Electronic toss circuit

The circuit given here can be used for tossing head or tail. There are many games in which a tossing is required to start and this circuit can be used in all such instances.

The circuit uses two ICs NE 555 timer (IC1) and 74LS76 dual JK flip flop (IC2).The IC 1 is wired as an astable multi vibrator operating at 10Hz.The output of IC1 is inverted by using the transistor Q1.The collector of Q1 is connected to the pin 1 of IC2 via the push button switch S1.The IC2 is wired in toggle mode. When push button S1 is pressed the output pins 14 and 15 of IC2 starts toggling in state. The LEDs connected to these pins also toggles (Since the frequency of toggling is 10Hz, we feel both LEDs glowing).When push button S1 is released either one of the LED remains ON indicating the head or tail.

Circuit diagram with Parts list.

Notes.

• The circuit can be powered from 5 V DC.
• Switch S1 is a push button switch.
• The ICs must be mounted on holders.
• The circuit can be assembled on a general purpose PCB.

Automobile turn signal circuit.

This is a simple circuit that can be used as a sequential signal light in automobiles. The circuit is based on two ICs. A TS 555 CN CMOS timer IC and a CD4017 decade counter IC. The IC1 is wired as an astable multivibrator to trigger the counter IC. When triggered, the outputs of the IC 2 (pins 3, 2, 4 and 7) will go high and low in sequence and the speed of this sequencing will be proportional to the triggering frequency. The transistors Q1 to Q4 drives the corresponding LEDs. The switch S1 can be used to select the direction of turning and the LEDs arranged at the corresponding side of the vehicle will start sequencing.

Circuit diagram with Parts list.

 Notes.

• The switch S1 can be the existing changeover switch of the vehicle it self.
• The circuit can be powered of the 12V available from the vehicle itself.
• The color of the LED depends on your choice .
• The ICs must be mounted on IC holders.
• Assemble the circuit on a good quality PCB .
• Be careful with the wiring of this circuit because any wrong connection may put the electricals of your vehicle  in trouble.

Whistle to beep circuit

This simple circuit produces a beeping sound that lasts for around 3 seconds whenever you make a whistle. The CMOS Hex inverter CD4049 is the heart of this circuit. Out of the six inverters in CD4049, U1a is wired as an audio amplifier which amplifies the signal picked up by the microphone M1.The U1b is wired as a band pass filter with center frequency around 2KHz.The filter is necessary in order to pass the frequency corresponding to whistling sound and suppress all other frequencies .If the filter is not there, the circuit could easily get false triggered.U1d is wired as a 3S delay monostable multivibrator.The output U1d drives the astable multivibrator formed by U1e and U1f.The astable multivibrator is operating around 4Hz.The combined effect is a intermittent beeping sound that lasts for around 3S.Transistor Q1 is used to drive the buzzer B1.

Circuit diagram with Parts list.

Notes.

• Assemble the circuit on a good quality PCB.
• The circuit can be powered from a 3V battery.
• IC U1 is a CMOS CD4049 Hex inverter.
• M1 can be an electret microphone.
• B1 can be a 3V piezo buzzer.
• Mount the IC on a holder.
• The duration of beeping can be adjusted by varying the components C4 and R9.

Jet engine sound generator

This jet engine sound generator circuit is based on the sound generator IC HT2844P from Holtek Semiconductors. This particular IC can make four sounds namely low speed sound of jet engine, high speed sound of jet engine, missile sound and machine gun sound. Each of these sounds can be activated by connecting the pins 12, 13, 14and 15 to ground by using the respective push button switches. Resistor R3 can be used for manually increasing or decreasing the speed.LED D1 gives a visible indication of the sound.

Circuit diagram.

Notes.

• The circuit can be powered from a 3V battery.
• Do not give more than 3.3V to the IC.
• K1 can be a 200mW/8 Ohm speaker.
• IC1 must be mounted on a holder.

