applications:

1. A very frequent use of these circuits is in the tuning circuits of analogue radios.

Adjustable tuning is commonly achieved with a parallel plate capacitor which allows the value of
to be changed and tune to stations on
different frequencies. For the IF stage in the radio where the tuning is preset in the
factory the more usual solution is an adjustable core in the inductor to adjust L.
2. Oscillators
3. Voltage multiplier

4. Pulse discharge circuit

TEMPERATURE CONTROLLED DC FAN

Fan control is the management of the rotational speed of an electric fan. There are many types of electric fans and many types of fan controls .

All fans which are used now a day are controlled manually by voltage regulators which have different stages of speed. This process is done manually which can be done automatically by the use of this circuit. Here we are introducing an efficient fan speed regulation circuit, by which the speed of a fan can be controlled depending up on the room temperature. The circuit is highly efficient since energy loss can be minimized by power saving as the circuit automatically adjusts the fans speed.

CIRCUIT DIAGRAM:

WORKING:

Here is a simple circuit based on two transistors that can be used to control the speed of a 12 V DC fan depending on the temperature. A thermistor (R1) is used to sense the temperature. When the temperature increases the base current of Q1 (BC 547) increases which in turn decreases the collector voltage of the same transistor. Since the collector of Q1 is coupled to the base of Q2 (BD 140), the decrease in collector voltage of Q1 forward biases the Q2 more and so do the speed of the motor. Also, the brightness of the LED will be proportional to the speed of the motor.

COMPONENTS USED:

• RESISTOR:It is a passive component and mainly employed in the circuit to direct the flow of current in the circuit. Resistors are broadly classified as fixed type and variable type.
• R1-Thermistor is a kind of temperature dependent resistor and its resistance varies depending on the temperature in its vicinity.
• R2,R3,R4,R5,R6,R7 – 1K
• D1 (1n4148) – It is a semiconductor device and it permit the current to flow merely in forward direction and block the current in backward direction.
• LED1– LED is a semiconductor device and generally work as an indicator in any circuit and works on low voltage and current.
• C1 (1uf) – Capacitors are mainly employed in the circuit to store the charges. A dielectric medium flows in it which is used to separate the two conducting plates inside it.
• Q1-Q2 (BC547,BD 140) – Transistor is a semiconductor device mainly used to amplify the current.
• POWER SUPPLY OF 12 VOLT .

CIRCUIT MODIFICATIONS:

As in the above circuit we are using the two transistors q1 and q2 ,we can also build the circuit by using the op-amp 741IC and thermistor as a sensor given below the circuit diagram.

CIRCUIT DIAGRAM:















APPLICATIONS:

• CONTROLLING OF ROTATION OF FANS
  

BURGLAR ALARM

This optical burglar alarm uses two 555 timer ics (ic1 and ic2). Both the ics are wired as astable multivibrators. The first astable multivibrator built around ic1 produces low frequencies, while the second astable multivibrator built around ic2 produces audio frequencies.
General-purpose darlington photo-transistor t1 is used as the light sensor. To increase the sensitivity of the circuit, npn transistor t2 is used.
Place phototransistor t1 where light falls on it continuously. Phototransistor t1 receives light to provide base voltage to transistor t2. As a result, transistor t2 conduct to keep reset pin 4 of ic1 at low level. This disables the first multivibrator (ic1) and hence the second multivibrator (ic2) also remains reset so the alarm (ls1) does not sound.

CIRCUIT DIAGRAM:

WORKING:

When light falling on darlington phototransistor t1 is obstructed, transistor t2 stops conducting and reset pin 4 of ic1 goes high. This enables the first multivibrator (ic1) and hence also the second multivibrator (ic2). As a result, a beep tone is heard from speaker ls1. The beep rate can be varied by using preset vr1, while the output frequency of ic2 can be varied by using another preset vr2.
This circuit works off a simple 6v-12v dc power supply.

