Simple LED Flasher Circuit

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Luxurious Toilet Bathroom Controller

Smart controller for your toilet and bathroom. The light and fan will automatic on when someone entere toilet or bathroom and off when no person inside it.


Aged persons in the house and guests often fumble while searching for the toilet and bathroom switches at night. Also, very few of us take care to switch off the lights of toilets/bathrooms after using them. The circuit given here helps to overcome both the problems. The figure shows two symmetrical circuits (one each for toilet and bathroom) sharing common power supply and a melody generator-cum-audio warning unit. The reed switches S1 and S2 are of normally-open type, operated by permanent magnets appropriately fixed to the doors of bathroom and toilet, respectively. When the doors of bathroom and toilet are closed, the reed switches are also closed, and vice versa. (Door is assumed in closed condition with nobody inside bathroom/toilet, i.e. reed switch is activated.) 

The operational features of the circuit are: 

• Lamp and exhaust fan are switched on when the door is opened.
• Soft music is played continuously until the door is closed from inside/out side.
• With a person inside the room, lamp and fan remain on, until the door is reopened. They go off when the door is reopened.
• Visual indication of whether the toilet/bathroom is occupied/vacant is given by two bicolour LEDs fixed on a panel, which may be fitted near the door with corresponding ‘toilet’/’bathroom’ labels on them. Here the LED colour turns from ‘green’ to ‘red’ if the room gets occupied, and vice-versa.
• If the door is opened once, and not closed back within 10 seconds, the lamp and fan are automatically switched off, thus conserving electricity. But the music remains on as a reminder that the door is not closed.
• For cleaning of bathroom/toilet with doors kept open, a parallel on/off switch is included on the switchboard to bypass the relay contacts and manually control the switching on/off of the light and exhaust fan. (This is the service mode.) In this case, the music remains on as long as the door remains open. In case of failure of the unit, the same on/off switch can be used as usual until the circuit is repaired.
• Due to battery backup facility, even with power failure, when a person is inside, the door status is maintained. However, the lamp and fan will be on only on mains resumption.
• Also, when a person leaves the room during power failure, with door closed, the lamp and fan are kept off on resumption of power. (Intelligent-mode!)
• However, the circuit can be fooled by opening and closing the door within 10 seconds, without entering inside. In this case, the lamp and fan will continue to be on and would require reopening and closing of the door to bring the circuit to order.

This problem can be prevented to some extent by using a hydraulic door opener, which would approximately take 10 seconds to close the opened door. A delay period of 10 seconds is deliberately chosen for letting the person inside the toilet/bathroom in normal case! IC1 is a dual positive edge-triggered ‘D’ type flip-flop. IC1(a) gets triggered when bathroom door (and switch S1) is opened and hence IC1(b) toggles, as Q output of IC1(a) is connected to clock input pin of IC1(b). As a result, relay RL1 energises through transistor T3, thereby switching on the lamp and exhaust fan. (Please refer to Fig. 2, the separate wiring diagram of lamp and exhaust fan via the N/O contacts of the relay.) 

Simultaneously, pin 2 (Q) of IC1(a) goes low, switching transistor T5 ‘on’, which switches on melody generator IC4, letting out a sweet audio tune via transistor T6 and loudspeaker. In normal condition, when someone opens the bathroom door and gets inside within preset time of IC3(a) (10 seconds here), and closes the door from inside, the music stops with lamp and fan ‘on’. Now, in case someone opens the door before or after use, and forgets to shut it, the lamp and exhaust fan are switched off after 10 seconds but the music remains ‘on’ as a reminder that the door is to be closed. 

This happens due to mono multivibrator (MMV) IC3(a), which resets pin 10 of IC1(b) through transistor T1 after 10 seconds. (This period can be adjusted by varying the values of resistor R11 and/or capacitor C7.) It should be noted here that although IC3 is used as ‘MMV’, it is triggered here with a positive pulse through its pin 4 (reset pin) rather than its pin 6 (trigger pin). This arrangement makes it unique for setting and resetting IC3 through pin 4, and resetting IC1(a) through pin 5 of IC3 and transistor T1. Battery backup facility ensures memory backup during power failure. Power supply uses a normal 2-diode full-wave rectifier circuit, which needs no further explanation. 

