Report on Embedded System by Kaushal Babu

7/29/2019 Report on Embedded System by Kaushal Babu

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INTRODUCTION

An embedded system is a computer system designed to perform one or more dedicatedfunctions often with real-time computing constraints. It is embedded as part of a completedevice often including hardware and mechanical parts. By contrast, a general-purposecomputer, such as a personal computer (PC), is designed to be flexible and to meet a widerange of end-user needs. Embedded systems control many devices in common use today

Picture of the internals of an ADSL modem/router. A modern example of an embeddedsystem. Labelled parts include a microprocessor , RAM , and flash memory .Embedded systems are controlled by one or more main processing cores that are typicallyeither microcontrollers or digital signal processors (DSP). The key characteristic,

however, is being dedicated to handle a particular task, which may require very powerfulprocessors. For example, air traffic control systems may usefully be viewed as embedded,even though they involve mainframe computers and dedicated regional and nationalnetworks between airports and radar sites ( each radar probably includes one or moreembedded systems of its own).

Since the embedded system is dedicated to specific tasks, design engineers can optimizeit to reduce the size and cost of the product and increase the reliability and performance.Some embedded systems are mass-produced, benefiting from economies of scale.Physically, embedded systems range from portable devices such as digital watches andMP3 players, to large stationary installations like traffic lights, factory controllers, or the

systems controlling nuclear power plants. Complexity varies from low, with a singlemicrocontroller chip, to very high with multiple units, peripherals and networks mountedinside a large chassis or enclosure.

In general, "embedded system" is not a strictly definable term, as most systems havesome element of extensibility or programmability. For example, handheld computersshare some elements with embedded systems such as the operating systems andmicroprocessors which power them, but they allow different applications to be loadedand peripherals to be connected. Moreover, even systems which don't exposeprogrammability as a primary feature generally need to support software updates. On acontinuum from "general purpose" to "embedded", large application systems will have

subcomponents at most points even if the system as a whole is "designed to perform oneor a few dedicated functions", and is thus appropriate to call "embedded".

VARIETY OF EMBEDDED SYSTEMSEmbedded systems span all aspects of modern life and there are many examples of theiruse. Telecommunications systems employ numerous embedded systems from telephoneswitches for the network to mobile phones at the end-user. Computer networking usesdedicated routers and network bridges to route data.


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Consumer electronics include personal digital assistants (PDAs), mp3 players, mobilephones, videogame consoles, digital cameras, DVD players, GPS receivers, and printers.

Many household appliances, such as microwave ovens, washing machines anddishwashers, are including embedded systems to provide flexibility, efficiency andfeatures. Advanced HVAC systems use networked thermostats to more accurately andefficiently control temperature that can change by time of day and season. Homeautomation uses wired- and wireless-networking that can be used to control lights,climate, security, audio/visual, surveillance, etc., all of which use embedded devices forsensing and controlling Transportation systems from flight to automobiles increasinglyuse embedded systems. New airplanes contain advanced avionics such as inertialguidance systems and GPS receivers that also have considerable safety requirements.Various electric motorsbrushless DC motors, induction motors and DC motors areusing electric/electronic motor controllers. Automobiles, electric vehicles, and hybrid

vehicles are increasingly using embedded systems to maximize efficiency and reducepollution. Other automotive safety systems include anti-lock braking system (ABS),Electronic Stability Control (ESC/ESP), traction control (TCS) and automatic four-wheeldrive.

PC Engines' ALIX.1C Mini-ITX embedded board with an x86 AMD Geode LX 800together with Compact Flash, miniPCI and PCI slots, 44-pin IDE interface, audio, USBand 256MB RAM.

An embedded Router Board 112 with U.FL-RSMA pigtail and R52 miniPCI Wi-Fi cardwidely used by wireless Internet service providers (WISPs) in the Czech Republic.

Medical equipment is continuing to advance with more embedded systems for vital signsmonitoring, electronic stethoscopes for amplifying sounds, and various medical imaging(PET, SPECT, CT, MRI) for non-invasive internal inspections.

In addition to commonly described embedded systems based on small computers, a newclass of miniature wireless devices called motes are quickly gaining popularity as thefield of wireless sensor networking rises. Wireless sensor networking, WSN, makes useof miniaturization made possible by advanced IC design to couple full wirelesssubsystems to sophisticated sensors, enabling people and companies to measure a myriadof things in the physical world and act on this information through IT monitoring andcontrol systems. These motes are completely self contained, and will typically run off abattery source for many years before the batteries need to be changed or charged.


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HISTORY

In the earliest years of computers in the 194050s, computers were sometimes dedicatedto a single task, but were far too large and expensive for most kinds of tasks performedby embedded computers of today. Over time however, the concept of programmablecontrollers evolved from traditional electromechanical sequencers, via solid state devices,to the use of computer technology.

One of the first recognizably modern embedded systems was the Apollo GuidanceComputer, developed by Charles Stark Draper at the MIT Instrumentation Laboratory. Atthe project's inception, the Apollo guidance computer was considered the riskiest item inthe Apollo project as it employed the then newly developed monolithic integrated circuits

to reduce the size and weight. An early mass-produced embedded system was theAutonetics D-17 guidance computer for the Minuteman missile, released in 1961. It wasbuilt from transistor logic and had a hard disk for main memory. When the Minuteman IIwent into production in 1966, the D-17 was replaced with a new computer that was thefirst high-volume use of integrated circuits. This program alone reduced prices on quadnand gate ICs from $1000/each to $3/each [permitting their use in commercial products.Since these early applications in the 1960s, embedded systems have come down in priceand there has been a dramatic rise in processing power and functionality. The firstmicroprocessor for example, the Intel 4004, was designed for calculators and other smallsystems but still required many external memory and support chips. In 1978 NationalEngineering Manufacturers Association released a "standard" for programmable

microcontrollers, including almost any computer-based controllers, such as single boardcomputers, numerical, and event-based controllers.

As the cost of microprocessors and microcontrollers fell it became feasible to replaceexpensive knob-based analog components such as potentiometers and variable capacitorswith up/down buttons or knobs read out by a microprocessor even in some consumerproducts. By the mid-1980s, most of the common previously external system componentshad been integrated into the same chip as the processor and this modern form of themicrocontroller allowed an even more widespread use, which by the end of the decadewere the norm rather than the exception for almost all electronics devices.

The integration of microcontrollers has further increased the applications for whichembedded systems are used into areas where traditionally a computer would not havebeen considered. A general purpose and comparatively low-cost microcontroller mayoften be programmed to fulfill the same role as a large number of separate components.Very few additional components may be needed and most of the design effort is in thesoftware. The intangible nature of software makes it much easier to prototype and testnew revisions compared with the design and construction of a new circuit not using anembedded processor.


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CHARACTERISTICS

1. Embedded systems are designed to do some specific task, rather than be ageneral-purpose computer for multiple tasks. Some also have real-time performanceconstraints that must be met, for reasons such as safety and usability; others may havelow or no performance requirements, allowing the system hardware to be simplified toreduce costs.2. Embedded systems are not always standalone devices. Many embedded systemsconsist of small, computerized parts within a larger device that serves a more generalpurpose. For example, the Gibson Robot Guitar features an embedded system for tuningthe strings, but the overall purpose of the Robot Guitar is, of course, to play music.Similarly, an embedded system in an automobile provides a specific function as asubsystem of the car itself.

3. The program instructions written for embedded systems are referred to asfirmware, and are stored in read-only memory or Flash memory chips. They run withlimited computer hardware resources: little memory, small or non-existent keyboardand/or screen.

USER INTERFACE

Embedded systems range from no user interface at alldedicated only to one tasktocomplex graphical user interfaces that resemble modern computer desktop operatingsystems. Simple embedded devices use buttons, LEDs, graphic or character LCDs (forexample popular HD44780 LCD) with a simple menu system

A more sophisticated devices use graphical screen with touch sensing or screen-edgebuttons provide flexibility while minimizing space used: the meaning of the buttons canchange with the screen, and selection involves the natural behaviour of pointing at what'sdesired. Handheld systems often have a screen with a "joystick button" for a pointingdevice.

Some systems provide user interface remotely with the help of a serial (e.g. RS-232,USB, IC, etc.) or network (e.g. Ethernet) connection. In spite of the potentially necessaryproprietary client software and/or specialist cables that are needed, this approach usuallygives a lot of advantages: extends the capabilities of embedded system, avoids the cost ofa display, simplifies BSP, allows to build rich user interface on the PC. A good exampleof this is the combination of an embedded web server running on an embedded device(such as an IP camera or network routers. The user interface is displayed in a webbrowser on a PC connected to the device, therefore needing no bespoke software to beinstalled.


