A coaxial transmission line possesses a certain capacitance per unit of length. This capacitance is defined by:

C = 24ε log pF/(D/d) Metre

C is the capacitance
D is the outside conductor diameter
d is the inside conductor diameter
ε is the dielectric constant of the insulator.

A long run of coaxial cable can build up a large capacitance. For example, a common type of coax is rated at 65 pF/metre. A 150 metre roll thus has a capacitance of (65 pF/m) (150 m), or 9750 pF.

When charged with a high voltage, as is done in performing breakdown voltage tests at the factory, the cable acts like a charged high voltage capacitor. Although rarely if ever lethal to humans, the stored voltage in new cable can deliver a nasty electrical shock and can irreparably damage electronic components.

The normal mode in which a coaxial cable propagates a signal is as a transverse electromagnetic (TEM) wave, but others are possible – and usually undesirable. There is a maximum frequency above which TEM propagation becomes a problem, and higher modes dominate.

Coaxial cable should not be used above a frequency of:

FCUT−OFF = 1/ 3.76(D + d) √ε

F is the TEM mode cut-off frequency
D is the diameter of the outer conductor in mm

d is the diameter of the inner conductor in mm ε is the dielectric constant When maximum operating frequencies for cable are listed it is the TEM mode that is cited. Beware of attenuation, however, when making selections for microwave frequencies.

A particular cable may have a sufficiently high TEM mode frequency, but still exhibit a high attenuation per unit length at X or Ku-bands.



When an RF cable is mismatched, i.e. connected to a load of a different impedance to that of the cable, not all the power supplied to the cable is absorbed by the load. That which does not enter the load is reflected back down the cable.

This reflected power adds to the incident voltage when they are in phase with each other and subtracts from the incident voltage when the two are out of phase. The result is a series of voltage – and current – maxima and minima at halfwavelength intervals along the length of the line. The maxima are referred to as antinodes and the minima as nodes.

The voltage standing wave ratio is the numerical ratio of the maximum voltage on the line to the minimum voltage: VSWR = Vmax/Vmin. It is also given by: VSWR = RL/Z0 or Z0/RL (depending on which is the larger so that the ratio is always greater than unity) where RL = the load resistance.

The return loss is the power ratio, in dB, between the incident (forward) power and the reflected (reverse) power. The reflection coefficient is the numerical ratio of the reflected voltage to the incident voltage.

The VSWR is 1, and there is no reflected power, whenever the load is purely resistive and its value equals the characteristic impedance of the line. When the load resistance does not equal the line impedance, or the load is reactive, the VSWR rises above unity.

A low VSWR is vital to avoid loss of radiated power, heating of the line due to high power loss, breakdown of the line caused by high voltage stress, and excessive radiation from the line. In practice, a VSWR of 1.5:1 is considered acceptable for an antenna system, higher ratios indicating a possible defect.




The range of powers, voltages and currents encountered in radio engineering is too wide to be expressed on linear scale. Consequently, a logarithmic scale based on the decibel (dB, one tenth of a bel) is used.

The decibel does not specify a magnitude of a power, voltage or current but a ratio between two values of them. Gains and losses in circuits or radio paths are expressed in decibels.

The ratio between two powers is given by:

Gain or loss, dB = 10 log10 P1/P2

where P1 and P2 are the two powers.

As the power in a circuit varies with the square of the voltage or current, the logarithm of the ratio of these quantities must be multiplied by twenty instead of ten. To be accurate the two quantities under comparison must operate in identical impedances:

Gain or loss, dB = 20 log10 V1/V2

To avoid misunderstandings, it must be realized that a ratio of 6 dB is 6 dB regardless of whether it is power, voltage or current that is referred to: if it is power, the ratio for 6 dB is four times; if it is voltage or current, the ratio is two times



There are a number of scatter modes of propagation. These modes can extend the radio horizon a considerable amount. Where the radio horizon might be a few tens of kilometres, underscatter modes permit very much longer propagation.

For example, a local FM broadcaster at 100MHz might have a service area of about 40 miles, and might be heard 180 miles away during the summer months when Sporadic- E propagation occurs. One summer, a television station in Halifax, Nova Scotia, Canada, was routinely viewable in Washington, DC in the United States during the early morning hours for nearly a week.

Sporadic-E is believed to occur when a small region of the atmosphere becomes differentially ionized, and thereby becomes a species of ‘radio mirror’. Ionospheric scatter propagation occurs when clouds of ions exist in the atmosphere.

These clouds can exist in both the ionosphere and the troposphere, although the tropospheric model is more reliable for communications. A signal impinging this region may be scattered towards other terrestrial sites which may be a great distance away. The specific distance depends on the geometry of the scenario.

There are at least three different modes of scatter from ionized clouds: back scatter, side scatter, and forward scatter. The back scatter mode is a bit like radar, in that signal is returned back to the transmitter site, or in regions close to the transmitter.

Forward scatter occurs when the reflected signal continues in the same azimuthal direction (with respect to the transmitter), but is redirected toward the Earth’s surface. Side scatter is similar to forward scatter, but the azimuthal direction might change.

