July 31, 2009

Small FM Transmitter

Small FM Transmitter

Nothing critical here. To get a bit of tuning out of the coil you could put a 4-40pF trimmer capacitor (optional) parallel over the 1 µH coil, L1.
C1/C4 and C5/C6 are ceramic capacitors, preferably NPO (low noise) types. C2/C3 are electrolytic or can be tantalum types.
The antenna is nothing more than a piece of 12" wire or a piece of piano wire from 6" to 12".

To find the signal on your receiver, make sure there is a signal coming into the microphone, otherwise the circuit won't work. I use an old mechanical alarm clock (you know, with those two large bells on it). I put this clock by the microphone which picks up the loud tick-tick. I'm sure you get the idea... Or you can just lightly tap the microphone while searching for the location of the signal on your receiver.

NOTE : Battery is strictly recommended to reduce the noise.

Parts List
R1,R3 = 100K
R2 = 10K
R4 = 470 ohm
C1,C4 = 470pF
C2,C3 = 4.7µF, 16V, electrolytic
C5,C6 = 4.7pF
C7 = 4-40pF trimmer cap (optional, see text)
L1 = 1µH
Q1,Q2 = 2N2222, NPN transistor
Mic = Microphone
B1 = 9 Volt, Alkaline battery


Circuit Diagram


NOTE : Click the image for better quality

July 26, 2009

Transformer

In real this is how an TRANSFORMER looks like..
the transformer is a device that transfers electrical energy from one end of the coil to the another coil by mutual induction method......

http://upload.wikimedia.org/wikipedia/commons/7/7a/Transformer-hightolow_smaller.jpg

Introduction of transformer..

A transformer makes use of Faraday's law and the Ferromagnetic properties of an iron core to efficiently raise or lower AC voltages. It of course cannot increase power so that if the voltage is raised, the current is proportionally lowered and vice versa.

How the ideal transformer looks like



Relation between transformers & Faraday's law..



Formulas for transformers.............



Concepts of transformers...............





Types of transformers...

STEPUP TRANSFORMER:-

http://www.physics.sjsu.edu/becker/physics51/images/32_16_Step-up_transformer.JPG

A "step-up transformer" allows a device that requires a high voltage power supply to operate from a lower voltage source. The transformer takes in the low voltage at a high current and puts out the high voltage at a low current.

STEPDOWN TRANSFORMER:-

http://wpcontent.answers.com/wikipedia/commons/thumb/6/64/Transformer3d_col3.svg/350px-Transformer3d_col3.svg.png

A "step-down transformer" allows a device that requires a low voltage power supply to operate from a higher voltage. The transformer takes in the high voltage at a low current and puts out a low voltage at a high current.

Common Types of Transformer...

Following are the few common types of transformer

Power Transformer - These operate at 50 to 400 Hz at a absolute nominal line voltage from 105 to 130 V. They are actually made with single and multiple secondaries with various step-up and step-down turns ratios.

Secondary Transformer - Secondaries transformer could have a single tap, multiple taps and even sometimes no tap. Some units are prepared with a tapped primary. Output voltage could start ranging from three to several thousand volts with output currents from .01 to 1500 A.

The Cores Transformer - The cores transformers are made up of iron or steel laminations. They are packaged in a hermetically sealed case especially for military or space use or with an open frame or even plastic enclosure for commercial, consumer or any industrial use.

Isolation Transformer - These types of transformer operate with a one-to-one turn’s ratio between primary and secondary, as isolating the line from the secondary load. Usually, an isolation transformer further comprises of Faraday shield, which is in fact a screen of nonmagnetic metal wound between the primary and secondary and then connected to the transformer core.

The Shield Transformer - The shield transformer acts particularly to prevent capacitive coupling of spurious signals and sound between windings, and it as well reduces transformer efficiency by improving leakage current.

Control Transformer - These are used as small power transformer for controlling components like relays and low voltage ac control devices. Common output voltages come in 12 and 24 Vac at current capabilities of 4 to16 A.

Autotransformer - Autotransformers are types of single winding with either fixed or variable step-up or step-down turn’s rations. They are actually smaller and less pricey than the two-winding types.

Audio Transformer - These vary from the power transformer types in, which they are used to give matching electrical characteristics of an output amplifier to that of any normal load speaker. In high-fidelity audio systems, they further operate from 20 Hz to 20 KHz. This audio transformer comprises of voice communications only and operates from 200 to 500 Hz.

