Hardware Reference
In-Depth Information
Building a Circuit that Lights an.LED
The circuit in Figure 5-4 is a simple circuit that can be used to test components. For any
circuit to work, a
voltage
must be applied to it. A 3-volt battery needs to be connected
to the strips at the top and bottom of the breadboard, which are called power rails.
These are long rails that connect the full length of the breadboard, and are a convenient
method of providing electrical power to lots of components at the same time. The red
component is a
light-emitting diode (LED)
, which is a type of light that you will meet
in a moment. The component with coloured bands on it is a
resistor
, and the black
device at the bottom of that is a button. If you follow the wires from the battery right
round through all the components in the circuit, you eventually end up back at the bat-
tery again. This is a complete electrical circuit, and when you press the button, electri-
cal
current
will flow and the LED will light up.
Voltage
is the difference in electrical energy between two points in a circuit. It
is the electrical equivalent of water pressure in pipes, and it is this pressure that
causes a current to flow through a circuit. Voltage is measured in
volts
(V).
A
Light-emitting diode (LED)
lights up when electricity passes through it. A
diode only allows current to pass in one direction. An LED will only light up if
you pass current through it in the correct direction. LEDs come in a variety of
colours and have one short leg (the cathode or negative) and one long leg (the
anode or positive), which helps you to determine which way they need to be
placed in a circuit for current to flow through them.
A
resistor
is an electrical component that resists current in a circuit. For example,
LEDs can be damaged by too much current, but if you add the correct value
resistor in your circuit with the LED to limit the amount of current, the LED will
be protected. Resistance is measured in
Ohms
, and often indicated by the use of
the Omega symbol Ω. You need to pick a resistor with the correct value to limit
the current through a circuit; the value of a resistor is shown by coloured bands
that are read from left to right. You can find out about the resistor colour code