Unfortunately, there are often multiple reflections from the ionized cloud. When these reflections are able to reach the receiving site, the result is a rapid, fluttery fading that can be of quite profound depths.

Meteor scatter is used for communication in high latitude regions. When a meteor enters the Earth’s atmosphere it leaves an ionized trail of air behind it. This trail might be thousands of kilometres long, but is very short lived.

Radio signals impinging the tubular metre ion trail are reflected back towards Earth. If the density of meteors in the critical region is high, then more or less continuous communications can be achieved.

This phenomenon is noted in the low VHF between 50 and about 150 MHz. It can easily be observed on the FM broadcast band if the receiver is tuned to distant stations that are barely audible. If the geometry of the scenario is right, abrupt but short-lived peaks in the signal strength will be noted.



Reflection, refraction and diffraction may provide signals in what would otherwise be areas of no signal, but they also produce interference.

Reflected – or diffracted – signals may arrive at the receiver in any phase relationship with the direct ray and with each other. The relative phasing of the signals depends on the differing lengths of their paths and the nature of the reflection.

When the direct and reflected rays have followed paths differing by an odd number of half-wavelengths they could be expected to arrive at the receiver in anti-phase with a cancelling effect. However, in the reflection process a further phase change normally takes place.

If the reflecting surface had infinite conductivity, no losses would occur in the reflection, and the reflected wave would have exactly the same or opposite phase as the incident wave depending on the polarization in relation to the reflecting surface.

In practice, the reflected wave is of smaller amplitude than the incident, and the phase relationships are also changed. The factors affecting the phasing are complex but most frequently, in practical situations, approximately 180◦ phase change occurs on reflection, so that reflected waves travelling an odd number
of half-wavelengths arrive in phase with the direct wave while those travelling an even number arrive anti-phase.

As conditions in the path between transmitter and receiver change so does the strength and path length of reflected signals. This means that a receiver may be subjected to signal variations of almost twice the mean level and practically zero, giving rise to severe fading.

This type of fading is frequency selective and occurs on troposcatter systems and in the mobile environment where it is more severe at higher frequencies. A mobile receiver travelling through an urban area can receive rapid signal fluctuations caused by additions and cancellations of the direct and reflected signals at half-wavelength intervals.

Fading due to the multi-path environment is often referred to as Rayleigh fading. Rayleigh fading, which can cause short signal dropouts, imposes severe restraints on mobile data transmission.



Trouble with PCI devices can be caused by
Software bugs.
Software settings.
Hardware faults.
Device conflicts.

The standard way to fix software bugs is to obtain the latest card driver from the manufacturer. This can usually be achieved via the manufacturers’ website. These websites often contain details of hardware or software conflicts.

Some boards will not work if they are present in the same machine as other devices. An example of this occurred in the PC of one of the authors. It was fitted with a PCI SCSI card that allowed a SCSI scanner to work very well.

All was well until the scanner and its SCSI cable were removed. After this, the IDE CD-ROM drive eject button caused the system to reboot. Removing the now unused PCI SCSI card failed to resolve the problem.

It had to be reinserted, the driver removed via the Windows 98 Control Panel and the card removed again before a reboot caused the ‘new hardware found’ dialogue. Problems with seemingly unrelated devices are not uncommon. This problem was discovered via the Microsoft knowledge base website.

Only after trying to resolve software/hardware conflicts should a hardware fault be suspected. If a card is suspected of giving trouble, shut down the system, remove the card and install it in a second PC. If the trouble persists in the second PC, the card is probably faulty - repair is not usually economic.

Without specialist equipment, troubleshooting the PCI can be tricky. Test equipment such as the PCI diagnostics card from UltraX Inc. ( ill test the PCI bus when other devices are dead or missing.

TIP: If you need to upgrade a device driver, it is often better to uninstall the old one first. Reinstallation sometimes retains old (and possibly faulty) software components such as .DLL files.



Initially devised by Intel and subsequently supported by the PCI Special Interest Group (PCI-SIG), the Peripheral Component Interconnect bus has become established as arguably the most popular and ‘future proof bus standard available today. It avoids the IRQ conflicts of the ISA bus by using plug and play.

With plug and play, the system configures itself by allowing the PCI BIOS to access configuration registers on each add-in board at bootup time. As these configuration registers tell the system what resources they need (I/O space, memory space, interrupts, etc.), the system can allocate its resources accordingly, making sure that no two devices conflict.

The PCI BIOS cannot directly query ISA devices to determine which resources they need. This can sometimes give rise to problems in systems using both ISA and PCI. A PCI board’s 1/0 address and interrupt are not fixed, and can change every time the system boots.

PCI offers flexible bus mastering. This means that any PCI device can take control of the bus at any time, allowing it to shut out the CPU. Devices use bandwidth as available, even all the bandwidth, if no other demands are made for it.

Bus mastering works by sending request signals when a device wants control of the bus and the requestbeing
granted if data traffic allows it.

Because the PCI bus is not connected directly to the CPU (it is separated by an interface formed by a dedicated ‘PCI chipset’) the bus is sometimes referred to as a ‘mezzanine bus’. This technique offers two advantages over the earlier VL bus specification:

I. Reduced loading of the bus lines on the CPU (permitting a longer data path and allowing more bus cards to be connected to it).