Radio Frequency Transformer - These radio frequency transformers operate at a fixed high frequency with a capacitor across primary, secondary or sometimes even both to create a tuned or resounding circuit. Most types normally use an air core; however some are made up of ferrite slug to allow any sort of adjustment for inductance windings over a given range. They are generally assembled in aluminum-shielded container to reduce pickup or radiation of magnetic fields.

Pulse Transformer - These types are used for the generation and transmission of square wave pulses with emphasis on fast rise and fall times of the pulse and high-frequency response. These transformers are packaged in a miniature enclosure, 1/4 inch to 1/2 inch in diameter, and use an air core.



Working of transformer................




Transformer refers to the static electromagnetic setting which can transfer power from one circuit to another one. In AC circuits, AC voltage, current and waveform can be transformed with the help of Transformers. Each transformation is usually to transfer from one circuit to another one by the way of electromagnetism, but it has no direct relation with this circuit. It also can be transformed through electromagnetism (electrical manner). This electromagnetism is known as auto-transformer.
   Transformer plays an important role in electronic equipment. AC and DC voltage in Power supply equipment are almost achieved by transformer’s transformation and commutation. At the same time the electrical parameters transformed by transformer are not one but a few ones.
Most of the isolation, matching and impedance in the circuit carry out by transformer.  Most of isolation, matching and impedance in the circuit carry out by transformer.Simple schematic diagram of the transformer is shown in (1-1). It is connected by closed-magnet (iron cores), two windings and AC power supply. The winding is called the primary winding; another winding is connected with load, and it is called secondary windings.

No-load state of Transformer: viz. the disconnecting state between he secondary winding and load (Figure 1-2). Connect the primary winding and the power supply of AC voltageU1, and then it will produce alternating current I0, this current is called no-load currents. This current set up alternating magnetic flowφ0 which is closed along iron core magnetic circuit. At the same time, it traverses the primary winding and secondary winding, and then produces inducting electromotive forceE2 (secondary no-load voltage).


Circuit symbol for transformers...

circuit symbol Transformer with two windings and iron core.
circuit symbol Step-down or step-up transformer. The symbol shows which winding has more turns, but not usually the exact ratio.
circuit symbol Transformer with three windings. The dots show the relative configuration of the windings.
circuit symbol Transformer with electrostatic screen preventing between the windings.

Doorbell for the Deaf

Doorbell for the Deaf

This circuit provides a delayed visual indication when a door bell switch is pressed. In addition, a DPDT switch can be moved from within the house which will light a lamp in the door bell switch. The lamp can illuminate the words "Please Wait" for anyone with walking difficulties.

doorbell circuit



The circuit uses standard 2 wire doorbell cable or loudspeaker wire. In parallel with the doorbell switch, S1, is a 1N4001 diode and a 12 volt 60mA bulb. The bulb is optional, it may be useful for anyone who is slow to answer the door, all you need to do is flick a switch inside the house, and the bulb will illuminate a label saying Please Wait inside the doorbell switch or close to it. The double pole double throw switch sends the doorbell supply to the lamp, the 22 ohm resistor is there to reduce current flow, should the doorbell switch, S1 be pressed while the lamp is on. The resistor needs to be rated 10 watts, the 0.5 Amp fuse protects against short circuits.

When S2 is in the up position (shown as brown contacts), this will illuminate the remote doorbell lamp. When down, (blue contacts) this is the normal position and will illuminate the lamp inside the house. Switch S1 will then charge the 47u capacitor and operate the transistor which lights the lamp. As a door bell switch is only pressed momentarily, then the charge on the capacitor decays slowly, resulting in the lamp being left on for several seconds. If a longer period is needed then the capacitor may be increased in value.

Touch Switch

Touch Switch

This circuit uses a 555 timer as the bases of the touch switch. When the plate is touched the 555 timer is triggered and the output on pin 3 goes high turning on the LED and the buzzer for a certain period of time. The time that the LED and the buzzer is on is based on the values of the capacitor and resistor connected to pin 6 & 7. The 10M resistor on pin 2 causes the the circuit to be very sensitive to the touch.

Circuit Diagram

July 25, 2009

Geomagnetic field detector

Geomagnetic Field Detector

This basic oscillator will detect the Earth magnetic field. The ferrite rod and coil are taken from an old Medium Wave receiver and a small magnet is glued at one end. Tune to a medium wave commercial station until you hear a beat note. Any movement of the ferrite rod will produce an audible note that depends on the prevailing Earth magnetic field. Screening is essential. Use a plastic box padded, on the inside, with copper wires running parallel to the rod and grounded in one place only. A small hole is made in the box in order to adjust the trimmer capacitor with a plastic screwdriver. An American equivalent to the BC337 could be the 2N2369A but I did not try it out.