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PROCESSORS IN EMBEDDED SYSTEMS

Embedded processors can be broken into two broad categories: ordinary microprocessors(P) and microcontrollers (C), which have many more peripherals on chip, reducing

cost and size. Contrasting to the personal computer and server markets, a fairly largenumber of basic CPU architectures are used; there are Von Neumann as well as variousdegrees of Harvard architectures, RISC as well as non-RISC and VLIW; word lengthsvary from 4-bit to 64-bits and beyond (mainly in DSP processors) although the mosttypical remain 8/16-bit. Most architecture come in a large number of different variantsand shapes, many of which are also manufactured by several different companies.A long but still not exhaustive list of common architectures are: 65816, 65C02, 68HC08,68HC11, 68k, 8051, ARM, AVR, AVR32, Blackfin, C167, Coldfire, COP8, Cortus

APS3, eZ8, eZ80, FR-V, H8, HT48, M16C, M32C, MIPS, MSP430, PIC, PowerPC,R8C, SHARC, SPARC, ST6, SuperH, TLCS-47, TLCS-870, TLCS-900, Tricore, V850,x86, XE8000, Z80, AsAP etc.

Block Diagram

+5V +12V

D7

D0

POWERSUPPLY

UNIT

IR

SENSOR

CURRENT

AMPLIFIER

MICROCONTROLLER

89C51

OUTPUT

RELAYS


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Bock descriptionPower supply

Power supply used is a regulated power supply which generates +5v vDC formicrocontroller.The MC78XX/LM78XX/MC78XXA series of three terminal positive regulators areavailable in the TO-220/D-PAK package and with several fixed output voltages, makingthem useful in a wide range of Applications. Each type employs internal current limiting,Thermal shut down and safe operating area protection, making itessentially indestructible. If adequate heat sinking Is provided, they can deliver over 1Aoutput current. Although designed primarily as fixed voltage regulators,these devices can be used with external components to obtain adjustable voltages andcurrents.

Microcontroller

A microcontroller (also MCU or C) is a functional computer system-on-a-chip. Itcontains a processor core, memory, and programmable input/output peripherals.

Microcontrollers include an integrated CPU, memory (a small amount of RAM, programmemory, or both) and peripherals capable of input and output.

It emphasizes high integration, in contrast to a microprocessor which only contains aCPU (the kind used in a PC). In addition to the usual arithmetic and logic elements of ageneral purpose microprocessor, the microcontroller integrates additional elements such

as read-write memory for data storage, read-only memory for program storage, Flashmemory for permanent data storage, peripherals, and input/output interfaces. At clockspeeds of as little as 32KHz, microcontrollers often operate at very low speed comparedto microprocessors, but this is adequate for typical applications. They consume relativelylittle power (milliwatts or even microwatts), and will generally have the ability to retainfunctionality while waiting for an event such as a button press or interrupt.

Power consumption while sleeping (CPU clock and peripherals disabled) may be justnanowatts, making them ideal for low power and long lasting battery applications.

Microcontrollers are used in automatically controlled products and devices, such as

automobile engine control systems, remote controls, office machines, appliances, powertools, and toys. By reducing the size, cost, and power consumption compared to a designusing a separate microprocessor, memory, and input/output devices, microcontrollersmake it economical to electronically control many more processes.


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Circuit diagram

Circuit description

1. Regulated Supply: A 5 V Of Battery Is used To Provide Power To The WholeBranches Of The Circuit . As the microcontroller works on 5 v , so a regulatedsupply of 5 v is provided through IC 7805 all branches ( microcontroller , IRsensors and opamps)

2. TSOP 1738 SENSORS (IR RECEIVER) :Infrared (IR) radiation iselectromagnetic radiation whose wavelength is longer than that of visible light,but shorter than that of terahertz radiation and microwaves. The name means"below red" (from the Latin infra, "below"), red being the color of visible lightwith the longest wavelength. Infrared radiation has wavelengths between about750 nm and 1 mm, spanning three orders of magnitude. Infrared sensors transmitsinfrared radiations in all the directions to sense the hurdles , if the transmittedradiations reflects back then it senses a obstacle automatically generate signal.


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3. Microcontroller: We are using AT89C51 microcontroller which belongs toAtmel, 8051 family. The AT89C51 is a low-power, high-performance CMOS 8-bit microcontroller with 4K bytes of Flash programmable and erasable read onlymemory (PEROM).The output provided from the codes generated is fed to theinput port of the microcontroller and it works according to the program fed .

Infrared Transmitter & Receiver

IR LED emits infrared radiation. This radiation illuminates the surface in front of LED.Surface reflects the infrared light. Depending on reflectivity of the surface, amount oflight reflected varies. This reflected light is made incident on reverse biased IR sensor.When photons are incident on reverse biased junction of this

diode, electron-hole pairs are generated, which results in reverseleakage current. Amount of electron-hole pairs generated depends onintensity of incident IR radiation. More intense radiation results inmore reverse leakage current. This current can be passed through aresistor so as to get proportional voltage. Thus as intensity ofincident rays varies, voltage across resistor will vary accordingly.

This voltage can then be given to OPAMP based comparator.Output of the comparatorcan be read by uC.

INFRARED LED PHOTOTRANSISTOR
http://elecrom.files.wordpress.com/2008/02/sensor.jpg


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TSOP 1738:

Description

The TSOP1738series are miniaturized receivers forInfrared remote control systems. PIN diode andPreamplifier are assembled on lead frame, the epoxypackage is designed as IR filter.The demodulated output signal can directly beDecoded by a microprocessor. TSOP1738 is theStandard IR remote control receiver series, supportingAll major transmission codes.

PIN DESDRIPTION:-GNDVSOUT

Features

_ Photo detector and preamplifier in one package_ internal filter for PCM frequency

_ TTL and CMOS compatibility_ Output active low_ Low power consumption_ High immunity against ambient light_ Continuous data transmission possible(up to 2400 bps)

_ Improved shielding against electrical field disturbance


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Microcontroller

The AT89S51 is a low-power, high-performance CMOS 8-bit microcontroller with 4Kbytes of In-System Programmable Flash memory. The device is manufactured usingAtmels high-density nonvolatile memory technology and is compatible with theindustry-standard 80C51 instruction set and pinout. The on-chip Flash allows the programmemory to be reprogrammed in-system or by a conventional nonvolatile memoryprogrammer. By combining a versatile 8-bit CPU with In-System Programmable Flash on

a monolithic chip, the Atmel AT89S51 is a powerful microcontroller which provides ahighly-flexible and cost-effective solution to many embedded control applications. TheAT89S51 provides the following standard features: 4K bytes of Flash, 128 bytes ofRAM, 32 I/O lines, Watchdog timer, two data pointers, two 16-bit timer/counters, afivevector two-level interrupt architecture, a full duplex serial port, on-chip oscillator,and clock circuitry. In addition, the AT89S51 is designed with static logic for operationdown to zero frequency and supports two software selectable power saving modes. TheIdle Mode stops the CPU while allowing the RAM, timer/counters, serial port, and


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interrupt system to continue functioning. The Power-down mode saves the RAM contentsbut freezes the oscillator, disabling all other chip functions until the next external

interrupt or hardware reset.

Pin Description

VCC Supply voltage (all packages except 42-PDIP).GND Ground (all packages except 42-PDIP; for 42-PDIP GND connects only the logiccore and the embedded program memory).VDD Supply voltage for the 42-PDIP which connects only the logic core and theembedded program memory.PWRVDD Supply voltage for the 42-PDIP which connects only the I/O Pad Drivers. The

application board MUST connect both VDD and PWRVDD to the board supply voltage.PWRGND Ground for the 42-PDIP which connects only the I/O Pad Drivers. PWRGNDand GND are weakly connected through the common silicon substrate, but not throughany metal link. The application board MUST connect both GND and PWRGND to theboard ground.

Port 0 Port 0 is an 8-bit open drain bi-directional I/O port. As an output port, each pincan sink eight TTL inputs. When 1s are written to port 0 pins, the pins can be used ashigh-impedance inputs. Port 0 can also be configured to be the multiplexed low-orderaddress/data bus during accesses to external program and data memory. In this mode, P0has internal pull-ups. Port 0 also receives the code bytes during Flash programming andoutputs the code bytes during program verification. External pull-ups are requiredduring program verification.

Port 1 Port 1 is an 8-bit bi-directional I/O port with internal pull-ups. The Port 1 outputbuffers cansink/source four TTL inputs. When 1s are written to Port 1 pins, they arepulled high by theinternal pull-ups and can be used as inputs. As inputs, Port 1 pins thatare externally being pulled low will source current (IIL) because of the internal pull-ups.Port 1 also receives the low-order address bytes during Flash programmingandverification.

