TELEPHONE SET SYSTEM BASIC ELECTRONIC TUTORIALS

HOW A TELEPHONE WORKS? WHAT YOU NEED TO KNOW ABOUT THE TELEPHONE

The telephone arrived as a practical instrument over a century ago in 1876, an outgrowth of experiments on a device to send multiple telegraph signals over a single wire. Alexander Graham Bell, a native of Scotland, while conducting electrical experiments spilled acid on his trousers.

His reaction, the now-famous “Mr. Watson, come here, I want you,” brought Thomas A. Watson on the run not only because of his employer‘s distress, but because the words had been carried by electricity into Watson’s room and reproduced clearly on his receiving set.


The simple instrument being tested on Court Street in Boston on March 10, 1876, wasn’t very practical (the acid was used in the system), but improvement followed so rapidly that putting into action Bell’s concept of a public telephone network-“this grand system . . . whereby a man in one part of the country may communicate by word of mouth with another in a distant place”-was well under way by January 1878, when the first commercial exchange was operated in New Haven. By 1907, one hotel alone (the Waldorf Astoria in New York City) had 1,120 telephones and processed 500,000 calls per year.

The American Telephone and Telegraph Company (AT&T) was incorporated in March 1885 to manage the explosive growth of the fledgling telephone network across the United States. Virtually since the beginning, AT&T worked as a legal, regulated monopoly. This means that AT&T was allowed to establish, maintain, and control a single, universal network across the country without any competition, as well as provide all telephone sets and switching equipment to the general public. The federal government regulated its policies, practices, and fees. This set the groundwork for the development of the most advanced and efficient telecommunications system in the world.


Telephones have simple appearance and operation yet it performs a surprising number of functions. The most important ones are:

1. It requests the use of the telephone system when the handset is lifted.
2. It indicates that the system is ready for use by receiving a tone, called the dial tone.
3. It sends the number of the telephone to be called to the system. This number is initiated by the caller when the number is pressed (or the dial is rotated in older telephones).
4. It indicates the state of a call in progress by receiving tones indicating the status (ringing, busy, etc.).
5. It indicates an incoming call to the called telephone by ringing bells or other audible tones.
6. It changes speech of a calling party to electrical signals for transmission to a distant party through the system. It changes electrical signals received from
a distant party to speech for the called party.
7. It automatically adjusts for changes in the power supplied to it.
8. It signals the system that a call is finished when a caller “hangs up’’ the handset.

Of course, for a telephone to be of any use, it must be connected to another telephone. In the very early days of telephony, the phones were simply wired together with no switching. As the number of phones increased this became impractical, so the local exchange or central office was established to handle the switching and other functions.

EVOLUTION OF MICROPROCESSORS TUTORIALS

WHAT IS THE EVOLUTION OF MICROPROCESSORS?


The evolution of microprocessors has been known to follow Moore’s law, which suggests that the complexity of an integrated circuit, with respect to the minimum component cost, doubles every 24 months.

This rule has been generally followed, since the humble beginning of microprocessors as the drivers for calculators to the present-day scenario where every system, from the largest mainframes to the smallest handheld computers, uses a microprocessor at its core.


The first microprocessor was introduced in 1971 by the Intel Corporation. It was a four-bit microprocessor, Intel 4004. Other four-bit microprocessors developed were Intel 4040 by Intel, PPS-4 by Rockwell International, T3472 by Toshiba and so on.

The first eight-bit microprocessor, named Intel 8008, was also developed by Intel in the year 1972. All these microprocessors were made using PMOS technology. The first microprocessor using NMOS technology was Intel 8080, developed by Intel in the year 1973.

Intel 8080 was followed by Intel 8085 in the year 1975, which became very popular. Other popular eight-bit microprocessors were Zilog’s Z80 (1976) and Z800, Motorola’s MC6800 (1974) and MC6809 (1978), National Semiconductor’s NSC 800, RCA’s 1802 (1976) and so on.

The first multichip 16-bit microprocessor was National Semiconductor’s IMP-16, introduced in 1973. The first 16-bit single-chip microprocessor was Texas Instrument’s TMS 9900. Intel’s first 16-bit microprocessor was Intel 8086 introduced in the year 1978.