The purpose of using bi-color LED1 and LED2 is that, initially when the door is closed these emit green light— as the green LED part gets the supply via resistor R15— to indicate that bathroom/toilet is vacant. When bathroom/toilet is occupied, transistor T3/T4 conduct to light up the red LED part as well. Melody generator IC4 (UM66) is switched on through diodes D3/D4 and transistor T5, which conducts when IC1(a) pin 2 or IC2(a) pin 2 goes low. When transistor T5 conducts, zener ZD1 breaks down and supplies regulated 3.9V to IC4, to produce a melodious tune via transistor T6 and the speaker. As most toilets and bathrooms are ‘attached’ nowadays, only a single circuit is required, and the circuit can be wired on a general-purpose veroboard. A small modification of the circuit, by adding additional SPST switch S3, as shown in Fig. 2, needs to be done inside the wooden switchboard box. This permits the user to operate the lamp and fan during cleaning of the toilet or for bypassing the circuit, when bathroom or toilet undergo repair work.

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Bicycle Horn Using Tone Generator KA2411

An interesting circuit of a bicycle horn based on a popular, low cost telecom ringer chip is described here. This circuit can be powered using the bicycle dynamo supply and does not require batteries, which need to be replaced frequently. The section comprising diodes (D1 and D2) and capacitors (C1 and C2) forms a half-wave voltage-doubler circuit. The output of the voltage doubler is fed to capacitor C3 via resistor R1. The maximum DC supply that can be applied to the input terminals of IC1 is 28V. Therefore zener diode ZD1 is added to the circuit for protection and voltage regulation. The remainder of the circuit is the tone generator based on IC1 (KA2411). 

The dual-tone output signal from pin 8 of IC1 is fed to the primary of transformer X1 (same as used in transistor radios) via capacitor C6. The secondary of X1 is connected to a loudspeaker directly. In case you are interested in connecting a piezoceramic element in place of the loudspeaker, remove capacitor C6, transformer X1, and the loudspeaker. Connect one end of the piezoceramic disk to pin 5 of IC1 and the other end to pin 8 of IC1 through a 1/4W, 1-kiloohm resistor. IC1 KA2411 is also available in COB style, with the same pin configuration. Both packages work equally well.

However, to get the best results with the COB package, change values of resistors R2 through R4 to 330-kilo-ohm, capacitor C4 to 0.47µF, 63V electrolytic (positive end to pin 3 of IC1), and C5 to 0.005µF, 63V. This bicycle horn project can also be used as a telephone extra ringer by just removing all components on the left side of capacitor C3 and connecting the circuit shown in Fig. 2 to the terminals of capacitor C3.

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50W Audio Amplifier Using IC TDA1562

The integrated output amplifier described in this article consists of little more than one integrated circuit. It is intended especially for use in motor vehicles and other battery-operated applications. Although it appears simple and hardly worth looking at, the amplifier can produce an appreciable audio power output. The circuit diagram in Figure 2 emphasizes how few external components are needed to construct a complete output amplifier.

For instance, the new device does not need compensation networks to enhance the stability. Also, because of the absence of switch-on phenomena, there is no need for a switch-on delay network. There is, of course, still a need for supply line decoupling capacitors. Capacitors C5 and C6 are required for Class-H operation, about which more in the box. The value of input capacitors C1 and C2 is relatively low, thanks to the high input impedance of the IC. Switched RC network R4-C4 at the ‘mode select’ input (pin 4) serves to switch the IC to ‘mute’ or ‘standby’.

