Dancing Light Circuit Diagram

Here is a simple circuit which can be used for decoration purposes or as an indicator. Flashing or dancing speed of LEDs can be adjusted and various dancing patterns of lights can be formed.The circuit consists of two astable multivibrators. One multivibrator is formed by transistors T1 and T2 while the other astable multivibrator is formed by T3 and T4. Duty cycle of each multivibrator can be varied by changing RC time constant. This can be done through potentiometers VR1 and VR2 to produce different dancing pattern of LEDs. Total cost of this circuit is of the order of Rs 30 only. Potentiometers can be replaced by light dependent resistors...

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Zener Diode Tester Circuit Diagram

Here is a handy zener diode tester which tests zener diodes with breakdown voltages extending up to 120 volts. The main advantage of this circuit is that it works with a voltage as low as 6V DC and consumes less than 8 mA current. The circuit can be fitted in a 9V battery box. Two-third of the box may be used for four 1.5V batteries and the remaining one-third is sufficient for accommodating this circuit. In this circuit a commonly available transformer with 230V AC primary to 9-0-9V, 500mA secondary is used in reverse to achieve higher AC voltage across 230V AC terminals. Transistor T1 (BC547) is configured as an oscillator and driver to obtain...

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Telephone Ringer Using 556 Dual Timers Circuit Diagram

Using modulated rectangular waves of different time periods, The circuit presented here produces ringing tones similar to those produced by a telephone.The circuit requires four astable multivibrators for its working. Therefore two 556 ICs are used here. The IC 556 contains two timers (similar to 555 ICs) in a single package. One can also assemble this circuit using four separate 555 ICs. The first multivibrator produces a rectangular waveform with 1-second ‘low’ duration and 2-second ‘high’ duration. This waveform is used to control the next multivibrator that produces another rectangular waveform.A resistor R7 is used at the collector of transistor...

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Metal Detector Circuit Diagram

The circuit described here is that of a metal detector. The opera- tion of the circuit is based on superheterodyning principle which is commonly used in superhet receivers. The circuit utilises two RF oscillators. The frequencies of both oscillators are fixed at 5.5 MHz. The first RF oscillator comprises transistor T1 (BF 494) and a 5.5MHz ceramic filter commonly used in TV sound-IF section. The second oscillator is a Colpitt’s oscillator realised with the help of transistor T3 (BF494) and inductor L1 (whose construction details follow) shunted by trimmer capacitor VC1. These two oscillators’ frequencies (say Fx and Fy) are mixed in the mixer...

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Magnetic Proximity Sensors Circuit Diagram

Here is an interesting circuit for a magnetic proximity switch which can be used in various applications.The magnetic proximity switch circuit, in principle, consists of a reed switch at its heart. When a magnet is brought in the vicinity of the sensor (reed switch), it operates and controls the rest of the switching circuit. In place of the reed switch, one may, as well, use a general-purpose electromagnetic reed relay (by making use of the reed switch contacts) as the sensor, if required. These tiny reed relays are easily available as they are widely used in telecom products. The reed switch or relay to be used with this circuit should be the...

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A Simple Remote Control Tester Circuit Diagram

Here is a handy gadget for test- ing of infrared (IR) based remote control transmitters used for TVs and VCRs etc. The IR signals from a remote control transmitter are sensed by the IR sensor module in the tester and its output at pin 2 goes low. This in turn switches on transistor T1 and causes LED1 to blink. At the same time, the buzzer beeps at the same rate as the incoming signals from the remote control transmitter. The pressing of different buttons on the remote control will result in different pulse rates which would change the rate at which the LED blinks or the buzzer beeps. When no signal is sensed by the sensor module, output pin 2...

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Long Range FM Transmitter Circuit Diagram

The power output of most of these circuits are very low because no power amplifier stages were incorporated.The transmitter circuit described here has an extra RF power amplifier stage, after the oscillator stage, to raise the power output to 200-250 milliwatts. With a good matching 50-ohm ground plane antenna or multi-element Yagi antenna, this transmitter can provide reasonably good signal strength up to a distance of about 2 kilometres.The circuit built around transistor T1 (BF494) is a basic low-power variable-frequency VHF oscillator. A varicap diode circuit is included to change the frequency of the transmitter and to provide frequency...

