DID YOU KNOW?
Electronic
component sizes have been effectively reducing by
half about every 18 months over the years!
The same progress in design, manufacture and
miniaturisation also enabled computer processor
(CPU) speeds to be doubled every 18 months during
that this time! However there is a limit to this
continual increase in CPU clock speeds by using
these traditional methods, and different types of
processor architecture will emerge in the future.


Photo' showing some older
components on the left and some newer ones on the
right

The effect of
miniaturisation is quite noticeable even when
working with the very ordinary components involved
in the construction of typical 'homebrew'
projects, i.e. components with leads intended for
use on an ordinary circuit board. Typical
resistors and capacitors are very much smaller now
than they were 20 years ago.
This
process of miniaturisation has progressed beyond
the 'ordinary' components that are used in
everyday home built projects and equipment built
on ordinary circuit boards, since there is a limit
to how small a component can be and remain useable
for such work. Today's powerful personal
computers, laptops, mobile 'phones and digital
cameras are made possible by the use of very large
scale integrated circuits and tiny 'surface mount'
components such as resistors and capacitors that
are often the size of a pin head and are therfore
rather more difficult to work with for the home
constructor.

RESISTOR COLOUR
CODES AND CAPACITOR CONVERSION TABLE
When
constructing electronic projects it will be
necessary to determine the exact value of
resistors, which are colour coded, and
capacitors, which sometimes have confusing
numbers on them. I have therefore included
some tables for both Resistors and Capacitors to
help identify their values.
For some simple
ideas on solderless construction techniques have a
look at the Crystal
Sets 2 page.

RESISTOR COLOUR
CODES
MDS975.CO.UK
RESISTORS
WITH FOUR COLOURED BANDS
For traditional resistors there are usually
FOUR coloured bands. The first two
coloured bands will show the first two digits,
the third band provides the
multipier by which the first two digits
must be multiplied (i.e number of zeros);
together this gives the value of the resistor
(the resistance) in Ohms. The fourth
coloured band indicates the tolerance of the
resistor, that is how close the actual
resistance may be to the value
indicated. A 1k Ohm (1000 Ohm) resistor
with a 20% tolerance could have a value
anywhere between 800 and 1200 Ohms.
The
tolerance band is sometimes spaced further
apart from the other three bands, which
helps when deciding which way round to read
off the value, which is sometimes difficult
to establish immediately.

FIRST DIGIT
First
Colour Band

SECOND DIGIT
Second
Colour Band

MULTIPLIER
Third
Colour Band

BLACK

0


0


x 1

BROWN

1 

1


x 10

RED

2 

2


x 100

ORANGE

3 

3


x 1,000

YELLOW

4 

4


x 10,000

GREEN

5 

5


x 100,000

BLUE

6 

6


x 1,000,000

VIOLET

7 

7


x 10,000,000

GREY

8 

8


x 100,000,000

WHITE

9 

9


x 1,000,000,000

Tolerance
Fourth
Colour Band:
BROWN
1%

RED
2% 
GOLD
5% 
SILVER
10% 
SALMON
20% 


Examples:
BROWN BLACK
BROWN SILVER = 10 X 10 = 100 Ohms (Usually
expressed as 100R) 10% Tolerance
YELLOW
VIOLET RED GOLD = 47 X 100 = 4700 Ohms
(Usually expressed as 4.7K) 5% Tolerance
ORANGE
ORANGE YELLOW SILVER = 33 X 10,000 = 330000 Ohms
(Usually expressed as 330K) 10% Tolerance

RESISTORS WITH FIVE COLOURED BANDS
A
number of resistors have FIVE coloured
bands to indicate their resistance value
and tolerance. The first three bands
indicate the first three digits, the fourth
band provides the multipier by which
the first three digits must be multiplied
(i.e. number of zeros) the result gives the
value of the resistor. The fifth
band indicates the tolerance. Again
it is often difficult to tell which way
round to read off the value, but the
tolerance band is usually spaced a little
further apart from the first four bands.

