51 microcontroller design with four key input and 1 digital tube display simple trick lock, the specific requirements: (1) four buttons, respectively 0,1,2,3;

(2) the password set in advance is a number between 0 ~ 3;
(3) digital tube display "-", said wait for password input;
(4) about 3 s password correctly display "P", and through the P3.0 port open the lock. According to "E" about 3 s, continue to keep it locked,