Circuit Diagram

555 Timer Theory & Design

555 Timer Theory & Design

The 555/556 timer is one of the most versatile and popular chips made. It is very inexpensive and easy to use. There are two basic modes of operation. 1: Monostable Mode and 2: Astable Mode. In the monostable mode the 555 acts as a "one - shot". It would be used for the purpose of obtaining a one pulse of variable length. In the astable mode the 555 will re-trigger itself to output a stream of pulses of variable length. Basic information about the timers are shown below.

555/556 Timer info

555/556 Timer info

Monostable Mode

In the basic monostable mode the timer will be triggered by applying a negative pulse to pin 2. That will cause the output of the timer to output a pulse on pin 3 for a time period determined by the values of R1 and C1 in the circuit below. The supply voltage has no effect on the length of the pulse. The formula to determine the duration of the output pulse is as follows T = R1 x C1. For example if R1= 100k ohms and C1= 10uf then the length of the pulse would be 1 second. Typically circuit designers already know what the length of the pulse is going to be, they would then need to calculate the values of R1 and C1. In this case we will have to pick a value for either R1 or C1 and then calculate the value of the other component. To obtain a 10 second timing pulse we will use a 100k ohm resistor for R1 and calculate C1's value. C1 = T / R1. C1 = 100uf. To calculate the value of R1 when the value of C1 is known the formula would be R1 = T / C1.

Monostable Mode

Astable Mode
In the astable mode of operation pin 2 and 6 are tied together to cause the timer to re-trigger itself. The output pulse is on pin 3. The output pulse is shown in the diagram below. To calculate the T1 time (output high) use the following formula T1 = .693(R1 + R2)C1. To calculate the T2 time (output low) use the formula T2 = .693( R1 x C1 ). If you need to know the frequency of the output use this formula Freq. = 1.44 / (R1 + 2R2)C1.

Astable Mode" border="1">

Simplest Wireless Headphone

Simplest Wireless Headphone
A basic Infra Red Link for audio communication for distances up to 10 feet.

Working

The transmitter comprises a single amplifying stage driving two series connected IR LEDS. The input source is connected to J1. Please note that the device will pass a small DC current through it and also directly bias the transistor. A suitable device is therefore a high output crystal microphone. These can produce high output voltages up to 1 Volt but this will be reduced by the transistors low input impedance.

The receiver is three stages, the first stage being a photo-transistor. Stages two and three form a high gain darling-ton emitter follower, the bias for the whole stage derived through R2 and the photo-transistor itself. C1 and R3 form a filter to reduce interference from fluorescent lighting and other hum sources. The output is via Jack J2. Note also that the output device will pass a small DC current so a medium impedance loudspeaker or headphones are a good choice here.

Circuit Diagram


NOTE : Click the diagram for better Quality.

Brightness Changing Christmas Star

Brightness Changing Christmas Star

This circuit can be used to construct an attractive Christmas Star. When we switch on this circuit, the brightness of lamp L1 gradually increases. When it reaches the maximum brightness level, the brightness starts decreasing gradually. And when it reaches the minimum brightness level, it again increases automatically. This cycle repeats.

Working

The increase and decrease of brightness of bulb L1 depends on the charging and discharging of capacitor C3. When the output of IC1 is high, capacitor C3 starts discharging and consequently the brightness of lamp L1 decreases. IC2 is an opto-isolator whereas IC1 is configured as an astable multi vibrator. The frequency of IC1 can be changed by varying the value of resistor R2 or the value of capacitor C1. Remember that when you vary the frequency of IC1, you should also vary the values of resistors R3 and R4 correspondingly for better performance. The minimum brightness level of lamp L1 can be changed by adjusting potentiometer VR1. If the brightness of the lamp L1 does not reach a reasonable brightness level, or if the lamp seems to remain in maximum brightness level (watch for a minute), increase the in-circuit resistance of potentiometer VR1. If in-circuit resistance of potentiometer VR1 is too high, the lamp may flicker in its minimum brightness region, or the lamp may remain in ‘off’ state for a long time. In such cases, decrease the resistance of potentiometer VR1 till the brightness of lamp L1 smoothly increases and decreases. When supply voltage varies, you have to adjust potentiometer VR1 as stated above, for proper performance of the circuit. A triac such as BT136 can be used in place of the SCR in this circuit.