Port 2 Port 2 is an 8-bit bi-directional I/O port with internal pull-ups. The Port 2 outputbuffers can sink/source four TTL inputs. When 1s are written to Port 2 pins, they arepulled high by the internal pull-ups and can be used as inputs. As inputs, Port 2 pins thatare externally being pulled low will source current (IIL) because of the internal pull-ups.Port 2 emits the high-order address byte during fetches from external program memoryand during accesses to external data memory that use 16-bit addresses (MOVX @DPTR). In this application, Port 2 uses strong internal pull-ups when emitting 1s. Duringaccesses to external data memory that use 8-bit addresses (MOVX @ RI), Port 2 emits


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the contents of the P2 Special Function Register. Port 2 also receives the high-orderaddress bits and some control signals during Flash programming and verification.

Port 3 Port 3 is an 8-bit bi-directional I/O port with internal pull-ups. The Port 3 outputbuffers can sink/source four TTL inputs. When 1s are written to Port 3 pins, they arepulled high by the internal pull-ups and can be used as inputs. As inputs, Port 3 pins thatare externally being pulled low will source current (IIL) because of the pull-ups.Port 3 receives some control signals for Flash programming and verification.Port 3 also serves the functions of various special features of the AT89S51, as shown inthe following table.

RST Reset input. A high on this pin for two machine cycles while the oscillator isrunning resets the device. This pin drives High for 98 oscillator periods after the

Watchdog times out. The DISRTO bit in SFR AUXR (address 8EH) can be used todisable this feature. In the default state of bit DISRTO, the RESET HIGH out feature isenabled.

ALE/PROG Address Latch Enable (ALE) is an output pulse for latching the low byte ofthe address during accesses to external memory. This pin is also the program pulse input(PROG) during Flash programming. In normal operation, ALE is emitted at a constantrate of 1/6 the oscillator frequency and may be used for external timing or clockingpurposes. Note, however, that one ALE pulse is skipped during each access to externaldata memory. If desired, ALE operation can be disabled by setting bit 0 of SFR location8EH. With the bit set, ALE is active only during a MOVX or MOVC instruction.Otherwise, the pin is weakly pulled high. Setting the ALE-disable bit has no effect if themicrocontroller is in external execution mode.

PSEN Program Store Enable (PSEN) is the read strobe to external program memory.When the AT89S51 is executing code from external program memory, PSEN is activatedtwice each machine cycle, except that two PSEN activations are skipped during eachaccessto external data memory.EA/VPP External Access Enable. EA must be strapped to GND in order to enable thedevice to fetch code from external program memory locations starting at 0000H up toFFFFH. Note, however, that if lock bit 1 is programmed, EA will be internally latched onreset. EA should be strapped to VCC for internal program executions. This pin alsoreceives the 12-volt programming enable voltage (VPP) during Flashprogramming.

XTAL1 Input to the inverting oscillator amplifier and input to the internal clockoperating circuit.XTAL2 Output from the inverting oscillator amplifier


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Project source code

VAR1 equ r7 ;Temporary Variable

TEMP equ 10H ;Temp variable

COUNT equ 11H ;Count

ADDR equ 12H ;Device address

CMD equ 13H ;Command

FLIP bit 00H ;Flip bit

TOG bit 01H ;Temp bit for flip

IR equ P3.3 ;IR Receiver connected to this pin

SW1 equ P2.0 ;Switch 1 connected here








SWport equ P2 ;Port at which switches are connected


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org 00H ;Start of prog

mov SWport,#00H ;switch all relays off!

mov sp,#50H ;Stack pointer initialization

clr TOG ;Clear temp bit

main:

jb IR,$ ;Wait for first bit

mov VAR1,#255 ;3.024mS delay

djnz VAR1,$

mov VAR1,#255

djnz VAR1,$

mov VAR1,#255

djnz VAR1,$

mov VAR1,#255

djnz VAR1,$

mov VAR1,#255

djnz VAR1,$

mov VAR1,#100

djnz VAR1,$

mov c,IR ;Read Flip bit

mov FLIP,c

clr A

mov COUNT,#5 ;Count for address


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fadd:

mov VAR1,#255 ;1.728mS delay for each bit

djnz VAR1,$

mov VAR1,#255

djnz VAR1,$

mov VAR1,#255

djnz VAR1,$

mov VAR1,#4

djnz VAR1,$

mov c,IR

rlc a

djnz COUNT,fadd

mov ADDR,A ;Save the address

clr a

mov COUNT,#6 ;Count for Command

fcmd:

mov VAR1,#255 ;1.728mS Delay for each bit

djnz VAR1,$

mov VAR1,#255

djnz VAR1,$

mov VAR1,#255

djnz VAR1,$

mov VAR1,#4


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djnz VAR1,$

mov c,IR

rlc a

djnz COUNT,fcmd

mov TEMP,CMD ;Save the old command

mov CMD,a ;Save the new command

mov a,ADDR ;Cheack for valid address

cjne a,#00,nvalid

mov a,TEMP

cjne a,CMD,valid ;Check for valid command

nvalid:

ljmp main

valid: ;Key press check

clr a

mov c,FLIP

rlc a

mov TEMP,a

clr a

mov c,TOG

rlc a

cjne a,TEMP,valid1

sjmp nvalid

valid1:


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mov c,FLIP

mov TOG,c

mov a,CMD

clr c

cjne a,#1,skip1 ;Check for SW1

jb SW1,isset1

setb SW1

ljmp main

isset1:

clr SW1

ljmp main

skip1:


jb SW2,isset2

setb SW2

ljmp main

isset2:

clr SW2

ljmp main

skip2:


jb SW3,isset3

setb SW3


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ljmp main

isset3:

clr SW3

ljmp main

skip3:


jb SW4,isset4

setb SW4

ljmp main

isset4:

clr SW4

ljmp main

skip4:


jb SW5,isset5

setb SW5

ljmp main

isset5:

clr SW5

ljmp main

skip5:



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jb SW6,isset6

setb SW6

ljmp main

isset6:

clr SW6

ljmp main

skip6:


jb SW7,isset7

setb SW7

ljmp main

isset7:

clr SW7

ljmp main

skip7:


jb SW8,isset8

setb SW8

ljmp main

isset8:

clr SW8

ljmp main


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skip8:

cjne a,#0CH,exit ;Check for all switches

mov SWport,#00H

ljmp main

exit:

ljmp main

END ;End of program


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Relays

The relay takes advantage of the fact that when electricity flows through a coil,it becomes an electromagnet.The electromagnetic coil attracts a steel plate, which is attached to a switch. Sothe switch's motion (ON and OFF) is controled by the current flowing to thecoil, or not, respectively.

A very useful feature of a relay is that it can be used to electrically isolatedifferent parts of a circuit.It will allow a low voltage circuit (e.g. 5VDC) to switch the power in a highvoltage circuit (e.g. 100 VAC or more).

The relay operates mechanically, so it can not operate at high speed.

There are many kind of relays. You can select one according to your needs.The various things to consider when selecting a relay are its size, voltage andcurrent capacity of the contact points, drive voltage, impedance, number ofcontacts, resistance of the contacts, etc.The resistance voltage of the contacts is the maximum voltage that can beconducted at the point of contact in the switch. When the maximum is exceeded,the contacts will spark and melt, sometimes fusing together. The relay will fail.The value is printed on the relay.


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On the left in thephotograph is a smallrelay with a coil driving

voltage of 12 VDC. Ithas two electricallyindependant points ofcontact (switches.)Although the resistanceand permissible voltageand current at the pointof contact are indistinct,I think that it willhandle several hundredmA.

The relay on the right inthe photograph can beused to control a 100VAC system. Itsdriving voltage is 3VDC, and if it is used tocontrol an AC system,the maximum resistancevoltage is 125 VAC,and the permissible

current limit is 1A. If it is used to control a DC system, the maximum resistancevoltage is DC30V, and the permissible current limit is 2A. It has one contactonly.Both types of relay can be mounted on the PWB; the spacing of the componentleads is a multiple of 0.1 inches. It can also be mounted onthe universal PWB.

The physical dimensions of the relay on the left are width 19.5 mm, height 10mm, and depth 10 mm.The one that is on the right has the width 20 mm, height 15 mm, and depth 11mm.The relay pictured to the right is able to handle a little larger electric power.