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A Simple Car Battery Charger Circuit Diagram

This very simple circuit uses a transformer ,two diodes , a capacitor and an ammeter.To charge a battery just connect the + and - terminals of the circuit to the corresponding terminals of the battery.When the battery is not charged, the ammeter reading shows 1-3 amps.When the battery is fully charged the ammeter reads Zero or nearly zero, after which the battery should be removed from thecharger.The circuit is a full wave rectifier using 2 diodes for rectification. The capacitor is used for smoothing.I think the circuit works fine without the capacitor since the battery itself acts a BIG capacitor. But when you are using thecircuit to supply...

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Analog To Digital Converter Circuit Diagram

Normally analogue-to-digital con-verter (ADC) needs interfacing through a microprocessor to convert analogue data into digital format. This requires hardware and necessary software, resulting in increased complexity and hence the total cost.The circuit of A-to-D converter shown here is configured around ADC 0808, avoiding the use of a microprocessor. The ADC 0808 is an 8-bit A-to-D converter, having data lines D0-D7. It works on the principle of successive approximation. It has a total of eight analogue input channels, out of which any one can be selected using address lines A, B and C. Here, in this case, input channel IN0 is selected by grounding...

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Simple Variable Frequency Oscillator Circuit Diagram

This is a very simple circuit utilising a 555 timer IC to generate square wave of frequency that can be adjusted by a potentiometer.With values given the frequency can be adjusted from a few Hz to several Khz.To get very low frequencies replace the 0.01uF capacitor with a higher value.The formula to calculate the frequency is given by:1/f = 0.69 * C * ( R1 + 2*R2)The duty cycle is given by:% duty cycle = 100*(R1+R2)/(R1+ 2*R2)In order to ensure a 50% (approx.) duty ratio, R1 should be very small when compared to R2. But R1 should be no smaller than 1K.A good choice would be, R1 in kilohms and R2 in megaohms. You can then select C to fix the range...

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Digital Volume Control Circuit Diagram

This circuit could be used for replacing your manual volume control in a stereo amplifier. In this circuit, push-to-on switch S1 controls the forward (volume increase) operation of both channels while a similar switch S2 controls reverse (volume decrease) operation of both channels.A readily available IC from Dallas semiconductor, DS1669 is used here.FEATURES: * Replaces mechanical variable resistors * Electronic interface provided for digital as well as manual control * Wide differential input voltage range between 4.5 and 8 volts * Wiper position is maintained in the absence of power * Low-cost alternative...

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Soft Button Type Motor Direction Controller Circuit Diagram

This circuit can control a small DC motor, like the one in a tape recorder. When both the points A & B are "HIGH" Q1 and Q2 are in saturation. Hence the bases of Q3 to Q6 are grounded. Hence Q3,Q5 are OFF and Q4,Q6 are ON . The voltages at both the motor terminals is the same and hence the motor is OFF. Similarly when both A and B are "LOW" the motor is OFF.When A is HIGH and B is LOW, Q1 saturates ,Q2 is OFF. The bases of Q3 and Q4 are grounded and that of Q4 and Q5 are HIGH. Hence Q4 and Q5 conduct making the right terminal of the motor more positive than the left and the motor is ON. When A is LOW and B is HIGH ,the left terminal of the...

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Light Flasher Circuit Diagram

This is a very basic circuit for flashing one or more LEDS and also to alternately flash one or more LEDs.It uses a 555 timer setup as an astable multivibrator with a variable frequency.With the preset at its max. the flashing rate of the LED is about 1/2 a second. It can be increased by increasing the value of the capacitor from 10uF to a higher value. For example if it is increased to 22uF the flashing rate becomes 1 second.There is also provision to convert it into an alternating flasher. You just have to connect a LED and a 330ohm as shown in Fig.2 to the points X and Y of Fig.1. Then both the LEDs flash alternately.Since the 555 can supply...