 When the supply voltage is switched on, the IC is first switched automatically to the ‘mute’ mode and to ‘on’ only after a short delay. The time constant R4-C4 is a few tenths of a second and this delay between the two states is sufficient to obviate disturbing (and annoying) switch-on phenomena. Switch S1 enables the amplifier to be switched to ‘standby' when the use of the amplifier is not needed for a period of time. When that time has elapsed, the amplifier is quickly reverted to normal operation. The current drain in the standby mode is virtually negligible at only 200µA. Resistor R3 prevents a short-circuit current ensuing when S1 is being closed at the instant C4 is being discharged.

Measurement results (at Ub=14.4 V)
Supply voltage

• 8–18 V

Sensitivity

• 760 mV r.m.s.

Input impedance

• 70 kΩ

Power output

• 54 W r.m.s. into 4 Ω (f=1 kHz; THD+N=1%)

Harmonic distortion (THD+N)

• at 1 W into 4 Ω: 0.046% (1 kHz)
• 0.29% (20 kHz)
• at 35 W into 4 Ω: 0.12% (1 kHz)
• 0.7% (20 kHz)

Signal-to-noise ratio (with 1 W into 4 Ω)

• 88 dBA

Power bandwidth

• 7.5 Hz – 185 kHz (at 25 W into 4 Ω)

Quiescent current

• about 135 mA (‘on’)

Resistors:

• R1 = 1MΩ
• R2 = 4kΩ7
• R3 = 1kΩ
• R4 = 100kΩ

Capacitors:

• C1,C2 = 470nF
• C3,C4 = 10µF 63V radial
• C5,C6,C8 = 4700µF 25V radial
• (18mm max. dia., raster 7.5 mm)
• C7 = 100nF, raster 5 mm

Semiconductors:

• D1 = high-efficiency-LED
• IC1 = TDA1562Q (Philips)

Miscellaneous:

• S1 = single-pole on/off switch
• Four spade connectors, PCB mount Heatsink for IC1 (Rth<2.5 K/W)

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Infrared Proximity Detector Alarm

 Infrared Proximity Detector Alarm Circuit Diagram

This circuit can be built from readily available low-cost components, some of which may even be hiding in your junkbox! The indicated value of 22 Ω for resistor R1 causes an average current of about 65 mA through infrared emitter D1. Because the IRED is pulsed at a duty factor of about 50% through the action of T1 and IC1, a peak current of 128 mA flows during every half cycle. This may seem a lot but in fact is well within the safe specification of the LD274. The LM567 PLL IC is configured to supply a switching frequency of about 20 kHz. When the infrared beam emitted by D1 is reflected by a nearby object, IC1, through receiver diode D2 and transistor T2, receives the recovered 20 kHz signal at its input, pin 3. Because the ‘567 PLL is then locked, the IC output (pin 8), drops low, triggering the 555 chip in monostable mode (IC2) and so causing acoustic actuator Bz1 to sound. The monostable remains on as long as the reflected signal is being received. Because of the presence of T3, capacitor C5 is allowed to charge only when no signal is being received. In that condition, the 555 is turned off automatically after a time determined by R9-C5. Using the component values shown, this will be about 5 seconds. Obviously D1 and D2 should be mounted such that the latter can only pick up reflected infrared light.

The choice of the two infrared components used in this circuit will be uncritical but they must be ‘band’ compatible, i.e., generate (D1) and respond to (D2) the same wavelength. The operating point of the receiver input circuit is rather dependent on ambient day-light levels and the value of R4 may need to be adjusted a little to ensure a voltage of between 1.5 V and 4 V on the collector of T1 when no signal is being received. Some dc buzzers cause a lot of back-emf so it may be necessary to insert a diode in series with the output of IC1. If necessary, this diode should preferably be a Schottky type because of the inherent low voltage drop of about 0.4 V as opposed to 0.65 V for a typical small-signal silicon diode.

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Simple Mini FM Receiver / Radio Receiver

This is a very simple and mini fm radio receiver with good performances that works great even if the sensitivity is not too high. The working principle of this fm receiver may seem a little unusual. It is made of an oscillator (T2 and T3) that is synchronized with the received frequency of T1. This transistor works as a broadband preamplifier in VHF range.  The oscillator is adjusted between 87 … 108 MHz with C5. Because of the synchronization, the oscillator output will have the same frequency deviation as the received signal from the fm antenna. This deviations are caused by the broadcasted audio informations. The frequency modulated signal show up on P1 + R5. Low pass filter R6/C6 extracts the audio signal and then is amplifier by T4 … T6 and transmitted at the output through C9 capacitor.