II. Making the bus ‘processor independent’.

The original PCI bus was designed for operation at clock speeds of 33MHz. With a 32-bit data path, the 33MHz clock rate implies a maximum data transfer rate of around 130Mbyte/s (about the same as VL bus). Like the VL bus, the PCI bus connector is similar to that used for MCA. To cater for both 32- and 64-bit operation, PCI bus cards may have either 62 or 94 pins.

Later PCI implementations had a bus clock rate up to 66 MHz, giving up to 132 MB per second transfer rate over the 32-bit bus.



Most motherboard problems are related to cabling and connections. Ensure all cables are connected firmly. Ribbon cables and power cables can often come loose.

Ensure all ‘plugin’ items such as the CPU, RAM modules and adapters such as video cards, modems, etc. are inserted correctly. Contacts can become oxidized or dirty: as a quick fix, remove and reinsert the item several times to wear away the oxide.

This is not a long-term solution, the parts should be removed and cleaned with a good quality contact cleaner.

Other problems are often related to specific hardware but check the items below first.

-Remove all add-on cards except the graphics adapter and start the machine. If that fails to give a running machine, check connections, settings, CPU and RAM compatibility, etc. in the motherboard technical specification.

Keep the PC speaker connected but not any external speakers. Reset the BIOS settings to their default values. On some boards there is a jumper or other way to clear the BIOS settings.

-Is there sufficient power from the power supply?

-Try a different keyboard.

-Check for bent pins on the board. You might be lucky if you try to

-Try disabling the cache in the BIOS. If this makes the machine work, straighten them. If not, you will need to buy a new board!



Replacing the CPU
The processor chip (regardless of type) is invariably fitted in a socket or a slot and this makes removal and replacement quite straightforward provided that you take reasonable precautions.

The following describes the stages in removing and replacing a CPU chip:

1. Switch 'off, disconnect from the supply and gain access to the system board.

2. Ensure that you observe the safety and static precautions at all times. Have some anti-static packing available to receive the CPU when it has been removed.

3. Locate the CPU and ensure that there is sufficient room to work all around it (you may have to move ribbon cables or adapter cards to gain sufficient clearance to use the extraction and insertion tools).

4. Depending on the design of the socket/slot, release the catch that holds the CPU in place.

5. Immediately deposit the chip in an anti-static container (do not touch any of the pins).

6. Pick up the replacement chip from its anti-static packing. Position the insertion chip over the socket and ensure that it is correctly orientated.

7. Reassemble the system (replacing any adapter cards and cables that may have been removed in order to gain access or clearance around the CPU). Reconnect the system and test.

Upgrading the CPU
A relentless increase in the power of the CPU makes this particular component a prime candidate for upgrading a system in order to keep pace with improvements in technology.

Moore’s law says that the number of transistors used in microprocessors will double every 18 months. The progress seems to correlate well with this ‘law’.

Although Moore’s law refers to the number of transistors in an integrated circuit, the clock speed of Intel processors seems to conform quite well with the ‘law’.

TIP: Before attempting a CPU upgrade it is well worth giving careful attention to the cost effectiveness of the upgrade - in many cases there may be other ways of improving its performance for less outlay. In particular, if you are operating on a limited budget it may be worth considering a RAM or hard disk upgrade before attempting to upgrade the CPU. In both cases, significant improvements in performance can usually be achieved at moderate cost.



The basic components of a microcomputer system are:
1. A central processing unit (CPU).
2. A memory, comprising both ‘read/write’ and ‘read-only’ devices (commonly called RAM and ROM respectively).
3. A mass storage device for programs andjor data (e.g. a floppy and/or hard disk drive).
4.  A means of providing user input and output (via a keyboard and display interface).
5. Interface circuits for external input and output (I/O). These circuits (commonly called ‘ports’) simplify the connection of peripheral devices such as printers, modems, mice, and joysticks.

In a microcomputer (as distinct from a mini or mainframe machine) the functions of the CPU are provided by a single VLSI microprocessor chip (e.g. an Intel 8086, 8088, 80286, 80386, 80486, or Pentium). The microprocessor is crucial to the overall performance of the system.

Indeed, successive generations of PC are normally categorized by reference to the type of chip used. The ‘original’ PC used an 8088, AT systems are based on an 80286, ’386 machines use an 80386, and so on.

Semiconductor devices are also used for the fast redd/write and readonly memory. Strictly speaking, both types of memory permit ‘random access’ since any item of data can be retrieved with equal ease regardless of its actual location within the memory. Despite this, the term ‘RAM’ has become synonymous with semiconductor read/write memory. (VLSI means very large scale integration, i.e. a complex chip.) 

The semiconductor ROM provides non-volatile storage for part of the operating system code (this ‘BIOS’ code remains intact when the power supply is disconnected). The semiconductor RAM provides storage for the remainder of the operating system code (the ‘DOS’), applications programs and transient data (including that which corresponds to the screen display).

It is important to note that any program or data stored in RAM will be lost when the power supply is switched off or disconnected. The only exception to this is a small amount of ‘CMOS memory’ kept alive by means of a battery.