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Pot Plant Water Tester Circuit Diagram

This simple device checks if their is water in a pot plant. You stick the two probes(paperclips)into the pot plant and if the LED lights, it means there is water in the pot plant.You need to adjust the 47k potentiometer to set the level at which the LED goes ...

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Simple IF Signal Generator Circuit Diagram

Here is a versatile circuit of IF signal generator which may be of interest to radio hobbyists and professionals alike.Transistors T1 and T2 form an astable multivibrator oscillating in the audio frequency range of 1 to 2 kHz. RF oscillator is built around transistor T3. Here again a 455kHz ceramic filter/resonator is employed for obtaining stable IF. The AF from multivibrator is coupled from collector of transistor T2 to emitter of transistor T3 through capacitor C3. The tank circuit at collector of transistor T3 is formed using medium wave oscillator coil of transistor radio, a fixed 100pF capacitor C5 and half section of a gang capacitor (C6).The...

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Electronic Scooring Game Circuit Diagram

You can play this game alone or with your friends. The circuit comprises a timer IC, two decade counters and a display driver along with a 7-segment display. The game is simple. As stated above, it is a scoring game and the competitor who scores 100 points rapidly (in short steps) is the winner. For scoring, one has the option of pressing either switch S2 or S3. Switch S2, when pressed, makes the counter count in the forward direction, while switch S3 helps to count downwards. Before starting a fresh game, and for that matter even a fresh move, you must press switch S1 to reset the circuit. Thereafter, press any of the two switches, i.e. S2 or...

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Soft ON/OFF Switch Circuit Diagram

Modern electronic equipment incorporate "push-to-on-push-to-off" switches that do not make the clicking noise as with old equipment. An example of this is the power button on a ATX computer cabinet. Here is a circuit that does the same. It can be used to turn on/off any electronic/electrical equipment that operates on any range of voltages.When the "ON/OFF" button is pressed once, the equipment goes on and stays on. It goes off when the button is pressed again. The circuit is straight forward. It uses a JK CMOS FlipFlop to with its JK terminals tied high to achieve the toggling action. The clock is provided by the push button used for on/off...

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Analog To Digital Converter Circuit Diagram

Normally analogue-to-digital con-verter (ADC) needs interfacing through a microprocessor to convert analogue data into digital format. This requires hardware and necessary software, resulting in increased complexity and hence the total cost.The circuit of A-to-D converter shown here is configured around ADC 0808, avoiding the use of a microprocessor. The ADC 0808 is an 8-bit A-to-D converter, having data lines D0-D7. It works on the principle of successive approximation. It has a total of eight analogue input channels, out of which any one can be selected using address lines A, B and C. Here, in this case, input channel IN0 is selected by grounding...

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Charge Monitor For 12 V Circuit Diagram

A battery is a vital element of any battery-backed system. In many cases the battery is more expensive than the system it is backing up. Hence we need to adopt all practical measures to conserve battery life.As per manufacturer's data sheets, a 12V rechargeable lead-acid battery should be operated within 10. IV and 13.8V. When the battery charges higher than 13.8V it is said to be overcharged, and when it discharges below 10.IV it can be deeply discharged. A single event of overcharge or deep discharge can bring down the charge-holding capacity of a battery by 15 to 20 per cent.It is therefore necessary for all concerned to monitor the charge...

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Audio Level Meter (VU Meter) Circuit Diagram

This circuit uses just one IC and a very few number of external components. It displays the audio level in terms of 10 LEDs. The input voltage can vary from 12V to 20V, but suggested voltage is 12V.The LM3915 is a monolithic integrated circuit that senses analog voltage levels and drives ten LEDs providing a logarithmic 3 dB/step analog display. LED current drive is regulated and programmable, eliminating the need for current limiting resistors.The IC contains an adjustable voltage reference and an accurate ten-step voltage divider. The high-impedance input buffer accepts signals down to ground and up to within 1.5V of the positive supply. Further,...