Dancing light cricuit

Here is a simple dancing light circuit based on NE555 (IC1) & CD4017 (IC2) . The IC1 is wired as an astable multivibrator to provide the clock pulses for the CD4017. For each clock pulse receiving at the clock input (pin14) of IC CD4017, the outputs Q0 to Q9 (refer pin diagram of CD 4017) becomes high one by one alternatively. The LEDs connected to these pins glow in the same fashion to give a dancing effect. The speed of the dancing LEDs depend on the frequency of the clock pulses generated by the IC1.

Circuit diagram with Parts list.

Notes.

• Assemble the circuit on a good quality PCB or common board.
• The ICs must be mounted on holders.
• The speed of the dancing LEDs can be adjusted by varying POT R2.
• The capacitor C1 must be rated 15V.
• Using different color LEDs could produce a better visual effect.

CD 4017 Pin configuration.

Musical car reverse horn circuit

Here is a simple circuit that will produce a musical horn when ever your car is in reverse gear.The circuit uses two ICs for the operation, voltage regulator 7805(IC1) and musical tone generator UM66(IC2). The IC1 reduces the car battery voltage to 5V. The diodes D1 & D2 in combination  produces an additional  drop of 1.4 V to give a 3.6 V supply for the UM66. The supply voltage of UM 66 should not  be more than 4V. When ever the car is in reverse gear ,the reverse gear switch of the car gets activated and the circuit gets connected to the car battery. The UM66 starts playing the music tone. The transistor T1 amplifies the output of UM66 to drive the loudspeaker.

Circuit diagram with Parts list.

.

……………………………………

Notes.

• Assemble the circuit on  a good quality PCB or common board.
• Place the circuit on a waterproof place in the dashboard.
• The switch S1 is the reverse gear switch of the car.
• Before attempting the circuit,have  a good idea about the electrical wiring of your car.A wrong connection may damage your car’s electricals.
• The transistor Q1 is not very specific.Any medium power NPN  audio transistor will do the job.You could easily find one from your electronics junk box.

Dark detector circuit

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

Circuit diagram with Parts list. 

 

Notes. 

• The LDR ,R4 can be any general purpose LDR.
• The circuit must be assembled on  a good quality PCB or  common board.
• The circuit can be powered from a 9V PP3 battery.
• The POT,R3 can be sued as a volume controller.
• Mount the IC1 on a holder.It will make replacements easy.

FM Radio jammer

Circuit shown here can be used to jam FM radios in its vicinity. The circuit is nothing but a classic single transistor oscillator operating in the VHF region. Working principle of the circuit is very simple and straight forward. Powerful VHF oscillations from the circuit will interfere with the FM signals to nullify it. Jammer circuits like this are illegal in many countries and you must assemble this circuit on your own responsibility. This circuit is intended only for fun and i request you not to misuse it.
Circuit diagram.

Notes.

• For L1 make 6 turns of 16AWG enamelled copper wire on a 9mm plastic former.
• The circuit can be powered using a 9V PP3 battery.
• For extended range, use an antenna.
• A 30cm long wire connected anywhere on the coil will do for the antenna.
• For better performance, assemble the circuit on a good PCB.

FM Stereo

AN7415 is a monolithic integrated circuit that can be used in FM stereo demodulation applications. The operating voltage range is 1.6 to 7Vdc. Two AA dry cells are enough for powering this IC and it makes the AN7415 suitable for handheld FM radio applications. AN7415 has low current consumption (2.6mA), low distortion, good channel separation and high gain. The IC is available in 16 pin DIL package.

Description.