This ‘battery-backed’ memory is used to retain important configuration data, such as the type of hard and floppy disk fitted to the system and the amount of RAM present.



The symbols used thus far in the chapter for representing different types of gate are the ones that are better known to all of us and have been in use for many years. Each logic gate has a symbol with a distinct shape.

However, for more complex logic devices, e.g. sequential logic devices like flip-flops, counters, registers or arithmetic circuits, such as adders, subtractors, etc., these symbols do not carry any useful information. A new set of standard symbols was introduced in 1984 under IEEE/ANSI Standard 91–1984.

The logic symbols given under this standard are being increasingly used now and have even started appearing in the literature published by manufacturers of digital integrated circuits. The utility of this new standard will be more evident in the following paragraphs as we go through its salient features and illustrate them with practical examples.


What Is ESMR?

Enhanced Specialized Mobile Radio (ESMR) systems use digital radio transmissions similar to other digital technologies. Spread-spectrum modes, such as frequency hopping, are common.

One major difference from other networks is that in an ESMR system, connections between users is almost instantaneous, compared to the typical delays required to dial and set up a call in a public cellular network.This capability allows the ESMR carrier to offer walkie-talkie–like services on its network, as well as cellular calling.

This is a great advantage for large work groups who need to be in constant contact with just a touch of a button, for example a construction crew. ESMR services also allow customers to contact many people at the same time, much like a CB radio, thus creating a multiple person “call.”

Examples of ESMR networks include Ericsson’s Enhanced Digital Access Communications System (EDACS), Motorola’s Integrated Dispatch Enhanced Network (iDEN), and the Nextel System. Delivery and courier services, which depend on mobility and speed, also typically employ ESMR for voice communications between the delivery vehicles and the office.

The technology consists of a dispatcher in an office plotting out the day’s events for the driver.When the driver arrives at his location, he radios the dispatcher and lets him know his location.The benefit of ESMR is its ability to act like a CB radio, allowing all users on one channel to listen, while still allowing two users to communicate personally.This arrangement allows the dispatcher to coordinate schedules for both pick-ups and deliveries, and to track the driver’s progress.

Drivers with empty loads can be routed to assist backlogged drivers. Drivers that are on the road can be radioed if a customer cancels a delivery.This type of communication benefits delivery services in two major areas, saving time and increasing efficiency.

Benefits of ESMR
ESMR is a unique digital service that allows the user a couple ways to communicate, including:

Push-to-talk features that operate like walkie-talkies allow users to talk directly to another person without delay in setting up the call

Group calling allows users to talk to many people at one time

Digital transmissions assure privacy

Two-way data features are available

International systems allow the use of one handset anywhere the service is available


What Is TDMA? 

Time Division Multiple Access (TDMA) divides wireless conversations by frequency and time to increase the capacity of the network. TDMA uses a single voice channel for multiple calls by taking each call, breaking it into timed sections of a digital transmission to the tower, and reassembling the call based on the timeslot.

For example, call A has all its parts put into timeslot A, call B has its parts put into timeslot B, and each are sent in one transmission to the tower, where the calls are put back together for transmission to the other party. TDMA was one of the original digital systems used and has gone through many revisions to make sure it utilizes the network to the best of its abilities.

Based on a limited number of time slots for each call in a channel, TDMA has no accommodations for silence in a telephone conversation. In other words, once a call is initiated, the channel/timeslot pair belongs to the phone for the duration of the call.

Each channel using TDMA technology for wireless calls is further divided into time slots. Each timeslot is assigned to a different user.The transmitter transmits information for all time slots at the same frequency and the receivers receive all the timeslots but listen only to the time slot they have been allocated.

The net effect is that the efficiency of the channel is increased by a multiple of the number of timeslots that are being used. Most common second-generation TDMA phone systems use three timeslots.

Benefits of TDMA
TDMA was one of the first technologies to expand analog’s voice capabilities beyond one call per channel.TDMA has many other benefits:

Provides advanced features like caller ID, text messaging

Economizes bandwidth

Provides voice clarity and overall call quality, even over long distances

Is difficult to decode, therefore only minimal eavesdropping is possible

Uses less battery power (when compared to analog)

Offers voice privacy


What Is GSM?

Global Systems for Mobile Communication (GSM) is the main technology used by the international digital wireless systems; however, GMS is used only by a small percentage of wireless carriers in the United States. GSM is interesting in that it uses a modified and far more efficient version of TDMA.

GSM keeps the idea of time slots on frequency channels, but corrects several major shortcomings. Since the GSM timeslots are smaller than TDMA, they hold less data but allow for data rates starting at 300 bits per second. Thus, a call can use as many timeslots as necessary up to a limit of 13 kilobits per second.

When a call is inactive (silence) or can be compressed more, fewer timeslots are used.To facilitate filling in gaps left by unused timeslots, calls do frequency hopping in GSM.This means that calls will jump between channels and timeslots to maximize the system’s usage.A control channel is used to communicate the frequency hopping and other information between the antenna tower and the phone.

The architecture used by GSM consists of three main components: a mobile station, a base station subsystem, and a network subsystem. These components work in tandem to allow a user to travel seamlessly without interruption of service, while offering the flexibility of having any device used permanently or temporarily by any user.