FIRST
DIGIT
First
Colour Band

SECOND DIGIT
Second Colour Band

THIRD DIGIT
Third Colour band

MULTIPLIER
Fourth Colour Band 
BLACK

0 

0


0


x
1

BROWN

1


1


1


x
10

RED

2


2


2


x
100

ORANGE

3


3


3


x
1,000

YELLOW

4


4


4


x
10,000

GREEN

5


5


5


x
100,000

BLUE

6


6


6


x
1,000,000

VIOLET

7


7


7



GREY

8


8


8

GOLD

x
0.1 
WHITE

9


9


9

SILVER

x
0.01 
Tolerance
Fifth
Colour Band:

BROWN
1%










Examples:
BROWN BLACK
BLACK BLACK BROWN = 100 X 0 = 100 Ohms (100R) 1%
Tolerance
YELLOW
VIOLET BLACK BROWN BROWN = 470 X 10 =
4700 Ohms (4.7K) 1% Tolerance
ORANGE
ORANGE BLACK ORANGE BROWN = 330 X 1000 =
330000 Ohms (330K) 1% Tolerance
N.B. Five band resistors are always +/ 1%
tolerance
SURFACE MOUNT RESISTORS  SMD (Surface
Mount Devices)  SMT (Surface Mount
Technology)
I have encountered two types of Surface Mount
Resistor. The main type seems to be the standard
tolerance type which is marked with three identifier
digits, the other is a precision tolerance type
marked with four identifier digits:
SMD Resistors with Three
Digits:
The first two digits are the significant digits, the
third is the number of zeros (i.e. power of 10).
Example:
270 would indicate a 27 Ohm device: 27 with no
zeros (10^0) = 27 Ohms
(To avoid confusion some devices omit the last digit
so 27 Ohms would be marked simply as 27 and 33 Ohms
would be marked as 33 etc.)
271 would indicate a 270 Ohm device: 27 plus 1
zero (10^1) = 270 Ohms
682 would indicate a 6.8K Ohm device: 68 plus
2 zeros (10^2) = 6,800 Ohms
333 would indicate a 33K Ohm device: 33 plus 3
zeros (10^3) = 33,000 Ohms
274 would indicate a 270K Ohm device. 27 plus
4 zeros (10^4) = 270,000 Ohms
475 would indicate a 4.7M Ohm device. 47 plus
5 zeros (10^5) = 4,700,000 Ohms
A device marked 000 or 0 has essentially no
(extremely small) resistance and would be used as a
'link' on an SMD PCB.
SMD resistors having a value lower than 10 ohms:
2R7 = 2.7 ohms
0R27 = 0.27 ohms
0R05 = 0.05 ohms
(In these cases the R indicates the decimal point 
familiar on many schematic circuit diagrams.)
SMD Resistors with
Four
Digits (Precision Tolerance):
In this case the first three digits are the
significant digits. The fourth digit indicates the
number of zeros (i.e. the power of ten). E.G:
2700 would indicate a 270 Ohm device: 270 plus
no zeros (10^0) = 270 Ohms
2703 would indicate a 270K Ohm device. 270
plus 3 zeros (10^3) = 270,000 Ohms
4704 would indicate a 4.7M Ohm device. 470
plus 4 zeros (10^4) = 4,700,000 Ohms
Such a device marked 000 or 0000 has essentially no
(extremely small) resistance and would be used as a
'link' on an SMD PCB.

