Resistors - The Current Valve
Circuit Symbol
Resistors restrict the flow of electrical current. The
higher the value of resistance (measured in ohms) the lower the current
traveling through it
will be.
Think of current as water moving through a system of
pipes (wire connections) and resistors are the valves that allow you to
regulate how much water goes through a particular pipe over a given
period of time.
Unlike most of the other electronic components, resistors are
non-directional. This means that you don't ever have to worry about
which way you stick them onto a circuit board; they just work. (However,
it is very important for other components to be
placed in the proper direction!)
Function
Resistance is measured in ohms, the symbol for an ohm being an omega
 .
The most frequently used resistor values are often given in k
(1 kilo-ohm = 1000
)
and M
(1 mega-ohm = 1000 k).
Most resistors will have four colored bands.
Three of the bands are used to indicate the resistance value and the fourth indicates the tolerance of the part.
Some resistors will have five colored bands.
In these cases the first four indicate the resistance value and the last one is the tolerance band.
In either case, you need to separate the tolerance band from the
resistance bands.
The tolerance band will usually either be gold or silver, or it will be
separated from the other bands by a larger space than the rest.
Once you've identified the tolerance band, start reading
the resistance bands from the other end of the resistor.
Most resistors have 4 bands:
-
The first
band gives the first digit.
-
The second
band gives the second digit.
-
The third
band indicates the number of zeros.
-
The fourth
band is used to shows the tolerance (precision) of the resistor, this
may be ignored for most circuits.
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