Utilizing the three separate components of the GSM network, this type of communication is truly portable.A user can place an identification card called a Subscriber Identity Module (SIM) in the wireless device, and the device will take on the personal configurations and information of that user.

This includes telephone numbers, home system, and billing information. Although the United States has migrated towards CDMA and TDMA as the premier mode of wireless communications, a large part of the world uses GSM.

Benefits of GSM
GSM networks cover the most wireless users around the world and the technology is gaining favor in the United States because of the following benefits:

Provides integrated voice, high-speed two-way data, fax, and short message services capabilities

Offers advanced features such as caller ID, text messaging

Offers superior voice clarity and overall call quality

Provides personal identification tied to a Subscriber

 Information Module (SIM) card that can be used in multiple phones, not tying the user to one phone

 Offers voice privacy

Uses less battery power (when compared to analog)

Enables a single technology handset to work around the world where GSM is available (as long as the frequencies are accessible by the handset)


What Is CDMA?

Code Division Multiple Access (CDMA) is often referred to as the most interesting, but hardest to implement method of carrying wireless services. CDMA systems have no channels, but instead encode each call as a coded sequence across the entire frequency spectrum. Each conversation is modulated, in the digital domain, with a unique code that makes it distinguishable from the other calls in the frequency spectrum.

CDMA is the newest of the multiple access technologies; it is not yet as widely used but is showing great promise. CDMA does not divide the allocated block of frequencies into individual channels. It assigns a unique code to each signal and then combines all the signals into a single large channel.

The receiver receives the integrated signal and uses the same code just to process the desired signal. CDMA is gaining popularity as a third-generation (3G) wireless phone technology because it is very efficient at utilizing bandwidth, plus it is natively very secure because all conversations are uniquely encoded.

The fact that CDMA shares frequencies with neighboring wireless towers allows for easier installation of extra capacity, since extra capacity can be achieved by simply adding extra cell sites and shrinking power levels of nearby sites.The downside to CDMA is the complexity of deciphering and extracting the received signals, especially if there are multiple signal paths (reflections) between the phone and the wireless tower (called multipath interference).

As a result, CDMA phones are sometimes more expensive than other digital phones and CDMA antenna site equipment is three to four times the price of the other digital network equivalents.

Benefits of CDMA
CDMA networks cover more wireless users in the United States than any other digital standard and include benefits such as:

Advanced features like caller ID, text messaging

Voice clarity and overall call quality

The ability to filter out background noise and interference

Fewer dropped calls (as compared to analog)

Improved security and privacy—the digitally encoded, spread spectrum transmissions minimizes eavesdropping

Α large number of customers who can share the same radio frequencies

The greatest customer capacity of network equipment for low cost

Less battery power (when compared to analog)



The full-scale deflection of the universal high-input-resistance voltmeter circuit shown in the figure depends on the function switch position as follows:

(a) 5V DC on position 1
(b) 5V AC rms in position 2
(c) 5V peak AC in position 3
(d) 5V AC peak-to-peak in position 4

The circuit is basically a voltage-tocurrent converter. The design procedure is as follows:

Calculate RI according to the application from one of the following equations:
(a) DC voltmeter: RIA = full-scale EDC/IFS
(b) RMS AC voltmeter (sine wave only): RIB = 0.9 full-scale ERMS/ IFS
(c) Peak reading voltmeter (sine wave only): RIC = 0.636 fullscale EPK/IFS
(d) Peak-to-peak AC voltmeter (sine wave only): RID = 0.318 full-scale EPK-TO-PK / IFS

The term IFS in the above equations refers to meter’s full scale deflection current rating in amperes. It must be noted that neither meter resistance nor diode voltage drops affects meter current.

Note: The results obtained during practical testing of the circuit in EFY lab are tabulated in Tables I through IV. A high-input-resistance op-amp, a bridge rectifier, a microammeter, and a few other discrete components are all that are required to realise this versatile circuit.

This circuit can be used for measurement of DC, AC RMS, AC peak, or AC peak-to-peak voltage by simply changing the value of the resistor connected between the inverting input terminal of the op-amp and ground. The voltage to be measured is connected to non-inverting input of the op-amp.



This circuit uses a complementary pair comprising npn metallic transistor T1 (BC109) and pnp germanium transistor T2 (AC188) to detect heat (due to outbreak of fire, etc) in the vicinity and energise a siren. The collector of transistor T1 is connected to the base of transistor T2, while the collector of transistor T2 is connected to relay RL1.

The second part of the circuit comprises popular IC UM3561 (a siren and machine-gun sound generator IC), which can produce the sound of a fire-brigade siren. Pin numbers 5 and 6 of the IC are connected to the +3V supply when the relay is in energised state, whereas pin 2 is grounded. A resistor (R2) connected across pins 7 and 8 is used to fix the frequency of the inbuilt oscillator.

The output is available from pin 3. Two transistors BC147 (T3) and BEL187 (T4) are connected in Darlington configuration to amplify the sound from UM3561. Resistor R4 in series with a 3V zener is used to provide the 3V supply to UM3561 when the relay is in energised state. LED1, connected in series with 68 ohm resistor R1 across resistor R4, glows when the siren is on.

