FREQUENCY MODULATION (FM) BROADCASTING BASIC TUTORIALS

WHAT IS FREQUENCY MODULATION (FM) BROADCASTING?

The monophonic system of FM broadcasting was developed to allow sound transmission of voice and music for reception by the general public for audio frequencies from 50 to 15,000 Hz, all to be contained within a +/−75-kHz RF bandwidth.

This technique provided higher fidelity reception than was available with standard broadcast AM along with less received noise and interference. FM broadcasting in the U.S. is allocated the 88–108 MHz frequency band.

Pre-emphasis is employed in anFMbroadcast transmitter to improve the received signal-to-noise ratio. The pre-emphasis upper-frequency limit is based on a time constant of 75 μs as required by the FCC for FM broadcast transmitters.

Audio frequencies from 50 to 2120 Hz are transmitted with normal FM; whereas audio frequencies from 2120 Hz to 15 kHz are emphasized with a larger modulation index. There is significant signal-to-noise improvement at the receiver, which is equipped with a matching de-emphasis circuit.

LEAD ACID BATTERY CHARGER CIRCUIT BASIC ELECTRONICS PROJECT

CIRCUIT ON HOW TO MAKE LEAD ACID BATTERY CHARGER?

This is a basic electronic project on how to make a Lead Acid Battery Charger. The circuit can be seen below:

Thic circuit furnishes an initial voltage of 2.5 Volts per cell at 25 degrees celcius to rapidly charge a battery. The LM301A compares the voltage drop across R1 with an mV referenced set by R2.


The LM 334 temperature sensor should be placed by near or on the battery to decrease the charging voltage by 4 mV/ deg cel for each cell.

ELECTROSCOPE DEFINITION BASICS AND TUTORIALS

WHAT IS AN ELECTROSCOPE?

The Electroscope.  It has been shown experimentally that an electric charge can be detected because it attracts light objects such as pith balls, bits of paper, etc.

Any device used for detecting electric charges is called an electroscope.  In its simplest form, an electroscope consists of a pith ball hanging on the end of a silk thread.  By touching it with a body of a known charge, you have an instrument that can detect charged bodies and that can indicate the type of charge (polarity).


To illustrate, if you touch the pith ball with a glass rod, which has been rubbed with silk, you charge the pith ball positively.  Any other charged body that is brought near the pith ball will repel it if the body is positive or attract it if the body is negative.  The force of repulsion or attraction indicates the strength of the field surrounding the charged bodies.

A better and more sensitive device is the leaf electroscope shown in figure 1-7. It is two thin sheets of metal foil (usually gold or aluminum) called leaves, supported by a wire or stem whose ends pass through a block of sealing wax or insulating material to a metal ball or cap.

The leaves are usually sealed in a glass container to prevent air currents and moisture from affecting the instrument. The sensitivity of the instrument depends on several factors, the main two being the thickness and the type of material the leaves are made of.

If the ball receives either a positive or a negative charge, it causes the leaves to spread apart.  The leaves spread because like charges repel.  When a charge of positive electricity is placed on the leaves, the spread of the leaves will increase when the ball is approached by a positively charged body.  On the other hand, a negatively charged body brought near the ball or cap will decrease the spread.

You can place a charge on the leaves by bringing a charged body near, but without making physical contact with, the ball.  This is charging by induction.

As soon as you remove the charged body, the electroscope is no longer charged unless you provided some means for it to gain or to lose some electrons while the charge was being induced.  You can do this by connecting a wire from the electroscope to some neutral conducting object, such as ground.

Then, if a charged body is brought near the electroscope, electrons can leave if the charge is negative or enter if the charge is positive.  If the wire is disconnected before the charged body is removed, the electroscope will remain charged oppositely to the charge that induced it.

This is charging by conduction because the electroscope comes into direct contact with the charged body.

SINE WAVE GENERATOR ELECTRONIC PROJECT CIRCUIT

HOW TO MAKE SINE WAVE GENERATOR?


Many electronic devices depend upon the shape of the signals. It is very easy to produce
squarewave signals from sine wave, but reproducing sinewave signals from the square wave is quite difficult.

In case of static squarewave-to-sinewave converter, in low frequency range, we can get accurate sine wave, but in high frequency range the shape will not be a true sine wave. Here is a solution to that problem.

