PROGRAMMABLE NUMBER LOCK SYSTEM
Programmable number lock system is a
high security number lock system that can be used to lock electronic devices.
The present system is very user friendly. This system is a combination of
software and hardware at its best. We have used a 8051 microcontroller kit for interfacing
our system.
In the present design we can activate or deactivate 9 devices. Each device is locked using a 4 digit code (password). The code can be set as per the user’s desire, hence the name ‘PROGRAMMABLE‘. To activate (unlock) the device, the user should enter the code that had been entered when the device was locked. In case the user enters the wrong code a silent alarm will be activated.
BLOCK DIAGRAM
The system has three units, namely:
- Keyboard unit.
- Display unit.
- 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 units are connected to this unit.
All these three units are merged
together to form the whole system.
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 is 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.
Working of the system:
When the system 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 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 ,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.
The ‘Electronic device number lock’ system is a high security system. The main application kept in mind during the design of this system is to secure expensive electronic devices and machinery. The access to such devices can be restricted to particular users only. The system is highly secured since the code can be changed every time the user locks it.
This can also be used an physical lock by using solenoid and thus can be used to lock safes in banks or other institutions.
Regular electronic number lock available in the market can lock/unlock just one device, but this design can lock/unlock up to nine devices.
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