Its driving voltage is 12 VDC, maximum resistance voltage is AC 240V, and thepermissible current limit is 5A in case of AC system. In a DC system, themaximum resistance voltage is DC 28V, and the permissible current limit is 5A.

This type of relay can not be mounted on the PWB. It needs a socket, andmounts on the case or some other place with a screw.The dimensions are width 22 mm, height 35 mm, and depth 20 mm.
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BASIC ELECTRONICS

Resistors

The resistor's function is to reduce the flow of electric current.This symbol is used to indicate a resistor in a circuit diagram, known as a schematic.Resistance value is designated in units called the "Ohm." A 1000 Ohm resistor is typically shownas 1K-Ohm ( kilo Ohm ), and 1000 K-Ohms is written as 1M-Ohm ( megohm ).

There are two classes of resistors;fixed resistorsand thevariable resistors. They are alsoclassified according to the material from which they are made. The typical resistor is made ofeither carbon film or metal film. There are other types as well, but these are the most common.The resistance value of the resistor is not the only thing to consider when selecting a resistor for

use in a circuit. The "tolerance" and the electric power ratings of the resistor are also important.The tolerance of a resistor denotes how close it is to the actual rated resistence value. Forexample, a 5% tolerance would indicate a resistor that is within 5% of the specified resistancevalue.The power rating indicates how much power the resistor can safely tolerate. Just like youwouldn't use a 6 volt flashlight lamp to replace a burned out light in your house, you wouldn't usea 1/8 watt resistor when you should be using a 1/2 watt resistor.

The maximum rated power of the resistor is specified in Watts.Power is calculated using the square of the current ( I2 ) x the resistance value ( R ) of theresistor. If the maximum rating of the resistor is exceeded, it will become extremely hot, and

even burn.Resistors in electronic circuits are typicaly rated 1/8W, 1/4W, and 1/2W. 1/8W is almost alwaysused in signal circuit applications.When powering a light emitting diode, a comparatively large current flows through the resistor,so you need to consider the power rating of the resistor you choose.

Rating electric powerFor example, to power a 5V circuit using a 12V supply, a three-terminal voltage regulatoris usually used.However, if you try to drop the voltage from 12V to 5V using only a resistor, then youneed to calculate the power rating of the resistor as well as the resistance value.

At this time, the current consumed by the 5V circuit needs to be known.Here are a few ways to find out how much current the circuit demands.Assemble the circuit and measure the actual current used with a multi-meter.Check the component's current use against a standard table.

Assume the current consumed is 100 mA (milliamps) in the following example.7V must be dropped with the resistor. The resistance value of the resistor becomes 7V /0.1A = 70(ohm). The consumption of electric power for this resistor becomes 0.1A x0.1A x 70 ohm = 0.7W.
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Resistance value

As for the standard resistance value, the values used can be divided like a logarithm. ( Seethe logarithm table )For example, in the case of E3, The values [1], [2.2], [4.7] and [10] are used. They divide10 into three, like a logarithm.In the case of E6 : [1], [1.5], [2.2], [3.3], [4.7], [6.8], [10].In the case of E12 : [1], [1.2], [1.5], [1.8], [2.2], [2.7], [3.3], [3.9], [4.7], [5.6], [6.8], [8.2],[10].It is because of this that the resistance value is seen at a glance to be a discrete value.The resistance value is displayed using the color code( the colored bars/the colored stripes, because the average resistor is too small to have the value printed on it with numbers.You had better learn the color code, because almost all resistors of 1/2W or less use thecolor code to display the resistance value.

Fixed ResistorsA fixed resistor is one in which the value of its resistance cannot change.

Carbon film resistorsThis is the most general purpose, cheap resistor. Usually the tolerance of the resistancevalue is 5%. Power ratings of 1/8W, 1/4W and 1/2W are frequently used.Carbon film resistors have a disadvantage; they tend to be electrically noisy. Metal filmresistors are recommended for use in analog circuits. However, I have never experienced

any problems with this noise.The physical size of the different resistors is as follows.

From the top of the photograph1/8W1/4W1/2W

Rough size

Rating power(W)

Thickness(mm)

Length(mm)

1/8 2 3

1/4 2 6

1/2 3 9


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This resistor is called a Single-In-Line(SIL) resistor network. Itis made with many resistors of the same value, all in one

package. One side of each resistor is connected with one side ofall the other resistors inside. One example of its use would be tocontrol the current in a circuit powering many light emittingdiodes (LEDs).In the photograph on the left, 8 resistors are housed in thepackage. Each of the leads on the package is one resistor. The

ninth lead on the left side is the common lead. The face value of the resistance is printed.( It depends on the supplier. )Some resistor networks have a "4S" printed on the top of the resistor network. The 4Sindicates that the package contains 4 independent resistors that are not wired togetherinside. The housing has eight leads instead of nine. The internal wiring of these typical

resistor networks has been illustrated below. The size (black part) of the resistor networkwhich I have is as follows: For the type with 9 leads, the thickness is 1.8 mm, the height5mm, and the width 23 mm. For the types with 8 component leads, the thickness is 1.8mm, the height 5 mm, and the width 20 mm.

Metal film resistors

Metal film resistors are used when a higher tolerance (more accurate value) is needed.They are much more accurate in value than carbon film resistors. They have about0.05% tolerance. They have about 0.05% tolerance. I don't use any high toleranceresistors in my circuits. Resistors that are about 1% are more than sufficient. Ni-Cr(Nichrome) seems to be used for the material of resistor. The metal film resistor is usedfor bridge circuits, filter circuits, and low-noise analog signal circuits.

From the top of the photograph1/8W (tolerance 1%)1/4W (tolerance 1%)

Rough size

Rating power(W)

Thickness(mm)

Length(mm)

1/8 2 3

1/4 2 6


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1W (tolerance 5%)2W (tolerance 5%)

1 3.5 12

2 5 15

Variable Resistor:-There are two general ways in which variable resistors are used. One is thevariable resistor which value is easily changed, like the volume adjustment of Radio. The other issemi-fixed resistor that is not meant to be adjusted by anyone but a technician. It is used to adjustthe operating condition of the circuit by the technician. Semi-fixed resistors are used to

compensate for the inaccuracies of the resistors, and to fine-tune a circuit. The rotation angle of thevariable resistor is usually about 300 degrees. Some variable resistors must be turned many timesto use the whole range of resistance they offer. This allows for very precise adjustments of theirvalue. These are called "Potentiometers" or "Trimmer Potentiometers."

In the photograph to the left, the variable resistor typically used for volume controls can be seen onthe far right. Its value is very easy to adjust.The four resistors at the center of the photograph are the semi-fixed type. These ones are mountedon the printed circuit board.The two resistors on the left are the trimmer potentiometers.

This symbol is used to indicate a variable resistor in a circuit diagram.There are three ways in which a variable resistor's value can change according to the rotation angleof its axis.When type "A" rotates clockwise, at first, the resistance value changes slowly and thenin the second half of its axis, it changes very quickly.The "A" type variable resistor is typically used for the volume control of a radio, for example. It iswell suited to adjust a low sound subtly. It suits the characteristics of the ear. The ear hears lowsound changes well, but isn't as sensitive to small changes in loud sounds. A larger change is


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needed as the volume is increased. These "A" type variableresistors are sometimes called "audio taper" potentiometers.As for type "B", the rotation of the axis and the change of

the resistance value are directly related. The rate of changeis the same, or linear, throughout the sweep of the axis. Thistype suits a resistance value adjustment in a circuit, abalance circuit and so on.They are sometimes called "linear taper" potentiometers.

Type "C" changes exactly the opposite way to type "A". In the early stages of the rotation of theaxis, the resistance value changes rapidly, and in the second half, the change occurs more slowly.This type isn't too much used. It is a special use.As for the variable resistor, most are type "A" or type "B".

CDS Elements

Some components can change resistance value by changes in the amount of light hittingthem. One type is the Cadmium Sulfide Photocell. (Cd) The more light that hits it, thesmaller its resistance value becomes.There are many types of these devices. They vary according to light sensitivity, size,resistance value etc.

Pictured at the left is a typical CDS photocell. Its diameter is 8 mm, 4 mm high, with a cylinderform. When bright light is hitting it, the value is about 200 ohms, and when in the dark, theresistance value is about 2M ohms.

This device is using for the head lamp illumination confirmation device of the car, for example.