To test the working of the circuit, bring a burning matchstick close to transistor T1 (BC109), which causes the resistance of its emitter-collector junction to go low due to a rise in temperature and it starts conducting. Simultaneously, transistor T2 also conducts because its base is connected to the collector of transistor T1.

As a result, relay RL1 energises and switches on the siren circuit to produce loud sound of a fire brigade siren. Lab note. We have added a table to enable readers to obtain all possible sound effects by returning pins 1 and 2 as suggested in the table.



Technology providers, publishers, and device makers are collaborating to develop standards and copy protection mechanisms to avoid the pitfalls that have tripped up other trailblazers in digital content. Issues that need to be standardized include content platforms, file formats, and systems for copy protection, and the secure exchange of content.

Government officials and industry executives are advising the eBook industry to act swiftly to avoid the same types of problems that have plagued the music and video industries—piracy of MP3 audio and disabling the content scrambling protection for DVDs.

To be profitable the eBook industry must protect their most valuable asset, the content, by focusing on digital rights management and copy protection. Early eBooks were protected from piracy by requirements for specialized electronic devices made available through exclusive deals between the device manufacturer and the book publisher.

Today, eBook content can be read on any Windows PC using standardized software such as Acrobat Reader, from Adobe Systems Inc., or Microsoft’s Microsoft Reader software. eBooks can also be read with products such as:

■ A Palm PDA running Peanut Press reader software from Peanut Press Inc.
■ Aportis Doc software from Aportis Technologies
■ TealDoc from TealPoint Software.

eBooks support on Windows CE or Pocket PC devices is provided via Microsoft Reader or the Peanut Press reader. Support for specialty eBook hardware such as Gemstar’s Nuvomedia or Softbook’s eBook platform is available via reader software based on the Open eBook (OEB) File Format.

Consumers expect that when they purchase eBook content they can view it on any of the devices currently available. This is not always possible because of the use of different platforms and file formats. If the read anywhere eBook is to become a reality then standards must be established for content and file formats, digital rights management, distribution, and book product information.

The recently released publication structure and file format standards from the OEB Forum are still in development and only address electronic content. Standards on device classes and how content is displayed remain unresolved. Portability must be addressed in the next 18 to 24 months if the industry hopes to see convergence devices accommodate the eBook technology with telephony, other PDA content, and DVD storage.

The lack of a standard file format is a major barrier to market growth. Publishers converting printed texts undergo time-consuming and costly processes to accommodating divergent file formats for existing reader systems. Microsoft and Adobe are locked in a battle for platform dominance. Until standards are established publishers need to support all eBook platforms.

Adobe’s Portable Document Format (PDF) is the market leader for existing digital content. But PDF’s conventionalsized page display is not optimized for small screens. eBook readers that support the OEB File Format, such as Microsoft Reader, the Peanut Press reader, Aportis Doc, and TealDoc are growing in popularity. However, translating files from Adobe Systems’ PDF to the OEB file format is a significant task for publishers.

The largest obstacle to a dramatic increase of eBook titles is that publishers are reluctant to release additional titles until there is a standard and secure method for exchanging and protecting eBook content. One industry effort that is working towards a standard for secure content exchange is the Electronic Book Exchange System (EBX). Spearheaded by Glassbook Inc. and the EBX Working

Group the EBX system currently under development would secure content transfers via public/ private key encryption. The industry is also considering other technologies for content exchange and digital rights management (DRM). Extensible Rights Markup Language (XrML), a secure and royalty-free language developed by Xerox Corp. and ContentGuard Inc., is under consideration as a standard for all DRM systems.

Time is running out for the eBook industry to stay a step ahead of the piracy problem. Some eBook titles have already been pirated. Several illegal postings of the latest in the Harry Potter series appeared for download shortly after the volume’s print release. In addition, some users are suspected of having downloaded copies of King’s Ride the Bullet without payment.

Making digital content widely available to consumers will help control piracy if publishers move quickly to provide digital content through a variety of channels. Consumers must be educated that selling, obtaining, or using unlicensed electronic content it is a criminal offense.



The eBook book is an electronic version of content normally contained in newspapers, magazines or books. The content is created and stored in a computer file format that can be accessed by a variety of computer hardware and software applications.

The content can be as unique as the electronic medium itself and contain audio, video, or live hyperlinks. Or it can be as familiar as its print counterparts. eBook content can be downloaded from the Web or received as an email file attachment.

eBooks on diskette or CD-ROM are sent through the mail and sold in bookstores. An eBook is similar to a paper book and contains:

■ Cover art
■ Title page

■ ISBN number
■ Copyright notice
■ Editor
■ Publisher.

eBooks allow users to:
■ Electronically search the text for specific words and phrases
■ Change the font size and style
■ Type notes electronically and organize them within the text
■ Create highlights and bookmarks
■ Hyperlink to specific parts of the text.

In the future, eBooks will be able to link to other websites with related topics and access a dictionary that pronounces the words aloud.

Benefits of Using eBooks
■ Once a book has been converted to an electronic form (such as Microsoft Word or Adobe Acrobat document), it can be stored and transmitted at minimal cost and impact to the environment.

