Micro-Scholarship, What it is, How can it help me.pdf
Teach-In Electronics
1. 50 Everyday Practical Electronics, November 2010
Teach-In 2011
By Mike and Richard Tooley
0ARTªª)NTRODUCTIONªTOªSIGNALSªINª
ELECTRONICªCIRCUITSªANDªSYSTEMS
/URª4EACH
)NªSERIESªISªDESIGNEDªTOªPROVIDEªYOUªWITHªAªBROAD
BASEDªINTRODUCTIONªTOªELECTRONICSª7EªHAVEªª
ATTEMPTEDªTOªPROVIDEªCOVERAGEªOFªTHREEªOFªTHEªMOSTªIMPORTANTªELECTRONICSªUNITSªTHATªAREªCURRENTLYªSTUDIEDªINª
MANYªSCHOOLSªANDªCOLLEGESªINªTHEª5+ª4HESEªINCLUDEª%DEXCELª4%#ª,EVELªªAWARDS
9. ª!MAZEªWILLªSHOWªYOUªTHEª@WOWªFACTOR ª
TO RECOGNISE SIGNALS FROM THE SHAPE
OF THEIR WAVEFORMS
EING ABLE TO lREADm AND INTERPRET A
CIRCUIT DIAGRAM OR lSCHEMATICm IS AN
ESSENTIAL SKILL REQUIRED OF EVERY ELEC
TRONIC TECHNICIAN AND ENGINEER -ANY
DIFFERENT PARTS AND DEVICES ARE USED IN
ELECTRONIC CIRCUITS
10. AND IT IS IMPORTANT
THAT YOU SHOULD BE ABLE TO RECOGNISE
THEM
11. BOTH FROM THE SYMBOLS THAT WE
USE TO REPRESENT THEM IN THEORETICAL
CIRCUIT DIAGRAMS AND ALSO FROM THEIR
PHYSICAL APPEARANCE
ERS FORMS OF lBODY LANGUAGEm )N FACT
12. LIFE WOULD BE VERY DIFÚCULT WITHOUT
SIGNALS q THINK ABOUT DRIVING A CAR
OR MOTORBIKE IN HEAVY TRAFÚCØ )N THIS
SECTION WE WILL LOOK AT HOW SIGNALS ARE
USED IN ELECTRONICS
13. HOW THEY CAN BE
CONVERTED FROM ONE FORM TO ANOTHER
17. AND
SEQUENCES OF BINARY CODED DIGITS OR
CJUT 3IGNALS THAT VARY CONTINUOUSLY IN
LEVEL ARE REFERRED TO AS ANALOGUE SIG
NALS
18. WHILE THOSE THAT USE DISCRETE IE
ÚXED LEVELS ARE REFERRED TO AS DIGITAL
SIGNALS 3OME TYPICAL ANALOGUE AND
DIGITAL SIGNALS ARE SHOWN IN IG
.OTICE HOW THE DIGITAL SIGNAL EXISTS
ONLY AS A SERIES OF DISCRETE VOLTAGE
LEVELS
19. WHILE THE ANALOGUE SIGNAL VARIES
CONTINUOUSLY FROM ONE VOLTAGE LEVEL
TO ANOTHER
7($+,1
$ %52$'%$6(' ,1752'87,21
72 (/(7521,6
:
% %'). THIS NEW 5FBDI*O
SERIES BY INTRODUCING
THE SIGNALS USED TO CONVEY
INFORMATION IN ELECTRONIC CIRCUITS
20. AND
THE UNITS THAT WE USE TO MEASURE THE
QUANTITIES IN ELECTRONIC CIRCUITS 7E
CONCLUDE THIS PART BY LOOKING AT SOME
SIMPLE ELECTRONIC CIRCUITS THAT YOU CAN
BUILD AND TEST USING #IRCUIT 7IZARD
SOFTWARE SEE PAGES AND
3IGNALSªINªELECTRONICªCIRCUITSª
ANDªSYSTEMS
4HIS ÚRST PART OF OUR 4EACH
)N SERIES
WILL PROVIDE YOU WITH AN INTRODUC
TION TO THE SIGNALS THAT CONVEY JO
GPSNBUJPO IN ELECTRONIC CIRCUITS 7E
WILL ALSO INTRODUCE YOU TO SOME OF THE
UNITS THAT ARE USED WHEN MEASURING
ELECTRICAL QUANTITIES
22. VOLTAGE AND FREQUENCY 9OU WILL
LEARN ABOUT THE DIFFERENCE BETWEEN
ANALOGUE AND DIGITAL SIGNALS AND HOW
,EARN
3IGNALSªANDªSIGNALªCONVERSION
)N ALL FORMS OF COMMUNICATION SIG
NALS ARE USED TO CONVEY INFORMATION
4HE SIGNALS THAT WE USE IN EVERYDAY
LIFE CAN TAKE MANY FORMS
27. Everyday Practical Electronics, November 2010 51
Teach-In 2011
3IGNALS CAN ALSO BE QUITE EASILY
CONVERTED FROM ONE FORM TO ANOTHER
OR EXAMPLE
28. THE SIGNAL FROM THE
STAGE MICROPHONE AT A LIVE RADIO
BROADCAST WILL BE AN ANALOGUE SIGNAL
AT THE POINT AT WHICH THE ORIGINAL
SOUND IS PRODUCED IE ON STAGE
!FTER APPROPRIATE PROCESSING WHICH
MIGHT INVOLVE AMPLIÚCATION ANDOR
REMOVAL OF NOISE AND OTHER UNWANTED
SOUNDS IT MIGHT THEN BE CONVERTED
TO A DIGITAL SIGNAL FOR RADIO TRANSMIS
SION
29. AND THEN CONVERTED BACK TO AN
ANALOGUE SIGNAL BEFORE BEING AMPLI
ÚED AND SENT TO THE LOUDSPEAKER AT
THE POINT OF RECEPTION
! DEVICE THAT CONVERTS AN ANALOGUE
SIGNAL TO DIGITAL FORMAT IS CALLED AN
BOBMPHVFUPEJHJUBM DPOWFSUFS !$#
30. WHILE ONE THAT CONVERTS A DIGITAL
SIGNAL TO ANALOGUE IS REFERRED TO AS A
EJHJUBMUPBOBMPHVF DPOWFSUFS $!#
!N ELECTRONIC SYSTEM THAT USES BOTH
ANALOGUE AND DIGITAL SIGNALS IS SHOWN
IN IG
%LECTRONICªUNITS
! NUMBER OF UNITS ARE COMMONLY
USED IN ELECTRONICS
31. SO WE SHALL START
BY INTRODUCING SOME OF THEM ,ATER
32. WE
WILL BE PUT THESE UNITS TO USE WHEN WE
SOLVESOMESIMPLECIRCUITPROBLEMS
33. BUT
SINCE ITmS IMPORTANT TO GET TO KNOW THESE
UNITS AND ALSO TO BE ABLE TO RECOGNISE
THEIR ABBREVIATIONS AND SYMBOLS WE
HAVE SUMMARISED THEM IN 4ABLE
0LEASE NOTEØ
REQUENCY AND BIT RATE ARE VERY
SIMILAR 4HEY BOTH INDICATE THE SPEED
AT WHICH A SIGNAL IS TRANSMITTED
34. BUT BIT
RATE IS USED FOR DIGITAL SIGNALS WHILE FRE
QUENCY IS USED WITH ANALOGUE SIGNALS
'JH 5ZQJDBM BOBMPHVF BOE EJHJUBM TJHOBMT
'JH O FMFDUSPOJD TZTUFN UIBU VTFT CPUI BOBMPHVF BOE EJHJUBM TJHOBMT
4ABLE 3OMEªELECTRICALªQUANTITIESªANDªUNITSªOFªMEASUREMENT
3DUDPHWHU 8QLW $EEUHYLDWLRQ 1RWHV
(OHFWULF SRWHQWLDO 9ROW 9 $ SRWHQWLDO RI 9 RQH 9ROW
39. (OHFWULF FXUUHQW $PSHUH $ $ FXUUHQW RI $ IORZV LQ DQ HOHFWULFDO FRQGXFWRU ZKHQ HOHFWULF FKDUJH LV
EHLQJ WUDQVSRUWHG DW WKH UDWH RI RXORPE SHU VHFRQG
(OHFWULF SRZHU :DWW : 3RZHU LV WKH UDWH RI XVLQJ HQHUJ $ SRZHU RI : RQH :DWW
40. FRUUHVSRQGV WR -RXOH RI HQHUJ EHLQJ XVHG HYHU VHFRQG
(OHFWULFDO UHVLVWDQFH 2KP : $Q HOHFWULF FLUFXLW KDV D UHVLVWDQFH RI : ZKHQ D SG VHH DERYH
41. RI 9 LV
GURSSHG DFURVV LW ZKHQ D FXUUHQW RI $ LV IORZLQJ LQ LW
)UHTXHQF +HUW] +] $ VLJQDO KDV D IUHTXHQF RI +] RQH +HUW]
42. LI RQH FRPSOHWH FFOH RI
WKH VLJQDO RFFXUV LQ D WLPH LQWHUYDO RI V RQH VHFRQG
43. %LW UDWH %LWV SHU
VHFRQG
ESV $ VLJQDO KDV D ELW UDWH RI ELW SHU VHFRQG LI RQH FRPSOHWH ELQDU GLJLW LV
WUDQVPLWWHG LQ D WLPH LQWHUYDO RI V
(or amp)
44. 52 Everyday Practical Electronics, November 2010
Teach-In 2011
0LEASE NOTEØ
4O AVOID CONFUSION BETWEEN THE
SYMBOLS AND THE ABBREVIATIONS THAT WE
USE FOR UNITS
45. THE FORMER ARE NORMALLY
DISPLAYED IN ITALIC FONT OR EXAMPLE
46. A CAPITAL LETTER 6 IS USED AS BOTH THE
ABBREVIATION FOR VOLTAGE AND FOR ITS UNIT
SYMBOL THE 6OLT 7HEN USED AS A SYM
BOL IN A FORMULA IT IS CONVENTIONALLY
SHOWN IN ITALIC AS 7 AND WHEN USED
AS SHORTHAND FOR VOLTS IT IS SHOWN IN
NORMAL NON
ITALIC FONT AS l6m
-ULTIPLESªANDª
SUB
MULTIPLESª
5NFORTUNATELY
53. :
4O MAKE LIFE A LOT EASIER WE USE A
STANDARD RANGE OF MULTIPLES AND SUB
MULTIPLES 4HESE USE A PREÚX LETTER IN
ORDER TO ADD A MULTIPLIER TO THE QUOTED
VALUE
54. AS SHOWN IN 4ABLE
0LEASE NOTEØ
%XPONENT NOTATION IS OFTEN USEFUL
WHEN PERFORMING CALCULATIONS USING
VERY LARGE OR VERY SMALL NUMBERS
9OU CAN USE EXPONENT NOTATION
BY PRESSING THE EXPONENT % OR
ENGINEERING %.' BUTTON ON YOUR
CALCULATOR
#ONVERTINGªTOFROMªMULTIPLESª
ANDªSUB
MULTIPLES
#ONVERTING TO AND FROM MULTIPLES
AND SUB
MULTIPLES IS ACTUALLY QUITE
EASY
55. AS THE FOLLOWING EXAMPLES SHOW
%XAMPLE
$POWFSU
)[ UP L)[ 4O DO THIS
YOU JUST NEED TO MOVE THE DECIMAL
POINT UISFF PLACES TO THE MFGU 4HIS IS
THE SAME AS DIVIDING BY
64. M6 IN 6
-OVING THE DECIMAL
POINT THREE PLACES TO THE
RIGHT TELLS US THAT 6
M6
%XAMPLE
$POWFSU
LCQT
UP .CQT 4O DO THIS YOU
NEED TO MOVE THE DECI
MAL POINT UISFF PLACES
TO THE MFGU 4HIS IS THE
SAME AS DIVIDING BY
74. IS EQUIVALENT TO
MOVING THE DECIMAL POINT SIX PLACES
TO THE LEFT
7AVEFORMSªANDªWAVEFORMª
MEASUREMENT
! GRAPH SHOWING THE VARIATION OF
VOLTAGE OR CURRENT PRESENT IN A CIRCUIT
'JH 4PNF DPNNPO XBWFGPSNT
Multiple Exponent notation Prefix Abbreviation Example
u1,000,000,000 u
Giga G 1.2GHz (1,200 million Hertz)
u1,000,000 u
Mega M 2.2M: (2.2 million Ohms)
u1,000 u
Kilo k 4kbs (4,000 bits per second)
u1 u
None none 220: (220 Ohms)
u u
Milli m 45mV (0.045 Volts)
u u
Micro P 33PA (0.000033 Amps)
u u
Nano n 450nW (0.00000045 Watts)