Other ResistorsThere is another type of resistor other than the carbon-film type and the metal filmresistors. It is the wirewound resistor.A wirewound resistor is made of metal resistance wire, and because of this, they can bemanufactured to precise values. Also, high-wattage resistors can be made by using a thickwire material. Wirewound resistors cannot be used for high-frequency circuits. Coils areused in high frequency circuits. Since a wirewound resistor is a wire wrapped around aninsulator, it is also a coil, in a manner of speaking. Using one could change the behavior

of the circuit. Still another type of resistor is the Ceramic resistor. These are wirewoundresistors in a ceramic case, strengthened with a special cement. They have very highpower ratings, from 1 or 2 watts to dozens of watts. These resistors can become extremelyhot when used for high power applications, and this must be taken into account whendesigning the circuit. These devices can easily get hot enough to burn you if you touchone.


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The photograph on the left is ofwirewound resistors.The upper one is 10W and isthe length of 45 mm, 13 mmthickness.The lower one is 50W and isthe length of 75 mm, 29 mmthickness.The upper one is has metalfittings attached. These devicesare insulated with a ceramiccoating.

The photograph on above is aceramic (or cement) resistor of5W and is the height of 9 mm,9 mm depth, 22 mm width.

Thermistor ( Thermally sensitive resistor )

The resistance value of the thermistor changes according to temperature.This part is used as a temperature sensor.

There are mainly three types of thermistor.NTC(Negative Temperature Coefficient Thermistor)

: With this type, the resistance value decreases continuously as thetemperature rises.

PTC(Positive Temperature Coefficient Thermistor): With this type, the resistance value increases suddenly when thetemperature rises above a specific point.


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CTR(Critical Temperature Resister Thermistor): With this type, the resistance value decreases suddenly when thetemperature rises above a specific point.

The NTC type is used for the temperature control.

The relation between the temperature and the resistance value of the NTC type canbe calculated using the following formula.

R : The resistance value at the temperature T

T : The temperature [K]

R0 : The resistance value at the reference temperature T0T0 : The reference temperature [K]

B : The coefficient

As the reference temperature, typically, 25C is used.The unit with the temperature is the absolute temperature(Value of which 0was -273C) in K(Kelvin).25C are the 298 kelvins.

Resistor color code

Color Value MultiplierTolerance

(%)

Black 0 0 -

Brown 1 1 1

Red 2 2 2

Orange 3 3 0.05

Yellow 4 4 -

Example 1(Brown=1),(Black=0),(Orange=3)

10 x 103 = 10k ohmTolerance(Gold) = 5%


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Green 5 5 0.5

Blue 6 6 0.25Violet 7 7 0.1

Gray 8 8 -

White 9 9 -

Gold - -1 5

Silver - -2 10

None - - 20

Example 2(Yellow=4),(Violet=7),(Black=0),(Red=2)

470 x 102 = 47k ohmTolerance(Brown) = 1%

Capacitors

The capacitor's function is to store electricity, or electrical energy.The capacitor also functions as afilter, passing alternating current(AC), and blocking direct current(DC).

This symbol is used to indicatea capacitor in a circuit diagram.

The capacitor is constructed with twoelectrode plates facing eachother, butseparated by an insulator.

When DC voltage is applied to the capacitor, an electric charge is stored oneach electrode. While the capacitor is charging up, current flows. The currentwill stop flowing when the capacitor has fully charged.When a circuit tester, such as an analog meter set to measure resistance, isconnected to a 10 microfarad (F) electrolytic capacitor, a current will flow, butonly for a moment. You can confirm that the meter's needle moves off of zero,but returns to zero right away.When you connect the meter's probes to the capacitor in reverse, you will notethat current once again flows for a moment. Once again, when the capacitor hasfully charged, the current stops flowing. So the capacitor can be used as a filter


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that blocks DC current. (A "DC cut" filter.)However, in the case of alternating current, the current will be allowed to pass.

Alternating current is similar to repeatedly switching the test meter's probesback and forth on the capacitor. Current flows every time the probes areswitched.

The value of a capacitor (the capacitance), is designated in units called theFarad ( F ). The capacitance of a capacitor is generally very small, so units suchas the microfarad ( 10-6F ), nanofarad ( 10-9F ), and picofarad (10-12F ) are used.Recently, an new capacitor with very high capacitance has been developed. TheElectric Double Layer capacitor has capacitance designated in Farad units.These are known as "Super Capacitors."

Sometimes, a three-digit code is used to indicate the value of a capacitor. Thereare two ways in which the capacitance can be written. One uses letters andnumbers, the other uses only numbers. In either case, there are only threecharacters used. [10n] and [103] denote the same value of capacitance. Themethod used differs depending on the capacitor supplier. In the case that thevalue is displayed with the three-digit code, the 1st and 2nd digits from the leftshow the 1st figure and the 2nd figure, and the 3rd digit is a multiplier whichdetermines how many zeros are to be added to the capacitance. Picofarad ( pF )units are written this way.For example, when the code is [103], it indicates 10 x 103, or 10,000pF = 10nanofarad( nF ) = 0.01 microfarad( F ).

If the code happened to be [224], it would be 22 x 104 = or 220,000pF = 220nF= 0.22F.Values under 100pF are displayed with 2 digits only. For example, 47 would be47pF.

The capacitor has an insulator( the dielectric ) between 2 sheets of electrodes.Different kinds of capacitors use different materials for the dielectric.

Breakdown voltage When using a capacitor, you must pay attention to themaximum voltage which can be used. This is the "breakdown voltage." Thebreakdown voltage depends on the kind of capacitor being used. You must be

especially careful with electrolytic capacitors because the breakdown voltage iscomparatively low. The breakdown voltage of electrolytic capacitors isdisplayed as Working Voltage.The breakdown voltage is the voltage that when exceeded will cause thedielectric (insulator) inside the capacitor to break down and conduct. When thishappens, the failure can be catastrophic.


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I will introduce the different types of capacitors below. Electrolytic Capacitors(Electrochemical type capacitors)

Aluminum is used for the electrodes by using a thin oxidization membrane.Large values of capacitance can be obtained in comparison with the size of thecapacitor, because the dielectric used is very thin.The most important characteristic of electrolytic capacitors is that they havepolarity. They have a positive and a negative electrode.[Polarised] This meansthat it is very important which way round they are connected. If the capacitor issubjected to voltage exceeding its working voltage, or if it is connected withincorrect polarity, it may burst. It is extremely dangerous, because it can quiteliterally explode. Make absolutely no mistakes.Generally, in the circuit diagram, the positive side is indicated by a "+" (plus)symbol.

Electrolytic capacitors range in value from about 1F to thousands of F.Mainly this type of capacitor is used as a ripple filter in a power supply circuit,or as a filter to bypass low frequency signals, etc. Because this type of capacitoris comparatively similar to the nature of a coil in construction, it isn't possible touse for high-frequency circuits.The photograph on the left is an example of the different values of electrolyticcapacitors in which the capacitance and voltage differ.From the left to right:1F (50V) [diameter 5 mm, high 12 mm]47F (16V) [diameter 6 mm, high 5 mm]100F (25V) [diameter 5 mm, high 11 mm] 220F (25V) [diameter 8 mm, high

12 mm]


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1000F(50V)

[diameter 18mm,high 40mm]The sizeof thecapacitor

sometimes depends on themanufacturer. So the

sizes shown here on this page are justexamplesIn the photograph to the right, themark indicating the negative lead ofthe component can be seen.You need to pay attention to thepolarity indication so as not to make amistake when you assemble thecircuit.

Tantalum Capacitors

Tantalum Capacitors are electrolytic capacitors that is use a material calledtantalum for the electrodes. Large values of capacitance similar to aluminumelectrolytic capacitors can be obtained. Also, tantalum capacitors are superior toaluminum electrolytic capacitors in temperature and frequency characteristics.When tantalum powder is baked in order to solidify it, a crack forms inside. Anelectric charge can be stored on this crack.These capacitors have polarity as well. Usually, the "+" symbol is used to showthe positive component lead. Do not make a mistake with the polarity on thesetypes.Tantalum capacitors are a little bit more expensive than aluminum electrolytic

capacitors. Capacitance can change with temperature as well as frequency, andthese types are very stable. Therefore, tantalum capacitors are used for circuitswhich demand high stability in the capacitance values. Also, it is said to becommon sense to use tantalum capacitors for analog signal systems, because thecurrent-spike noise that occurs with aluminum electrolytic capacitors does notappear. Aluminum electrolytic capacitors are fine if you don't use them forcircuits which need the high stability characteristics of tantalum capacitors.


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The photograph on the left illustrates the tantalumcapacitor.

The capacitance values are as follows, from the left:

0.33 F (35V)0.47 F (35V)10 F (35V)

The "+" symbol is used toshow the positive lead of the component. It is

written on the body.