Caution: While adjusting potentiometer VR1, care should be taken to avoid electrical shock.

Circuit Diagram

Quick Draw

Quick Draw

A GAME for you Guys..............

The object of Quick Draw is to test your reaction time against your opponent's. A third person acts as a referee and begins the duel by pressing S1, which lights LED1. Upon seeing LED1 go on, you try to outdraw your opponent by moving S2 from "Holster" position to "Draw" position before your opponent moves S3 from "Holster" to "Draw" position. Who ever gets there first will light the corresponding LED and will automatically prevent the other LED from lighting, clearly indicating a winner.

Circuit Diagram

Quick Draw Circuit

July 24, 2009

FM Jammer

FM Jammer

This device can be very illegal if you attach an external antenna so don't. adjust frequency by turning trimmer. and jams the fm signals within a circumference of 50m.

Circuit Diagram


NOTE : 1.1nH is an alternative for the inductor.

July 23, 2009

TIMER-CUM-CLAP SWITCH

APPLIANCE TIMER-CUM-CLAP SWITCH

When planning for a weekend outing to return late in the evening, we are often in an ambivalence whether to leave the staircase/outside light ‘on’ or ‘off.’ We sometimes miss our favourite TV programme because we forget to switch on the TV in time. If we are in the habit of taking an afternoon nap, we either turn on the mosquito repellent earlier than required or get up being bitten by mosquitoes. The timer-cum-clap switch presented here can solve all these problems and many more. It is a simple circuit that can be programmed to turn on household appliances like lights, fans, TV sets, music systems, etc exactly at a preset time and turn off at
another preset time automatically, thereby saving on electricity. You can turn the appliance ‘on’ or ‘off’ with the clap of your hand, if so desired, without having to touch the unit physically.
The transistor-based timer circuit uses readily available components, is easy to assemble as well as inexpensive, and can be programmed to switch on/off a load from one second to 100 hours in advance. To make the circuit cost-effective as well as simple to construct, a general-purpose
digital clock is incorporated as the basic timing device. The alarm output of the clock is used to toggle the output power supply for switching an appliance ‘on’ or ‘off.’