The circuit shown below is of a PLL FM stereo demodulator designed based on the AN7415. C1 is the input coupling capacitor which blocks any DC voltage present in the multiplexed input signal. LED D1 is an indicator LED and R1 is its current limiting resistor. C4 and C5 are the DC decoupling capacitors for the left and right output channels. C2 and C3 are the noise bypass capacitors for the left and right output channels. POT R2 can be used for adjusting the channel separation. Resistor R5 and capacitors C7 and C8 forms a low-pass filter network for the internal DC amplifier circuitry (see the block diagram of AN7415). C10 is a filter capacitor for the IC’s internal Schmitt trigger amplifier circuitry. C9 is a ripple filter capacitor for the voltage stabilizer circuit inside the AN7415. Resistor R3, POT R4 and Capacitor C6 sets the time constant of the internal VCO circuit. Hence POT R4 can be used for adjusting the VCO frequency. A 19KHz frequency check signal is available at the PIN 12 of the IC. Switch S1 can be used for enabling and disabling forced mono function.

Circuit diagram.

AN7415 stereo decoder

Notes.

• Well designed and good quality PCB improves the performance.
• Input supply voltage range is from 1.6V to 7VDC.
• I recommend 3VDC for powering the circuit.
• POT R4 can be used for adjusting the voltage controlled oscillator (VCO) frequency.
• POT R2 can be used for setting the channel separation.
• Recommended LED indicator current is 40mA.
• Maximum power dissipation is 80mW.

Home Radio

A circuit diagram that can be used for the generation of CW Morse code is shown here.This circuit can be very useful those who would like practice Ham Radio.The circuit is nothing but an astable multivibrator based on NE 555.The frequency of oscillations of the circuit depends on the components R1,R2 & C1.The circuit can be powered from a 9V PP3 battery.

Circuit diagram with Parts list.

Notes. 

• The POT R2 can be used for frequency adjustments.
• POT R3 can be used for volume adjustments.
• The switch S1 can  be a Morse code key.

Working of Fingerprint Scanner

USB fingerprint scanner

For the past few years fingerprint scanners were considered to be a very costly and high end technology. We have seen it only in thriller and sci-fi movies. But now, these devices have been popping up in almost all places like offices, police stations and also our laptops. You also get to buy fingerprint USB scanners for almost $100. In this post we will learn the use, applications and also the working of fingerprint scanners in detail.

Use of Fingerprint scanners

Suppose you have a fingerprint scanner enabled laptop. You need to visit a site which you haven’t seen for a long time. You even forgot the password to see your own profile. Thus you will have to get a new password by entering your e-mail address. All these problems can be solved by using a password storing fingerprint reader.

The main thing to do is use the same password and user-name for all websites that you use. Store the password in the fingerprint scanner software. Scan your finger with the help of the device and store it in reference to the password and user-name you have provided. Thus, when you visit the site again in future, all you have to do is swipe your finger on the device and the associated user-name and password will be filled automatically to the site.

The scanning procedure can also be used for identity recognition as well as locking and protecting your computer files.

History of fingerprint scanners

This identification device has been commercialized from the late 19^th century. The device is the most popular among all the identification devices because of its ease in acquisition, and also the number of sources that are available for its data collection. It has found its vast use in law enforcement and immigration purposes. The basics of this identification process comes from “Galton points” – a certain characteristics defined by Sir Francis Galton, through which the fingerprints can be identified.

The exact automation of this technology began in the year 1969, when the FBI wanted an identification system using fingerprints. For this the FBI made deals with the National Institute of Standards and Technology (NIST), to make developments on the searching, matching as well as scanning process. For this, the NIST worked with the minutiae technology, which is actually a smaller version of Galton points to develop the fingerprint scanning technology. The two main problems they faced were extracting the minutiae from each fingerprint and also comparing, matching and also searching the lists of minutiae from large list of fingerprints. The best prototype was first exhibited in the year 1975 by the FBI. A capacitive scanning technique was used as its working basics. More work on making automatic digital inked fingerprints, compression of the image and so on is still being done.

About fingerprints

Before going in detail about the technology used, it is very important to know about the basics of our fingerprints. The basic information about fingerprint is that it is unique for each person. Even a twin brother will not have the same fingerprint. Thus each fingerprint is used to store a unique identifiable piece of information. The uniqueness in each fingerprint is due to the peculiar genetic code of DNA in each person. This code causes the formation of a different pattern of our fingerprint.