Ceramic CapacitorsCeramic capacitors are constructed with materials such as titanium acid bariumused as the dielectric. Internally, these capacitors are not constructed as a coil,so they can be used in high frequency applications. Typically, they are used incircuits which bypass high frequency signals to ground.These capacitors have the shape of a disk. Their capacitance is comparativelysmall.

The capacitor on the left is a 100pF capacitor with a diameter of about 3 mm.The capacitor on the right side is printed with 103, so 10 x 103pF becomes 0.01F. The diameter of the disk is about 6 mm.Ceramic capacitors have no polarity.Ceramic capacitors should not be used for analog circuits, because they candistort the signal.


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Multilayer Ceramic Capacitors

The multilayer ceramic capacitor has a many-layered dielectric. These capacitors are small in size,and have good temperature and frequencycharacteristics.Square wave signals used in digital circuitscan have a comparatively high frequency componentincluded.This capacitor is used to bypass the high frequency

to ground.

In the photograph, the capacitance of the component on the left is displayed as

104. So, the capacitance is 10 x 104 pF = 0.1 F. The thickness is 2 mm, theheight is 3 mm, the width is 4 mm.The capacitor to the right has a capacitance of 103 (10 x 103 pF = 0.01 F). Theheight is 4 mm, the diameter of the round part is 2 mm.These capacitors are not polarized. That is, they have no polarity.


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Polystyrene Film

CapacitorsIn these devices, polystyrenefilm is used as the dielectric.This type of capacitor is notfor use in high frequencycircuits, because they areconstructed like a coil inside.They are used well in filtercircuits or timing circuitswhich run at several hundredKHz or less.

The component shown on the left has a redcolor due to the copper leaf used for theelectrode. The silver color is due to the useof aluminum foil as the electrode.

The device on the left has a height of 10mm, is 5 mm thick, and is rated 100pF.The device in the middle has a height of 10mm, 5.7 mm thickness, and is rated 1000pF.The device on the right has a height of 24

mm, is 10 mm thick, and is rated 10000pF.These devices have no polarity.

Electric Double Layer Capacitors (Super Capacitors)

This is a "Super Capacitor," which is quite a wonder.The capacitance is 0.47 F (470,000 F).I have not used this capacitor in an actual circuit.

Care must be taken when using a capacitor with such a large capacitance inpower supply circuits, etc. The rectifier in the circuit can be destroyed by a hugerush of current when the capacitor is empty. For a brief moment, the capacitor ismore like a short circuit. A protection circuit needs to be set up.

The size is small in spite of capacitance. Physically, the diameter is 21 mm, theheight is 11 mm.


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Care is necessary, because these devices do have polarity.

Polyester Film CapacitorsThis capacitor uses thin polyester film as the dielectric.They are not high tolerance, but they are cheap and handy. Their tolerance is

about 5% to 10%.

From the left in thephotographCapacitance: 0.001 F(printed with 001K)[the width 5 mm, the height

10 mm, the thickness 2 mm]Capacitance: 0.1 F (printedwith 104K)[the width 10 mm, the height11 mm, the thickness 5mm]Capacitance: 0.22 F (printedwith .22K)

[the width 13 mm, the height 18 mm, thethickness 7mm]

Care must be taken, because different

manufacturers use different methods todenote the capacitance values.

Here are some other polyester film capacitors.

Starting from the left

Capacitance: 0.0047 F (printed with 472K)[the width 4mm, the height 6mm, the thickness 2mm]Capacitance: 0.0068 F (printed with 682K)[the width 4mm, the height 6mm, the thickness 2mm]Capacitance: 0.47 F (printed with 474K)[the width 11mm, the height 14mm, the thickness 7mm]


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These capacitors have nopolarity.

Polypropylene CapacitorsThis capacitor is used whena higher tolerance isnecessary than polyestercapacitors offer.Polypropylene film is usedfor the dielectric. It is saidthat there is almost nochange of capacitance in

these devices if they are used with frequencies of 100KHz or less.The pictured capacitors have a tolerance of 1%.

From the left in the photographCapacitance: 0.01 F (printed with 103F)[the width 7mm, the height 7mm, the thickness 3mm]Capacitance: 0.022 F (printed with 223F)[the width 7mm, the height 10mm, the thickness 4mm]

Capacitance: 0.1 F(printed with 104F)[the width 9mm, the height

11mm, the thickness 5mm]

When I measured thecapacitance of a 0.01 Fcapacitor with the meterwhich I have, the error was+0.2%.

These capacitors have nopolarity.

Mica Capacitors

These capacitors use Mica for the dielectric. Mica capacitors have good stabilitybecause their temperature coefficient is small. Because their frequencycharacteristic is excellent, they are used for resonance circuits, and high


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frequency filters. Also, theyhave good insulation, and so

can be utilized in highvoltage circuits. It was oftenused for vacuum tube styleradio transmitters, etc.Mica capacitors do not havehigh values of capacitance,and they can be relativelyexpensive.

Pictured at the right are"Dipped mica capacitors." These can handle up to 500 volts.

The capacitance from the leftCapacitance: 47pF (printed with 470J)[the width 7mm, the height 5mm, the thickness 4mm]Capacitance: 220pF (printed with 221J)[the width 10mm, the height 6mm, the thickness 4mm]Capacitance: 1000pF (printed with 102J)[the width 14mm, the height 9mm, the thickness 4mm]These capacitors have no polarity.

Metallized Polyester Film Capacitors

These capacitors are a kind of a polyester film capacitor. Because theirelectrodes are thin, they can be miniaturized.

From the left in the photographCapacitance: 0.001F (printed with 1n. n means nano:10-9)Breakdown voltage: 250V[the width 8mm, the height 6mm, the thickness 2mm]Capacitance: 0.22F (printed with u22)Breakdown voltage: 100V[the width 8mm, the height 6mm, the thickness 3mm]Capacitance: 2.2F (printed with 2u2)

Breakdown voltage: 100V[the width 15mm, the height 10mm, the thickness 8mm]Care is necessary, because the component lead easily breaks off from thesecapacitors. Once lead has come off, there is no way to fix it. It must bediscarded.

These capacitors have no polarity.


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Variable Capacitors

Variable capacitors are used for adjustment etc. of frequency mainly.

On the left in the photograph is a "trimmer," which uses ceramic as thedielectric. Next to it on the right is one that uses polyester film for the dielectric.The pictured components are meant to be mounted on a printed circuit board.

When adjusting the value of a variable capacitor, it is advisable to be careful.One of the component's leads is connected to the adjustment screw of thecapacitor. This means that the value of the capacitor can be affected by thecapacitance of the screwdriver in your hand. It is better to use a specialscrewdriver to adjust these components.

Pictured in the upper left photograph are variable capacitors with the followingspecifications:Capacitance: 20pF (3pF - 27pF measured)[Thickness 6 mm, height 4.8 mm]Their are different colors, as well. Blue: 7pF (2 - 9), white: 10pF (3 - 15), green:30pF (5 - 35), brown: 60pF (8 - 72).

In the same photograph, the device on the right has the following specifications:Capacitance: 30pF (5pF - 40pF measured)[The width (long) 6.8 mm, width (short) 4.9 mm, and the height 5 mm]

The components in the photograph on the right are used for radio tuners, etc.They are called "Varicons" but this may be only in Japan.The variable capacitor on the left in the photograph, uses air as the dielectric.


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DIODES

A diode is a semiconductor device which allowscurrent to flow through it in only one direction.Although a transistor is also a semiconductor device,it does not operate the way a diode does. A diode isspecifically made to allow current to flow through it in only one direction. Someways in which the diode can be used are listed here.

A diode can be used as a rectifier that converts AC (Alternating Current) toDC (Direct Current) for a power supply device.

Diodes can be used to separate the signal from radio frequencies.Diodes can be used as an on/off switch that controls current.

This symbol is used to indicate a diode in a circuit diagram.

The meaning of the symbol is (Anode) (Cathode).Current flows from the anode side to the cathode side.

Although all diodes operate with the same general principle, there are differenttypes suited to different applications. For example, the following devices arebest used for the applications noted.

Voltage regulation diode(Zener Diode)The circuit symbol is .It is used to regulate voltage, by taking advantage of the fact that Zenerdiodes tend to stabilize at a certain voltage when that voltage is applied inthe opposite direction.

Light emitting diode

The circuit symbol is .This type of diode emits light when current flows through it in the forwarddirection. (Forward biased.)

Variable capacitance diode

The circuit symbol is .The current does not flow when applying the voltage of the oppositedirection to the diode. In this condition, the diode has a capacitance like thecapacitor. It is a very small capacitance. The capacitance of the diodechanges when changing voltage. With the change of this capacitance, thefrequency of the oscillator can be changed.