The coil details are presented in the fm receiver circuit diagram. The radio receiver is adjusted on different stations with the help of C5. P1 potentiometer is adjusted untill the best reception is obtained. If we attach an audio amplifier and a speaker then this fm receiver can be made very compact as a pocket radio.

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Rain Director / Water Sensor

Water is a conductor of electricity. When water is in contact with the probe then there is a flow of current toward the base of  NPN transistor (BC548), which conducts. With the conduction of NPN transistor, electron reaches to Q2, which is a PNP transistor . PNP transistor (BC558) also conducts and current flows through the speaker. In a speaker there is inductive coil which causes motion in one direction and after that produces induce current, which is in opposite direction to the flow of current this induced current in the form of pulse, flows through a capacitor, resistance and makes 1st transistor BC548 off for an inter-well and after-that it relaxes to previous state. This process repeats again and again till probe is in contact with water and an oscillation is created in the circuit. Speaker diaphragm vibrates and gives a tone. Frequency of the circuit depends on the value of Coil impendence, Capacitor and Resistance Value.

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Petrol/Diesel Level Sensor

This sensor is particularly suitable for use in small spaces, such as the petrol tank of a  motorbike. It has the advantage of not having any moving parts, unlike a conventional sensor with a float and float arm that make it difficult to fit in a tank.

The sensor circuit is made from standard, inexpensive components and can be put together for little money.

The operating principle is  based on  measuring  the forward volt-ages of two identical diodes (check this  first by measuring  them).  The forward voltage of a diode decreases with increasing junction temperature. lf a resistor is placed close to one of the two diodes, it will be heated slightly if it extends above the surface of the  petrol. For best results,the other diode (used for reference) should be located at the same level. lf the diodes are covered by the petrol in the tank, the heating resistor will not have any effect because it will be cooled by the petrol. An opamp compares the voltage across the two diodes, with a slightly smaller current passing through the reference diode. 

a

When the petrol level drops, the output of the opamp goes high and the output transistor switches on. This causes a sense resistor to be connected in parallel with the sensor output. Several sensor circuits can be used together, each with its own switched sense resistor connected in parallel with the output, and the resulting output  signal can be used to drive a meter or the like.

Using this approach, the author built a petrol tank' sensors trip' tank consisting of five PCBs, each fitted with two sensor circuits. With this sensor strip installed at an angle in the tank, a resolution of approximately 1.5 litre per sensor is possible. Many tanks have an electrical fitting near the bottom for connection to a lamp on the instrument panel that indicates the reserve level. The sensor strip can be used in its place. You will have to experiment a bit with the values of the sense resistors, but do not use values lower than around'100 O. It is also important to fit the diodes and heater resistor in a little tube with a small opening at the bottom so that splashing petrol does not cool the heater resistor, since this would result in false readings.

The circuit should be powered from a regulated supply voltage of 5 to 6 V to prevent the heating resistors from becoming too hot. After testing everything to be sure that it works properly, it's a good idea to coat the circuit board with epoxy glue to provide better protection against the petrol.

Tip: you can use the well-known 1M3914 to build a LED display with ten LEDs, which can serve as a level indicator. Several examples of suitable circuits can be found in back issues of Elektor.

Note: this sensor circuit is not suitable for use in conductive liquids.

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High and Low Voltage Cut-Off with Delay and Alarm

Simple and easy build High and Low Voltage Cut-Off with Delay and Alarm Circuit. This straight forward circuit will protect electrical appliances from over voltage as well as under voltage. The circuit also produces an alarm when the power supply comes back. An ideal circuit for home to protect your valuable equipments from voltage fluctuations. The same circuit with some modifications can be used  to make a automatic voltage stabilizer. 

