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Introduction
to
Programmable number lock system:
The
system has three units, namely:
( i ) Keyboard
unit.
( ii ) Display
unit.
( iii ) Control
unit.
The keyboard unit consists of 9 number keys, 1
unlock key and 1 lock key. These are all push button switches.
This unit is used to select the desired device and to enter
the codes into the system. It is also used to request the
system to lock/unlock the selected device.
The
display section contains 5 seven segment display. This unit displays
the device number and the code entered. This section is
detachable. If detached it does not affect the working of the
whole system. This unit also contains password reset button
and an LED to indicate the error when the device is already
locked and user wants to lock the device again. The error
indicator also indicates an error when the system is already
unlocked and the user tries to unlock the same.
The control unit is the heart of our system. It contains
the necessary circuitry for the control of the device .This
unit controls 9 devices, which is lock/unlock by
selecting it using the keyboard and entering the password. If
the code entered to unlock the device is wrong, then a silent
alarm is triggered .The keyboard unit and the display unit are
connected to this unit.
All these three
units are merged together to form the whole system.
Block
diagram of
Programmable number lock system:
Click here to know about 8051 Microcontroller:
Working of the system:
When the system is initially installed the reset button is
pressed. This key is present in the control unit. This unlocks
all the devices. This is to avoid undesired functioning of the
system.
To lock a
particular device the device number is selected using the
keyboard. Once the device is selected the user has to press
the lock key present in the keyboard. Now the device waits for
the user to enter the the code. The user can enter a 4 digit
number using the keyboard as per his desire. Once all the 4
digits are entered the system electronically locks the
selected device.
In the
same manner to unlock a particular device, the device number
is entered using the keyboard. Once the device number is
selected the code for the selected device is entered. If the
entered code matches the code that had been entered while that
particular device was locked then the selected device will be
activated (unlocked). If the codes do not match each other a
silent alarm will be triggered (a LED placed in the control
section. Shown in figure 3).An error indicator (placed in the
display section) is provided if any user tries to lock a
device which has already been locked or vice versa.
If the
user is half way entering the code or has done an error while
entering the code and wants to start over all again then a
reset button is provided in the display section. By pressing
this button the user can start from entering the device number
and so on.
The number
of devices which the system can control can be increased by
addition of a few components in the control unit. More
security can be achieved by increasing the number of digits in
the code. This can be done by minor changes in the program.
The system uses the internal RAM of the 8051 to store the code
and hence puts a lower limit to the number of digits in the
code and also the number of devices the system can control.
Once the system is installed only the display unit and
keyboard unit will be accessible to the user. Access to the
control unit should be provided only to an official personal
since it contains the system reset button.
System:
In this section
we will be explaining the hardware design these units
individually. Each unit description is accompanied by its
circuit diagram.
KEYBOARD UNIT
:
The
keyboard used in this system is an encoder type. It uses IC
74147 priority encoder to convert the entered the digits to
its corresponding binary codes. IC 74147 has a active low
inputs as well as active low outputs (for more details please
refer the corresponding data sheets). Each of the pins are
activated using push to on switches. These switches ground the
encoder inputs to activate that particular number giving the
equivalent BCD code. This is then given as input to IC 7404
which is an inverter. To avoid loading of 7404 by the later
stages transistor switches are provided to each of its
outputs. The circuit diagram of the keyboard is as given in
the next section.
DISPLAY
UNIT
:
The logic
used here is shift and display i.e. when the next number is
entered the previous number is shifted to the left by one unit
and then the next number is displayed. To achieve this we have
used IC 7496 which is a 5–bit shift register (for more details
please refer the corresponding data sheets). The data lines
from control section are given serially to the registers as
shown in the circuit. The clock to these registers is given by
the program every time a button on the keyboard is pressed.
The shifting used here is parallel shifting. The outputs of
the registers are given to CD4511 BCD to seven segment
decoder. The seven segment display used are common cathode
type since the output of the decoder is high when activated.
This section consists of a reset switch which is used to reset
the display.
Control unit
The program codes for this project is given in
the next page
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