A fingerprint consists of ridges and valleys. They together provide friction for the skin. The main identification of the skin is based upon the minutiae, which actually is the location and direction of the ridge endings and splits along a ridge path. The image shown below represents two types of minutiae. Take a look.

Fingerprint

The image below shows all the other characteristics of a fingerprint. These characteristics may also be helpful during the process of minutiae extraction. Take a look.

Fingerprint Characteristics

The unique information used for the identification includes the flow of the friction ridges, the sequence and also the presence/absence of the individual friction ridge path features.

How Fingerprint scanner works

There are mainly two types of scanning methods for this technology. Either an optical or capacitance scanner is used to scan and make a picture of your finger. Though both the methods produce the same type of image, the making of it is completely different.

This scanned image is then compared with an earlier existing finger print of yours to get the correct identity. The comparison is carried out by the processor and the comparison is made between the valleys and ridges. Though the steps are simple, very complex algorithms must be carried out to perform this operation. Though your whole fingerprint is recorded, the computer takes only parts of the print to compare with other records.

The two types of scanners used are

1. Optical Scanner

The main part of an optical scanner is the Charge Coupled Device. To know more about it click on the link below.

TAKE A LOOK : CHARGE COUPLED DEVICES (CCD)

The electrical signal created in response to the light hitting on the CCD forms pixels which are collectively joined to form an image. These pixels are converted using and ADC to make a digital image.

The scanning device consists of a glass plate, on top of which you are supposed to place your finger. After the scanning takes place, an inverted image of the finger is stored. This image will show the ridges and valleys of your finger. The ridges can be spotted by the darker areas where the light reflection is greater. The valleys can be spotted by the lighter areas, where the light reflected is lesser.

The scanner is also designed to recheck the image captured. The scanner checks whether the image captured has an satisfactory pixel darkness. If a problem is seen in the checking process, the image will be rejected and the suitable adjustments will be made so as to get a better quality picture. After all these procedures, the image will be compared with the existing stored images.

2. Capacitance Scanner

The figure of a simple capacitance sensor is shown below. Take a look.

Capacitance Scanner

While an optical scanner uses light to scan the image, a capacitance scanner uses electrical current to display the image

The principle of capacitance is used in this device. As shown in the diagram, each sensor consists of arrays of cells. These cells have two conductor plates, which are covered with an insulating layer. Thus, they form a simple capacitor which is used to store the charge. The cells are so small that their actual size will be smaller than the width of a ridge from our finger. These sensors will then be connected to an integrator. The output of the integrator will be given to the input of an inverting operational amplifier. This op-amp will consist of hundreds of transistors, resistors and capacitors.  This op-amp is alters the input voltage with respect to the reference voltage provided to the other input. The non-inverting input is connected to the ground. The inverting input is given to the reference voltage and then to the feedback circuit. This feedback circuit is given to the amplifier output and also includes the two conductor plates.

When the finger is placed for recognition, it acts as another capacitor plate. It is separated with the help of insulating layers. When moving the finger from one point to another, the capacitance changes due to the variation in distance between the capacitor plates. Thus, the output voltage is recorded with the change in output voltage according to the appearance of ridges and valleys. A perfect output image of the fingerprint is thus obtained.

This device is much better than an optical scanner as it is very compact and harder to trick. The device needs a real fingerprint shape to get the output. The optical scanner a dark and light pattern is more than enough to make an output image. Though an optical scanner needs CCD devices for sensing, a capacitance scanner needs only semi-conductor chips.

Advantages

• You are actually able to provide a physical evidence of yourself.
• This type of an identity cannot be easily faked like identity cards.
• Though you can guess a password of another person, it cannot be done so in the case of a fingerprint.
• You may lose your identity card. But, you are not going to lose your fingerprint. The same will be the case of a password.