■ Storing eBooks on computer drives, diskettes, and CD-ROMs take less shelf space and weighs less than printed books. Dedicated handheld reading devices weigh approximately 15 ounces and store up to twenty books. Adding memory allows the user to store additional books.

■ Updated documents can be downloaded and accessed immediately.

■ Storing books in electronic format reduces warehousing and shipping costs.

■ Writers and publishers have the freedom to explore small niche markets bringing readers original works unlimited by genre lines, market size, or print capabilities.

■ eBooks can be enhanced with live hyperlinks, sound, animation, and simulation capabilities.

■ Using the self-contained software users can bookmark, annotate, and search the entire eBook.

■ eBooks files can be carried and accessed anywhere with a portable PC, PDA, or eBook reading device

■ Business and recreational travelers can download eBooks to their notebook PCs without adding weight or taking up space in their luggage.

Professionals such as doctors, lawyers, and pharmacists are already utilizing eBooks. Businesses, government personnel, colleges, universities, and schools are attracted to eBooks for a number of reasons. EBooks offer convenient storage capacities and the ability to update and download the most current documents.

Schools, colleges, universities, and libraries are piloting content delivery via portable and desktop PCs and eBook reading devices. These provide students with the latest e-textbooks and digital libraries without adding weight to backpacks.

People with special reading needs now have more books and magazines available to them with eBooks. A simple font size change turns an eBook into a large print edition and some file formats are compatible with screen reading technology.

Overall, eBooks provide improved onscreen reading quality, portability, storage capabilities, current content, and quick delivery to readers. Consumers have access to full-length novels and texts, annotated editions, short fiction and nonfiction, magazines, articles, news and current events.


What is BIOS?

All motherboards include a small block of Read Only Memory (ROM) which is separate from the main system memory used for loading and running software. The ROM contains the PC’s BIOS and this offers two advantages.

The code and data in the ROM BIOS need not be reloaded each time the computer is started, and they cannot be corrupted by wayward applications that write into the wrong part of memory. A flash-upgradeable BIOS may be updated via a floppy diskette to ensure future compatibility with new chips, add-on cards etc.

The BIOS is comprised of several separate routines serving different functions. The first part runs as soon as the machine is powered on. It inspects the computer to determine what hardware is fitted.

Then it conducts some simple tests to check that everything is functioning normally—a process called the power-on self-test. If any of the peripherals are plug-and-play devices, the BIOS assigns the resources. There’s also an option to enter the Setup program.

This allows the user to tell the PC what hardware is fitted, but thanks to automatic self-configuring BIOS, this is not used so much now.

If all the tests are passed, the ROM tries to boot the machine from the hard disk. Failing that, it will try the CD-ROM drive and then the floppy drive, finally displaying a message that it needs a system disk. Once the machine has booted, the BIOS presents DOS with a standardized API for the PC hardware. In the days before Windows, this was a vital function. But 32-bit “protect mode” software doesn’t use the BIOS, so it is of less benefit today.

Most PCs ship with the BIOS set to check for the presence of an operating system in the floppy disk drive first, then on the primary hard disk drive. Any modern BIOS will allow the floppy drive to be moved down the list so as to reduce normal boot time by a few seconds.

To accommodate PCs that ship with a bootable CD-ROM, most BIOS allow the CD-ROM drive to be assigned as the boot drive. BIOS may also allow booting from a hard disk drive other than the primary IDE drive. In this case, it would be possible to have different operating systems or separate instances of the same OS on different drives.

Windows 98 (and later) provides multiple display support. Since most PCs have only a single AGP slot, users wishing to take advantage of this will generally install a second graphics card in a PCI slot. In such cases, most BIOS will treat the PCI card as the main graphics card by default.

However, some allow either the AGP card or the PCI card to be designated as the primary graphics card. While the PCI interface has helped by allowing IRQs to be shared more easily, the limited number of IRQ settings available to a PC remains a problem for many users.

For this reason, most BIOS allow ports that are not in use to be disabled. It will often be possible to get by without needing either a serial or a parallel port because of the increasing popularity of cable and ADSL Internet connections and the ever-increasing availability of peripherals that use the USB interface.



Binary–Gray Code Conversion
A given binary number can be converted into its Gray code equivalent by going through the following steps:

1. Begin with the most significant bit (MSB) of the binary number. The MSB of the Gray code equivalent is the same as the MSB of the given binary number.

2. The second most significant bit, adjacent to the MSB, in the Gray code number is obtained by adding the MSB and the second MSB of the binary number and ignoring the carry, if any. That is, if the MSB and the bit adjacent to it are both ‘1’, then the corresponding Gray code bit would be a ‘0’.

3. The third most significant bit, adjacent to the second MSB, in the Gray code number is obtained by adding the second MSB and the third MSB in the binary number and ignoring the carry, if any.

4. The process continues until we obtain the LSB of the Gray code number by the addition of the LSB and the next higher adjacent bit of the binary number.