4ABLE 3OMEªCOMMONªMULTIPLESªANDªSUB
MULTIPLES
75. Everyday Practical Electronics, November 2010 53
Teach-In 2011
%XAMPLE
XBWFGPSN IBT B GSFRVFODZ PG
)[ 8IBU JT UIF QFSJPEJD UJNF PG UIF
XBWFGPSN
(ERE WE MUST USE THE RELATIONSHIP
U G
WHERE G (Z
(ENCE
76. U S OR MS
%XAMPLE
XBWFGPSN IBT B QFSJPEJD UJNF PG
NT 8IBU JT JUT GSFRVFODZ
(ERE WE MUST USE THE RELATIONSHIP G
U
WHERE U MS OR S
(ENCE
77. G (Z
!MPLITUDE
4HE AMPLITUDE OR QFBL WBMVF OF A
WAVEFORM IS A MEASURE OF THE EXTENT OF
ITS VOLTAGE OR CURRENT EXCURSION FROM
THE RESTING VALUE USUALLY ZERO 4HE
QFBLUPQFBL VALUE FOR A WAVE
79. IS TWICE ITS PEAK VALUE SEE IG
4HESE UNITS ARE USUALLY MORE CONVEN
IENT TO USE WHEN TAKING MEASUREMENTS
FROM A WAVEFORM DISPLAY
0ULSEªWAVEFORMS
7HEN DESCRIBING RECTANGULAR AND
PULSE WAVEFORMS WE USE A DIFFERENT
SET OF PARAMETERS SEE IG 4HESE
INCLUDE
/N TIME
80. TON
4HIS IS THE TIME FOR WHICH THE PULSE
IS PRESENT AT ITS MAXIMUM AMPLITUDE
4HIS IS SOMETIMES REFERRED TO AS THE
lNBSL UJNFm
.OTE THAT WHEN A PULSE IS NOT PER
FECTLYRECTANGULAR IE
85. WHEN A PULSE IS NOT PER
FECTLY RECTANGULAR AND TAKES SOME
TIME TO CHANGE FROM ONE LEVEL TO AN
OTHER
86. WE DEÚNE THE OFF TIME AS THE
TIME FOR WHICH THE PULSE AMPLITUDE
FALLS BELOW OF ITS MAXIMUM
VALUE
0ULSE PERIOD
87. T
4HIS IS THE TIME FOR ONE COMPLETE
CYCLE OF A REPETITIVE PULSE WAVEFORM
4HE PERIODIC TIME IS THUS EQUAL TO THE
SUM OF THE ON AND OFF TIMES BUT ONCE
AGAIN
88. NOTE THAT THIS IS ONLY VALID IF THE
PULSE TRAIN IS REPETITIVE AND IS MEAN
INGLESS IF THE PULSES OCCUR AT RANDOM
INTERVALS
7HEN A PULSE TRAIN IS NOT PERFECTLY
RECTANGULAR
89. THE PULSE PERIOD IS MEAS
URED AT THE AMPLITUDE POINTS
IS KNOWN AS A WAVEFORM 7AVEFORMS
SHOW US HOW VOLTAGE OR CURRENT SIG
NALS VARY WITH TIME 4HERE ARE MANY
COMMON TYPES OF WAVEFORM ENCOUN
TERED IN ELECTRONIC CIRCUITS
96. USUALLY COMPRISE MANY
DIFFERENT SIGNAL COMPONENTS AT DIFFER
ENT FREQUENCIES 0ULSE WAVEFORMS ARE
OFTEN CATEGORISED AS EITHER REPETITIVE OR
NON
REPETITIVE THE FORMER COMPRISES
A PATTERN OF PULSES THAT REPEATS REGU
LARLY
97. WHILE THE LATTER COMPRISES PULSES
WHICH EACH CONSTITUTE A UNIQUE EVENT
3OME COMMON WAVEFORMS ARE SHOWN
IN IG
REQUENCY
4HE FREQUENCY OF A REPETITIVE WAVE
FORM IS THE NUMBER OF CYCLES OF THE
WAVEFORM WHICH OCCUR IN UNIT TIME IE
ONE SECOND REQUENCY IS EXPRESSED
IN (ERTZ (Z
98. AND A FREQUENCY OF (Z
IS EQUIVALENT TO ONE CYCLE PER SECOND
(ENCE
100. CYCLES OF IT WILL OCCUR IN
EVERY SECOND
0ERIODIC TIME
4HE PERIODIC TIME OR PERIOD OF A
WAVEFORM IS THE TIME TAKEN FOR ONE
COMPLETE CYCLE OF THE WAVE SEE IG
4HE RELATIONSHIP BETWEEN PERIODIC
TIME AND FREQUENCY IS THUS
U G OR G U
WHERE U IS THE PERIODIC TIME IN S AND
G IS THE FREQUENCY IN (Z
'JH 0OF DZDMF PG B TJOFXBWF WPMUBHF
TIPXJOH JUT QFSJPEJD UJNF
'JH 0OF DZDMF PG B TJOFXBWF WPMU
BHF TIPXJOH JUT QFBL BOE QFBLUPQFBL
WBMVFT
0ULSE REPETITION FREQUENCY
101. PRF
4HE PULSE REPETITION FREQUENCY PRF
IS THE RECIPROCAL OF THE PULSE PERIOD
(ENCE
QSG U U/. U/
-ARK TO SPACE RATIO
4HE MARK TO SPACE RATIO OF A PULSE
WAVE IS SIMPLY THE RATIO OF THE ON TO
OFF TIMES (ENCE
'JH QVMTF XBWFGPSN TIPXJOH mPOn BOE mPGGn UJNFT
102. 54 Everyday Practical Electronics, November 2010
Teach-In 2011
REPLACE THE ENTIRE UNIT IN MUCH THE
SAME WAY AS WE WOULD REPLACE A SET OF
EXHAUSTED BATTERIES
.BSL UP TQBDF SBUJP U/. U/
.OTE THAT
103. FOR A PERFECT SQUARE WAVE
THE MARK TO SPACE RATIO WILL BE
104. BECAUSE U/. U/
$UTY CYCLE
4HE DUTY CYCLE OF A PULSE WAVE IS
THE RATIO OF THE ON TIME TO THE ON PLUS
OFF TIME AND IS USUALLY EXPRESSED AS
A PERCENTAGE (ENCE
%VUZ DZDMF U/. U/. U/ ¯
U/. U ¯
OR A PERFECT SQUARE WAVE
106. ªBATTERIESªANDªPOWERª
SUPPLIES
#ELLS AND BATTERIES PROVIDE THE
POWER FOR A WIDE RANGE OF PORTABLE
AND HAND
HELD ELECTRONIC EQUIPMENT
4HERE ARE TWO BASIC TYPES OF CELL
QSJNBSZ AND TFDPOEBSZ
0RIMARY CELLS PRODUCE ELECTRICAL
ENERGY AT THE EXPENSE OF THE CHEMI
CALS FROM WHICH THEY ARE MADE AND
ONCE THESE CHEMICALS ARE USED UP
107. NO
MORE ELECTRICITY CAN BE OBTAINED FROM
THE CELL !N EXAMPLE OF A PRIMARY
CELL IS AN ORDINARY 6 !! ALKALINE
BATTERY
)N SECONDARY CELLS
108. THE CHEMICAL
ACTION IS REVERSIBLE 4HIS MEANS THAT
THE CHEMICAL ENERGY IS CONVERTED
INTO ELECTRICAL ENERGY WHEN THE CELL
IS DISCHARGED
109. WHEREAS ELECTRICAL
ENERGY IS CONVERTED INTO CHEMI
CAL ENERGY WHEN THE CELL IS BEING
CHARGED !N EXAMPLE OF A SECONDARY
CELL IS A 6 !! NICKEL CADMIUM
.I#AD BATTERY
)N ORDER TO PRODUCE A BATTERY
111. AS SHOWN
IN IG 4HE VOLTAGE PRODUCED BY A
BATTERY WITH N CELLS WILL BE O TIMES THE
VOLTAGE OF ONE INDIVIDUAL CELL ASSUM
ING THAT ALL OF THE CELLS ARE IDENTICAL
URTHERMORE
112. EACH CELL IN THE BATTERY
WILL SUPPLY THE SAME CURRENT
3ERIES CONNECTED CELLS ARE OFTEN USED
TO FORM BATTERIES OR EXAMPLE
117. USES SIX 6
LEAD
ACID SECONDARY CELLS CONNECTED
IN SERIES
7HERE AN ELECTRONIC CIRCUIT DERIVES
ITS POWER FROM AN !# MAINS SUPPLY
118. WE SOMETIMES SHOW THE SUPPLY AS A
BOX WITH TWO TERMINALS ONE MARKED
POSITIVE AND ONE MARKED NEGATIVE
4REATING THE POWER SUPPLY AS A SEPARATE
UNIT HELPS KEEP THE CIRCUIT SIMPLE )F
THE POWER SUPPLY FAILS WE CAN SIMPLY
'JH 4PNF UZQJDBM DFMMT BOE CBUUFSJFT VTFE JO FMFDUSPOJD FRVJQNFOU
'JH 4ZNCPMT GPS DFMMT BOE CBUUFSJFT
'JH 4FSJFT BSSBOHFNFOU PG DFMMT
'JH CMPDL TDIFNBUJD SFQSFTFOUBUJPO PG UIF QPXFS TVQQMZ JO 'JH
'JH UZQJDBM QPXFS TVQQMZ
119. Everyday Practical Electronics, November 2010 55
Teach-In 2011
0LEASE NOTEØ
7E REFER TO THE OUTPUT VOLTAGE PRO
DUCED BY A BATTERY OR A POWER SUPPLY
AS AN ELECTROMOTIVE FORCE %- %LEC
TROMOTIVE FORCE IS MEASURED IN VOLTS
121. WE REFER TO THE VOLTAGE
DROP ACROSS AN ELECTRONIC COMPONENT
SUCH AS A RESISTOR OR CAPACITOR AS A
POTENTIAL DIFFERENCE PD 0OTENTIAL
DIFFERENCE IS ALSO MEASURED IN VOLTS
6
4HE BEST WAY TO DISTINGUISH BE
TWEEN %- AND PD IS TO REMEMBER
THAT %- IS THE lCAUSEm AND PD IS THE
lEFFECTm
! TYPICAL POWER SUPPLY WHICH HAS
AN !# MAINS INPUT AND $# OUTPUT IS
SHOWN IN IG IG SHOWS
HOW WE CAN REPRESENT THE POWER SUP
PLY USING A SIMPLE CMPDL TDIFNBUJD
EJBHSBN .OTE THAT WE HAVE NOT SHOWN
ANY SWITCHES
122. FUSES OR INDICATORS IN
THIS DIAGRAMØ
#HECKªnª(OWªDOªYOUªTHINKªYOUªAREªDOING
3HORT ANSWER QUESTIONS
%XPLAIN THE DIFFERENCE BE
TWEENANALOGUEANDDIGITALSIGNALS
,IST THE UNITS USED FOR EACH OF
THE FOLLOWING ELECTRICAL QUANTITIES
A CURRENT
B POTENTIAL
C POWER
D RESISTANCE
E FREQUENCY
F BIT RATE
%XPLAIN WHAT IS MEANT BY EACH
OF THE FOLLOWING ABBREVIATIONS
A M6
B K(Z
C !
D -(Z
E K:
F N7
D KBPS
!N AMPLIÚER REQUIRES AN
INPUT SIGNAL OF 6 %XPRESS
THIS IN M6
!N !$# OPERATES AT A BIT RATE
OF KBPS %XPRESS THIS IN -BPS
! CURRENT OF Ž! ÛOWS IN A
RESISTOR %XPRESS THIS IN M!
! RADIO SIGNAL HAS A FRE
QUENCY OF -(Z %XPRESS
THIS IN K(Z
! PORTABLE #$ PLAYER USES A
BATTERY WHICH HAS FOUR 6 CELLS
CONNECTED IN SERIES 7HAT %-
DOES THIS BATTERY SUPPLY
%XPLAINTHEDIFFERENCEBETWEEN
%- AND PD
%XPLAIN THE DIFFERENCE BE
TWEENPRIMARYCELLSANDSECONDARY
CELLS
,ONG ANSWER QUESTIONS
IG BELOW SHOWS AN ELEC
TRONIC SYSTEM THAT USES BOTH ANALOGUE
AND DIGITAL SIGNALS 4AKE A CAREFUL
LOOK AT THE DIAGRAM AND SEE IF YOU
CAN UNDERSTAND HOW IT WORKS BEFORE
ANSWERING THE FOLLOWING QUESTIONS
A %XPLAINTHEPURPOSEOFTHESYSTEM
B !T WHICH POINTS !