Other 16-bit microprocessors developed by Intel were Intel 80186 (1982), Intel 8088, Intel 80188 and Intel 80286 (1982). Other popular 16-bit microprocessors include Motorola’s 68000 (1979), 68010 and 68012, Zilog’s Z8000, Texas Instruments TMS 9900 series and so on.

32-bit microprocessors came into existence in the 1980s. The world’s first single-chip 32-bit microprocessor was introduced by AT&T Bell Labs in the year 1980. It was named BELLMAC- 32A. The first 32-bit processor introduced by Intel was iapx 432, introduced in 1981.

The more popular 32-bit microprocessor was Intel 80386, introduced by Intel in 1985. It was widely used for desktop computers. The 32-bit microprocessor family of Intel includes Intel 486, Pentium, Pentium Pro, Pentium II, Pentium III and Pentium IV.

AMD’s K5, K6 and K7, Motorola’s 68020 (1985), 68030 and 68040, National Semiconductor’s 32032 and 32332 and Zilog’s Z80000 are other popular 32-bit microprocessors. All these microprocessors are  based on CISC (Complex Instruction Set Computers) architecture.

The first commercial RISC (Reduced Instruction Set Computers) design was released by MIPS Technologies, the 32-bit R2000. Some of the popular RISC processors include Intel’s 80860 and 80960, Motorola’s 88100 and Motorola’s, IBM and Apple’s PowerPC series of microprocessors.

While 64-bit microprocessor designs have been in use in several markets since the early 1990s, the early 2000s have seen the introduction of 64-bit microchips targeted at the PC market. Some of the popular 64-bit microprocessors are AMD’s AMD64 (2003) and Intel’s x86-64 chips. Popular 64-bit RISC processors include SUN’s ULTRASPARC, PowerPC 620, Intel’s Itanium, MIPS R4000, R5000, R10000 and R12000 and so on.

SIMPLE ELECTRONIC ORGAN PROJECT

HOW TO MAKE A SIMPLE ELECTRONIC ORGAN?


It uses the popular NE555 integrated circuit, which contains a circuit which will periodically switch the voltage on the output pin between the supply voltage and zero. Just how frequently this switching occurs depends upon the components external to the integrated circuit.

If this switching occurs several hundred or thousand times a second, the change in voltage produced will generate a musical note when connected to a small loudspeaker. The circuit is shown below:

Parts list
Resistors: all 0.25 watt, 5% tolerance
R1 2.7 kilohms (k )
R2 1 Megohm (M )
P1–P5 Preset resistor 100 kilohms (k )
P6, P7 Preset resistor 50 kilohms (k )
P8 Preset resistor 25 kilohms (k )
P9, P10 Preset resistor 10 kilohms (k )
Capacitor
C1 100 nanofarads (nF) or 0.1 microfarad ( F)
Integrated circuit
IC1 NE555 timer chip
Additional items
S Loudspeaker >60 ohms (Maplin)
1 off battery clip (for PP3 battery)
1 off spade terminal
12 off solder pins ‘Veropins’
3 off 10 cm lengths of ‘hook-up’ wire


Check first that each component is in the correct place. When inserting the NE555 chip, first make sure that the end carrying the notch lies over the end of the holder with the notch; then, make sure each pin of the chip lies directly above the hole into which it fits, before pressing gently to insert the chip into the socket.

Make sure the battery connections are correct, and insert the battery into the clip. Nothing should happen, except for a click from the loudspeaker; touching the spade on any of the pins should produce a coarse note from the speaker.

If nothing happens, check everything again; don’t assume that wires go where you think they go! After you get the first note, all the others should work, too, but they will sound off-tune at first. The organ needs tuning up by adjusting the 10 preset variable resistors P1 to P10.

If you have a piano, the organ can be tuned by comparison of the notes with those on the piano. The frequencies are given in Hertz (abbreviation Hz), and represent the number of times the IC switches on and off every second. If the sound coming from the loudspeaker is too loud or very distorted, then try putting an 330 resistor (colour code orange, orange, brown) in series with the loudspeaker.