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Bass Treble Tone Control Circuit Diagram

The LM1036 is a DC controlled tone (bass/treble), volume and balance circuit for stereo applications in car radio, TV and audio systems. An additional control input allows loudness compensation to be simply effected. Four control inputs provide control of the bass, treble, balance and volume functions through application of DC voltages from a remote control system or, alternatively, from four potentiometers which may be biased from a zener regulated supply provided on the circuit. Each tone response is defined by a single capacitor chosen to give the desired characteristic.Features: * Wide supply voltage range, 9V to 16V * Large...

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Audio Light Modulator Circuit Diagram

Audio light modulations add to the enjoyment of music during functions organised at home or outdoors. Presented here is one such simple circuit in which light is modulated using a small fraction of the audio output from the speaker terminals of the audio amplifier. The output from the speaker terminals of audio amplifier is connected to a transformer (output transformer used in transistor radios) through a non-polarised capacitor. The use of transformer is essential for isolating the audio source from the circuit in The sensitivity control potentiometer VR1 provided in the input to transistor T1 may be adjusted to ensure that conduction takes...

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5 Band Graphic Equalizer Circuit Diagram

This circuit uses a single chip, IC BA3812L for realizing a 5 band graphic equalizer for use in hi-fi audio systems.The BA3812L is a five-point graphic equalizer that has all the required functions integrated onto one IC. The IC is comprised of the five tone control circuits and input and output buffer amplifiers. The BA3812L features low distortion, low noise, and wide dynamic range, and is an ideal choice for Hi-Fi stereo applica-tions. It also has a wide operating voltage range (3.5V to 16V), which means that it can be adapted for use with most types of stereo equipment.The five center frequencies are independently set using external capacitors,...

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Ultrasonic Switch Circuit Diagram

Circuit of a new type of remote control switch is described here. This circuit functions with inaudible (ultrasonic) sound. Sound of frequency up to 20 kHz is audible to human beings. The sound of frequency above 20 kHz is called ultrasonic sound. The circuit described generates (transmits) ultrasonic sound of frequency between 40 and 50 kHz. As with any other remote control system this cirucit too comprises a mini transmitter and a receiver circuit. Transmitter generates ultrasonic sound and the receiver senses ultrasonic sound from the transmitter and switches on a relay. The ultrasonic transmitter uses a 555 based astable multivibrator. It...

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Sound Controlled Flip Flop Circuit Diagram

Described here is a very inexpensive solution to many phono-controlled applications like remote switching on, for instance, or activating a camera, tape recorder, burglar alarms, toys, etc. The circuit given here employs a condenser microphone as the pick-up. A two-stage amplifier built around a quad op-amp IC LM324 offers a good gain to enable sound pick-up upto four metres. The third op-amp is configured as a level detector whose non-inverting terminal is fed with the amplified and filtered signal available at the output of the second op-amp. The inverting input of the third op-amp is given a reference voltage from a potential divider consisting...

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Ultrasonic Pest Repellent Circuit Diagram

It is well know that pests like rats, mice etc are repelled by ultrasonic frequency in the range of 30 kHz to 50 kHz. Human beings can’t hear these high-frequency sounds. Unfortunately, all pests do not react at the same ultrasonic frequency. While some pests get repelled at 35 kHz, some others get repelled at 38 to 40 kHz. Thus to increase the effectiveness, frequency of ultrasonic oscillator has to be continuously varied between certain limits. By using this circuit design, frequency of emission of ultrasonic sound is continuously varied step-by-step automatically. Here five steps of variation are used but the same can be extended up to 10...

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Indicator For Telephone Circuit Diagram

Many a times one needs an extra telephone ringer in an ad joining room to know if there is an incoming call. For example, if the telephone is installed in the drawing room you may need an extra ringer in the bedroom. All that needs to be done is to connect the given circuit in parallel with the existing telephone lines using twin flexible wires. This circuit does not require any external power source for its operation. The section comprising resistor R1 and diodes D5 and LED1 provides a visual indication of the ring. Remaining part of the circuit is the audio ringer based on IC1 (BA8204 or ML8204). This integrated circuit, specially designed...