The circuit shown here uses five ICs. The squarewave signal is fed at pin 1 of IC1 (CD 4024). IC1 is a 7-bit counter, but here only 6 bits are made use of. The first four bits are fed as a signal bus to IC3 (CD4066) quad bilateral switch through IC2 (CD4077B) that contains four exclusive NOR gates.

It converts the 4-bit signal bus to ‘up mode’ and ‘down mode’ hexadecimal signals, simultaneously. The converted signal bus switches on and off the ladder switches inside CD4066. As a result, the net resistance of ladder varies.

This varying resistance varies the charging and discharging current of capacitor C1 in the feedback path of IC5 (LM741). The charging and discharging mode is controlled by IC4 (CD4011). In fact, capacitor C1 works as an integrator.

The sinewave producing circuit needs 64- bit squarewave pulse for360o sine wave. A missing pulse in this 64-bit sequence produces ramp. In this circuit, all ICs except IC5 are CMOS ICs and hence the current consumption is very low.

The value of capacitor C1 may be calculated from the relationship: C1 = 0.27/f0 μF. The value shown in the circuit is for 50Hz output frequency. The shape of the sinewave output may be corrected using presets VR1 and VR2.

COMMONLY USED IC COUNTERS AND REGISTERS BELONGING TO TTL CMOS & ECL LOGIC FAMILIES

A Table of Commonly used IC counters and registers belonging to the TTL, CMOS and ECL logic families


Type Number Function Logic FAMILY

7490 Decade counter TTL
7491 Eight-bit shift register (serial-in/serial-out) TTL
7493 Four-bit binary counter TTL
74160 BCD decade counter with asynchronous CLEAR TTL
74161 Four-bit binary counter with asynchronous CLEAR TTL
74162 BCD decade counter with synchronous CLEAR TTL
74163 Four-bit binary counter with synchronous CLEAR TTL

74164 Eight-bit shift register (serial-in/parallel-out) TTL
74165 Eight-bit shift register (parallel-in/serial-out)
74166 Eight-bit shift register (parallel-in/serial-out) TTL
74178 Four-bit parallel access shift register TTL
74190 Presettable BCD decade UP/DOWN counter TTL
74191 Presettable four-bit binary UP/DOWN counter TTL
74192 Presettable BCD decade UP/DOWN counter TTL
74193 Presettable four-bit binary UP/DOWN counter TTL
74194 Four-bit right/left universal shift register TTL
74198 Eight-bit universal shift register (parallel-in/parallel-out bidirectional) TTL
74199 Eight-bit universal shift register (parallel-in/parallel-out bidirectional) TTL
74290 Decade counter TTL
74293 Four-bit binary counter TTL
74390 Dual decade counter TTL
74393 Dual four-bit binary counter TTL
4014 B Eight-bit static shift register CMOS
(synchronous parallel or serial-in/serial-out)
4015 B Dual four-bit static shift register CMOS
(serial-in/parallel-out)
4017 B Five-stage Johnson counter CMOS
4021 B Eght-bit static shift register CMOS
(asynchronous parallel-in or synchronous serial-in/serial-out)
4029 B Synchronous presettable four-bit UP/DOWN counter CMOS
4035 B Four-bit universal shift register CMOS
40160 B Decade counter with asynchronous CLEAR CMOS
40161 B Binary counter with asynchronous CLEAR CMOS
40162 B Decade counter CMOS
40163 B Binary Counter CMOS
40192 B Presettable BCD UP/DOWN counter CMOS
40193 B Presettable Binary UP/DOWN counter CMOS
4510 B Presettable UP/DOWN BCD counter CMOS
4518 B Dual four-bit decade counter CMOS
4520B Dual four-bit binary counter CMOS
4522 B Four-bit BCD programmable divide-by-N counter CMOS
4722 B Programmable counter/timer CMOS
4731 B Quad 64-bit static shift register CMOS
MC 10136 Universal hexadecimal counter ECL
MC 10137 Universal decade counter ECL
MC 10141 Four-bit universal shift register ECL
MC 10154 Binary counter (four-bit) ECL
MC 10178 Four-bit binary counter ECL