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forestevanescentΗλεκτρονική - Συσκευές

2 Νοε 2013 (πριν από 3 χρόνια και 5 μήνες)

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Introduction




In our project we designed a circuit which contains a micro controller which
collects the data from sensors placed at different locations of device & display
them into LCD.


Now after collecting the data micro controller compares them wit
h standard
values (pre defined for each sensor on normal working conditions) & if it detects
deviation from normal values it gives a buzzer sound & if it crosses the maximum
limit it trip off the unit for a fixed duration & records the collected data into
EEPROM.

Now if the number of tripping exceeds the 10 no. it permanently trip the unit
& starts them only after detecting the password.


The utility of this circuit are:


1.

To warn the manufacturer at the initial stage of fault so that manufacturer
can take

proper corrective action before serious damage to device occurs
which saves a lot of money required to reconstruct the device and other
associated losses.

2.

Performance observation of the device.

3.

Monitoring of the device.
















Block Diagram Explan
ation




A) Sensors:


This is the part of circuit which senses the different parameters of the unit.

To make the circuit unit independent it is necessary to use a conditioning unit
between sensor & multiplexer. The conditioning unit will automatically main
tain
the output level of signals between desired limits.



B) Multiplexer:


This is required to select sensors one by one for analog to digital conversion of
their values (output). When we are using single ADC the multiplexer must be
analog in nature becau
se we have to connect the analog signals.



C) A/D Converter:


This unit converts the analog signals coming from multiplexer in to 8bit parallel
digital data which is a must for Micro controller operation because Micro
controller can not work with analog s
ignals directly.



D) Micro controller:


As the name indicates this unit has the over all command of all blocks or this unit
decides when to use & which unit has to be used. Since it is a programmable
device it provides the facility to update the device w
ithout changes in hardware &
it also reduces the hardware required to implement the circuit.


E) LCD Display:


Display plays an important role whenever we want a user friendly system because
user can see & read the information from display & can get better

understanding
about the system. Since we want to display alphabets for massages & digits for
readings we required a alphanumeric LCD display so we use a 16 character , 2 line
display best suitable for our requirement because our massage length to not grea
ter
then 16 character, so they can be displayed on single line only.



F)

EEPROM R/W


As we consider a SIM it’s a memory card or ROM which can be erased
electrically because many EEPROM requires different voltage levels to program,
we need a voltage level
shifter or Converter to interface it with microcontroller
which have only two level outputs 5VDC & 0V DC.


G)

EEPROM


It’s a two terminal memory device which stores the Information about the energy
in a predefined format it contains 10, 8bit number interrel
ated by some
mathematical function so that it can not be charged by unauthorized persons
although we have used here a chip which can be used for 256 bytes of memory so
that in future we can incorporate some additional features also in same card.



H)
Key Pad


This section consist the keys one to reset the controller & other one to provide the
password.



I)

Indications & Beeper


Although we are using here a LCD display to display the information but it is still
requirement of a system that it sho
uld create the special attention of user to read
same specific information on LCD this is done by this block. It generates a beeping
sound on over loading mode. So that user need not to read the LCD frequently
(when not required).







J) Relay & tripping unit


To disconnect the supply when tripped.





















Working



At this end we firstly use the different types of sensors according to the system t
o
be monitored & the o/p of sensors is applied to multiplexer IC CD4051 which is an
8x1 analog multiplexer but because we are using only four sensors , we ground the
third selection line to make the mux 4x1.




The selection of mux line is done by micro co
ntrollers pin 21&
22 which are the two least significant bits of port 2 of micro controller as it
provides the selection signals to mux the mux connects the particular sensors o/p to
ADC 0804 pin6 through a resistor (1k) & zener (5v), the resistor & zener
protect
the ADC by limiting the maximum voltage upto 5v because a voltage greater than
this can cause permanent damage to ADC 0804.




Because ADC 0804 works on successive approximation the
weightage of MSB defined by biasing of pin no.9 which is adjustabl
e by 2.2k,
hence we can adjust ADC to convert the analog signal from zero to any defined
level upto 5v. To perform the conversion IC also requires a clock which is
generated here by a 10k resistor & 150 pf capacitor thus providing a clock of
approximately
600 KHz.




To convert the analog signals available at pin 6 of the IC we
require a WR pulse at the pin 3 of IC & this pulse is provided by pin 23 (p2.2) of
micro controller. After getting the WR pulse IC needs some time to (approx.100

s)
convert analog si
gnal into digital. After conversion ADC produces the 8 bit digital
o/p which is collected by micro controller by its port zero.




Now micro controller matches the data with programme written
in assembly language & if it detects the abnormal reading it sta
rts the 3 min. timer
designed by 555 IC. The 555 IC is working here in mono stable mode & produces
the high o/p at its pin 3 for 3 mins. & this high signal drives the tr. BC548B which
operates the relay. Since relay consists of a coil hence to protect the
transistor
during switching a free wheeling diode is connected across the coil.



If micro controller detects that sensors reading is crossing the
dangerous limits it also operates the relays to turn off the unit.