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CD-Rom Audio CD Without Computer Circuit Diagram

Most of the CDROMS available have an Audio-Out Output to either plug in the headphones or connect it to an amplifier.This circuit enables one to use the CDROM as a stand alone Audio CD player without the computer.This circuit is nothing but a power supply which supplies +5v, +12V and Ground to the CDROM drive andhence can be used without the computer.You should buy a D-type power connecter to connect this circuit's outputs to the CDROM.The details of the D connector are shown along with the circuit diagram.Note that the D-connector goes into the CDROM in only one way and hence prevents any damage due to wrong connection.Ensure that the 12V(yellow)...

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Infra Red Headphone Circuit Diagram

Using this low-cost project one can reproduce audio from TV without disturbing others. It does not use any wire connection between TV and headphones. In place of a pair of wires, it uses invisible infrared light to transmit audio signals from TV to headphones. Without using any lens, a range of up to 6 metres is possible. Range can be extended by using lenses and reflectors with IR sensors comprising transmitters and receivers.IR transmitter uses two-stage transistor amplifier to drive two series-connected IR LEDs. An audio output transformer is used (in reverse) to couple audio output from TV to the IR transmitter. Transistors T1 and T2...

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Intercom Using Transistor Circuit Diagram

The circuit comprises a 3-stage resistor-capacitor coupled amplifier. When ring button S2 is pressed, the amplifier circuit formed around transistors T1 and T2 gets converted into an asymmetrical astable multivib-rator generating ring signals. These ring signals are amplified by transistor T3 to drive the speaker of earpiece.Current consumption of this intercom is 10 to 15 mA only. Thus a 9-volt PP3 battery would have a long life, when used in this circuit.For making a two-way intercom, two identical units, as shown in figure, are required to be used. Output of one amplifier unit goes to speaker of the other unit, and vice versa. For single-battery...

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Stereo Channel Selector Circuit Diagram

The add-on circuit presented here is useful for stereo systems. This circuit has provision for connecting stereo outputs from four different sources/channels as inputs and only one of them is selected/connected to the output at any one time.When power supply is turned ‘on’, channel A (AR and AL) is selected. If no audio is present in channel A, the circuit waits for some time and then selects the next channel (channel B). This search operation continues until it detects audio signal in one of the channels. The inter-channel wait or delay time can be adjusted with the help of preset VR1. If still longer time is needed, one may replace capacitor...

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Timed Burglar Alarm Circuit Diagram

This is a simple but effective alarm circuit which can reset its self after a time that you select. it has normally open and normally closed triggers which make this circuit very practical. This alarm has normally open and normally closed triggers. It's on a 555 timer so the alarm will reset it's self after a certain amount of time. The time is adjustable with the variable resistor in the circuit. The alarm has a reset switch which you can replace with a key switch to make it more secure, and you can change the triggers to other types of door or window switched too. The alarm uses a relay which is connected to a siren but you can replace the...

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Infra Red Beam Alarm Circuit diagram

This circuit can be used as an Infrared beam barrier as well as a proximity detector.The circuit uses the very popular Sharp IR module (Vishay module can also be used). The pin nos. shown in the circuit are for the Sharp & VIshay modules. For other modules please refer to their respective datasheets.The receiver consists of a 555 timer IC working as an oscillator at about 38Khz (also works from 36kHz to 40kHz) which has to be adjusted using the 10K preset. The duty cycle of the IR beam is about 10%. This allows us to pass more current through the LEDS thus achieving a longer range.The receiver uses a sharp IR module. When the IR beam from...