123. # ETC
DO THE SIGNALS EXIST IN DIGITAL FORM
AND AT WHICH POINTS DO THEY EXIST IN
ANALOGUE FORM
C 7HAT FORM DO THE SIGNALS HAVE
WHEN THEY ARE PRESENT IN THE WIRELESS
RADIO LINK
'JH 4FF 2VFTUJPO
'JH 4FF 2VFTUJPO
D #AN YOU
SUGGEST ANY AD
VANTAGES ANDOR
DISADVANTAGES OF
THE SYSTEM
IG
SHOWS A WAVE
FORM DIAGRAM
A 7HAT TYPE
OF WAVEFORM IS
SHOWN
B 7HAT IS THE AMPLITUDE OF THE
WAVEFORM
C 7HAT IS THE PERIOD OF THE WAVE
FORM
D 7HAT IS THE REPETITION FRE
QUENCY OF THE WAVEFORM
E 7HAT IS THE MARK
TO
SPACE
RATIO OF THE WAVEFORM
124. 56 Everyday Practical Electronics, November 2010
Teach-In 2011
2.% OF THE PROBLEMS WITH ELEC
TRONICS IS SIMPLY THE AMOUNT OF
KIT THAT YOU NEED TO GET STARTED %VEN
A BASIC STARTER SET
UP COULD RUN IN TO
HUNDREDS OF POUNDS SOLDERING IRON
134. A
FULL RANGE OF lVIRTUAL TEST EQUIPMENTm
ALONG WITH REAL
TIME SIMULATION AND
TOOLS TO HELP YOU ACTUALLY VISUAL
ISE THE OPERATION OF YOUR CIRCUITS
4HEREmS ALSO THE ABILITY TO BUILD
BREADBOARD CIRCUITS AND CONVERT
YOUR CIRCUITS INTO A PRINTED CIRCUIT
BOARD 0# DESIGN THAT CAN THEN BE
MANUFACTURED 7E REALLY FEEL THAT
ITmS THE IDEAL WAY TO GET STARTED WITH
ELECTRONICS
137. WE WILL GIVE
AWAY A GSFF #$
2/- CONTAINING A
lDEMOm VERSION OF THE #IRCUIT 7IZARD
3IMULATION
3TUDENTS OF ELECTRONICS ARE OFTEN
CONFUSED BY THE FACT THAT YOU CANmT
ACTUALLY SEE WHATmS GOING ON INSIDE
A CIRCUIT )N A MECHANICAL MACHINE
ITmS EASY TO SEE THINGS MOVING AND
WORKING
138. BUT WE HAVE NONE OF THESE
VISUAL CLUES WHEN WORKING ON AN
ELECTRONIC CIRCUIT
#OMPUTER SIMULATION NEATLY OVER
COMES THIS PROBLEM BY PROVIDING A
VISUAL REPRESENTATION OF WHATmS GOING
ON UNDER THE SURFACE 4HIS MIGHT IN
CLUDE THE ÛOW OF CURRENT IN WIRES
143. BEINGABLETOMAKEEFFECTIVEUSEOF
SOFTWARE TOOLS IS NOW A KEY SKILL FOR ANY
ASPIRINGELECTRONICENGINEERORHOBBYIST
! STANDARD LICENCE FOR #IRCUIT
7IZARD COSTS AROUND | AND CAN BE
PURCHASED FROM THE EDITORIAL OFÚCE OF
%0% q SEE THE 5+ SHOP ON OUR WEBSITE
WWWEPEMAGCOM URTHER INFORMA
TION CAN BE FOUND ON THE .EW 7AVE
#ONCEPTS WEBSITE WWWNEW
WAVE
CONCEPTSCOM 4HE DEVELOPER ALSO OF
FERS AN EVALUATION COPY OF THE SOFTWARE
THE SOFTWARE THAT WILL BE GSFF WITH 1
NEXT MONTH (OWEVER
150. WEmRE GOING TO
LOOK AT INSTALLING AND GETTING STARTED
WITH #IRCUIT 7IZARD )N FUTURE MONTHS
WE WILL BE USING THE SOFTWARE TO IN
VESTIGATE THE THEORY AND CIRCUITS THAT
YOU WILL MEET IN l,EARNm 7EmLL ALSO
DEVELOP ELECTRONIC DEVICES AND USE
#IRCUIT 7IZARD TO DESIGN AND PRODUCE
0#S SO THAT YOU CAN MAKE THE REAL
THINGØ
)NSTALLATION
)NSTALLATION OF #IRCUIT 7IZARD IS VERY
STRAIGHTFORWARD
151. AND ITmS A SURPRISINGLY
SMALL INSTALLATION FOR WHAT IS SUCH A
POWERFUL PIECE OF SOFTWARE /UR INSTALL
PROCESS TOOK NO MORE THAN QUARTER OF
AN HOUR FROM START TO ÚNISH $URING THE
INSTALLATION PROCESS YOUmLL BE ASKED TO
ENTER A LICENCE KEY WHICH WILL BE SUP
PLIED WITH YOUR INSTALL DISC
7HEN YOU RUN #IRCUIT 7IZARD FOR THE
ÚRST TIME YOU WILL BE ASKED TO OBTAIN A
RELEASE CODE
152. WHICH CAN BE DONE OVER
THE lPHONE OR VIA THE DEVELOPERmS WEB
SITE WHERE THE RELEASE CODE IS THEN SUB
SEQUENTLY E
MAILED TO YOU 4HIS NEEDS
TO BE DONE WITHIN A
DAY WINDOW OR
THE SOFTWARE WILL CEASE TO LOAD
IRSTªLOOKS
4HE USER INTERFACE IS BOTH CLEAN AND
INTUITIVE 4HE MAIN WHITE DRAWING
AREA ÚLLS MOST OF THE SCREEN
153. WITH THE
STANDARD 7INDOWS MENUS AND TOOLBAR
ACROSS THE TOP ! TABBED PANE ON THE
RIGHT
HAND SIDE OF THE SCREEN PRESENTS
A l'ETTING 3TARTEDm MENU
154. WHERE YOU
CAN ACCESS VARIOUS SAMPLESTUTORIALS
AND GAIN HELP
#LICKING THE l'ALLERYm TAB EXPOSES
AN EXTENSIVE LIBRARY OF COMPONENTS
AND TEST EQUIPMENT 4ABS ON THE FAR
LEFT OF THE SCREEN ALLOW YOU TO SEE YOUR
CIRCUIT IN VARIOUS DIFFERENT lVIEWSm
4HESE ARE DESIGNED TO HELP YOU SEE
WHATmS ACTUALLY GOING ON IN YOUR CIR
CUITS BY COLOURING ANDOR ANIMATING
THE CIRCUIT DIAGRAM TO SHOW VOLTAGES
CURRENTS
4HIS IS A REALLY NIFTY FEATURE
155. AL
LOWING YOU TO ACTUALLY SEE ELECTRON
ICS IN ACTION 4HERE ARE A NUMBER OF
PRESET VIEWS OR YOU CAN CREATE YOUR
OWN TO SUIT !LONG THE BOTTOM OF THE
SCREEN A ROW OF TABS ALLOWS YOU TO
CHANGE BETWEEN DIFFERENT PAGES OF
YOUR DESIGN
l$RAWINGm IS WHERE YOU WOULD AC
TUALLY ENTER AND SIMULATE A CIRCUIT
156. l0# ,AYOUTm IS WHERE YOU WOULD
PRODUCE A 0# DESIGN AS WELL AS
WORKING WITH VIRTUAL TEST EQUIPMENT
AND BREADBOARDS INALLY
157. lILL OF
-ATERIALSm GENERATES AN INVENTORY
COSTING OF THE COMPONENTS USED IN
YOUR CIRCUIT
INDINGªYOURªWAYªAROUND
Y FAR THE BEST WAY TO GET STARTED
WITH #IRCUIT 7IZARD IS TO FOLLOW THE
GUIDED TOUR SCREEN VIDEOS AND EX
PERIMENT WITH THE SAMPLE CIRCUITS
PROVIDED !LL OF THESE ARE DIRECTLY
ACCESSIBLE FROM THE l'ETTING 3TARTEDm
PAGE IN THE RIGHT
HAND PANE CLICK ON
'JH MPHJDCBTFE FMFDUSPOJD EJDF JO mMPHJD WJFXn TIPXJOH EJHJUBM TJHOBM MFWFMT BU FBDI QPJOU JO UIF DJSDVJU
'JH $JSDVJU 8J[BSEnT
(BMMFSZ PG DPNQPOFOUT BOE
UFTU FRVJQNFOU
158. 58 Everyday Practical Electronics, November 2010
Teach-In 2011
THE l!SSISTANTm TAB IF THE CIRCUIT GALLERY
VIEW IS SHOWN
4HE SCREEN VIDEOS EXPLAIN THE BASIC
OPERATION OF THE SOFTWARE BUT LACK
SOUND
159. WITH ONLY WRITTEN DESCRIPTIONS
APPEARING ON THE SCREEN THIS DOES
MAKE FOR SLOW PROGRESS )F YOUmRE A CON
ÚDENT COMPUTER USER YOU MAY WANT TO
JUST JUMP STRAIGHT IN AND EXPLORE OVER
ÚFTY SAMPLE CIRCUITS THAT ARE INCLUDED
AND GET TO KNOW THE SOFTWARE HANDS
ON
SOME SIMPLE CIRCUITS THAT WILL BE UN
DERPINNED BY THE THEORY COVERED IN OUR
l,EARNm SECTION 5NTIL THEN
160. YOU MIGHT
LIKE TO GET YOURSELF A COPY OF #IRCUIT
7IZARD AND HAVE A PLAYØ )F YOUmRE RE
ALLY KEEN TO GET STUCK IN
162. WHERE YOU CAN
DOWNLOAD SOME FURTHER EXAMPLES
'JH $JSDVJU 8J[BSE QSPWJEFT B
HPPE TFMFDUJPO PG TUBSUFS NBUFSJBMT
4HE SAMPLE CIRCUITS ARE SPLIT BY COM
PLEXITY INTO THREE FOLDERS SIMPLE
164. WHICH REALLY SHOWCASE THE EXTENSIVE
FEATURES OF THE SOFTWARE 4HE SAMPLE
CIRCUITS ARE EXCELLENT AND CONTAIN
INSTRUCTIONS ON HOW TO TEST OUT THE CIR
CUIT q THEYmRE ALSO REALLY EDUCATIONAL
165. SO YOU MIGHT EVEN LEARN SOMETHING
ABOUT ELECTRONICS AS YOU DISCOVER THE
SOFTWARE TOOØ
)N NEXT MONTHmS INSTALMENT
166. WEmLL
BE SHOWING YOU HOW TO ENTER AND TEST
:!6%/2-3 ARE USUALLY DIS
PLAYED USING AN INSTRUMENT
CALLED AN OSCILLOSCOPE 9OU WILL LEARN
MORE ABOUT THIS INSTRUMENT LATER IN
THE SERIES /SCILLOSCOPES CAN BE STAND
ALONE TEST INSTRUMENTS SEE IG OR
THEY CAN BE VIRTUAL INSTRUMENTS THAT
USE A 0#mS IN
BUILT SIGNAL PROCESSING
CAPABILITIES EG
167. THE ANALOGUE
TO
DIGITAL
CONVERTER IN A 0# SOUND CARD
IG SHOWS A TYPICAL VIRTUAL IN
STRUMENT DISPLAY OBTAINED BY USING A
SOUNDCARD OSCILLOSCOPE PROGRAM 4HE
PROGRAM RECEIVES ITS DATA FROM THE
COMPUTERmSSOUNDCARDWITHASAMPLING
RATE OF K(Z AND A RESOLUTION OF
BITS 4HE DATA SOURCE CAN BE SELECTED
BY THE 0#mS OWN SOUND CARD CONTROLS
EG
172. TRIANGLE AND SAWTOOTH
WAVEFORMS IN THE FREQUENCY RANGE FROM
TO K(Z 4HESE SIGNALS ARE AVAILABLE
AT THE SPEAKER OUTPUT OF THE SOUND CARD
4AKE A CAREFUL LOOK AT IG AND
USEITTOANSWERTHEFOLLOWINGQUESTIONS
A 7HAT TYPE OF WAVEFORM IS SHOWN
B 7HAT TOTAL TIME INTERVAL IS DIS
PLAYED ON THE SCREEN (INT LOOK AT THE
HORIZONTAL SCALE
C 7HAT SETTINGS ARE USED FOR THE
VERTICAL AND HORIZONTAL SCALES ON THE
OSCILLOSCOPE DISPLAY
D 7HAT IS THE GREATEST POSITIVE VOLT
AGE PRESENT IN THE WAVEFORM SAMPLE
E 7HAT IS THE GREATEST NEGATIVE VOLT
AGE PRESENT IN THE WAVEFORM SAMPLE
F 7HAT IS THE OVERALL PEAK
PEAK
VOLTAGE OF THE WAVEFORM
'JH 4FF UIF *OWFTUJHBUF RVFTUJPOT
4HEª#IRCUITª7IZARDªWAY
)NVESTIGATE
'JH UZQJDBM CFODI PTDJMMPTDPQF
173. Everyday Practical Electronics, November 2010 59
Teach-In 2011
!NSWERSªTOª1UESTIONS
!NALOGUE SIGNALS VARY CON
TINUOUSLY IN VOLTAGE AND CURRENT
WHILST DIGITAL SIGNALS CAN ONLY
EXIST IN DISCRETE LEVELS OF VOLTAGE
OR CURRENT
A !MPERE
184. G KILOBITS
PER SECOND
M6
-BPS
M!
K(Z
6
%- IS USED TO DESCRIBE
THE OUTPUT VOLTAGE PRODUCED BY A
BATTERY OR POWER SUPPLY 0OTENTIAL
DIFFERENCE IS USED TO DESCRIBE THE
VOLTAGE DROP THAT APPEARS ACROSS A COM
PONENT SUCH AS A RESISTOR OR CAPACITOR
0RIMARY CELLS PRODUCE ELEC
TRICAL ENERGY FROM A NON
REVERSIBLE
CHEMICAL REACTION AND MUST BE DIS
POSED OF WHEN EXHAUSTED 3ECONDARY
CELLS MAKE USE OF A REVERSIBLE CHEMI
CAL REACTION AND CAN BE RECHARGED AND
USED AGAIN
A 7IRELESS DATA LINK BETWEEN
COMPUTER SYSTEMS
185. B ! DIGITAL
ANALOGUE # ANALOGUE $ ANALOGUE
% ANALOGUE DIGITAL
193. E
!MAZE
$OWNLOAD A COPY OF THE 3OUNDCARD
/SCILLOSCOPE SOFTWARE AND INVESTIGATE
THE OPERATION OF THE PROGRAM USING
SOME TYPICAL SIGNALS APPLIED TO THE
MICROPHONE OR AUXILIARY INPUTS OF A
0# 4HE SOFTWARE IS AVAILABLE FROM
#HRISTIAN :EITNITZmS WEBSITE HTTP
WWWZEITNITZDE#HRISTIANSCOPE?EN
.EXTªMONTH
)N NEXT MONTHmS 5FBDI*O WE
SHALL BE LOOKING AT RESISTORS AND CA
PACITORS%XAMPLESOFTHESETWOPASSIVE
COMPONENTS ARE FOUND IN ALMOST EVERY
ELECTRONIC CIRCUIT URTHERMORE
195. THESE TWO COMPONENTS
FORM THE BASIS OF A WIDE RANGE OF ELEC
TRONIC TIMING AND DELAY CIRCUITS
7E SHALL BE INVESTIGATING THE BE
HAVIOUR OF THESE CIRCUITS USING #IRCUIT
7IZARD
For more information, links and
other resources please check
out our Teach-In website at:
www.tooley.co.uk/
teach-in
www.technobotsonline.com
TechnobotsElectronic Mechanical Components
With over 5,100 products available to order online, Technobots
provides one of the widest range of components for the
Shop callers welcome: Technobots Ltd, 60 Rumbridge Street,
Totton, Hampshire SO40 9DS Tel: 023 8086 4891
Get our 120 page A4 catalogue free with your
next order by quoting 'discount coupon code'
EPE05 at the checkout
Battery Products
Chargers PSU's
Opto Electronics
Gears, Pulleys
Cams
Controller Boards
Including Arduino
Chain sprockets
Breakout Boards
from Sparkfun
Bearings from 1mm bore
Switches
Relays
Projects kits
Robotics Wheels
LCD displays
Pneumatics Shafts
Adaptors
Tools
Cable, Fuses etc..
