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 need to be multiplied by
the third digit in
order to obtain the value in PICOFARADS (pF) as
above. The letter is
present to indicate the tolerance of the
component. So 100
would be 10pF multiplied by zero i.e. 10pF.
103
is 10pF
multiplied by
1000 ie 10,000pF or to put is another way 0.01
microfarads. 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 = 1000pF 10% Tolerance
102J = 0.001uF 5% Tolerance
473J = 47,000 pF i.e. 47nF or 0.047 uF 5%
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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