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Beeper Circuit Diagram

This circuit produces the sound of a beeper like the one in pagers which produces a "beep-beep" sound. Basically the circuit consists of a 555 timer oscillator which is turned ON and OFF periodically.The first IC(left) oscillates at about 1Hz. The second IC is turned ON and OFF by the first IC.The first IC determines how fast the second IC is turned ON/OFF and second IC determines the tone of the final output.By varying the VR1, the changeover rate can be adjusted. By varying VR2 the tone can be adjusted.If you know something about electronics, you can try replacing the 2nd 555 IC circuit with a piezoelectric buzzer. This saves one IC and associated...

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Big Ben Sound Circuit Diagram

This circuit produces the famous Big Ben sound. It produces the "ding dong" sound when switched ON.Basically the circuit alternates between two frequencies which are adjustable. This produces the "ding-dong" sound.The first IC(left) oscillates at about 1Hz. The second IC's tone is modulated by the changing voltage at the output of the first IC.The first IC determines how fast the changeover from one frequency to the other takes place and second IC determines the tone of the final output.By varying the VR1, the changeover rate can be adjusted. By varying VR2 the tone can be adjust...

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Police Siren Circuit Diagram

This circuit produces a sound similar to the police siren.It makes use of two 555 timer ICs used as astable multivibrators. The frequency is controlled by the pin 5 of the IC.The first IC (left) is wired to work around 1Hz. The 47uF capacitor is charged and discharged periodically and the voltage across it gradually increases and decreases periodically.This varying voltage modulates the frequency of the 2nd IC. This process repeats and what you hear is the sound remarkably similar to the police siren.Two presets VR1 and VR2 are provided to vary the siren period of repetition and the tone of the siren.By varying VR1 you can set how fast the siren...

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Factory Alarm Circuit Diagram

This circuit produces a sound similar to a factory siren.It makes use of a 555 timer Ic used as an astable multivibrator of a center frequency of about 300Hz.The frequency is controlled by the pin 5 of the IC. When the supply is switched ON, the capacitor charges slowly and this alters the voltage at pin 5 of the IC hence the frequenct gradually increases.After the capacitor is fully charged, the frequency no longer increases. Now when the push button siren control switch is held depressed, the capacitor discharges and the siren frequency also decreases.The presets VR1 and VR2 should be adjusted for optimum performan...

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Daylight Alarm Circuit Diagram

The circuit presented here wakes you up with a loud alarm at the break of the daylight. Once again the 555 timer is used here. It is working as an astable multivibrator at a frequency of about 1kHz.The circuit's operation can be explained as follows:When no light falls on the LDR, the transistor is pulled high by the variable resistor. Hence the transistor is OFF and the reset pin of the 555 is pulled low. Due the this the 555 is reset.When light falls on the LDR, its resistance decreases and pulls the base of the transistor low hence turning it ON. This pulls the reset pin 4 of the 555 high and hence enables the 555 oscillator and a sound is...

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Fire Alarm Circuit Diagram

This circuit warns the user against fire accidents. It relies on the smoke that is produced in the event of a fire. When this smoke passes between a bulb and an LDR, the amount of light falling on the LDR decreases. This causes the resistance of LDR to increase and the voltage at the base of the transistor is pulled high due to which the supply to the COB (chip-on-board) is completed. Different COBs are available in the market to generate different sounds.The choice of the COB depends on the user. The signal generated by COB is amplified by an audio amplifier. In this circuit, the audio power amplifier is wired around IC TDA 2002. The sensitivity...

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Car Anti Theft Wireless Alarm Circuit Diagram

This FM radio-controlled anti- theft alarm can be used with any vehicle having 6- to 12-volt DC supply system. The mini VHF, FM transmitter is fitted in the vehicle at night when it is parked in the car porch or car park. The receiver unit with CXA1019, a single IC-based FM radio module, which is freely available in the market at reasonable rate, is kept inside. Receiver is tuned to the transmitter's frequency. When the transmitter is on and the signals are being received by FM radio receiver, no hissing noise is available at the output of receiver. Thus transistor T2 (BC548) does not conduct. This results in the relay driver transistor T3 getting...

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