Disadvantages

• An optical scanner can be fooled by showing a picture of a finger instead of a real finger. Capacitance scanners can also be fooled by swiping a mould of a finger by including ridges and valleys. If it is some serious business, a thief could also cut-off the person’s finger and swipe it on the scanner.
• If you have misplaced your credit card you can easily get a new one. But, if someone has moulded a same fingerprint as yours, there is no way to replace it.

Three phase auto changer circuit

This circuit is a modification of  High & Low voltage cut-off with delay& alarm circuit  appeared in Circuits today, which I have tried and found to be quite reliable. You can adopt this circuit with small modification. Use a transformer with secondary 15 – 0 – 15 AC Volt at 500mA, for 18Volt relay operation. Normally any modern electrical / electronic equipment can operate with 230 Volt ± 15% AC supply. That is, it can stand normal voltage operating range of 195 to 265 Volts. It may misbehave beyond this voltage range. You can choose the practical voltage required for the low end high cut off to change over to other phase.

Circuit diagram.

Connection diagram.

Notes.

• Set VR3 for minimum voltage to switch on the relay (Say 195 Volt input).
• Set VR1 to switch off the relay above a particular voltage (say 260Volt input).
• You can use a 100μF 40 Volts good make in parallel with relay for chatter free operation.
• Each Phase you have to use one module as above.
• The relay interconnections are shown in the connection diagram above.
• T1 can be a 15-015 V secondary, 230V primary, 500mA step down transformer

Easy-To-Build AC Power Meter

If your goal is to save on electricity, you must first measure the ac current flowing through your appliances. The formula for power is the product of the ac line voltage and the measured current. Presented here is a demonstration of how to build an ac power meter using a current transformer (see the figure).

The current transformer is similar to an ordinary voltage transformer, except that a primary wire is generally absent around the core. The primary coil is constructed by winding either one of the wires connecting an ac plug and an outlet around the core (two turns, in this case).

Current ratio flowing through the primary and secondary wires is inversely proportional to the turns ratio of the transformer. The secondary ac current is rectified and smoothed by D1 and C. The R1 and R2 shunt resistors yield a correct full scale for the meter. You may need to combine a few standard value resistors to create the odd-valued R1 and R2. D2 is used to bypass the opposite-phase current.

The transformer may be broken if the secondary circuit is open with a high current on the primary wire. Of course, a voltage transformer doesn't fire when the secondary is short-circuited.

Ampere-meter

The ampere-metre which has the symbol A m, A-m, or A·m is the SI unit for pole strength in a magnet.

Contents   [hide]  1 Derivation 2 Usefulness 3 Misconceptions 4 References

[edit]Derivation

Einstein proved that a magnetic field is the relativistic part of an electric field. This means that while an electric field acts betweencharges, a magnetic field acts between moving charges (as a charge moves through space more quickly and through time more slowly, its electromagnetic force becomes more magnetic and less electric). Therefore, the pole strength is the product of charge and velocity.

[edit]Usefulness

Few calculations actually involve the strength of a pole in ampere-metres because a single magnetic pole has never been isolated. Magnets are dipoles which require more complicated calculations than monopoles. However, the strength of a magnetic field is measured in teslas and one tesla is one newton per ampere-metre which confirms that the unit for pole strength is indeed the ampere-metre.

[edit]Misconceptions

The idea that magnetic forces act on moving charges is clear in an electromagnet but not obvious in a permanent magnet. In fact, all substances have charges moving in them all of the time, one of the difficulties in reaching absolute zero. In most substances, all of the magnetic fields produced by this motion cancel each other out, but magnetic substances have more proper alignment. At the microscopic level, many molecules are magnets — hydrogen fluoride for example is a dipole. Polarity is most often expressed in terms of electronegativity but the strength of its poles could be expressed in ampere-metres as well.

[edit]References