COMPONENT USED:

Resistors (all ¼-watt, ± 5% Carbon unless stated otherwise)

R1, R5 = 1 KΩ
R2 = 100 KΩ
R3 = 4.7 KΩ
R4 = 10 KΩ
VR1 = 1 MΩ
VR2 = 100 KΩ

Capacitor:
C1 = 1 µF/16V
C2 = 0.01 µF
C3 = 0.047 µF
C4 = 0.01 µF
C5 = 47 µF/25VSemiconductors:
IC1, IC2 = NE555
T1 = 2N5777 Photo Transistor
T2 = BC547
LED1 = RED LED
Miscellaneous
LS1 = 8Ω / 0.5W


MODIFICATIONS:

HERE WE CAN USE THE ONE TRANSISTOR Q1 AND SPDT SWITCH AND WINDOW FOIL.

APPLCATIONS:

• Residential, commercial, industrial, and military properties

BATTERY OPERATED MINI NIGHT LAMP

This is the circuit of a low power led night lamp that will automatically switch off at day time. The cmos timer ic ts555cn is wired as a square wave generator operating at around 5hz.The Output voltage from the ic1 is doubled using the combination of capacitor c2 and diode d2 in order to drive the led. The led can be a bright white led. At day time the resistance of ldr drops to few k ohms and inhibits the ic from producing oscillations.

CIRCUIT DIAGRAM WITH PARTS LIST:

Notes.

Assemble the circuit on a general purpose pcb.

The circuit can be powered from two 1.5v cells in series.

Any diode can be used in place of d2, but schottky diode like 1n5819 will give more brightness.

The ic1 must be cmos type because other types won’t operate at low voltages like 3v.

An optional switch can be added in series with the battery ( not shown in circuit) to provide an manual on/off.

COMPONENTS USED:

RESISTOR:

R2,R1=1M

R3=47K

R4=LDR

CAPACITORS:

C1=100uF

C2=220uF

DIODE:

D1,D2=1N5819

555 TIMER

MODIFICATIONS:

This circuit can be made by using two transistors(bd 139 ,bd140) and ldr senser with 12 v battry.

APPLCATIONS:

• HOME APPLIANCES

DARK DETECTOR CIRCUIT

The dark detector circuit shown here can be used to produce an audible alarm when the light inside a room goes OFF. The circuit is build around timer IC NE555. A general purpose LDR is used for sensing the light. When proper light is falling on the LDR its resistance is very low. When there is no light the LDR resistance increases. At this time the IC is triggered and drives the buzzer to produce an alarm sound. If a transistor and relay is connected at the output (pin3) of IC1 instead of the buzzer, electrical appliances can be switched according to the light.

CIRCUITR DIAGRAM:

COMPONENT USED:

The LDR ,R4 can be any general purpose LDR.

The circuit can be powered from a 9V PP3 battery.

The POT,R3 can be sued as a volume controller.

R1=100K

R2=1M

R3=1K

R4=LDR

C1=100PF

C2=1uF

MODIFICATIONS:

As in the above circuit we are using the 555timer , we can also buid the circuit by using the two transistors q1 and q2 bc547 as shown below.

Applications:

• home security

Photocell based night light

Many automatic night light circuits had been published here. This one uses a photocell for detecting the light intensity. At full light the resistance of the photocell will be few ten ohms and at darkness it will rise to several hundred ohms. The ic1 ua741 is wired as a comparator here. At darkness the resistance of photocell increases and so the voltage at the inverting input of the ic1 will be less than the reference voltage at the non inverting input. The output of the ic1 goes to positive saturation and it switches on the transistor to activate the relay. By this way the lamp connected through the relay contact glows. The diode d1 works as a freewheeling diode.

CIRCUIT DIARRAM:

COMPONENT USED:

Use 9V DC for powering the circuit.

POT R7 can be used to adjust the sensitivity of the circuit.

The relay K1 can be a 9V, 200 Ohm SPDT type.

L1 can be a 230V,60W lamp.

R8 can be a ORP 12 photocel

R1=10K

R2=10K

R3=10K

R6=1K

R7=1M

D1=1N40007

Q1=BC109

L1=1uH

9V POWER SUPPLY

MODIFICATIONS:

We can use the transistor BC558 and LDR senser to creat this above circuit.