Construction and Working
Transistors T6 and T7 are configured as a bistable flip-flop that has two stable states. Transistor T7 will be in cut-off mode corresponding to transistor T6 in conduction mode, and vice versa. When transistor T6 conducts, its collector potential is very near to the emitter potential, i.e., ground, and therefore there is no base current to transistors T7 through R6. Thus, transistor T7 is in cut-off state. The collector of T7 is above ground potential and the current flows through resistors R7 and R13 to maintain the base current of T6. Thus, T6 remains in conduction state and T7 in cut-off state indefinitely. Now, if a voltage pulse is applied to the base of transistor T7 from some external source, a momentary base current will trigger it into conduction and its collector potential will come down to near ground potential. Thus, the current flowing through resistor R13 will pass through the collector of T7 and there will be no current through R7, making T6 go into cut-off state and thereby raising the collector potential of T6 to some positive value. This, in turn, will keep T7 conducting. Now the base current of T7 will pass through resistors R14 and R6. This state will sustain until some external voltage is applied to the base of T6.The external voltage pulse (for switching) is taken from two sources: the alarm output of a clock or the sound picked up by condenser microphone ‘M’ after proper amplification by transistors T1, T2 and T3. Since most of the digital clocks give out negative pulses to the buzzer (whose other end is directly connected to the positive terminal of the battery), a reverse diode (D8) and a pnp transistor (T10) are used at this stage. The negative pulses are rectified by D8 and filtered by C9 to supply a steady base current of T10. Otherwise, the output will become noisy because of the pulsating nature of the alarm. (If the clock gives out positive pulses, T10 can be replaced with an npn transistor like BC547. Diode D8 has to be reversed and R18 has to be connected between the base of T10 and ground.) The external voltage pulse is fed at the common emitter of transistors T4 and T5 through capacitor C8. When the alarm starts (sending negative voltage pulses), capacitor C9 discharges through D8 and, at the same time, charges through R19, thus triggering the base current of T10. The emitter current of T10 charges capacitor C8,which passes through the emitter of either T4 or T5 depending on their bias. When T6 is conducting, T4 is forward biased and the voltage pulse is fed at the base of T7, bringing T7 into conduction and T6 into cut-off mode. This makes T5 forward-biased and T4 reverse-biased. The next voltage pulse, either through T10, D1 or D2 corresponding to the clock alarm, clap sound or operation of the reset switch, sends a base current of T6 through the emitter of T5 and the output changes over. When clap switch is not required, S2 can be turned off. S3 is the reset switch (push-to-on type), which is used to toggle the output between ‘on’ and ‘off’ states. R10-C7 and R8-C6 are parallel paths to R7 and R6 for quick switchover of the bistable latch. Two AA-size batteries supply 3V DC to the clock and maintain a positive voltage to the collectors of T6 and T7 through diode D7. This keeps the circuit active during power failures also. A step-down transformer supplies 12V DC to the relay coil and sound amplifier section. Diodes D5 and D6 are rectifier diodes and C5 is the ripple filter capacitor. Diode D4 prevents the 3V battery from draining out into the rest of the circuit. The digital clock is a commonly available digital calendar with at least one alarm setting and one countdown timer setting. The digital calendar, being cheap, keeps the total cost of the project low and allows for precise settings of the alarm times. The alarm can be set 24 hours in advance, while a second alarm can be selected in the countdown timer mode, which allows for setting of the time 100 hours (99:59:59 hours to be precise) in advance. Availability of more than one alarm setting in the clock will give the added advantage of setting multiple switching times. Instead of the digital calendar, any other digital clock or battery-operated quartz clock (with alarm) can also be used as the basic timing device, though the alarm time setting is less precise in case of the latter. Instead of one clock, multiple clocks can be wired by connecting diodes parallel to D8. Note that once set in the clock mode, the alarm operates daily at the same time. But in the countdown mode, it operates only once. So if an appliance is to be turned on and off daily at the same time without human intervention, at least two digital clocks have to be wired (if the clock does not have two alarm settings apart from the countdown timer). Indicator LEDs (fixed on LED sockets) show ‘on’ or ‘off’ condition of the output plug.before fixing the clock on the cabinet, open it carefully to disconnect its piezoelectric buzzer. The terminal that shows pulsating voltage during an alarm operation (detected with a multimeter) is connected to the base of T10 through D8 and R19. The internal battery is replaced and the terminals are connected to the external battery chamber with proper polarity. The operation of the circuit can be divided into two parts: clap mode and timer mode. The timer can be put in clap mode by turning on the clap switch (S2). The connected appliance can now be turned on/off by clapping with an audible intensity. The clock timer will function as usual in this mode. While clapping, leave a gap of a few seconds between two successive claps. Thus, the gadget will show better response because it has been designed to consider two overlapping claps as one, ignoring the second one. For timer mode, switch S2 is turned off. The alarm is set at the time when switchover is required. The second switchover time can be set in the countdown timer. For that, the time difference between the present time and the time at which switching is required is calculated and this time is set in the countdown timer. When setting is done, set the output plug as ‘on’ or ‘off’ (as desired) by pressing reset switch S3. While setting the alarm, ensure a delay of at least three minutes between two successive alarm times (on/off) to allow for the first alarm to subside completely. Otherwise, the unit may malfunction (ignore the second alarm).

Circuit Diagram



NOTE : Click the image for better Quality

July 21, 2009

EFY March 2009

Electronics For You March 2009


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SOFTWARES

Free PCB

Free PCB

Free PCB is a free, open-source PCB editor for Microsoft Windows, released under the GNU General Public License. It was designed to be easy to learn and easy to use, yet capable of professional-quality work. It does not have a built-in auto router, but it can use the Free Route web-based auto router at www.freerouting.net. Some of its features are:

  • 1 to 16 copper layers
  • Board size up to 60 inches by 60 inches
  • Uses English or metric units (i.e. mils or mm) for most functions.
  • Footprint libraries courtesy of Ivex Design International Inc.
  • Copper fill areas
  • Footprint Wizard and Footprint Editor for creating or modifying footprints
  • Imports and exports PADS-PCB net lists
  • Exports extended Gerber files (RS274X) and Excellon drill files
  • Design rule checker
  • Auto save

The layout for a small PCB is shown in the screenshot below.


