Environmental Engineering Reference
In-Depth Information
The control data moves to the I/O through the data
bus. If any result during data processing needs to
be remembered that should be stored in the data
memory. All the memories and I/O have addresses
so that they can be uniquely selected through the
address bus and then data can be moved through
the data bus to the right memory location or I/O
port. It is to be noted that, address bus is unidirec-
tional. This shows that, ALU can select memory
address and I/O port address. Whereas, data can
be moved from ALU to memory or memory to
ALU as the data bus is bi-directional.
in-built heavy storage battery is required. Motors
with low ratings cannot carry this heavy load and
should be replaced by heavy rating motors. Now
the motors need a heavier battery which in its
turn needs higher power motors. Thus, the system
enters into a vicious circle. On the other hand if
these standard microcontrollers are replaced by
low power microcontrollers with power rating
of 1 micro-Watt the system power consumption
sums up to 0.20001 Watts or 200 milli-Watts ap-
proximately. This power can be delivered by a
very light-weight battery.
Passive or No Battery Devices
NEED FOR LOW POWER
Radio Frequency Identification Devices (Agarwal,
2006) tags or RFID tags can be passive. Passive
tags have a very long life. If there is no wear and
tear it may work for ever. The tag functions when
it extracts power from the detector or interrogator.
Thus the tag power is limited and this may limit the
functionality of the tag. For information privacy,
cryptography or secret coding must be done on
the information sent by the tag (Stallings, 2003;
Mitra 2008). Cryptography is computationally
intensive and must function with the limited power
of the tag. Chae (2007) has shown that information
security can only be provided when an ultra low
power microcontroller MSP430 (Davies, 2008;
MSP430 documents webpage, 2010) a product
of Texas Instruments is used.
Is there any need for power optimization of a
microcontroller? Like any electronic device mi-
crocontrollers are low power device. In a system
the maximum power consumption takes place for
electrical machines. A dc motor may consume
energy at kilo-Watts. Compared to the machine
power a standard microcontroller consumes
only milli-Watt power. We can conclude that, in
a controlled system the power consumed by the
microcontroller is negligible. If a standard mi-
crocontroller consumes almost zero power then
what is the point to further minimize the power?
Rather we should try to optimize the electrical
machine power used in the system. Considering
specific examples we shall show that, at times a
small reduction in microcontroller power reduces
the power consumption of the electrical machine
used in the system. Following points justify the
need for a low power microcontroller.
Use of Unconventional
Energy Sources
Many unconventional energy sources e.g. solar
energy, wind power energy, vibration energy have
been identified. These are not widely used as the
power delivery capabilities of these sources are
very poor. These energy sources can be tapped
for an ultra low power microcontroller. Consider
a wireless sensor network (Sonavane, 2009) that
is used to prevent unauthorized tree cutting in a
dense forest. The sensor attached to the tree may
Object in Motion
Consider a tiny robot that moves on wheels. These
wheels are powered by 2 motors. There are 10
in-built microcontrollers to sense environment
and to control movement. Each unit has a power
rating of 100 milli-Watt. Total power consump-
