Basic Idea

Problems

With each family, offices, companies, business, schools and everywhere, we're completely need to secure our properties. Every door we should equip with a lock. Current markets are having many lock types and usually are mechanical lock; this mechanical lock had a big problem were low security, because it's easy to break by multipurpose kit.

Digital Locks generally are the security lock to prevent the devices, the property… from stealing. And when we want to unlock, we need to use the installed code. There are 2 general types in current market are Electric Digital Locks and Mechanic Digital Locks.

•  Mechanic Digital Lock: when unlock or lock we need to rotate the numerical circle in the lock to make a sequence couple with the installed sequence and the lock be unlocked.
• Electric Digital Lock: when unlock the lock, we need to enter the password is a sequence of numerical. If it's correct, the lock will be opened.

Generally, the Electric Digital Locks have more character and number to be installed, and longer of character sequence than Mechanic Digital Lock, so that Electric Digital Lock has the higher security. On the other hand, the actions in the Electric Digital Lock are easier with keyboard replace with rotate circle in the Mechanic Digital Lock. Moreover, when we want to change the password, it’s seemed to be easier because of keyboard action.

Electrical Digital Lock has high security, easy to use and have the alert action if we enter incorrect password more than condition times. The user interface, display the information about enter password, alert, changing the password make user more easily to use.

Figure 1: The digital lock with LCD display user interface

Coming up with the problems, we try to design and simulate the Digital Lock system, so that we can understand more about this system and figure out some solutions to improve it.

System Requirements

After consider many types of digital lock in current market, we have some requirements of a normal digital lock

• User interface easy to use.
• The password's length has high security.
• Password can change.
• Alert function when enter incorrect password 3 times.
• Rotate motor to control the door have precisely open and close.
•  The system work even when the electrics are shut down.
•  Portable digital lock system.
• The low voltage power used in lock system, do not make user into danger.

Component Selection

With the above requirement about the functions, we have chosen the main components:

• Micro Controller 16f877 with the EEPROM memory can storage the data even the electrics are gone out.
• LCD 16x2 display to show the information, to communicate with user.
• 16-key keyboard have numerical key and the function key to enter password and the open-close order to micro controller.
• Motor to control door open and close.
• Power supply prevent of power failure is accumulator.

Approaching Method

The most important of the digital lock is the keyboard scanning algorithm, and then is the saving and changing the password on the EEPROM. Also, we need some other parts are display the information into LCD display; it's also have some library installed so it's not complicate. Finally, it's the signal out to control the lock door. Therefore, the main algorithms we need to consider are:

• Key scanning algorithms.
• Password storage in EEPROM and changing password in EEPROM
• Display the information into LCD display.

CO