Capacitors
store electric charge. They are used with resistors in timing circuits
because it takes time for a capacitor to fill with charge. They are used to
smooth varying DC supplies by acting as a reservoir of charge. They are also
used in filter circuits because capacitors easily pass AC (changing) signals but
they block DC (constant) signals.
Diodes allow electricity to flow in only one direction. The arrow of the
circuit symbol shows the direction in which the current can flow. Diodes are
the electrical version of a valve and early diodes were actually called
valves.
Resistors restrict the
flow of electric current, for example a resistor is placed in series with a
light-emitting diode (LED) to limit the current passing through the LED.
Integrated Circuits are
usually called ICs or chips. They are complex circuits which have been
etched onto tiny chips of semiconductor (silicon). The chip is packaged in a
plastic holder with pins spaced on a 0.1" (2.54mm) grid which will fit the
holes on stripboard and breadboards. Very fine wires inside the package link
the chip to the pins
Lamps emit light when an
electric current passes through them. All of the lamps shown on this page
have a thin wire filament which becomes very hot and glows brightly
when a current passes through it. The filament is made from a metal with a
high melting point such as tungsten and it is usually wound into a small
coil. Filament lamps have a shorter lifetime than most electronic components
because eventually the filament 'blows' (melts) at a weak point
LEDs emit light when an
electric current passes through them.
Transistors amplify
current, for example they can be used to amplify the small output current
from a logic chip so that it can operate a lamp, relay or other high current
device. In many circuits a resistor is used to convert the changing current
to a changing voltage, so the transistor is being used to amplify voltage.
Variable resistors
consist of a resistance track with connections at both ends and a wiper
which moves along the track as you turn the spindle. The track may be made
from carbon, cermet (ceramic and metal mixture) or a coil of wire (for low
resistances). The track is usually rotary but straight track versions,
usually called sliders, are also available.
A relay is an
electrically operated switch. Current flowing through the coil of the relay
creates a magnetic field which attracts a lever and changes the switch
contacts. The coil current can be on or off so relays have two switch
positions and they are double throw (changeover) switches
An
LDR is an input
transducer (sensor) which converts brightness (light) to resistance. It is
made from cadmium sulphide (CdS) and the resistance decreases as the
brightness of light falling on the LDR increases