160+ dc model
motors + speed
controllers
Passsives,
Semiconductors
Sensors
connectors
etc..
Education Accounts
W
elcome
196. 50 Everyday Practical Electronics, December 2010
Teach-In 2011
By Mike and Richard Tooley
0ARTªª2ESISTORS
215. %XAMPLE
! CURRENT OF M! ÛOWS IN A :
RESISTOR 7HAT POTENTIAL DIFFERENCE
APPEARS ACROSS THE RESISTOR
ROM /HMmS ,AW
7 * ¯ 3 ¯ 6
.OTE THAT M! IS THE SAME AS
!
7($+,1
$ %52$'%$6(' ,1752'87,21
72 (/(7521,6
,
. THIS PART OF 4EACH
)N WE WILL
INTRODUCE YOU TO RESISTORS
217. TIMING AND DELAY CIRCUITS 7E
WILL ALSO USE #IRCUIT 7IZARD TO INVES
TIGATE /HMmS ,AW AS WELL AS ÚNDING
OUT WHAT HAPPENS IN A CIRCUIT WHEN A
CAPACITOR IS CHARGED AND DISCHARGED
,EARN
APPEAR ACROSS A RESISTANCE OF : WHEN
A CURRENT OF ! ÛOWS IN IT
2ESISTANCE CAN BE THOUGHT OF AS
AN OPPOSITION TO THE ÛOW OF ELECTRIC
CURRENT 4HE AMOUNT OF CURRENT THAT
WILL ÛOW IN A CIRCUIT WHEN A GIVEN
ELECTROMOTIVE FORCE %- IS APPLIED
TO IT IS INVERSELY PROPORTIONAL TO ITS
RESISTANCE )N OTHER WORDS
224. CURRENT IN AMPS
! AND RESISTANCE IN OHMS :
! POTENTIAL DIFFERENCE OF 6 WILL
worldmagsworldmags
worldmags
225. Everyday Practical Electronics, December 2010 51
Teach-In 2011
%XAMPLE
7HAT CURRENT WILL ÛOW WHEN A :
RESISTOR IS CONNECTED TO A 6 BATTERY
2EARRANGING THE FORMULA TO MAKE *
THE SUBJECT GIVES
4YPESªOFªRESISTOR
6ARIOUS TYPES OF ÚXED
236. PRESET AND VARIABLE RESIS
TORS HAVE ONLY TWO TERMINALS WHILE
POTENTIOMETERS EITHER PRESET OR
ROTARY TYPES HAVE THREE TERMINALS
.OTE ALSO THAT A PRESET OR VARIABLE
POTENTIOMETER CAN BE USED AS A VARI
ABLE RESISTOR BY SIMPLY IGNORING ONE
OF ITS END TERMINALS
237. OR
BY CONNECTING ITS MOVING
CONTACT TO ONE OF ITS OUTER
TERMINALS 4YPICAL CIRCUIT
SYMBOLS FOR VARIOUS TYPES
OF RESISTOR ARE SHOWN IN
IG
4HE SPECIÚCATIONS FOR
A RESISTOR USUALLY INCLUDE
THE VALUE OF RESISTANCE
EXPRESSED IN :
239. THE ACCURACY OR TOLER
ANCE OF THE MARKED VALUE
QUOTED AS THE MAXIMUM
PERMISSIBLE PERCENTAGE
DEVIATION FROM THE MARKED
'JH 7BSJPVT UZQFT PG SFTJTUPS
JODMVEJOH ÜYFE
QSFTFU BOE WBSJBCMF UZQFT
%XAMPLE
! CURRENT OF M! ÛOWS IN A RE
SISTOR WHEN IT IS CONNECTED TO A 6
POWER SUPPLY 7HAT IS THE VALUE OF
THE RESISTANCE
2EARRANGING THE FORMULA TO MAKE
3 THE SUBJECT GIVES
.OTE THAT M! IS THE SAME AS
!
'JH TJNQMF DJSDVJU JO XIJDI B CBUUFSZ TVQQMJFT
DVSSFOU UP B SFTJTUPS
'JH $JSDVJU TZNCPMT VTFE GPS
SFTJTUPST
9
,
5
P$$
9
5
,
: : : N:
worldmagsworldmags
worldmags
255. ¯K AND ¯- OF THE BASIC SERIES !
FURTHER SERIES % PROVIDES FOR RESIS
TORS WITH A TOLERANCE OF ‰
#ARBON AND METAL OXIDE RESISTORS ARE
NORMALLY MARKED WITH COLOUR CODES
THAT INDICATE THEIR VALUE AND TOLER
ANCE 3EE IG AND IG FOR THE
COLOUR CODES
2ELATIONSHIP BETWEEN VOLTAGE
262. * IS
THE CURRENT IN ! AND 7 IS THE VOLT
AGE IN 6
7E CAN COMBINE THIS RELATIONSHIP
WITH THE /HMmS LAW EQUATION THAT WE
MET EARLIER IN ORDER TO ARRIVE AT THE
FOLLOWING USEFUL EXPRESSIONS
%XAMPLE
7HAT POWER IS DISSIPATED IN A RE
SISTOR OF K: WHEN A VOLTAGE OF 6
APPEARS ACROSS IT
5SING THE PREVIOUS FORMULA GIVES
4ABLEªª4HEª%
265. Everyday Practical Electronics, December 2010 53
Teach-In 2011
CHARGE 4HEY ARE WIDELY USED IN POWER
SUPPLIES WHERE THEY ACT AS lRESERVOIRSm
FOR CHARGE AND ALSO IN MANY TIMING AND
WAVE
SHAPING CIRCUITS #APACITORS WILL
PASS ALTERNATING CURRENTS
266. BUT THEY WILL
lBLOCKm DIRECT CURRENT ONCE CHARGED
4HEY ARE THUS USED FOR COUPLING
SIGNALS WHICH ARE !# IN AND OUT OF
AMPLIÚER STAGES
4HE SPECIÚCATIONS FOR A CAPACITOR
USUALLY INCLUDE THE VALUE OF CAPACI
TANCE EXPRESSED IN
272. THE MAXIMUM EXPECTED VOLTAGE
APPLIED TO THE CAPACITOR #APACITORS
ARE USUALLY AVAILABLE WITH VALUES IN
THE % SERIES SEE 4ABLE
0LEASE NOTEØ
,ARGE VALUE CAPACITORS OFTEN USE
A CHEMICAL DIELECTRIC MATERIAL
273. AND
THEY REQUIRE THE APPLICATION OF A $#
POLARISINGª VOLTAGE IN ORDER TO WORK
#APACITORS
#APACITORS STORE ENERGY IN THE FORM
OF AN ELECTRIC ÚELD 7HEN A POTENTIAL
DIFFERENCE IS APPLIED TO TWO CONDUCT
ING PLATES AN ELECTRIC CHARGE WILL AP
PEAR ON THE PLATES AND AN ELECTRIC ÚELD
WILL APPEAR BETWEEN THE PLATES 4HE
ÚELD CAN BE CONCENTRATEDINTENSIÚED
BY PLACING AN INSULATING MATERIAL SUCH
AS POLYESTER ÚLM
274. MICA OR A CERAMIC
MATERIAL BETWEEN THE PLATES 4HIS MA
TERIAL IS KNOWN AS A DIELECTRIC
275. AND ITS
ELECTRICAL PROPERTIES HELP TO INCREASE
THE CAPACITANCE OF THE COMPONENT
SEE IG
#APACITORS PROVIDE US WITH A MEANS
OF STORING AND CONSERVING ELECTRIC
'JH 7BSJPVT UZQFT PG DBQBDJUPS
JODMVEJOH ÜYFE
QSFTFU BOE WBSJBCMF UZQFT
'JH #BTJD BSSBOHFNFOU PG B QBSBMMFM QMBUF DBQBDJUPS 'JH 4ZNCPMT VTFE GPS DBQBDJUPST
worldmagsworldmags
worldmags
276. 54 Everyday Practical Electronics, December 2010
Teach-In 2011
PROPERLY 4HIS VOLTAGE MUST BE APPLIED
WITH THE CORRECT POLARITY INVARIABLY
THIS IS CLEARLY MARKED ON THE CASE OF
THE CAPACITOR WITH A POSITIVE SIGN
OR NEGATIVE q SIGN OR A COLOURED STRIPE
OR OTHER MARKING AILURE TO OBSERVE
THE CORRECT POLARITY CAN RESULT IN OVER
HEATING
289. TO STORE
A LARGE AMOUNT OF ENERGY WE NEED A
CORRESPONDINGLY LARGER VALUE OF CA
PACITANCE FOR A GIVEN VALUE OF CHARGING
VOLTAGE 4HE FOLLOWING RELATIONSHIP
APPLIES
8 • $ 7
WHERE $ IS THE VALUE OF CAPACITANCE
IN
291. AND
8 IS THE STORED ENERGY IN JOULES
%XAMPLE
$ETERMINE THE CHARGE STORED IN A
CAPACITOR WHEN IT IS CHARGED TO
A POTENTIAL OF 6
4HE STORED ENERGY WILL BE GIVEN BY
PARTICULARLY IF THEY ARE HIGH
VOLTAGE
TYPES UNTIL YOU ARE CERTAIN THAT THE
CAPACITORS ARE FULLY DISCHARGED 3OME
CIRCUITS INCORPORATE lBLEEDm RESISTORS TO
SAFELY DISCHARGE LARGE VALUE CAPACITORS
WHEN THE EQUIPMENT IN WHICH THEY ARE
USED HAS BEEN SWITCHED OFF
#
2ªCIRCUITSª CHARGEªANDª
DISCHARGE
%ARLIER
292. WE MENTIONED THAT A CA
PACITOR IS A DEVICE FOR STORING ELECTRIC
CHARGE 4HIS CHARGE CAN BE STORED IN A
CAPACITOR BY CONNECTING IT TO A BATTERY
OR POWER SUPPLY VIA A SERIES RESISTOR
294. THE STORED CHARGE CAN BE DRAINED
AWAY BY CONNECTING A RESISTOR IN PARAL
LEL WITH THE CAPACITOR !FTER A PERIOD
OF TIME THERE WILL THEN BE NO CHARGE
REMAINING IN THE CAPACITOR
4HE TIME THAT IT TAKES TO CHARGE AND
DISCHARGE A CAPACITOR DEPENDS ON THE
VALUES OF CAPACITANCE AND RESISTANCE
295. AND THIS MAKES CAPACITORS IDEAL FOR USE
IN TIMING AND DELAY CIRCUITS ECAUSE
THIS IS SO IMPORTANT
296. ITmS WORTH LOOKING
AT THIS IN A LITTLE MORE DETAIL
3IMPLE CHARGING AND DISCHARGING
ARRANGEMENTS ARE SHOWN IN IG
)N THE CHARGING ARRANGEMENT SHOWN
IN IGA
297. THE CAPACITOR IS INITIALLY
UNCHARGED AND CURRENT WILL FLOW
AND CHARGE WILL BUILD UP INSIDE THE
CAPACITOR
298. QUICKLY AT ÚRST AND THEN
MORE SLOWLY
!S THE CAPACITOR BECOMES CHARGED
301. TO THE VOLTAGE OF
THE SUPPLY 73 !T THAT POINT WHEN
7# IS APPROXIMATELY EQUAL TO 73 WE
SAY THAT THE CAPACITOR IS FULLY CHARGED
4 9
WHERE 2 IS THE CHARGE IN COULOMBS
303. AND 7
IS THE POTENTIAL DIFFERENCE IN VOLTS
%XAMPLE
$ETERMINE THE CHARGE STORED IN A
CAPACITOR WHEN IT IS CHARGED TO
A POTENTIAL OF 6
4HE CHARGE STORED WILL BE GIVEN BY
%NERGYªSTORAGE
! CHARGED CAPACITOR ACTS AS A RESER
VOIR FOR CHARGE AND THE STORED ENERGY
CAN BE PUT TO GOOD USE SOME TIME
LATER 4HE AMOUNT OF ENERGY STORED IN
A CAPACITOR DEPENDS ON THE PRODUCT
'JH DBQBDJUPS DIBSHJOHEJTDIBSHJOH BSSBOHFNFOU
0LEASE NOTEØ
4HE ENERGY STORED IN A CAPACITOR IS
PROPORTIONAL TO THE SQUARE OF THE PO
TENTIAL DIFFERENCE BETWEEN ITS PLATES
4HUS
304. IF THE POTENTIAL DIFFERENCE IS
DOUBLED THE ENERGY STORED WILL IN
CREASE BY A FACTOR OF FOUR ,IKEWISE
306. THE STORED ENERGY WILL
INCREASE BY A FACTOR OF
0LEASE NOTEØ
! CHARGED CAPACITOR CAN REMAIN IN A
PARTIALLY CHARGED STATE FOR A VERY LONG
TIME IF THERE IS NO PATH FOR THE STORED
CHARGE TO DRAIN AWAY )TmS THEREFORE
IMPORTANT TO AVOID WORKING ON A CIR
CUIT THAT USES LARGE VALUE CAPACITORS
: ò 9
ò î î
î
î î
-
4 9 î
î
î
î
PP
worldmagsworldmags
worldmags
314. AND FOR THIS REASON WE SAY
THAT THE CAPACITOR IS FULLY DISCHARGED
AFTER A TIME INTERVAL EQUAL TO ÚVE TIMES
THE TIME CONSTANT 5 OR $3
%XAMPLE
! $3 CIRCUIT CONSISTS OF $
AND 3 -:
A 7HAT IS THE TIME CONSTANT OF THE
CIRCUIT
B )F THE CAPACITOR IS INITIALLY UN
CHARGED
315. HOW LONG WILL IT TAKE TO FULLY
CHARGE THE CAPACITOR
A 4HE TIME CONSTANT IS GIVEN BY
5 $3 ¯ -: SECONDS
.OTE THAT IF WE WORK IN AND -:
THE TIME CONSTANT WILL BE EXPRESSED
DIRECTLY IN SECONDS
B 4HE CAPACITOR WILL BE APPROXI
MATELY FULLY CHARGED AFTER 5 OR ¯
OR SECONDS
0LEASE NOTEØ
4HE VOLTAGE ACROSS THE PLATES OF A
CHARGINGCAPACITORGROWSEXPONENTIALLY
NOT LINEARLYØ AT A RATE DETERMINED BY
THE TIME CONSTANT OF THE CIRCUIT #ON
VERSELY
316. THEVOLTAGEACROSSTHEPLATESOFA
DISCHARGING CAPACITOR DECAYS EXPONEN
TIALLY NOTLINEARLYØ ATARATEDETERMINED
BY THE TIME CONSTANT OF THE CIRCUIT
! GRAPH SHOWING HOW THE CAPACITOR
VOLTAGE 7# INCREASES WITH TIME IS
SHOWNINIG4HISGRAPHISKNOWN
AS AN EXPONENTIALªGROWTH CURVE
4HE SPEED AT WHICH THE CAPACITOR
BECOMES CHARGED DEPENDS ON THE TIME
CONSTANT
323. AND
5 IS THE TIME CONSTANT IN SECONDS
9OU MIGHT NOW BE WONDERING HOW
LONG IT TAKES TO GVMMZ CHARGE THE CAPACI
TOR 4HE TRUE ANSWER IS THAT THE CAPACI
TOR VOLTAGE NEVER QUITE REACHES THE SUP
PLY VOLTAGE
324. EVEN IF YOU WAIT FOR A WFSZ
LONG TIME (OWEVER
326. AND FOR THIS REASON WE
SAY THAT THE CAPACITOR IS FULLY CHARGED
AFTER A TIME INTERVAL EQUAL TO ÚVE TIMES
THE TIME CONSTANT 5 OR $3
)NTHEDISCHARGINGARRANGEMENTSHOWN
INIGB
330. TO ZERO 6 !T THAT
POINT WHEN 7# IS APPROXIMATELY EQUAL
TO 6
331. WE SAY THAT THE CAPACITOR IS FULLY
DISCHARGED ! GRAPH SHOWING HOW THE
CAPACITOR VOLTAGE 7# DECREASES WITH
TIME IS SHOWN IN IG 4HIS GRAPH IS
KNOWN AS AN EXPONENTIALªDECAY CURVE
'JH (SBQI PG DBQBDJUPS WPMUBHF BHBJOTU UJNF GPS UIF
DIBSHJOH DJSDVJU
'JH (SBQI PG DBQBDJUPS WPMUBHF BHBJOTU UJNF GPS UIF
EJTDIBSHJOH DJSDVJU
Circuit Wizard
A Standard or Professional version
of Circuit Wizard can be purchased
from the editorial office of EPE – see
CD-ROMs for Electronics page and
the UK shop on our website (www.
