Environmental Engineering Reference
In-Depth Information
Figure 1. Basic building blocks of a microcon-
troller
control should be such that it minimizes the devia-
tion smoothly. A positive temperature deviation
should remain positive throughout the control
(Radakovic 2002).
Microcontroller is a very efficient controller
since it has all these attractive features of control.
Microcontroller finds wide use in embedded
systems (Kamal, 2003). To understand what
Embedded System is, we begin with an example.
Most of us use automatic washing machine to
wash our clothes. A fully automated washing
machine may automatically decide the quantity of
detergent, water temperature, time for wash etc.
(Yin-Win, 2009). These decisions will be made
by a microcontroller or a similar processor that is
embedded inside the washing machine. Though
there is a computing machine inside the washing
machine none thinks of doing some computation
with the help of a washing machine. Microcon-
troller is used to make the machine automatic but
it still washes clothes and does not function like
a computer. For this reason the microcontroller
is looked as an embedded system for the washing
machine. Embedded system can be defined as a
system with electronic processing capability that
is embedded in equipment whose primary task is
different from electronic processing. A desktop
computer has a microprocessor inside it to en-
dow it with computing or electronic processing
capabilities. But this microprocessor cannot be
called an embedded system, as desktop computer
is primarily used for computing i.e. its primary
task is quite similar to the microprocessor.
Microcontrollers are good candidates for real
time applications. In a real time application the
processor should be ready to accept the input at
a particular instant and the output from the pro-
cessor should be guaranteed after a definite time
interval. If a delayed output means a disaster then
the application is a hard real time application.
An embedded system in a satellite launcher may
generate specific outputs to control the speed at
different instants. Failure to give this specific
output at a specific instant shall end up in an un-
successful mission resulting in a heavy loss and
damage. In this case, the application is a hard real
time application.
Embedded systems have a great market poten-
tial. While purchasing an equipment or device the
customer asks for various automatic controls. A
customer expects a smooth shaving without any
cut in the skin from a safety razor. Proper use of
embedded system in a razor may give this satis-
faction. As the technology of embedded proces-
sor matures it finds more and more widespread
applications.
Now with the understanding of the role of a
microcontroller with some specific examples,
we can identify its basic building blocks and
interfaces as given in fig. 1. The function of a
microcontroller can be understood for the furnace
temperature control discussed earlier. The block,
I/O interface, interacts with the external world.
The temperature of the furnace is received from a
temperature sensor as an input and the control for
the heater element is sent as an output through this
interface. A microcontroller processes only binary
numbers. A stream of 1s (usually high voltage e.g.
2.5 volts) and 0s (usually low voltage e.g. 0 volt)
are received at the I/O. This stream can be received
serially bit by bit or can be received through the
parallel port. The temperature data is brought by
the data bus to the Arithmetic Logic Unit or ALU
and processed. A suitable algorithm executed in
the ALU determines the heater control current.