CAPACITOR
CONVERSION TABLE
MDS975.CO.UK
The unit of capacitance is the Farad. The
Farad, however, is too large a unit for use with
typical electronic circuits, so it is divided into
much smaller units, for example the microfarad
which is 0.000001 Farads.
LARGE CAPACITORS
Electrolytic
Probably the most common large capacity
capacitor is the Electrolytic type. Most Electrolytic
capacitors are clearly marked with the value of
the capacitor in microfarads (uF), the polarity of
the leads, and the working voltage. For this
reason electrolytic capacitors are often the
easiest capacitors to identify and use.
Most electrolytic capacitors will have clearly
printed on the body something like: "220µF 50volts".
It is very important to remember that most
electrolytic capacitors are polarised i.e. the
must be connected the correct way round in the
circuit  to identify polarity these capacitors
will generally have a (usually white) stripe
down one side with a
ve sign to indicate
that lead is to go only to the negative side of
the circuit and the +ve lead will usually be
longer than the ve lead to help identification.
Becuase DC is usually present in a circuit an
electrolytic capacitor must be connected the right
way round, if it is connected the wrong way round
it may explode, so be careful!
Tantalum
Another type of capacitor that is available
in large capacities is the Tantalum Bead
type, they are much smaller than electrolytic
capacitors and also usually have lower working
voltages. Tantalum capacitors are also polarised
and must be connected the right way round in
the circuit. Modern tantalum bead capacitors have
the value printed on the casing along with the
voltage and polarity marking.
Older ones use a colour code in the form of
stripes and a spot. The top two stripes give the
first two digits  using the colours in the table
below, and the spot is the multiplier: Grey Spot =
x 0.01 : White Spot = x 0.1
: Black Spot = x 1 . The third (bottom
stripe) is the voltage marking  yellow being
6.3V; black being 10V; green being 16V; blue being
20V; grey being 25V; white being 30V and pink
being 35V. The positive lead is the one on the
right hand side when the spot is facing you.
SMALL CAPACITORS
Small value capacitors will be unpolarised
and therefore can be connected into a circuit
either way around. Many circuits specify small
capacitors. They are available in a wide range of
values, with the various polyester types and
ceramic capacitors being popular choices.
Some circuits may specify capacitor values in microfarads(µF),
some
in
nanofarads
(nF) while others may use picofarads
(pF). The different and varied types of component
marking used on capacitors can all be rather
confusing!
PRINTED
VALUES
Some capacitors simply have the value
printed on them which sounds easy, but you have to
know if the number is in microfarads, nanofarads
or picofarads. It seems to be common that if, for
example, a capacitor is marked 0.22 this means
0.22 microfarads (µF) and if the printed marking
is, for example, 2n2 then this would be a 2.2nF
(nanoFarad) capacitor.
SIMPLE TWO
DIGIT MARKINGS
Often the capacitor will simply
be marked with a two digit number printed on the
body such as " 10" for
example. This indicates that it is a
10pF capacitor. However
you may find some capacitors marked "10n" and this
capacitor will have a value of 10nF (ie 10,000pF),
this is sometimes seen on polystyrene types and
some resin dipped ceramics.
CODED
THREE DIGIT MARKINGS
Many capacitors use a coded marking
system, and it seems that the majority of modern
capacitors that I have used in recent years fall
in to this category, so here is a guide:
When we get our bag full of bits through the post,
or eventually arrive home from the electronics
shop with our little plastic bag full of
components, keen to construct a circuit we will
often find that many capacitors are marked with a
three digit code such as " 103"
or " 104" and some
others have a three digit code plus a letter on
the end such as " 101K"
or " 102K".
This can lead to a bit of 'head scratching' before
construction of our exciting project can begin!
Once we can familiarise ourselves with these codes
or have a chart at hand then progress to the all
important construction stage will be much swifter.
The capacitors marked with three digits are
similar to resistors in that the first two digits
represent the value in Picofarads while the third
digit is the "multiplier". In order to obtain the
value in PICOFARADS (pF) take the first two digits
and then add on the number of zeros as indicated
by the third digit. 0 = add no zeros; 1 =
add one zero; 2 = add two zeros; 3 = add three
zeros etc:
So 100 would be 10pF
with no multiplier i.e. 10pF.
221
is therefore 22pF with a
multiplier of 10, i.e. 220pF, or to put it
another way 0.00022 microfarads.
473 is 47pF
multiplied by 1000 i.e. 47,000pF or to put is
another way 0.047 microfarads.
The letter is present to
indicate the tolerance of the component.
471K would be a 470pF
capacitor with a 10% tolerance.
Help is at hand.....
To help make sense of all this and to be able to
easily convert from nF to pF to uF etc. here are a
couple of very handy little tables:
The code marking, when decoded, will
provide the value in Picofarads (pF), but the
table below shows you the values in microfarads
(µF) and nanofarads (nF) too.

CODE / Marking

µF
microfarads

nF
nanofarads

pF
picofarads

1RO

0.000001

0.001

1

100

0.00001

0.01

10

101

0.0001

0.1

100

102

0.001

1

1,000

103

0.01

10

10,000

104

0.1

100

100,000

105

1

1,000

1,000,000

106

10

10,000

10,000,000

107

100

100000

100,000,000

Remember 1µF =
0.000001 Farad
10µF (microfarads) = 0.00001 F
1 nanofarad (nF) = 0.000000001 F
100 nanofarads (nF) = 0.0000001 F
1 picofarad (pF) = 0.000000000001 F
100 picofarads (pF) = 0.0000000001 F
270 picofarads (pF) = 0.00000000027 F
CAPACITOR TOLERANCE TABLE

C

+/
0.25pF

D

+/
0.5pF

F

1%

G

2%

J

5%

K

10%

M

20%

Z

+80 20%

Examples:
103K = 0.01µF
i.e 10nF with 10% Tolerance
104K = 0.1µF
i.e. 100nF with 10% Tolerance
334J = 0.33µF with 5% Tolerance
101K = 100pF or 0.1nF 10% Tolerance
102J = 0.001uF or 1nF or 1000pF 5%
Tolerance
473J = 47,000 pF i.e. 47nF or 0.047 uF
5% Tolerance
330K = 33pF 10% Tolerance