When the mains voltage is in the normal level, the voltage at the negative terminal of zener diode D4 will be less than 5.6 Volts. At this condition transistor T1 will not conduct. The same time voltage at the negative terminal of zener diode D5 will be greater than 5.6 and so the transistor T2 will be conducting. The relay will be activated and the green LED will be glowing.

When the mains voltage is higher than the set limit the transistor T1 becomes conducting since the voltage at the negative terminal of  D4 is greater than 5.6 V. At the same time transistor T2 will be non conducting which results in the deactivation of relay to cut the mains supply from load. When the mains voltage is less than the set limit transistors T1 & T2 becomes non conducting  making the relay to de-activate and cut the load from mains.

The timer NE555 is wired as a monostable multivibrator with a pulse width of 10ms.When the power comes back after a cut off a negative voltage is obtained at the trigger pin which triggers the IC NE555. The transistor T3 gets forward biased and it drives the buzzer to produce a beep as an indication of power resumption. Also the transistor T1 is made on which in turn makes T2 off. As a result the relay will remain de- activate for 10ms and this provides the sufficient delay and the equipment  is protected from surge voltages.

Notes :

• To calibrate the circuit a autotransformer is needed. Connect the output of autotransformer to the transformer primary.
• Set the voltage to 260V and adjust  VR1 to make the relay deactivated.
• Now set the autotransformer to 160V and adjust VR2  so that the relay is de-energized.
• VR3 can be used to vary the volume of buzzer.

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8 Stage LED VU Meter

The circuit below uses two quad voltage comparators (LM339) to illuminate a series of 8 LEDs indicating volume level. Each of the 8 comparators is biased at increasing voltages set by the voltage divider so that the lower right LED comes on first when the input is about 400 millivolts or about 22 milliwatts peak in an 8 ohm system.

The divider voltages are set so that each LED represents about twice the power level as the one before so the scale extends from 22 milliwatts to about 2.5 watts when all LEDs are lit. The sensitivity can be decreased with the input control to read higher levels. I have not built or tested this circuit, so please let me know if you have problems getting it working. The power levels should be as follows:

• 1 LED = 22mW
• 2 LEDs = 42mW
• 3 LEDs = 90mW
• 4 LEDs = 175mW
• 5 LEDs = 320mW
• 6 LEDs = 650mW
• 7 LEDs = 1.2 Watts
• 8 LEDs = 2.5 watts

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Bass Treble Tone Control

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 volume control range, 75 dB typical
Tone control, ±15 dB typical
Channel separation, 75 dB typical
Low distortion, 0.06% typical for an input level of 0.3 Vrms
High signal to noise, 80 dB typical for an input level of 0.3 Vrms
Few external components required

Note : 

Vcc can be anything between 9V to 16V and the output capacitors are 10uF/25V electrolytic

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Frost Alarm

Description

A simple thermistor triggered switch with adjustable threshold. It triggers with cold temperatures so may be used as a frost alarm or cold temperature switch.


Circuit Notes


The thermistor used has a resistance of 15k at 25°C and 45k at 0° Celsius. A suitable bead type thermistor can be found in the Maplin catalogue. The 100k pot allows this circuit to trigger over a wide range of temperatures.

If using a different thermistor then the control should match the new thermistor at its highest resistance, or be higher in value. The op-amp in this circuit is the ubiquitous 741. It may be catalogued as LM741, CA741 etc, all types will work. In this circuit it is used as a comparator. The non-inverting input (pin 3) is biased to half the supply voltage. The inverting input is connected to the junction of the thermistor and potentiometer. The control is adjusted so that the circuit is on when the thermistor is at the required temperature range. Once the thermistor is outside the temperature range its resistance alters and the op-amp output changes from near full supply to around 1 or 2 volts dc. There is insufficient voltage to turn on the transistor and the relay will not energise.

A slight amount of hysteresis is provided by inclusion of the 270k resistor. This prevents rapid switching of the circuit when the temperature is near to the switching threshold. 