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The graph on the right shows the electrical characteristics of a typical diode.

When a small voltage is applied to the diode in the forward direction, currentflows easily.Because the diode has a certain amount of resistance, the voltage will dropslightly as current flows through the diode. A typical diode causes a voltagedrop of about 0.6 - 1V (VF) (In the case of silicon diode, almost 0.6V)

This voltage drop needs to be taken into consideration in a circuit which usesmany diodes in series. Also, the amount of current passing through the diodesmust be considered.

When voltage is applied in the reverse direction through a diode, the diode willhave a great resistance to current flow.Different diodes have different characteristics when reverse-biased. A givendiode should be selected depending on how it will be used in the circuit.The current that will flow through a diode biased in the reverse direction willvary from several mA to just A, which is very small.

The limiting voltages and currents permissible must be considered on a case bycase basis. For example, when using diodes for rectification, part of the timethey will be required to withstand a reverse voltage. If the diodes are not chosencarefully, they will break down.


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Rectification / Switching /Regulation Diode

The stripe stamped on one end of thediode shows indicates the polarity of

the diode.The stripe shows the cathode side.The top two devices shown in the picture are diodes used for rectification. Theyare made to handle relatively high currents. The device on top can handle ashigh as 6A, and the one below it can safely handle up to 1A.However, it is best used at about 70% of its rating because this current value is amaximum rating.The third device from the top (red color) has a part number of 1S1588. Thisdiode is used for switching, because it can switch on and off at very high speed.However, the maximum current it can handle is 120 mA. This makes it well

suited to use within digital circuits.The maximum reverse voltage(reverse bias) this diode can handleis 30V.The device at the bottom of thepicture is a voltage regulation diodewith a rating of 6V. When this typeof diode is reverse biased, it willresist changes in voltage. If the inputvoltage is increased, the outputvoltage will not change. (Or anychange will be an insignificantamount.) While the output voltagedoes not increase with an increase ininput voltage, the output current will.This requires some thought for a


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protection circuit sothat too much currentdoes not flow.

The rated current limitfor the device is 30mA.Generally, a 3-terminal voltageregulator is used forthe stabilization of apower supply.

Therefore, this diode is typically used to protect the circuit from momentaryvoltage spikes. 3 terminal regulators use voltage regulation diodes inside.

Diode bridge

Rectification diodes are used to make DC from AC. It is possible to do only'half wave rectification' using 1 diode. When 4 diodes are combined, 'full waverectification' occurrs.Devices that combine 4 diodes in one package are called diode bridges. Theyare used for full-wave rectification.

The photograph on the left shows two examples of diode bridges.

The cylindrical device on the right in the photograph has a current limit of 1A.Physically, it is 7 mm high, and 10 mm in diameter.

The flat device on the left has a current limit of 4A. It is has a thicknessof 6 mm, is 16 mm in height, and 19 mm in width.

The photograph on the right shows a large, high-power diode bridge.It has a current capacity of 15A. The peak reverse-bias voltage is 400V.Diode bridges with large current capacities like this one, require a heat sink.Typically, they are screwed to a piece of metal, or the chasis of device in whichthey are used. The heat sink allows the device to radiate excess heat.As for size, this one is 26 mm wide on each side, and the height of the module

part is 10 mm.

Light Emitting Diode ( LED )

Light emitting diodes must be choosen according to how they will be used,because there are various kinds.The diodes are available in several colors. The most common colors are red and


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green, but there are even blue ones.

The device on the far right in the photograph

combines a red LED and green LED in onepackage. The component lead in the middle iscommon to both LEDs. As for the remaing twoleads, one side is for the green, the other for thered LED. When both are turned onsimultaneously, it becomes orange.

When an LED is new out of the package, the polarity of the device can bedetermined by looking at the leads. The longer lead is the Anode side, and theshort one is the Cathode side.

The polarity of an LED can also be determined using a resistance meter, or evena 1.5 V battery.

When using a test meter to determine polarity, set the meter to a low resistancemeasurement range. Connect the probes of the meter to the LED. If the polarityis correct, the LED will glow. If the LED does not glow, switch the meterprobes to the opposite leads on the LED. In either case, the side of the diodewhich is connected to the black meter probe when the LED glows, is the Anodeside. Positive voltage flows out of the black probe when the meter is set tomeasure resistance.

It is possible to use an LED to obtain a fixed voltage.The voltage drop (forward voltage, or VF) of an LED is comparatively stable atjust about 2V.

I explain a circuit in which the voltage was stabilized with an LED in"Thermometer of bending apparatus-2".
http://www.interq.or.jp/japan/se-inoue/e_acryla6.htmhttp://www.interq.or.jp/japan/se-inoue/e_acryla6.htmhttp://www.interq.or.jp/japan/se-inoue/e_acryla6.htmhttp://www.interq.or.jp/japan/se-inoue/e_acryla6.htm


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Shottky barrier diode

Diodes are used to rectify alternating current into direct

current. However, rectification will not occur when thefrequency of the alternating current is too high. This isdue to what is known as the "reverse recoverycharacteristic."The reverse recovery characteristic can be explained asfollows:

IF the opposite voltage is suddenly applied to a forward-biased diode, currentwill continue to flow in the forward direction for a brief moment. This time until

the current stops flowing is called the Reverse Recovery Time. The current isconsidered to be stopped when it falls to about 10% of the value of the peakreverse current.The Shottky barrier diode has a short reverse recovery time, which makes itideally suited to use in high frequency rectification.

The shottky barrier diode has the following characteristics.

The voltage drop in the forward direction is low.The reverse recovery time is short.

However, it has the following disadvantages.

The diode can have relatively high leakage current.The surge resistance is low.Because the reverse recovery time is short, this diode is often used for theswitching regulator in a high frequency circuit.


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Transistors

The transistor's finction is to amplify an electric current.Many different kinds of transistors are used in analog circuits, for differentreasons. This is not the case for digital circuits. In a digital circuit, only twovalues matter; on or off. The amplification abilitiy of a transistor is not relevantin a digital circuit. In many cases, a circuit is built with integrated circuits(ICs).Transistors are often used in digital circuits as buffers to protect ICs. Forexample, when powering an electromagnetic switch (called a 'relay'), or whencontrolling a light emitting diode. (In my case.)

Two different symbols are used for the transistor.

PNP type and NPN type

The name (standard partnumber) of the transistor, aswell as the type and the way itis used is shown below.

2SAXXXX PNP typehigh frequency2SBXXXX PNP typelow frequency2SCXXXX NPN typehigh frequency2SDXXXX NPN typelow frequency

The direction of the currentflow differs between the PNPand NPN type.When the power supply is theside of the positive (plus), theNPN type is easy to use.


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Appearance of the TransistorThe outward appearance of the transistorvaries. Here, two kinds are shown.

On the left in the photograph is a 2SC1815transistor, which is good for use in a digitalcircuit. They are inexpensive when I buy themin quantity. In Japan it costs 2,000 yen for apack of 200 pieces. (About 10 US cents/piecein 1998)

On the right is a device which is used when a large current is to be handled. Itspart number is 2SD880.

The electrical characteristics of each is as follows.

Item 2SC1815 2SD880

VCEO(V) 50 60

IC(mA) 150 3A

PC(mW) 400 30W

hFE 70 - 700 60 - 300

fT(MHz) 80 3

VCEO: The maximum voltage that can be handled across the collector(C)

and emitter(E) when the base(B) is open. (Not connected)

(It may be shown as VCE)

IC : The maximum collector(C) current.

PC :

Maximum collector(C) loss that continuously can cause itconsumedat surroundings temperature (Ta)=25C(no radiator)


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hFE : The current gain to DC at the emitter(E).(IC/IB)

fT : The maximum DC switching frequency. (the transision frequency)

Component Lead of the Transistor

Because the component leads differ between kinds of transistors,you need to confirm the leads with a datasheet, etc.

Example of 2SC1815 transistorPart number is printed on the flat face of the transistor, and indicates the front.

Right side : BaseCenter : CollectorLeft side : Emitter

Example of 2SD880 transistorPart number is printed on the flat face of the transistor, and indicates the front.

Right side : EmitterCenter : CollectorLeft side : Base

2SC1815 is opposite.


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Printed Wiring Boards

When assemblingan electroniccircuit, a board isneeded on whichthe componentscan be mountedand wiredtogether. Thisboard is called a

Printed WiringBoard (PWB).In Japan, theprinted wiringboard used to becalled a "PrintedCircuit Board."