The conversion process is further illustrated with the help of an example showing step-by-step conversion of (1011)2 into its Gray code equivalent:
Binary 1011
Gray code 1- - -
Binary 1011
Gray code 11- -
Binary 1011
Gray code 111-
Binary 1011
Gray code 1110

Gray Code–Binary Conversion

A given Gray code number can be converted into its binary equivalent by going through the following steps:

1. Begin with the most significant bit (MSB). The MSB of the binary number is the same as the MSB of the Gray code number.

2. The bit next to the MSB (the second MSB) in the binary number is obtained by adding the MSB in the binary number to the second MSB in the Gray code number and disregarding the carry, if any.

3. The third MSB in the binary number is obtained by adding the second MSB in the binary number to the third MSB in the Gray code number. Again, carry, if any, is to be ignored.

4. The process continues until we obtain the LSB of the binary number.

The conversion process is further illustrated with the help of an example showing step-by-step conversion of the Gray code number 1110 into its binary equivalent:

Gray code 1110
Binary 1- - -
Gray code 1110
Binary 10 - -
Gray code 1110
Binary 101
Gray code 1110
Binary 1011


Parts List:

R1 = 18K
R2 = 240 Ohm
R3 = 8.2K
R4 = 3K
R5 = 10 Ohm
M1 = Panel Meter (Anyone will work)

Design Considerations:You may have experiment with the values of R3 and R4 to get an accurate reading from the meter. Every meter is different, so a little bit of playing with the resistor values is required.Try using a variable resistor in place of R3 & R4 to get a value of resistance that works.



It is quite difficult to find the switch board in a dark room to turn on the light. Here’s a clap switch that allows you to switch on lights, fans, and motors sequentially by just clapping in the vicinity of the microphone used in the circuit.

The mains supply is stepped down to 15-0-15V AC by step-down transformer X1. The output of the transformer is rectified, filtered, and regulated by diodes D1 through D4, capacitors C1 through C4, and IC1 (regulator IC 7812) and IC2 (regulator IC 7912), respectively. Additional filtering is performed by capacitors C5 through C8 to get +12V, 0V (Gnd) and –12V DC required for the operation of the circuit.

The clap sound impulses are converted into electrical signals by a condenser microphone that forms a Wheatstone bridge together with resistors R4, R5, and R3. The microphone is suitably biased through resistor R3. The output of the microphone is coupled to op-amp IC 741 (IC3) having a voltage gain of 45.

The output of IC3, after passing through capacitor C10, is free from any DC component of signal. Capacitors C15 and C17 are used for spike and surge suppression. Diodes D5 and D6 and capacitor C11
form the detector circuit. Resistor R6 is used here for quick discharge of capacitor C10.

The detected clap signal is used to switch on transistor T1. On conduction of transistor T1, its collector voltage falls to trigger timer IC4 connected as a monostable. The combination of resistor R9 and capacitor C12 determine the pulsewidth of the monostable (about one second, with the component values shown).

AND gate IC5 (4081) is used as a buffer between the output of IC4 and clock input to decade counter IC6 (CD4017). Thus each clap causes outputs of IC6 to advance in sequential manner and switch on the corresponding devices.

If you want a lamp to be switched on when output Q1 goes high (after firstclap), then in place
of R11 and LED2 use a relay driver circuit at Q1 output similar to that used for Q2 output (for fan). As stated earlier, only one output of CD4017 can be high at any given time.

Thus first clap causes LED1 to go off and LED2 to glow. The second clap causesonly the fan toswitch onvia relay RL1. The third clapcauses the miniature12V motor to run. On fourth clap, Q4 output goes high momentarily to reset IC6 since Q4 output is connected to its reset pin 15. In reset state, LED1 connected to Q0 output lights up.


Project Circuit Diagram

Emergency lights using incandescent bulbs are inherently inefficient compared to those using fluorescent tubes. Here’s a versatile emergency light using fluorescent tubes. You can operate it using ready made inverter transformers, which are readily available in the market.

With this circuit you can drive two 6W, 22.8cm (9-inch) fluorescent tubes, with the option to use a single tube or a pair of tubes with the help of DPDT switch S2. Step-down transformer X1, diodes D1- D4, capacitor C1, and 5V regulator IC1 (7805) form a regulated power supply. 

A 2.7V zener (ZD1) in common terminal of the regulator props up the output voltage to 7.7 volts. The regulated voltage is applied to the battery through diodes D6 and D7, which cause a drop of about 1.4V across them. Thus the effective charging voltage is about 6.3V, which prevents overcharging of the battery as the terminal voltage of the battery cannot exceed 6.3V.

When AC mains supply is present, the battery starts charging and green LED1 glows to indicate the same. Diode D5 reverse biases transistor T1 forming part of the inverter oscillator and thus the tubes don’t glow. When mains supply fails, transistor T1 starts oscillating and supplies power to inverter transformer X2 and the tubes glow.

An on/off switch (S1) is used to switch off the light when it is not required. D882 (actually, 2SD882) is an npn power transistor in TO-126 package. It is mounted on a suitable heat-sink to prevent it from thermal runaway. 


This easy circuit provides a good gain to weak audio signals. Use it in front of an RF oscillator to make an RF transmitter that is very sensitive to sound.

Audio Pre Amplifier Circuit Below:

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