PCB Layout

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INVERTER WITH BATTERY LOW AND OVER LOAD INDICATOR

Inverters become a necessary device for a common man. Especially, in summer, the power shortage is more. We To overcome from the difficulties caused by power shortage by using inverters. This project is designed for 45W load. This project uses SG524 IC for SMPS control and LM339 to detect the over load, inverter on, charging on and battery low conditions. CFL loads are suggested for this project, as they consume low power and produce high intensity of lighting. These inverters play vital role especially in rural areas. A rechargeable 12V battery is used to store the energy during power availability. The back up time depends on the battery ampere – hour rating. This inverter can show the battery low condition and Over load conditions by 5mm LED indicator circuit. This project uses regulated 5V, 750mA power supply for microcontroller unit. 7805 three terminal voltage regulator is used for voltage regulation. Bridge type full wave rectifier is used to rectify the ac out put of secondary of 230/12V step down transformer.

BLOCK DIAGRAM 

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Clap Switch

Here is a Hobby Circuit for electronics hobbyists that can switch on & off a light, Fan, Radio etc., by the sound of clap. The sound of clap is received by a small microphone that is shown biased by resistor R1 in the circuit. The microphone changes sound wave in to electrical wave, which is further amplified by Q1. Transistor Q1 is used as common emitter circuit to amplify weak signals received by the microphone. Amplified output from the collector of transistor Q1 is  feed to the Bi stable Multivariate circuit also known as flip-flop circuit.

Circuit Diagram

How Clap Switch Works

    Flip flop circuit is made by using two Transistor, in our circuit Q2&Q3. In a flip-flop circuit, at a time only one transistor conduct and other cutoff and when it gets a trigger pulse from outside source then first transistor is cutoff and 2nd transistor conducts, thus output of transistor is either logic-0 or logic-1 and it remains in one state 0 or 1 until it gets trigger pulse from outer source.
    The pulse of clap, which is a trigger for flip-flop makes changes to the output state that is complementary (reverse). Output of flip-flop, which is in the low current form is unable to drive relay so we have used a current amplifier circuit by using Q4 that is a common emitter circuit. Output of Q4 is connected to a Relay (Electromagnetic switch) which works like a mechanical switch and it becomes easy for connecting other electrical appliance.
    The relay contact is connected to the power line and hence turns on/off any electrical appliance connected all the way through relay.
Clap Switch

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Active Phase Selector for Single Phase Load from 3 Phase Supply

ABSTRACT:  Phase absence is a very common and severe problem in any industry, home or office. Many times one or two phases may not be live in three phase supply. Because of this, many times, some electrical appliances will be on in one room and OFF in another room. This creates a big disturbance to our routine work.  This project is designed to check the availability of any live phase, and the load will be connected to the particular live phase only. Even a single phase is available, and then also, the load will be in ON condition.  This project is designed with AT89S52 MCU. This controller continuously checks for live condition of all phases connected to it, and the controller connects the load to the active phase using a Relay. This relay is driven with a transistor.  If two or three phases are live, the load will be connected to phase I only. An LCD is provided to display the status of the phase condition. Contrast control preset is given for LCD contrast control.  This project uses regulated 12V, 500mA power supply. 7805 three terminal voltage regulator is used for voltage regulation. Bridge type full wave rectifier is used to rectify the ac out put of secondary of 230/12V step down transformer

Block Diagram :

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HIGH SENSITIVITY INTELLIGENT BLIND STICK

        Now-a-days many accidents occur due to intense traffic. It is very difficult for blind people for path finding without others help. This project helps to facilitate blind people in path clearing assistance and obstacle detection.  In this project we are using an IR transmitter and Receiver circuit based path clearing assist cap. Path clearing assist cap is used to detect any obstacles. If any obstacle is found, the IR light will be reflected back and sensed by IR receiver and sends a signal to the buzzer driver circuit, which produces buzzer sound near hand.  This projects works very well even in night and day timings, irrespective of the lighting intensity. This project is reliable and effective. This project uses regulated 5V, 750mA power supply. Unregulated 12V DC is used for relay. 7805 three terminal voltage regulator is used for voltage regulation. Bridge type full wave rectifier is used to rectify the ac output of secondary of 230/12V step down transformer. This project can be powered by a simple 9V battery also for portability.