Nowadays in Japan the name "Printed Circuit Board" is not used because theinitials of "Printed Circuit Board" are "PCB." PCB also stands for"Polychlorinated Biphenyls (PCBs)," which is a poison. So in Japan, we refer tothe boards as "Printed Wiring Boards." In other countries, they are still refered

to as "Printed Circuit Boards," or PCBs.

Making a PWB takes a lot of work, and can be very difficult. For this reason,for many hand-made circuits, I often use a universal PWB.The universal PWB consists of an insulation board drilled with .8mm holes at0.1 inch (2.54 mm) intervals. The board is completely covered with these holesfrom edge to edge. The insulation board is comprised of fiberglass (glassepoxy), paper epoxy, or bakelite plastic.Centered around each hole on the bottom of the PWB is an 2mm copper leaf(known as the "land" or "pad").

To use the board, the parts are mounted on the face of the board, and thecomponent leads are passed through the nearest holes, to project through thebottom of the board, where the wires can be soldered together.The interval between the holes is 0.1 inches (2.54 mm), soDIP or SIP ICscanbe easily mounted.The photograph shows a PWB made of glass epoxy. The color is green.Paper epoxy boards have a beige color. In case of bakelite, the color is thinbrown.
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As for the size of the board, there are several kinds by the number of the holes.From the left side in the photograph

55 x 40 holes (size 160 x 115 mm)30 x 25 holes (size 95 x 72 mm)25 x 15 holes (size 72 x 47 mm)

There are various sizes in addition to what I have shown, so you can select aboard according to your needs.The boards can also be cut to size.

On the top right in the photograph, the back side is shown. The copper leaf onthis board has been pre-soldered ("tinned") to make soldering easier, so it has asilver color. If the board has not been pre-soldered, then it is seen to have a

copper color.

Wiring materials

Wire is used to electrically connect circuit parts, devices, equipment etc.

There are various kinds of wiring materials. On this page, I introduce the typethat is used for the assembly of electronic circuits.

The different types of wire can be divided largely into two categories: singlewire and twisted strand wire. It really doesn't matter which kind you use for agiven application, but usually, single wire is used to connect devices (resistors,capacitors ect) together on the PWB. (Parts that don't move)It is also used for jumper wiring.Twisted strand wire can bend freely, so it can be used for wiring on the PWB,and also to connect discrete pieces of equipment.If single wire is used to connnect separate equipment, it will break soon, as it is

not very flexible.

It is convenient to use the single tin coated wire of the diameter 0.32 mm for thewiring of PWB. If the diameter is larger, soldering becomes a little bit difficult.And if the diameter is too thin, it becomes difficult to bend the wire the way youwant it to stay.It's best to use whatever wire you are comfortable with, and not worry aboutthose things.


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If you want toconnect separated

parts on the PWB,twisted wirecovered with softinsulation materialis most convenientfor wiring.It's convenient towire the circuit

using differentcolor wires fordifferent

purposes.Otherwise, wiringthe circuit withmany wires thesame color getsconfusing.

The photographon the left shows several colors of twisted wire.It is called 0.12/7PVC.The pictured wire is comprised of 7 tin coated wires 0.12 mm each in diameter,

covered by very thin PVC plastic.

In the photograph to the right is pictured tin coated wire with a diameter of 0.32mm.It is convenient to use for wiring components, jumper wiring etc. when you arebuilding a circuit on a universal PWB.Pictured at the left is polyurethane wire, 0.4 mm in diameter.It is used for making coils.There are several kinds of coated wires. Tin coated wire colored silver,polyurethane enameled copper wire(UEW) which has a thin brown color,

polyester enameled copper wire (PEW) which is also thin brown, and enameledwire with a burnt brown color.Coated wire is used for making coil components like a transformers.

The PEW can not be soldered, because the polyester coating will not melt at thesoldering temperature. So if you want to solder PEW wire, you need to scrapethe enamel off the wire.


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In case of theUEW, you do notneed to scrape the

insulation off thewire, because thepolyurethane willmelt at thesolderingtemperature.

In this photograph is a tool used for wiring.Copper wire can be drawn out from the tip like the core of a pencil.

First, the wire is attached and solderd to the first lead of a given component.Next, the wire is drawn out from the tool and can be soldered at the desired leadof another component.The wire is polyurethane coated single wire of 0.2 mm thickness.

Soldering

Soldering is a process in which two or moremetalitems are joined together by meltingand flowing a filler metal into the joint, the filler metal having a relatively lowmeltingpoint. Soft soldering is characterized by the melting point of the filler metal, which is

below 400 C (800 F). The filler metal used in the process is calledsolder.

Soldering is distinguished frombrazingby use of a lower melting-temperature fillermetal; it is distinguished fromweldingby the base metals not being melted during thejoining process. In a soldering process, heat is applied to the parts to be joined, causingthe solder to melt and be drawn into the joint bycapillary actionand to bond to thematerials to be joined bywetting action. After the metal cools, the resulting joints are notas strong as the base metal, but have adequate strength, electrical conductivity, and water-tightness for many uses. Soldering is an ancient technique mentioned in the Bible andthere is evidence that it was employed up to 5000 years ago in Mesopotamia.

Applications

One of the most frequent application of soldering is assemblingelectronic componentstoprinted circuit boards(PCBs). Another common application is making permanent butreversible connections between copper pipes inplumbingsystems. Joints in sheet metalobjects such as food cans,roof flashing,rain guttersand automobileradiatorshave alsohistorically been soldered, and occasionally still are.Jewelrycomponents are assembledand repaired by soldering. Small mechanical parts are often soldered as well. Soldering is
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also used to join leadcameandcopper foilinstained glasswork. Soldering can also be

used to effect a semi-permanent patch for a leak in a container cooking vessel.

Solders

Soldering filler materials are available in many differentalloysfor differing applications.In electronics assembly, theeutecticalloy of 63% tin and 37% lead (or 60/40, which isalmost identical in performance to the eutectic) has been the alloy of choice. Other alloysare used for plumbing, mechanical assembly, and other applications.

A eutectic formulation has several advantages for soldering; chief among these is thecoincidence of theliquidusandsolidustemperatures, i.e. the absence of a plastic phase.

This allows for quicker wetting out as the solder heats up, and quicker setup as the soldercools. A non-eutectic formulation must remain still as the temperature drops through theliquidus and solidus temperatures. Any differential movement during the plastic phasemay result in cracks, giving an unreliable joint. Additionally, a eutectic formulation hasthe lowest possible melting point, which minimizes heat stress on electronic componentsduring soldering.

Lead-free solders are suggested anywhere children may come into contact (since childrenare likely to place things into their mouths), or for outdoor use where rain and otherprecipitation may wash the lead into the groundwater. Common solder alloys aremixtures of tin and lead, respectively:

63/37: melts at 183 C (361.4 F) (eutectic: the only mixture that melts at a point,instead of over a range)

60/40: melts between 183190 C (361374 F) 50/50: melts between 185215 C (365419 F)

Lead-free solder alloys melt around 250 C (482 F), depending on their composition.

For environmental reasons, 'no-lead' solders are becoming more widely used.Unfortunately most 'no-lead' solders are not eutectic formulations, making it moredifficult to create reliable joints with them. See complete discussion below; see also

RoHS.

Other common solders include low-temperature formulations (often containingbismuth),which are often used to join previously-soldered assemblies without un-soldering earlierconnections, and high-temperature formulations (usually containingsilver) which areused for high-temperature operation or for first assembly of items which must notbecome unsoldered during subsequent operations. Specialty alloys are available with
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properties such as higher strength, better electrical conductivity and higher corrosion

resistance.

Flux

In high-temperature metal joining processes (welding, brazing and soldering), theprimary purpose offluxis to prevent oxidation of the base and filler materials. Tin-leadsolder, for example, attaches very well to copper, but poorly to the various oxides ofcopper, which form quickly at soldering temperatures. Flux is a substance which is nearlyinert at room temperature, but which becomes stronglyreducingat elevated temperatures,preventing the formation of metal oxides. Secondarily, flux acts as awetting agentin thesoldering process, reducing thesurface tensionof the molten solder and causing it to

better wet out the parts to be joined.

Fluxes currently available include water-soluble fluxes (noVOC's required for removal)and 'no-clean' fluxes which are mild enough to not require removal at all. Performance ofthe flux needs to be carefully evaluated; a very mild 'no-clean' flux might be perfectlyacceptable for production equipment, but not give adequate performance for a poorly-controlled hand-soldering operation.

Traditionalrosinfluxes are available in non-activated (R), mildly activated (RMA) andactivated (RA) formulations. RA and RMA fluxes contain rosin combined with

Report on Embedded System by Kaushal Babu

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