This is done by taking the resistor and cutting its leads to about 5 mm; then, disconnect one speaker lead from the tab on the PCB (it doesn’t matter which). Solder one end of the resistor to the vacated speaker tab, and the free speaker lead to the other end of the resistor.

This will limit the volume of sound from the speaker, and lengthen the life of your battery. If it is still too loud, try a resistor of a larger value, or use a smaller resistor to make it louder.

GAS LEAKAGE ALARM ELECTRONICS PROJECT

HOW TO MAKE A GAS LEAKAGE ALARM?

This is a basic electronic project of Gas Leakage Alarm, using a SEN-1327. The circuit diagram below shows the circuit of the gas leakage alarm. The circuit operates off a 9V PP3 battery. Zener diode ZD1 is used to convert 9V into 5V DC to drive the gas sensor module.

The SEN-1327 gas sensor module from RhydoLABZ is used in this circuit. Its output goes high when the gas level reaches or exceeds certain point.

A preset in the module is used to set the threshold. Interfacing with the sensor module is done through a 4-pin SIP header. An MQ-6 gas sensor is used in the gas sensor module.

As per its datasheet, it has high sensitivity to propane, butane, isobutene, LPG and natural gas. The sensor can also be used to detect combustible gases, especially methane.

This circuit has been tested with LPG gas and was found to work satisfactorily. Whenever there is LPG concentration of 1000 ppm (parts per million) in the area, the OUT pin of the sensor module goes high.

This signal drives timer IC 555, which is wired as an astable multivibrator. The multivibrator basically works as a tone generator.

Output pin 3 of IC 555 is connected to LED1 and speaker-driver transistor SL100 through current-limiting resistors R5 and R4, respectively. LED1 glows and the alarm sounds to alert the user of gas leakage. The pitch of the tone can be changed by varying preset VR1. Use a suitable heat-sink for transistor SL100.

COAXIAL CABLE POWER RATINGS BASIC INFORMATION

POWER RATINGS OF COAXIAL CABLES



Power Rating
Both peak and average power ratings are required to fully describe the capabilities of a transmission line. In most applications, the peak power rating limits the low frequency or pulse energy, and the average power rating limits high-frequency applications, as shown in Fig. 4.4.

Peak power ratings are usually stated for the following conditions:
VSWR = 1.0
Zero modulation
One atmosphere of absolute dry air pressure at sea level

The peak power rating of a selected cable must be greater than the following expression, in addition to satisfying the average-power-handling criteria: E pk > Pt × (1 + M)2 × VSWR

where E pk is the cable peak power rating in kilowatts, Pt is the transmitter power in kilowatts, M is the amplitude modulation percentage expressed decimally (100%=1.0), and VSWR is the voltage standing wave ratio.

From this equation, it can be seen that 100% amplitude modulation will increase the peak power in the transmission line by a factor of 4. Furthermore, the peak power in the transmission line increases directly with VSWR.

The peak power rating is limited by the voltage breakdown potential between the inner and outer conductors of the line. The breakdown point is independent of frequency. It varies, however, with the line pressure (for an air-dielectric cable) and the type of pressurizing gas.

The average power rating of a transmission line is limited by the safe, long-termoperating temperature of the inner conductor and the dielectric. Excessive temperatures on the inner conductor will cause the dielectric material to soften, leading to mechanical instability inside the line.

The primary purpose of pressurization of an air-dielectric cable is to prevent the ingress of moisture. Moisture, if allowed to accumulate in the line, can increase attenuation and reduce the breakdown voltage between the inner and outer conductors.

Pressurizationwith high-density gases can be used to increase both the average power and the peak power ratings of a transmission line. For a given line pressure, the increased power rating is more significant for peak power than for average power.

High-density gases used for such applications include Freon 116 and sulfur hexafluoride. Figure 4.5 illustrates the effects of pressurization on cable power rating.

An adequate safety factor is necessary for peak and average power ratings. Most transmission lines are tested at two or more times their rated peak power before shipment to the customer.

This safety factor is intended as a provision for transmitter transients, lightning-induced effects, and high voltage excursions resulting from unforeseen operating conditions.