Block Diagram : 

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Auto mute for car audio deck

(Automatically Mute Your Car Audio System when you receive a call)

 Muting car’s audio deck, while talking on cell phone is an important yet difficult task. This project is designed to solve the problem. A sensitive IR transmitter and receiver pair is designed and fixed to a cell phone holder. Always the cell phone should be placed in the holder.  The transmitter unit continuously transmits IR rays. These IR rays are interrupted by the cell phone. Whenever the cell phone is lifted from the holder, the IR rays fall on the receiver and it sends a signal to switching circuit. A relay is driven by a relay driver circuit and the relay opens the deck speaker wires and the audio will be muted.  After the completion of the conservation, the cell phone should be kept back in the holder. Again the IR rays will be interrupted and the relay will be de-energized. Music will be played again normally.  This project uses regulated 12V, 750mA power supply. 7812 three terminal voltage regulator is used for voltage regulation. Bridge type full wave rectifier is used to rectify the ac out put of secondary of 230/18V step down transformer. 

Block Diagram    :

 

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Air flow detector circuit.

Description.

This circuit can give a visual indication of the rate of air flow.It can be also used to check whether there is air flow in a given space.

The filament of a incandescent bulb is the sensing part of the circuit.When there is no air flow the resistance of the filament will be low.When there is air flow the resistance drops , because the moving air will remove some of the heat generated in the filament.This variations in the resistance will produce variation of voltage across the filament.These variations will be picked up by the opamp (LM339) and the brightness of the LED at its output will be varied proportionally to the airflow.

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Humidity Detector Circuit

This humidity sensor consists of 2 copper conductors that are located at small distance from each other. The relay switches as soon as the moisture makes a connection that is more or less electrically conductive between the 2 electrodes.

How does the humidity detector works?
When the electrical resistance between the 2 sensors drops below a certain value then the Schmitt trigger (T1 and T2) switches. The RS N1/N2 bistable multivibrator is flipped through C1 so that in point B we have a low voltage and so T3 will close the relay.
The relay is opened when the 10K resistor is connected to point A, not to point B as shown in the schematic. You can use other sensors like LDR or NTC instead of the copper ones so you can use this circuit for detecting light or temperature.

Schematic of the Humidity Sensor Circuit

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LA4550 Audio Amplifier 4W BTL.

LA4550 is a 2 channel audio frequency power amplifier IC specifically designed for radio, tape-recorder use etc. The features of LA4550 are low quiescent current, built in 2 channels for stereo and bridge mode operation, excellent ripple rejection, good channel separation, negligible pop-up noise during power ON/OFF. The LA4550 can be operated from 12 Vdc and can deliver 4W of output power into an 8 ohm speaker.

Description.

In this circuit LA4550 is wired in bridge mode. For stereo application, two identical amplifier modes have to be built according to the circuit diagram. In the circuit capacitors C6 and C3 provides feedback and their value determines the lower cut-off frequency. Capacitors C1 and C7 are meant for bootstrapping. Branch C2, R1 and C8, R3 are meant for preventing oscillations, and so the high frequency stability of the LA4550 audio amplifier gets improved. Capacitors C9 and C10 are meant for coupling the speaker to the IC. C4 is a ripple filtering capacitor while C11 and C12 are meant for power supply filtering. Audio input can be applied to pin 8 of the IC with respect to the ground.

Circuit diagram.

Notes.

• Use 12 Vdc for powering the circuit.

• Maximum possible supply voltage is 13V.

• LA4550 requires a heat sink.

• The package style of LA4550 is DIP 12F and suitable heat sinks are available in the market.

• Use 8 ohm/10W as the loudspeaker.

• An optional 10K POT connected in series to the input line can be used as the volume control.

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