epemag.com) for a ‘special offer’.
Further information can be found
on the New Wave Concepts website;
www.new-wave-concepts.com.The
developer also offers an evaluation
copy of the software that will operate
for 30 days, although it does have
some limitations applied, such as only
being able to simulate the included
sample circuits and no ability to save
yourcreations,thisisthesoftwarethat
is free with EPE this month.
However, if you’re serious about
electronics and want to follow our
series, then a full copy of Circuit
Wizard is a really sound investment.
Virtually fully
discharged
worldmagsworldmags
worldmags
332. 56 Everyday Practical Electronics, December 2010
Teach-In 2011
,. 4()3 MONTHmS l,EARNm SECTION
WEmVE INTRODUCED YOU TO THE
BASICS OF RESISTORS AND CAPACITORS
!LMOST ALL ELECTRONIC CIRCUITS WILL
CONTAIN ONE OR BOTH OF THESE TYPES OF
COMPONENTS
333. SO ITmS REALLY IMPORTANT
THAT WE UNDERSTAND WHAT THEY DO
AND HOW THEY WORK
%LECTRONICS TEXT BOOKS OFTEN HAVE
LENGTHY AND CONFUSING EXPLANATIONS
WITH LOTS OF MATHEMATICAL FORMULAE
(OWEVER
334. THE BEST WAY TO REALLY GET
TO GRIPS WITH WHATmS GOING ON IS TO
EXPERIMENT WITH SOME SIMPLE CIR
CUITS 7E ARE GOING TO LOOK AT A FEW
OF THE SAMPLE CIRCUITS INCLUDED WITH
#IRCUIT 7IZARD
335. AS WELL AS GIVING YOU
SOME NEW CIRCUITS TO ENTER AND TRY
OUT FOR YOURSELF
/HM Sª,AWªINªPRACTICE
4O START WITH
336. WEmLL HAVE A LOOK
AT /HMmS ,AW IN PRACTICE /PEN THE
l/HMmS ,AWm SAMPLE CIRCUIT FROM
THE !SSISTANT PANEL ON THE RIGHT
HAND SIDE OF THE SCREEN BY SELECTING
l3AMPLE #IRCUITSm
337. THEN l%LEMENTARY
#IRCUITSm AND SCROLLING DOWN TO THE
l%LECTRICAL 4HEORYm SECTION
4HE CIRCUIT SEE IG IS ABOUT
AS SIMPLE AS IT COMES WITH A POWER
SOURCE A 6 00 BATTERY AND A
VARIABLE RESISTOR 7E ALSO HAVE TWO
MULTIMETERS ONE TO SHOW THE VOLT
AGE ACROSS THE RESISTOR AND ONE TO
SHOW THE CURRENT ÛOWING THROUGH IT
3IMULATION
0RESS THE PLAY BUTTON FOUND ON
THE TOOLBAR TO ACTIVATE THE SIMULA
TION 9OU SHOULD SEE VALUES APPEAR
ING ON THE MULTIMETERS
.OW TRY CHANGING THE VALUE OF THE
VARIABLE RESISTOR 62 BY CLICKING
ON THE END OF THE SHAFT q THE MOUSE
POINTER WILL CHANGE TO A POINTED
ÚNGER WHEN YOUmRE IN THE RIGHT
PLACE 9OUmLL THEN BE PRESENTED WITH
A VIRTUAL KNOB THAT YOU CAN TURN TO
THE DESIRED VALUE
.OTICE THAT AS YOU INCREASE THE
RESISTANCE
338. THE CURRENT FLOWING
THROUGH IT REDUCES AND WJDF WFSTB
.OTE THAT THE READINGS FOR CURRENT
ARE IN MILLIAMPS M!
4O TRY OUT THE THEORY THAT WE INTRO
DUCED
339. CHECK THE VALUES FOR VOLTAGE
AND CURRENT WHEN THE VARIABLE RESIS
TOR IS AT
341. AND CHECK THAT THEY OBEY /HMmS LAW
#HECKªnª(OWªDOªYOUªTHINKªYOUªAREªDOING
%XPLAIN BRIEÛY WHAT IS MEANT BY
RESISTANCE 7HAT UNITS ARE USED FOR
RESISTANCE AND WHAT SYMBOL IS USED
TO DENOTE THESE UNITS
%XPLAIN BRIEÛY WHAT IS MEANT
BY CAPACITANCE 7HAT UNITS ARE USED
FOR CAPACITANCE AND WHAT SYMBOL IS
USED TO DENOTE THESE UNITS
! CURRENT OF ! ÛOWS IN A :
RESISTOR 7HAT POTENTIAL DIFFERENCE
APPEARS ACROSS THE RESISTOR
7HAT CURRENT WILL ÛOW WHEN
A : RESISTOR IS CONNECTED TO A 6
BATTERY
! CURRENT OF M! ÛOWS IN A
RESISTOR WHEN IT IS CONNECTED TO A 6
POWER SUPPLY 7HAT IS THE VALUE OF
THE RESISTANCE
! VOLTAGE DROP OF 6 APPEARS
ACROSS A : RESISTOR 7HAT POWER IS
DISSIPATED IN THE RESISTOR
! RESISTOR IS RATED AT :
342. 7 7HAT IS THE MAXIMUM VOLT
AGE THAT CAN BE SAFELY APPLIED TO THIS
RESISTOR
! CAPACITOR IS
CHARGED TO A POTENTIAL OF 6
7HAT CHARGE IS PRESENT
'JH 4FF RVFTUJPO
! CHARGE OF # IS HELD IN A
N CAPACITOR 7HAT POTENTIAL AP
PEARSACROSSTHEPLATESOFTHECAPACITOR
! CHARGE OF # IS TO BE
PLACED ON THE PLATES OF A CAPACITOR
OF N 7HAT VOLTAGE IS NEEDED TO
DO THIS
! RESISTANCE OF K: IS CON
NECTED TO A CAPACITOR OF 7HAT
IS THE TIME CONSTANT OF THIS CIRCUIT
AND HOW LONG WILL IT TAKE FOR THE
CAPACITOR TO BECOME APPROXIMATELY
FULLY CHARGED
7HAT COMPONENTS ARE REPRE
SENTED BY THE CIRCUIT SYMBOLS SHOWN
IN IG
7HAT TYPE OF COMPONENT IS
SHOWN IN IG
'JH 4FF RVFTUJPO
ªªUILDªn ª
! RESISTOR IS MARKED WITH THE FOL
LOWING COLOURED BANDS BROWN
345. SILVER 7HAT IS THE VALUE OF THE
RESISTOR AND WHAT IS ITS TOLERANCE
! RESISTOR OF : AT ‰ IS
REQUIRED 7HAT SHOULD BE THE COLOUR
CODE FOR THIS COMPONENT
For more information,
links and other resources
please check out our
Teach-In website at:
www.tooley.co.uk/
teach-in
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346. Everyday Practical Electronics, December 2010 57
Teach-In 2011
#APACITORSªINªACTION
.OW WEmLL TAKE A LOOK AT CAPACITORS
IN ACTION /PEN l#APACITOR #HARGINGm
BY SELECTING 3AMPLE #IRCUITS
348. WHICH
SHOWS A VIRTUAL REPRESENTATION OF THE
'JH 5IF DBQBDJUPSDIBSHJOH TBNQMF DJSDVJU
#ALCULATE THE TIME CONSTANT
FOR THE CIRCUIT USING THE
VALUES OF $ AND 3 AND THEN
350. DRAW A VERTICAL
LINE UP FROM THAT VALUE ON THE
GRAPH FROM THE POINT AT WHICH
IT STARTED TO CHARGE AND READ
OFF THE VOLTAGE AT THIS POINT
$OES IT AGREE WITH WHAT YOU
WOULD EXPECT
4HE LAST SAMPLE CIRCUIT
THAT WEmLL LOOK AT IS A PRACTI
CAL APPLICATION OF CHARGING A
CAPACITOR /PEN l4RANSISTOR
4IMERm FROM l3AMPLE #IRCUITSm
FOUND UNDER lASIC #IRCUITSm
351. l'ENERALm 4HE CIRCUIT USES
A CAPACITOR TO CREATE A TIME
DELAY BEFORE THE BULB IS IL
LUMINATED )T DOES THIS BY
USING A PAIR OF TRANSISTORS
ACTING LIKE A SWITCH 7EmLL BE
LOOKING AT TRANSISTORS IN MORE
DETAIL IN SUBSEQUENT 4EACH
)N
EDITIONS
CIRCUIT
352. ALONG WITH AN OSCILLOSCOPE
SHOWING THE VOLTAGE ACROSS A
CAPACITOR #
3TART SIMULATING THE CIRCUIT AND
KEEP AN EYE ON THE lDOTm ON THE OSCIL
LOSCOPE SCREEN 7ATCH HOW IT RISES AS
THE CAPACITOR CHARGES /NCE THE TRACE
HAS LEVELLED OFF
353. ÛICK THE SWITCH TO START
DISCHARGING THE CAPACITOR AND AGAIN
WATCH THE OSCILLOSCOPE SCREEN TO SEE
HOW THE VOLTAGE FALLS WITH TIME
#IRCUITªDIAGRAM
4O SEE THE SCHEMATIC LAYOUT FOR
THE CIRCUIT
354. SWITCH TO THE l#IRCUIT
$IAGRAMm VIEW USING THE TABS ON THE
BOTTOM OF THE SCREEN 3TART THE SIMU
LATION AGAIN AND CONTROL THE SWITCH
TO ALLOW THE CAPACITOR TO CHARGE AND
DISCHARGE
4HE VOLTAGE ACROSS THE CAPACITOR IS
THEN PLOTTED ON THE GRAPH IN REAL TIME
#IRCUIT 7IZARD ALSO DEMONSTRATES THE
CHARGE BUILDING UP ON THE PLATES OF
THE CAPACITOR WITH BLUERED lPLUSSESm
AND lMINUSESm
)N l,EARNm WE SHOWED HOW TO CALCU
LATE THE TIME PERIOD USING THE FORMULA
5 $3
WHICH IS WHEN THE VOLTAGE
ACROSS THE CAPACITOR HAS REACHED
OF THE SUPPLY VOLTAGE AROUND
6 IN THIS CASE /NCE YOU HAVE A
NICE LOOKING PLOT FOR CHARGING AND
DISCHARGING
356. 58 Everyday Practical Electronics, December 2010
Teach-In 2011
3TART THE SIMULATION AND TEST THE
CIRCUITmS OPERATION !S THE CAPACITOR
CHARGES THE VOLTAGE ACROSS IT INCREASES
/NCE THE VOLTAGE REACHES A CERTAIN
VALUE THE TRANSISTORS lTURN ONm
357. ALLOW
ING CURRENT TO ÛOW FROM THE POSITIVE OF
THE BATTERY THROUGH THE BULB TO GROUND
6 AND THEREFORE LIGHTING IT
4HE LONGER IT TAKES FOR THE CAPACITOR
TO CHARGE
358. THE LONGER THE DELAY WILL BE
)S THE CAPACITOR BEING CHARGED OR
DISCHARGED
ªROM THE GRAPH
359. ESTIMATE THE TIME
CONSTANT OF THE $3 CIRCUIT (INT 4AKE
A LOOK AT IGØ
ªª4HEª#IRCUITª7IZARDªWAY
'JH (SBQI PG DBQBDJUPS WPMUBHF QMPUUFE BHBJOTU UJNF
XIJDI TIPXT ÜSTU
DIBSHF BOE UIFO EJTDIBSHF
BEFORE THE BULB LIGHTS 4HE CAPACITOR
CHARGES THROUGH THE VARIABLE RESISTOR
62 4HEREFORE
360. BY CHANGING THE
VALUE OF THE RESISTOR WE CAN CHANGE
HOW FAST THE CAPACITOR CHARGES AND
HENCE SET THE DELAY )TmS A BIT LIKE TURN
ING A TAP TO CHANGE HOW FAST YOU ÚLL
UP A BUCKET OF WATER 4RY SETTING THE
VARIABLE RESISTOR SO THAT THERE IS A TWO
SECOND DELAY BEFORE THE BULB LIGHTS
4HE DATA SHOWN IN 4ABLE WAS OBTAINED DURING AN EXPERIMENT ON A $3
CIRCUIT 5SE THIS DATA TO PLOT A GRAPH SHOWING HOW THE CAPACITOR VOLTAGE VARIES
WITH TIME AND THEN USE THE GRAPH TO ANSWER THE FOLLOWING QUESTIONS
)NVESTIGATE
ª)F THE VALUE OF 3 IS -:DETERMINE
THE VALUE OF $
ª(OW MUCH ENERGY IS STORED IN THE
CAPACITOR AT THE START OF THE EXPERIMENT
AND WHERE DOES THIS ENERGY GO
4ABLEªªª4ABLEªOFªRESULTSªFORªTHEªEXPERIMENTALª#
2ªCIRCUIT
Time (s) 0 5 10 15 20 25 30
Capacitor
Voltage 15.0 7.4 3.6 1.8 0.9 0.4 0.2
(V)
!MAZE
#APACITORS NORMALLY COME IN VERY
SMALL VALUES OR EXAMPLE A P CA
PACITOR HAS A VALUE OF
FARADS q THATmS A PRETTY SMALL NUMBERØ
)N FACT
361. A ONE FARAD CAPACITOR IS ENOR
MOUS RELATIVELY SPEAKING
7HATmS THE LARGEST VALUE CAPACITOR
THAT YOU CAN ÚND 4RY LOOKING AT HOW
CAPACITORS ARE USED IN SOME OF THE MOST
ELABORATE CAR AUDIO SYSTEMS
376. RED
.EXT MONTHØ
)N NEXT MONTHmS 4EACH
)N WE SHALL BE
LOOKING AT DIODES AND POWER SUPPLIES
'JH TFMFDUJPO PG DBQBDJUPST UIBU
QSPWJEF TPNF FYUSFNFMZ MBSHF WBMVFT
PG DBQBDJUBODF
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377. HandsOn Technology
http://www.handsontec.com
ISP to ICP Programming Bridge: HT-ICP200
In-Circuit-Programming (ICP) for P89LPC900
Series of 8051 Flash ȝControllers. ICP uses a
serial shift protocol that requires 5 pins to
program: PCL, PDA, Reset, VDD and VSS.