POLYESTER
CAPACITORS
WITH
COLOUR CODES:
It is quite
unusual to find capacitors with colour codes as
they are no longer manufactured, but they will
still be found in older equipment and parts boxes.
Sometimes you may run across such polyester caps
which will be marked with coloured stripes rather
than numbers. Three examples of these
polyester capacitors with colour codes can be seen
in the photograph below (Right hand side second
row down).
Below is the colour code for some of these
capacitors and gives the value in PICOFARADS (pF).

FIRST DIGIT
(pF)
First Colour

SECOND DIGIT
(pF)
Second Colour

MULTIPLIER
Third Colour

TOLERANCE
Fourth Colour 
BLACK

0


0


x 1 

20 percent

BROWN

1


1


x 10 


RED

2


2


x 100 


ORANGE

3


3


x 1000 


YELLOW

4


4


x 10,000 


GREEN

5


5


x 100,000 

5 percent

BLUE

6


6


x 1,000,000 


VIOLET

7


7


x 10,000,000 


GREY

8


8


x 100,000,000 


WHITE

9


9


x 1,000,000,000 

10 percent

The Fifth Colour
Band Is The Voltage Rating:
Brown
100 Volts 

Red
250 Volts 

Yellow
400 Volts 


The table for
polyester capacitors works in pretty much the same
way as for resistors.
Look at the photo below and reading from the top of
the capacitor the colours are:
Yellow = 4 Violet = 7 Orange =
Multiply by 1000 Black = 20 %
Tolorance Red = 250 Volts
This capacitor therefore has a value of 47,000
pF (i.e. 0.047µF) +/ 20% at 250V
It must be remembered that unlike resistors there is
no space between the coloured bands so if, for
example, you have 22,000 pF capacitor of this type
there will not be two separate thin red stripes but
one thick red stripe.


POLYSTYRENE
CAPACITORS:
These are quite
rare and often look like silvery plastic cans with
a wire at each end, and being made of polystyrene
are easily damaged by heat, so care is needed when
soldering with the use of a heatsink clip.
Polystyrene capacitors generally have the value in
pF (e.g. 470p) or nF (e.g 4.7n) and may have a
letter to indicate the tolerance as per the table
above (e.g. J  i.e. 5%) printed on the body and
so are quite easy to identify.

The photo below shows
some examples of capacitors both variable
trimmers, fixed electrolytics, ceramic disc,
polyester, tantalum bead and polystyrene types.
The polystyrene capacitors are shown on the bottom
left hand side with the silvery plastic cans 
they are quite rare today and the polystyrene is
easily melted so great care needs to be taken when
soldering.



More
on
voltage
markings.
Although this information is not
entirely confirmed, some
capacitors may have
voltage
indicated by a letter, as in the
table below: (But this
table is unconfirmed
information!)

D =
16 volts

Q =
500 volts

U
= 4000 volts

F
= 25 volts

R =
1000 volts

W =
5000 volts

H =
50 volts

S =
2000 volts

X =
6000 volts

K =
100 volts

T =
3000 volts

Y =
7500 volts

Automatic Conversion
Tool



LIGHT EMITTING DIODES
. 

LED's are
useful devices but need to be treated with
a little care, connected the right way
round and usually need a series resistor
which can be calculated using a fairly
simple formula. So I here is the basic
information you'll need. 

.

The symbol used for
an LED in circuit diagrams (schematic
diagrams) is shown below:
The photographs to the left and right show
the physical appearance of LED's.
Orientation
LED's must be connected into
circuits with the correct orientation
otherwise they will not work, or will be
damaged. The anode is the positive
(+ve) side of the device and this will
be indicated by the longer lead. The
shorter leg will be the cathode, which
is the negative (ve) side of the
device. The cathode is, additionally,
indicated by a 'flat' on the side of the
component's body.
Voltage



Light
Emitting Diodes are generally low
voltage devices and must not be
connected to directly into a circuit. If
they are they will almost certainly be
destroyed. LED's have to be connected
into circuits in series with a resistor
in order to reduce the current flowing
through the device to a safe level.
Calculating The Current Limiting
Resistor:
The series resistor can be
calculated using a simple formula, but the
technical specifications of the LED
concerned ideally need be known
beforehand.
The
Formula: R = (Vs  Vf) / If
Where:
R is the resistor value
Vs is the supply voltage
Vf is the forward voltage drop across the
LED (refer to LED data sheet)
If is the forward current through the LED
(refer to LED data sheet)



