AT89C52 MCU based multi-user password lock design (1)

Safety and security has become a social problem.

While the lock is guarded by portal since ancient times the iron General, it requires very high, it is necessary to secure reliable anti-theft and easy to use, this is the system locks to the development of the topic for a long time.

In the design of electronic locks and sale of AB locks are similar, but the main difference lies in the design of this decision by the master password lock to enter the password, the guests do not need to change locks to prevent the use of the lock to enter again, and only the primary talent has the right to change the password.

1 design ideas

The text in the user's password lock is equipped with an administrator user, the administrator has the right to revise the passwords.

There are two guest users, according to the Administrator's password to unlock it, you do not modify the password can be anything. Replace the household, you only need to replace the password to the administrator, so you avoid the hassle of changing locks, saves costs.

Password lock design uses universal plate production, therefore relates to components of the arrangement and alignment problems.

As with an administrator user (master user), you can own and two guest user password change, but also to limit both the guest user's right to modify the password. Therefore, in the password to modify procedures require careful handling, on entering the password to modify a program with two conditions. First of all, is the primary user of the system; secondly, the password to modify key is pressed. In the password input is also special attention, distinguish and confirm what the user enters the current system, i.e. user name and password needed condemnation for which they are designed.

2 system structure and principle

2.1 system structure

Multiple user password lock circuit design is divided into 6 parts: power supply, user display unit, crystal oscillator circuit, keyboard circuit, programming control part, function display unit.

By writing, layout, the 6 parts are combined to form a complete multi-user password lock control circuit, as shown in Figure 1.

2.2 system principle

First of all, to have a crystal oscillator circuit produces the operating clock to MCU internal parts to work properly.

Secondly, the use of parallel port P1 AT89C5l received a 4 × 4 matrix keyboard to P1.3 P1.0 ~ for output line to P1.4 ~ P1.7 for input lines. Matrix row and column line through two parallel interface and CPU communication. By scanning the rows and column values to identify the pressed key encoding to complete the password input, user input and switching, as well as identify, cancel order, password, modify command, user switching command and close the lock command input. Furthermore, the microcontroller through P2 port you want to display data signals to digital tube, direct control of the digital display, which is lit led to display the current user. The entire system to achieve a variety of signal tip function implementation.

3 the function module circuit design

3.1 keyboard circuit

Password lock to enter the password you would use the keyboard.

Design of a 4 × 4 keypad 0-9, in addition to these 10 numeric keys, "OK," "Cancel," "password change" and "locked" and "user switching", and "show off". 4 × 4 matrix arrangement can effectively save port resources, avoid using port expansion module. Install the keyboard, press the 4 × 4 format matrix. In the P1.4 ~ P1.7 output line add la high resistance to allow port exactly reset reset the high, low. La high resistance on the other end is connected together by 5 V power supply. The circuit shown in Figure 2.

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