ICP is different from ISP (In System
Programming) because it is done completely
by the microcontroller’s hardware and does
not require a boot loader.
Program whole series of P89LPC900
µController from NXP Semiconductors…
USB-RS232 Interface Card: HT-MP213
A compact solution for missing ports…
Thanks to a special integrated circuit from Silicon
Laboratories, computer peripherals with an RS232
interface are easily connected to a USB port. This
simple solution is ideal if a peripheral does not have a
USB port, your notebook PC has no free RS232 port
available, or none at all !
Classic P89C51 Development/Programmer Board: HT-MC-02
HT-MC-02 is an ideal platform for small to
medium scale embedded systems
development and quick 8051 embedded
design prototyping.
HT-MC-02 can be used as stand-alone
8051ȝC
Flash programmer or as a development,
prototyping, industry and educational
platform.
For professional, hobbyists…
378. 48 Everyday Practical Electronics, January 2011
Teach-In 2011
By Mike and Richard Tooley
0ARTªª$IODESªANDª0OWERª
3UPPLIES
/URª4EACH
)NªSERIESªISªDESIGNEDªTOªPROVIDEªYOUªWITHªAªBROAD
BASEDªINTRODUCTIONªTOªELECTRONICSª7EªHAVEªª
ATTEMPTEDªTOªPROVIDEªCOVERAGEªOFªTHREEªOFªTHEªMOSTªIMPORTANTªELECTRONICSªUNITSªTHATªAREªCURRENTLYªSTUDIEDªINª
MANYªSCHOOLSªANDªCOLLEGESªINªTHEª5+ª4HESEªINCLUDEª%DEXCELª4%#ª,EVELªªAWARDS
388. WHILE THAT TO THE O
TYPE
MATERIAL IS CALLED THE CATHODEª K
389. AS
SHOWN IN IG
ORWARDªANDªREVERSEªBIAS
)F THE ANODE OF A DIODE IS MADE
POSITIVE WITH RESPECT TO THE CATHODE
AND PROVIDED THAT THE RELATIVELY
SMALL CONDUCTION THRESHOLD VOLTAGE
IS EXCEEDED THE DIODE WILL FREELY
PASS CURRENT 4HIS CONDITION IS SHOWN
IN IG A AND IT IS REFERRED TO AS
FORWARDªBIAS
#ONVERSELY
390. WHEN THE CATHODE OF A
DIODE IS MADE POSITIVE WITH RESPECT
TO THE ANODE
391. THE DIODE WILL CEASE
TO CONDUCT 4HIS CONDITION IS SHOWN
IN IG B AND IT IS REFERRED TO AS
REVERSEª BIAS )N THE REVERSE
BIASED
CONDITION THE DIODE PASSES A NEGLIGIBLE
7($+,1
$ %52$'%$6(' ,1752'87,21
72 (/(7521,6
,EARN
INCLUDINGCONVERTINGALTERNATINGCURRENT
!# TO DIRECT CURRENT $#
! DIODE IS FORMED FROM A JUNCTION
OF O
TYPE AND Q
TYPE SEMICONDUCTOR
MATERIALS 4HE RESULTING DEVICE OFFERS
AN EXTREMELY LOW RESISTANCE TO CURRENT
ÛOW IN ONE DIRECTION AND AN EXTREMELY
HIGH RESISTANCE TO CURRENT ÛOW IN THE
OTHER .OTE THAT AN lIDEALm DIODE WOULD
CONDUCT PERFECTLY IN ONE DIRECTION AND
NOT AT ALL IN THE OTHER DIRECTION
,
.ª4()3
392. OUR THIRD INSTALLMENT OF
5FBDI*O
WE SHALL BE INTRO
DUCING YOU TO A COMPONENT THAT
ACTS RATHER LIKE A ONE
WAY STREET q THE
DIODE 7E SHALL BE USING #IRCUIT 7IZ
ARD TO INVESTIGATE HOW DIFFERENT TYPES
OF DIODE CONDUCT WHEN A VOLTAGE IS
APPLIED TO THEM )NVESTIGATE PROVIDES
YOU WITH AN OPPORTUNITY TO DELVE INTO
THE OPERATION OF A SIMPLE $# POWER
SUPPLY
393. WHILE !MAZE EXPLORES SOME
EXCITING DEVELOPMENTS IN LIGHT EMIT
TING DIODE ,%$ TECHNOLOGY
$IODES
! DIODE IS AN ELECTRONIC COMPONENT
THAT ALLOWS CURRENT TO ÛOW IN ONE DIREC
TION BUT NOT IN THE OTHER )N EFFECT
397. Everyday Practical Electronics, January 2011 49
Teach-In 2011
AMOUNT OF CURRENT AND BEHAVES LIKE
AN INSULATOR
$IODEªCHARACTERISTICS
4YPICAL *7 CHARACTERISTICS FOR GERMA
NIUM AND SILICON DIODES ARE SHOWN IN
IG)FYOUTAKEACAREFULLOOKATTHESE
GRAPHSYOUWILLSEETHATTHEAPPROXIMATE
FORWARDCONDUCTIONVOLTAGEFORAGERMA
NIUMDIODEIS6
398. WHILETHEVOLTAGEFOR
A SILICON DIODE IS APPROXIMATELY 6
$IODEªTYPES
$IODESAREOFTENDIVIDEDINTOSIGNALOR
RECTIÚER TYPES ACCORDING TO THEIR PRINCI
PALÚELDOFAPPLICATION3IGNALªDIODESRE
QUIRECONSISTENTFORWARDCHARACTERISTICS
WITHLOWFORWARDVOLTAGEDROP2ECTIlERª
DIODESNEEDTOBEABLETOCOPEWITHHIGH
VALUES OF REVERSE VOLTAGE AND LARGE VALUES OF FORWARD CURRENT
399. CONSISTENCY OF
CHARACTERISTICS IS OF SECONDARY IMPORTANCE IN SUCH APPLICATIONS
3EMICONDUCTOR DIODES ARE ALSO AVAILABLE CONNECTED IN A FOUR
DIODE BRIDGE
CONÚGURATION FOR USE AS A RECTIÚER IN AN !# POWER SUPPLY IG SHOWS A SE
LECTION OF VARIOUS DIODE TYPES
400. WHILE IG SHOWS THE SYMBOLS THAT ARE USED
TO REPRESENT THEM IN ELECTRONIC CIRCUIT SCHEMATICS
'JH 'PSXBSE BOE SFWFSTF DPOOFD
UJPOT GPS B EJPEF
'JH 5ZQJDBM WPMUBHFDVSSFOU DIBSBDUFSJTUJDT GPS UZQJDBM TJMJDPO BOE
HFSNBOJVN EJPEFT /PUF UIF EJGGFSFOU TDBMFT GPS QPTJUJWF BOE OFHBUJWF
WPMUBHF
'JH 7BSJPVT UZQFT PG EJPEF
JODMVEJOH SFDUJÜFS
TXJUDIJOH BOE
MJHIUFNJUUJOH UZQFT
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401. 50 Everyday Practical Electronics, January 2011
Teach-In 2011
2ECTIlERS
4HE MOST COMMON APPLICATION FOR
A DIODE IS THAT OF CHANGING ALTERNATING
CURRENT !# INTO DIRECT CURRENT $#
IG SHOWS A SIMPLE HALF
WAVE RECTI
ÚER POWER SUPPLY IN WHICH THE DIODE
PASSES CURRENT WHEN THE INCOMING VOLT
AGE IS POSITIVE
402. BUT BLOCKS CURRENT ÛOW
WHEN IT IS NEGATIVE )N ORDER TO MAIN
TAIN A CONSTANT VOLTAGE AT THE OUTPUT
403. A
RESERVOIR CAPACITOR IS CONNECTED ACROSS
THE $# OUTPUT TERMINALS 4HIS CAPACITOR
IS CHARGED ON POSITIVE HALF CYCLES AND
DISCHARGES ON NEGATIVE HALF CYCLES
405. FULL
WAVE POWER SUP
PLY THAT USES A BRIDGE RECTIÚER IS SHOWN
IN IG )N THIS CIRCUIT ONLY TWO OF THE
FOUR DIODES OF THE BRIDGE CONDUCT AT ANY
ONE TIME
407. DEPENDING ON THE POLARITY OF THE
INPUT VOLTAGE
4RANSFORMERS
0OWER SUPPLIES REQUIRE SOME MEANS
OF ISOLATING AND STEPPING DOWN THE !#
MAINS SUPPLY BEFORE THE RECTIÚER AND
RESERVOIRCAPACITOR4HISISACHIEVEDWITH
THE USE OF A STEP
DOWN TRANSFORMER
409. Everyday Practical Electronics, January 2011 51
Teach-In 2011
,IGHT
EMITTINGªDIODES
,IGHT
EMITTING DIODES ,%$ CAN BE
USED AS GENERAL
PURPOSE INDICATORS
#OMPARED WITH CONVENTIONAL ÚLAMENT
LAMPS
410. THEY OPERATE FROM SIGNIÚCANTLY
SMALLER VOLTAGES AND CURRENTS 4HEY ARE
ALSO VERY MUCH MORE RELIABLE THAN ÚLA
MENT LAMPS -OST ,%$S WILL PROVIDE A
REASONABLE LEVEL OF LIGHT OUTPUT WHEN A
FORWARD CURRENT OF AS LITTLE AS M! TO
M!