E.G. If
the LED specified has an If of of 20mA
(0.02 amps) and a Vf of 2.5 volts and is
to work in a circuit operating at 12
volts, the calculation would be:
R
= (12  2.5) / 0.02 so R = 475 Ohms,
or the next higher standard value.
In practice I usually find that with
most common and typical LED's that a
1.2K or 2.2K Ohm resistor in 12 volt
circuits is a good default value.
AC
Operation
For AC operation a diode such as a
IN4148 is placed in inverse parallel
with the LED and a resistor of half
the value calculated from the above
formula would be used.
Some Typical LED Specifications
The table contains the figures
necessary for calculating the value of
the series resistor for some typical
LED types. If possible, however,
always consult the data provided by
your LED's supplier or manufacturer
for the most accurate specifications.
LED 
Maximum
Forward Current
If 
Typical
Forward Voltage
Vf 
Maximum
Forward Voltage
Vf 
Maximum Reverse
Voltage Vr 
Standard Red 
30
mA 
1.7
V 
2.1
V 
5.0
V 
Standard
Green 
25
mA 
2.2
V

2.5
V 
5.0
V 
Standard
Yellow 
30
mA 
2.1
V

2.5
V 
5.0
V 
Bright Red 
25
 30 mA 
2.0
V 
2.5
V 
5.0
V 
Low Current
Types 
30
mA 
1.7
V 
2.0
V 
5.0
V 
Super Bright 
30
mA 
1.85
V 
2.5
V 
5.0
V 
High
Intensity 
30
mA 
4.5
V 
5.5
V 
5.0
V 
Take the usual care when soldering LED's
into a circuit, although they are
generally quite hardy it is possible to
damage them with excessive heat.
N.B. It is worth noting that there are
some high voltage LED's available that
have the necessary resistor built in to
the body and these may be connected
directly into 12 volt circuits.



OHMS LAW
. 
Calculating
A Voltage Drop
As described above, when using a device such as an
LED or filament lamp that has a lower voltage
requirement than that of the available supply, a
voltage dropping resistor can be included in the
circuit so that the correct voltage is applied to
the component in order that it will not be damaged
or be caused to fail prematurely.
Ohms law (described below) can be used to calculate
the the value of the resistor and also its power
rating.
Example: A 6 volt 300 milliamp bulb is to be used in
a 9 volt circuit. A voltage drop of 3 volts is
therefore required. The value of the resistor is
calculated by the following formula. R = V ÷ I
where R is resistance in Ohms, V is voltage in volts
and I is current in amps. So:
R = 3 ÷ 0.3 = 10 Ohms
The power dissipated (P) is calculated by
multiplying current by voltage: P = I x
V. So:
0.3 x 3 = 0.9 Watts. Therefore a 10 Ohm
resistor of at least 1 Watt will be required in this
example.
Another example: A 6 volt 60 mA bulb is to be used
in a 9 volt circuit. The voltage drop required is 3
volts:
R = 3 volts ÷ 0.06 amps = 50 Ohms (Use a 51 or
56 Ohm resistor, which are a practically available
values).
P = 0.06 amps x 3 volts = 0.18
watts A resistor of at least 1/4 watt
would be therefore be specified. More on Ohms law
below:
OHMS LAW:
The Ohm is the Si unit of electrical
resistance. It is equal to that of a conductor in
which a current of one amp is produced by a
potential of one volt.
Ohms Law: V= I
x R I = V ÷ R
R = V ÷ I
This can be more
easily remembered by using the V I R Triangle:
POWER
(Watts):
Where: P = Watts V
=Volts I = Current in Amps
P = V x
I V = P
÷ I
I = P ÷ V
P = I² x R
P = V² ÷ R
The RMS value of V & I must be
used in circuits using alternating current:
For AC circuits containing nonresistive
components P = V x I x PF
Where PF = Power Factor.
Power Factor is P ÷ S
P = real power, measured in Watts
S = apparent power measured in
voltamperes (VA)
. 
I hope this page has helped out a little!
Please let me know!
Having difficulty
in finding components? I have added some
ideas for electronic component
sources here >
Including some
ideas for sourcing Older Vintage Components

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