APPLCATIONS:

• HOME SECURITY
• HOME APPLIANCES

BAND PASS FILTER

A device that passes frequency within a certain range,and reject the

frequency outside the range. This filter can be made by combining the low pass filter with the high pass filter. An ideal bandpass filter would have a completely flat pass band (e.g. with no gain/attenuation throughout) and would completely attenuate all frequencies outside the pass band. In practice, no bandpass filter is ideal .The bandwidth of the filter is simply the difference between the upper and lower cutoff frequencies.

One of its type is R.C band pass filter .

RC Bandpass Filter:

As by connecting or “cascading” together a single Low Pass Filter circuit with a High Pass Filter circuit, we can produce another type of passive RC filter that passes a selected range or “band” of frequencies that can be either narrow or wide while attenuating all those outside of this range. This new type of passive filter arrangement produces a frequency selective filter known commonly as a Band Pass Filter.

Circuit Diagram:

Here in the above circuit we are using the 2resister ,2capacitor in series and parallel. Sin wave generator is connected with having frecuency10kHz.

Resister - .2k,1k
capacitor - 2.5uF

Resonance Frequency:At which the simple driving force will produce large amplitude oscillation.

WO =2piFO

Q-factor:A band-pass filter can be characterized by its q-factor higher q-factor narrow the pass band.

Q= WOL
R
CUT off Frequency: Frequency at which energy flowing through the system begins to be reduced rather than passing through.

FC= 1
2piRC


WAVEFORM OF R.C BAND PASS FILTER:

Applications:

• Many communications and sensor applications require a bandpass filter with wide bandwidth. This filter typically requires precision resistors and capacitors to obtain an accurate filter position and response.
• They are especially useful in remote areas that lack cell-signal coverage or cell towers 

Sawtooth Wave Generator

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 below. T1 is assumed to be the rise time and T2 is assumed to be the fall time.

WAVE FORM PATTERN:

CIRCUIT DIAGRAM:

Description:

Sawtooth waveforms can be generated by integrating square waves with unequal rise and fall times (asymmetrical square waves). The circuit shown above shows a setup for generating sawtooth wave. Here an NE555 timer IC is used for generating the asymmetric square wave and op amp integrator based on uA741 is used for integrating the asymmetric square wave.

The circuit diagram is shown above. 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. Read this article :  NE555 as astable multivibrator for a better understanding on NE555 based astable multivibrators..

The assymmetric square wave obtained at the output of NE555 is integrated by the inverting active integrator based on opamp IC uA741. Resistors R3 and R4 sets the gain of the opamp integrator. Resistor R4 in conjunction with capacitor C3 sets the bandwidth. Since the integrator is wired in inverting mode, the sawtooth wavform falls when the timer output is high and rises when the timer output is low.

COMPONENT USED:

POLAR CAPACITER:

An electrolytic capacitor is a capacitor that uses an electrolyte(an ionic

conducting liquid) as one of its plates to achieve a larger capacitance per unit volume than other

types. The large capacitance of electrolytic capacitors makes them particularly suitable for

passing or bypassing low-frequency signals and storing large amounts of energy. They are

widely used in power supply and interconnecting stages of amplifiers at audio frequencies.

C1 - 1uF

C2 - 1uF

C3 - 1uF

C4 - 1uF

C5 – 1uF

RESISTERS:

R1 - 86K

R2 - 10K

R3 - 3.3K

R4 - 2.2K

R5 - 100ohm

POWER SUPPLY : 9VOLT


MODIFICATIONS:
AS IN THE ABOVE CIRCUIT WE ARE USING 555TIMER ,BUT WE CAN ALSO USE TWO 741 IC TO GENERATE SAWTOOTH WAVES.
CIRCUIT DIAGRAM:

In this circuit a potentiometer is used (47K) . Use of the potentiometer is when the wiper moves towards -V ,the rise tim of the sawtooth become longer than the fall time. If the wiper moves towards +V , the fall time becomes more than the rise time.
Reason is when comparator output is at -ve saturation. When wiper moves to -ve supply, a negative voltage is added to inverting terminal. This causes the potential difference across R1 decreases and hence the current through the resistor and capacitor decreases . Then slope of the output, I/C decreases and un tern rise time decreases. When the comparator output goes positive , due to presence of negative voltage at the inverting terminal, potential difference of across the resistor R1 increases and hence current increases. Then slope increases and fall time decreases. And obtained output as sawtooth wave.