411. AT A FORWARD CONDUCTION VOLTAGE
OF AROUND 6
! TYPICAL ,%$ INDICATOR CIRCUIT IS
SHOWN IN IG 4HE ÚXED RESISTOR
413. IS USED TO SET THE FORWARD CURRENT OF
THE ,%$ IN THIS CASE ABOUT M! 4HE
VALUE OF THE RESISTOR MAY BE CALCULATED
FROM THE FORMULA
SHOWN IN IG 4HE PRIMARY AND SEC
ONDARY WINDINGS OF THE TRANSFORMER ARE
WOUNDONTHESAMELAMINATEDSTEELCORE
7HENCURRENTÛOWSINTHEPRIMARYWIND
INGITCREATESANALTERNATINGMAGNETICÛUX
THATISCOUPLEDTIGHTLYINTOTHESECONDARY
WINDING 4HIS
415. INDUCES AN %-
IN THE SECONDARY WINDING
4HERELATIONSHIPBETWEENTHEPRIMARY
AND SECONDARY TURNS AND VOLTAGES IS AS
FOLLOWS
WHERE70 AND73 ARETHEPRIMARYAND
SECONDARYVOLTAGES
416. WHILE/P AND/S ARE
THE PRIMARY AND SECONDARY TURNS .OTE
ALSOTHATTHETURNSRATIOFORATRANSFORMER
IS USUALLY QUOTED AS /P /S 3O
425. THE
VOLTAGE APPEARING ACROSS IT WILL REMAIN
SUBSTANTIALLY CONSTANT REGARDLESS OF THE
CURRENT ÛOWING 4HIS PROPERTY MAKES A
:ENER DIODE IDEAL FOR USE AS A VOLTAGE
REGULATOR
426. AS SHOWN IN IG
'JH UZQJDBM TFU PG ;FOFS EJPEF DIBSBDUFSJTUJDT
'JH TJNQMF ;FOFS EJPEF WPMUBHF SFHVMBUPS
'JH UZQJDBM -% JOEJDBUPS
'JH USBOTGPSNFS
WHERE 7G IS THE FORWARD VOLTAGE DROP
FOR THE ,%$ TYPICALLY AROUND 6
427. 7 IS
THE SUPPLY VOLTAGE AND * IS THE FORWARD
CURRENT
0LEASE NOTEØ
4HE LARGE VALUE RESERVOIR CAPACITOR
IN A POWER SUPPLY CAN OFTEN REMAIN IN
A PARTIALLY CHARGED STATE LONG AFTER THE
SUPPLY HAS BEEN SWITCHED OFF OR DISCON
NECTED ECAUSE OF THIS
428. IT IS IMPORTANT
TO EXERCISE GREAT CARE WHEN WORKING ON
POWER SUPPLY CIRCUITSØ
(a) Transformer symbol,
voltages and turns
(b) A typical transformer
3 3
6 6
9 1
9 1
I9 9
5
,
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429. 52 Everyday Practical Electronics, January 2011
Teach-In 2011
3KETCH THE CIRCUIT SYMBOL FOR A DIODE AND LABEL THE
ANODE AND CATHODE CONNECTIONS
7HAT IS A THE FORWARD RESISTANCE AND B THE REVERSE
RESISTANCE OF AN lIDEALm DIODE
7HICHOFTHEDIODESSHOWNINIGISCONDUCTING
#HECKªnª(OWªDOªYOUªTHINKª
YOUªAREªDOING
3TATE THE FORWARD CONDUCTION VOLTAGE FOR A A GERMA
NIUM DIODE AND B A SILICON DIODE
%XPLAIN BRIEÛY HOW A RECTIÚER OPERATES
%XPLAIN WHY A RESERVOIR CAPACITOR IS NEEDED IN A
POWER SUPPLY
)DENTIFYEACHOFTHEDIODESYMBOLSSHOWNINIG
'JH 4FF RVFTUJPO
! TRANSFORMER HAS PRIMARY TURNS AND SEC
ONDARY TURNS $ETERMINE THE SECONDARY OUTPUT VOLTAGE IF
THE PRIMARY IS SUPPLIED FROM A 6 !# MAINS SUPPLY
'JH 4FF RVFTUJPO
,. 4()3 MONTHmS lUILDm WE ARE GOING TO
TRY OUT SOME OF THE DIODE THEORY THAT WE
DISCUSSED EARLIER 4O START WITH
430. WEmLL CARRY
OUT SOME SIMPLE EXPERIMENTS WITH ORDINARY
SILICON DIODES TO SEE HOW THEY REALLY WORK
)N l,EARNm WE SAW HOW A DIODE ACTS LIKE A
ONE
WAY VALVE (OWEVER
431. BY USING A REALLY
HIGH REVERSE VOLTAGE WE CAN MAKE A DIODE
BREAK DOWN AND LET THROUGH CURRENT lBACK
WARDSm 7E ALSO KNOW THAT IT TAKES A LITTLE
VOLTAGE TO lOPEN UPm A DIODE AND MAKE IT START
LETTING CURRENT ÛOW THROUGH IT 3O LETmS TRY
THIS OUTØ
$IODEªTESTªCIRCUIT
%NTER THE CIRCUIT SHOWN IN IG 9OUmLL
ÚND THE DIODE IN THE l$ISCRETE SEMICONDUC
TORSm FOLDER
432. THE INPUT VOLTAGE IN l0OWER 3UP
PLIESmANDTHEMETERSINl6IRTUAL)NSTRUMENTSm
Y DEFAULT #IRCUIT 7IZARD WILL GIVE YOU AN
'JH 5FTUJOH B TJMJDPO EJPEF VTJOH
GPSXBSE CJBT
'JH 4FMFDUJOH UIF NPEFM GPS B EJPEF
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433. Everyday Practical Electronics, January 2011 53
Teach-In 2011
ªªUILDªnª4HEª#IRCUITª7IZARDªWAY
'JH YDFM HSBQI PG SFTVMUT GPS / JO GPSXBSE
CJBT
lIDEALm DIODE !S WE WANT TO SEE HOW
A REAL DIODE MIGHT WORK YOU NEED TO
SELECT A MODEL 4O DO THIS
434. DOUBLE CLICK
THE DIODE SYMBOL AND SELECT l.m
FROM THE l-ODELm DROP
DOWN LIST SEE
IG 4HE . IS A STANDARD
SILICON RECTIÚER DIODE AND IS VERY COM
MONLY USED
4EST
7HAT WE HAVE HERE IS A REALLY SIMPLE
CIRCUIT q PROBABLY NOT ONE THAT YOUmD
USE IN REAL LIFE (OWEVER
435. IT LETS US SEE
HOW MUCH CURRENT THE DIODE PASSES
DEPENDING ON WHAT VOLTAGE WE PUT
ACROSS IT 4O CARRY OUT OUR TEST
436. WHAT
WEmLL DO IS SLOWLY INCREASE THE VOLTAGE
ACROSS THE DIODE AND SEE WHAT CURRENT
ÛOWS THROUGH IT 4HIS WILL TELL US IF THE
DIODE IS CONDUCTING
IRST
437. TRY STARTING THE SIMULATION BY
HITTING THE PLAY BUTTON ON THE TOP BAR
5SE THE SLIDER TO VARY THE INPUT VOLT
AGE AND WATCH THE EFFECT 9OUmLL ONLY
NEED TO INCREASE THE VOLTAGE TO ABOUT
6
438. AT WHICH POINT THE DIODE SHOULD BE
CONDUCTING NICELY AND YOU SHOULD SEE
A LARGE VALUE FOR THE CURRENT
9OU MIGHT ÚND IT EASIER TO SET THE
LIMIT FOR THE INPUT VOLTAGE TO 6 ITmS SET
'JH YDFM HSBQI GPS / JO SFWFSTF CJBT
AT 6 BY DEFAULT q THIS WILL ALSO HELP
YOU WITH THE NEXT BITØ 9OU CAN DO THIS
BY DOUBLE CLICKING THE COMPONENT AND
CHANGING THE 6 TO 6
(OPEFULLY
439. YOU SHOULD NOTICE THAT IT
DOESNmT SIMPLY START LETTING A LARGE CUR
RENT PASS IMMEDIATELY q IT TAKES A LITTLE
VOLTAGE ACROSS IT TO REALLY lOPEN IT UPm
) ALWAYS LIKE TO THINK OF A DIODE LIKE
A SPRUNG ONE
WAY GATE ITmS EASY TO GET
THROUGH ITINTHERIGHTDIRECTION
440. BUTYOU
NEED TO PUT A LITTLE PRESSURE AGAINST IT IN
ORDER TO GET THROUGH
4AKINGªREADINGS
.OW LETmS GET A LITTLE MORE SCIENTIÚC
ABOUTTHINGSANDTAKESOMEREADINGS7E
CAN THEN DRAW UP A GRAPH OF OUR RESULTS
TO SEE WHATmS GOING ON
3TARTING FROM 6 AND STEPPING UP IN
6 M6 STEPS
441. INCREASETHEVOLTAGE
AND RECORD THE CURRENT ÛOWING THROUGH
THE DIODE /NCE YOUmVE GOT A FULL SET
OF RESULTS YOU CAN USE THEM TO DRAW A
GRAPH 4AKE CARE TO MAKE SURE THAT ALL OF
YOUR CURRENT READINGS ARE IN THE SAME
UNITS WHEN YOU PLOT YOUR GRAPHØ !N
EXAMPLE USING -ICROSOFT %XCEL IS SHOW
IN IG
!S YOU HAVE FOUND
442. ONCE WE GET TO
AROUND6THEDIODE
STARTS TO LET CURRENT
THROUGH
443. AND THIS IS
WHAT WEmD EXPECT FOR
A SILICON DIODE 3O
FAR WEmVE BEEN USING
THE DIODE lTHE RIGHT
WAY ROUNDm IN WHAT
WE CALL FORWARDªBIAS
.OW WEmLL SEE WHAT
HAPPENS WHEN WE
TURNTHEDIODEAROUND
SO THATmS ITmS IN REVERSEª
BIAS OR lBACKWARDSm
!LTER YOUR CIRCUIT TO THAT SHOWN IN
IG.OTICETHATASWELLASTHEDIODE
ORIENTATION CHANGING
444. THE TOP LIMIT ON
THE INPUT VOLTAGE HAS BEEN INCREASED
TO 6 3TART THE SIMULATION AND TRY
EXPERIMENTING WITH THE INPUT VOLTAGE
9OU SHOULD ÚND THAT ITmS REALLY HARD
TOGETADIODETOCONDUCTINREVERSEBIASØ
'OING BACK TO THE IDEA OF A DIODE AS A
ONE
WAY GATE IF YOU REALLY WANTED TO
GETTHROUGHITTHEWRONGWAYYOUWOULD
BE ABLE TO DO IT
445. BUT YOUmD HAVE TO WORK
REALLY HARD TO FORCE IT OPEN
4HEREFORE
446. ITmS NOT STRICTLY TRUE THAT A
STANDARDDIODEONLYLETSCURRENTTHROUGH
IN ONE DIRECTIONØ (OWEVER
448. IF YOU WERE USING A DIODE IN A LOW VOLT
AGE CIRCUIT IT IS UNLIKELY THAT A REVERSE
VOLTAGE WOULD EVER BE HIGH ENOUGH TO
BREAK IT DOWN
2ECORDVALUESFORTHEVOLTAGEANDCUR
RENT GOING UP IN STEPS OF 6 AND GRAPH
YOUR RESULTS 4IP YOUmLL ALSO NEED TO GO
TO 6 TO GET YOUR ÚNAL READINGØ 9OU
SHOULD OBTAIN SOMETHING THAT LOOKS LIKE
THE GRAPH SHOWN IN IG
)RU RXUFRS RI LUFXLW:L]DUG ²VHH '520SDJHV
'JH $JSDVJU GPS EJPEF UFTUJOH JO SFWFSTF CJBT
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449. 54 Everyday Practical Electronics, January 2011
Teach-In 2011
.OW REPEAT THIS FOR SOME MORE :ENER
VOLTAGE VALUES (EREmS OUR RESULTS FOR
THREE :ENER DIODES 6 6
450. 6
6 AND 6 6
)F YOU CARRIED OUT YOUR EXPERIMENTS
ACCURATELY
451. YOU SHOULD BE ABLE TO PRO
DUCE A GRAPH SIMILAR TO THAT SHOWN
IN IG .OTICE THAT THE CURRENT
RAPIDLY INCREASES THROUGH THE DIODE
ONCE IT REACHES THE :ENER VOLTAGE OF
THE DIODE
4HIS CAN BE EXTREMELY USEFUL IN
ELECTRONIC CIRCUITS 7E OFTEN USE :ENER
DIODES TO GIVE US EXACT REFERENCE
VOLTAGES AND TO REGULATE VOLTAGES DOWN
TO A SPECIÚC VALUE
3EMICONDUCTORMANUFACTURERSOFTEN
PRODUCE A GRAPH OF THE CHARACTERISTICS
OF THEIR DIODES SIMILAR TO THOSE THAT
YOUmVE CREATED (OWEVER
453. AND SHOW
THEM BOTH ON ONE GRAPH 4RY THIS
WITH YOUR RESULTS AND SEE IF YOU CAN
PRODUCEAMANUFACTURER
LIKEGRAPHFOR
THE.4AKEALOOKATOURS
454. WHICH
WEmVE SHOWN IN IG
3O WEmVE SEEN HOW A STANDARD DI
ODE LETS CURRENT THROUGH IN A FORWARD
DIRECTION ONCE THERE IS A SMALL VOLTAGE
ACROSS IT
455. BUT NORMALLY BLOCKS CURRENT
IN A REVERSE DIRECTION UNLESS WE APPLY
A REALLY LARGE VOLTAGE
:ENERªDIODES
$IODES ARE A REALLY USEFUL DEVICE TO
HELP US CONTROL WHERE CURRENT ÛOWS
IN A CIRCUIT AND ARE ESSENTIAL WHEN IT
COMES TO CONVERTING ALTERNATING CUR
RENT !# TODIRECTCURRENT $# WECALL
THIS VOLTAGE RECTIlCATION (OWEVER
458. AND RATHER USEFUL FEATURE WHEN
ITCOMESTOREVERSEBIAS4HESEARECALLED
:ENER DIODES
ASICALLY
459. WHEN WE MANUFACTURE A
:ENER DIODE WE CAN ENGINEER IT SO THAT
WE KNOW AT EXACTLY WHAT VOLTAGE IT WILL
BREAKDOWNINREVERSEBIASANDCONDUCT
9OU CAN PURCHASE A FULL RANGE OF :ENER
DIODESWITHDIFFERENTSPECIÚEDVOLTAGES
3O LETmS TRY OUR PREVIOUS DIODE EX
PERIMENTS
460. BUT WITH SOME :ENER DIODES
INSTEADOFORDINARYSILICONDIODES!LTER
YOUR REVERSE BIAS DIODE CIRCUIT SHOWN
IN IG BY CHANGING THE DIODE TO A
:ENER DIODE q SEE IG
7E NEED TO SPECIFY THE :ENER VOLTAGE
OF THE DIODE AND WE DO THIS IN THE SAME
WAY AS WE SELECTED THE DIODE MODEL
PREVIOUSLY
462. SELECT 6 6 THEN
SLOWLY INCREASE THE VOLTAGE ACROSS THE
DIODETAKINGREADINGSEVERY6UNTIL
THE CURRENT REACHES AROUND M!