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Misc Electronics

Misc Electronics

Functions
  • System
    Preferred componentsSelect component values used in all designs and step size for ctr-n and ctr-m
    Hot keysDefine hot keys for opening pages
  • Miscellaneous
    GeometryHandles: Circles, part of circles, triangles, squares, rectangles, trapezoid
    SoundSound speed and perceived sound levels
    Weather and air%RH, dew point, air pressure and other weather related calculations
    Periodic tableA periodic table with all elements, it has search functions and a few data for each element
    Photo lensSome lens calculations
    Photo lightSome light calculations
  • Calculations
    CalculatorCan do all the usual stuff, including mathematics.
    Tiny CalcCan do the same as the entry line in Calculator, but is very small when pulled out.
    Curve fitFits a curve to a collection of data points
    Ohms lawOhms law, impedance of capacitor and inductors, complex power
    Ohms law 3 phaseOhms law with complex power for 3 phase systems
    dBDecibel and neper, both power and voltage including volt/watt for a reference level
    Charge curveCapacitor/inductor charge/discharge with resistive, current and power loads (not all combinations supported)
    WaveformsCalculates RMS, mean, PEEK, DC, FFT for different waveforms.
  • Mechanical
    WiresCalculates resistance and power loss in wires, can also do conversion between USA and European units.
    Cable calculationsCalculate frequence response of a cable
    Fan coolingCalculates how big a fan to get rid of some power.
    Heat sinkCalculates junction temperature for specified power level and heat sink
    Printed circuit boardCalculate micro strip, strip line, track resistance and current
    Cable calculationsSimulate cables at low (audio) frequences
  • Components
    Capacitor designCalculate capacitance of different geometries
    Color codesConvert between color codes and numeric values for many types of components.
    ThermosensorsCalculates for PT100, NTC and all types of thermocouples
    Air coilAnalyze or design an air core inductor
    LedsColor/wavelength of leds and design of circuits to drive leds from DC or AC.
    Components type numbersTries to decode component codes
    Power MOSTurn on/off time and power loss estimation
  • MPU
    MPU TimersCalculates divide factors for up to five software timers
    Integer mathConverts real numbers to fractions, calculates primes and other integer stuff
    Serial communicationTiming and curves, use full when programming software uart's and IR rx/tx.
    CRC and check sumCalculate crc, check sum and modulus for data blocks, can also analyze a data block for what check sum/crc was used
  • Simple Circuit
    FoCalculates Fo for RC, RL, RLC circuits
    Series/parallelCalculate/design series/parallel connection of resistors, capacitors and inductors
    Charge timeCharge/discharge time for simple circuits (including 555).
    Voltage dividerDesign/analyze voltage dividers, can include component tolerance and load.
    Two portConversion between different types of two ports.
  • Circuit
    1. order filtersAnalyze and design 32 different filter configurations
    Attenuator networkDesign different kind of attenuators
    Power SupplyAnalyze and design power supplies with 78xx and LM317 style regulators

Screen Shots





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July 20, 2009

Elektor March 2004

Elektor March 2004


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Elektor February 2004

Elektor February 2004


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Elektor January 2004

Elektor January 2004


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EFY Project Ideas

Project Ideas Collection

July 19, 2009

EFY Project Ideas 2001

EFY Project Ideas 2001
This has a complete collection of the project ideas in the Electronics For You magazine in the year 2001.


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EFY Project Ideas 2000

EFY Project Ideas 2000

This has a complete collection of the project ideas in the Electronics For You magazine in the year 2000.

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July 18, 2009

SOLAR BUG

Solar Bug
This is a fun circuit, hide this solar-powered circuit suitably and see the reaction of your friends to the chirpy sound produced by it every few minutes. In all probability, it will coax them to find out where the sound is coming from. The circuit runs off a miniature solar power panel, which can be taken out from an old calculator such as Citizen CT-500. A panel giving 1.5V to 2.5V is required. Note that the circuit can work properly from a panel as small as 3 cm(square).

Working
If a digital voltmeter is connected across capacitor C2, a slow build-up of voltage can be observed when the panel is exposed to light. Transistors T1 and T2 form a relaxation oscillator.When C1 charges to 0.6V, transistor T1 conducts and the charge built up in C2 is discharged through the
piezobuzzer to produce a short beep. While testing the circuit, the value of resistor R1 can be reduced to, say, 1 kilo-ohm. Use a good-quality buzzer to ensure that the sound produced is
loud enough.

Circuit Diagram


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July 17, 2009

EPE December 2008

EPE December 2008


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DOOR BELL FOR DEAF CLICK HERE

Electronics is the study and use of electrical that operate by controlling the flow of electrons or other electrically charged particles in devices such as thermionic valves. and semiconductors. The pure study of such devices is considered as a branch of physics, while the design and construction electronic circuits to solve practical problems is called electronic engineering.

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