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For more information, links
and other resources please
check out ourTeach-In
website at:
www.tooley.co.uk/
teach-in
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464. ,%$S ARE A TYPE OF
DIODE THAT EMITS LIGHT WHEN THE DEVICE
IS FORWARD BIASED AND PASSING CURRENT
,%$SHAVEBEENAROUNDINVARIOUSFORMS
FOR QUITE A LONG TIME AND SO YOU WILL
ALREADY BE FAMILIAR WITH THEM AND HOW
THEY ARE USED ,%$S OFFER SOME NOTABLE
ADVANTAGES WHEN COMPARED WITH ÚLA
MENT LAMPS AND ÛUORESCENT DISPLAYS
p 4HEY ARE EXTREMELY RELIABLE AND
THEY CAN OPERATE FOR MANY TENS OR EVEN
HUNDREDS OF THOUSANDS OF HOURS IF USED
AT THEIR RATED CURRENT
p 4HEY ARE IMPERVIOUS TO HEAT
467. SO RUN COOL
p 4HEY OPERATE FROM LOW VOLTAGE AND
CURRENT
468. AND CAN BE EASILY INTERFACED TO
ELECTRONIC CIRCUITS
p 4HEY ARE RUGGED BECAUSE NO BREAK
ABLE GLASS IS USED IN THEIR CONSTRUCTION
!NSWERSªTOª1UESTIONS
3EE IG A
A ZERO B INÚNITE
$ AND $
A 6 B 6
3EE PAGE
3EE PAGE
A PHOTODIODE
B :ENER DIODE
C LIGHT
EMITTINGDIODE ,%$
6
)NVESTIGATE
!MAZE
IGSHOWSTHECIRCUITOFAPOWER
SUPPLY3TUDYTHECIRCUITCAREFULLY
469. LOOK
BACK AT WHAT WE DID IN 0ART AND THEN
ANSWEREACHOFTHEFOLLOWINGQUESTIONS
7HAT TYPE OF RECTIÚER IS USED IN
THE POWER SUPPLY
7HAT IS THE TURNS RATIO OF THE
TRANSFORMER
7HAT !# VOLTAGE WILL APPEAR AT THE
INPUT OF THE BRIDGE RECTIÚER
)F THE ,%$ HAS A FORWARD VOLTAGE OF
6
470. WHAT CURRENT IS SUPPLIED TO IT
7HAT POWER WILL BE DISSIPATED IN
THE :ENER DIODE
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'OINGªORGANIC
2ECENT ADVANCES IN SEMICONDUCTOR
TECHNOLOGY HAVE SEEN THE INTRODUCTION
OF WHITE lHIGH BRIGHTNESSm ,%$S THAT CAN
BE USED IN GROUPS OR ARRAYS TO REPLACE
LAMPSUSEDINDOMESTICLIGHTINGAPPLICA
TIONS$EVELOPEDBY+ODAKINTHES
471. ORGANIC LIGHT
EMITTING DIODES /,%$
SEEM POISED TO OUST THE ,#$ DISPLAY
JUST AS ,#$ TECHNOLOGY HAS ECLIPSED THE
#24 /,%$ PANELS ARE THINNER
473. BRIGHTER AND MORE ENERGY EFÚCIENT THAN
THEIR ,%$ COUNTERPARTS
!N /,%$ PANEL CONSISTS OF A LAYER OF
ORGANIC
474. LIGHT
EMITTING MATERIAL SAND
WICHED BETWEEN TWO CONDUCTORS AN
ANODE AND A CATHODE 4HE RESULTING
DEVICE IS ABOUT TIMES THINNER THAN
A HUMAN HAIR AND IT EMITS LIGHT WHEN
AN ELECTRIC CURRENT IS PASSED THROUGH IT
4HEREmS NO NEED FOR A BACKLIGHT BECAUSE
THE ORGANIC MATERIAL EMITS ITS OWN LIGHT
WHEN CHARGED
4HE ABSENCE OF A BACKLIGHT MEANS
THAT /,%$ DISPLAYS CAN BE EXTREMELY
THIN OR EXAMPLE
475. THE 3ONY 8%,
IS
ONLY MM THICK AND 3ONYmS PROTOTYPE
INCH /,%$ 46 USES A PANEL WHICH
HAS A THICKNESS OF AS LITTLE AS MMØ
)N THE SAME WAY THAT INKS ARE SPRAYED
ONTO PAPER DURING PRINTING
476. /,%$S CAN
BE SPRAYED ONTO SUBSTRATES USING INKJET
TECHNOLOGY 4HIS REDUCES THE COST OF
MANUFACTURING AND ALLOWS DISPLAYS TO
BE PRINTED ONTO VERY LARGE ÚLMS THAT CAN
BE USED IN GIANT SCREENS AND ELECTRONIC
BILLBOARDS 3O
477. IF YOU FANCY A
INCH
46 DISPLAY THAT ROLLS UP FOR STORAGE
478. OR
IF YOU THINK IT MIGHT BE USEFUL TO HAVE
A DISPLAY BUILT INTO YOUR CLOTHING
481. WE
WILL LOOK AT TRANSISTORS
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482. 46 Everyday Practical Electronics, February 2011
Teach-In 2011
By Mike and Richard Tooley
0ARTªª4RANSISTORS
/URª4EACH
)NªSERIESªISªDESIGNEDªTOªPROVIDEªYOUªWITHªAªBROAD
BASEDªINTRODUCTIONªTOªELECTRONICSª7EªHAVEª
ATTEMPTEDªTOªPROVIDEªCOVERAGEªOFªTHREEªOFªTHEªMOSTªIMPORTANTªELECTRONICSªUNITSªTHATªAREªCURRENTLYªSTUDIEDªINª
MANYªSCHOOLSªANDªCOLLEGESªINªTHEª5+ª4HESEªINCLUDEª%DEXCELª4%#ª,EVELªªAWARDS
490. ª!MAZEªWILLªSHOWªYOUªTHEª@WOWªFACTOR ªª
EXTREMELY SMALL AND THEY ARE PRO
DUCED IN A SINGLE SLICE OF SILICON
BY DIFFUSING IMPURITIES THROUGH A
PHOTOGRAPHICALLY REDUCED MASK
3IMPLIFIED REPRESENTATIONS OF
/1/ AND 1/1 TRANSISTORS ARE
SHOWN
494. BASE B AND
EMITTERª E
!N IMPORTANT POINT TO NOTE IS THAT
BOTH TYPES OF TRANSISTOR CONSIST OF
TWO DIODE 1
/ JUNCTIONS BACK
TO
BACK (OWEVER
495. ITmS IMPORTANT TO
REALISE THAT THE MIDDLE LAYER THE 1
TYPE BASE REGION IN AN /1/ TRANSIS
TOR OR THE /
TYPE BASE REGION IN THE
1/1 TRANSISTOR IS MADE EXTREMELY
NARROW
496. AND THIS ALLOWS CHARGE
7($+,1
$ %52$'%$6(' ,1752'87,21
72 (/(7521,6
,EARN
4RANSISTORS
4HERE ARE SEVERAL DIFFERENT TYPES
OF TRANSISTOR
497. BUT FOR CONVENIENCE
THEY ARE OFTEN DIVIDED INTO TWO MAIN
CATEGORIES BIPOLARªJUNCTIONªTRANSIS
TORSª *4 AND lELD
EFFECTªTRANSISTORSª
%4 !LTHOUGH THE PRINCIPLE ON
WHICH THEY OPERATE IS DIFFERENT
499. AND BECAUSE OF THIS WE WILL
FOCUS OUR ATTENTION ON *4 RATHER
THAN %4 DEVICES ! SELECTION OF
DIFFERENT TYPES OF TRANSISTOR INCLUD
ING *4 AND %4 DEVICES IS SHOWN
IN IG
IPOLAR JUNCTION TRANSISTORS ARE
MADE OF /1/ OR 1/1 JUNCTIONS
OF SILICON 3I 4HE JUNCTIONS ARE
,
. PART FOUR OF 5FBDI*O
500. WE WILL INTRODUCE YOU TO A COM
PONENT THAT CAN ACT AS BOTH AN
AMPLIÚER AND A SWITCH /RIGINALLY
CALLED A lTRANSFER RESISTORm
503. OR AS PART OF AN
INTEGRATED CIRCUIT
7E WILL USE #IRCUIT 7IZARD TO IN
VESTIGATE THE OPERATION OF A TRANSIS
TOR AS A DEVICE FOR AMPLIFYING AND
SWITCHING CURRENT 9OU WILL ALSO BE
ABLE TO CONSTRUCT AND TEST A SIMPLE
LIGHT ÛASHER THAT USES LIGHT
EMITTING
DIODES ,%$ INALLY
504. IN !MAZE WE
TAKE THIS ONE STEP FURTHER BY SHOW
ING YOU HOW TO DESIGN A PRINTED
CIRCUIT BOARD 0# LAYOUT FOR THE
,%$ ÛASHERØ
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505. Everyday Practical Electronics, February 2011 47
Teach-In 2011
CARRIERS TO PASS ACROSS IT RATHER THAN
ENTER OR EXIT AT THE BASE 4HUS
506. THE
MAIN CURRENT ÛOW IN A TRANSISTOR
IS FROM COLLECTOR TO EMITTER IN THE
CASE OF A /1/ TRANSISTOR
510. SHOW THE NORMAL VOLTAGES APPLIED
TO /1/ AND 1/1 TRANSISTORS AND THE
CURRENT ÛOW WITHIN THE DEVICE )T
IS IMPORTANT TO NOTE FROM THIS THAT
THE BASE
EMITTER JUNCTION IS FORWARD
BIASED
511. AND THE COLLECTOR
BASE JUNC
TION IS REVERSE BIASED
ECAUSE THE BASE REGION IS MADE
VERY NARROW
512. CHARGE CARRIERS ARE
SWEPT ACROSS IT AND ONLY A RELATIVELY
SMALL NUMBER APPEAR AT THE BASE
4O PUT THIS INTO CONTEXT
513. THE CUR
RENT ÛOWING IN THE EMITTER CIRCUIT IS
TYPICALLY TIMES GREATER THAN THAT
ÛOWING IN THE BASE
4HE EQUATION THAT RELATES CURRENT
ÛOW IN THE COLLECTOR
517. AND *# IS THE
COLLECTOR CURRENT ALL EXPRESSED IN
THE SAME UNITS
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518. 48 Everyday Practical Electronics, February 2011
Teach-In 2011
4HE VALUE OF *% CAN BE CALCULATED
BY RE
ARRANGING THE EQUATION *%
* *# TO MAKE *# THE SUBJECT
519. AS
FOLLOWS
*# *% q *# q M!
.OTE THAT ! IS THE SAME AS
M!
*4ªCIRCUITªCONlGURATIONS
2EGARDLESS OF WHETHER A *4 IS
AN /1/ OR 1/1 TYPE
521. AND
ALL TRANSISTOR BNQMJÜFS STAGES ARE
BASED ON ONE OF THESE 4HE THREE
CIRCUITS ARE BASED ON WHICH ONE OF
THE THREE TRANSISTOR CONNECTIONS IS
MADE COMMON TO BOTH THE INPUT AND
THE OUTPUT )N THE CASE OF *4S
524. MARKED 3- IN
IG WHICH CONVERTS THE OUTPUT
0LEASE NOTEØ
4HE DIRECTION OF CONVENTIONAL CUR
RENT ÛOW IS FROM COLLECTOR TO EMITTER
IN THE CASE OF AN /1/ TRANSISTOR
525. AND EMITTER TO COLLECTOR IN THE CASE
OF A 1/1 TRANSISTOR )N BOTH CASES
526. THE AMOUNT OF CURRENT ÛOWING FROM
COLLECTOR TO EMITTER IS DETERMINED BY
THE AMOUNT OF CURRENT ÛOWING INTO
THE BASE
0LEASE NOTEØ
4HERE ARE MANY DIFFERENT TYPES OF
TRANSISTOR )N THIS INSTALMENT OF 4EACH
)NWEAREJUSTLOOKINGATONEOFTHEMOST
COMMON TYPES
527. THE BIPOLAR JUNCTION
TRANSISTOR *4 IGSHOWSSYMBOLS
FOR SOME OF THE OTHER LESS
COMMON
TYPES THAT YOU MIGHT COME ACROSS
%XAMPLEª
! TRANSISTOR OPERATES WITH A COLLEC
TOR CURRENT OF M! AND AN EMITTER
CURRENT OF M! $ETERMINE THE
VALUE OF BASE CURRENT
4HE VALUE OF *% CAN BE CALCULATED
BY RE
ARRANGING THE EQUATION *% *
*# TO MAKE * THE SUBJECT
528. AS FOLLOWS
* *% q *#
(ENCE
* q M!
%XAMPLEª
! TRANSISTOR OPERATES WITH *%
M! AND * ! $ETERMINE
THE VALUE OF *#
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