3.1.8 Password Lock

Introduction

In this project, we will use a keypad and a LCD to make a combination lock. The LCD will display a corresponding prompt for you to type your password on the Keypad. If the password is input correctly, “Correct” will be displayed.

On the basis of this project, we can add additional electronic components, such as buzzer, LED and so on, to add different experimental phenomena for password input.

Required Components

In this project, we need the following components.

It’s definitely convenient to buy a whole kit, here’s the link:

Name	ITEMS IN THIS KIT	LINK
Raphael Kit	337	Raphael Kit

You can also buy them separately from the links below.

COMPONENT INTRODUCTION	PURCHASE LINK
GPIO Extension Board	BUY
Breadboard	BUY
Jumper Wires	BUY
Resistor	BUY
I2C LCD1602	BUY
Keypad	-

Schematic Diagram

T-Board Name	physical	wiringPi	BCM
GPIO18	Pin 12	1	18
GPIO23	Pin 16	4	23
GPIO24	Pin 18	5	24
GPIO25	Pin 22	6	25
GPIO17	Pin 11	0	17
GPIO27	Pin 13	2	27
GPIO22	Pin 15	3	22
SPIMOSI	Pin 19	12	10
SDA1	Pin 3
SCL1	Pin 5

Experimental Procedures

Step 1: Build the circuit.

Step 2: Change directory.

cd ~/raphael-kit/c/3.1.8/

Step 3: Compile.

gcc 3.1.8_PasswordLock.cpp -lwiringPi

Step 4: Run.

sudo ./a.out

After the code runs, use the keypad to enter the correct password: 1984. If the “CORRECT” appears on LCD1602, there is no wrong with the password; otherwise, “WRONG KEY” will appear.

Note

• If there is an error prompt wiringPi.h: No such file or directory, please refer to Install and Check the WiringPi.

• If you get Unable to open I2C device: No such file or directory error, you need to refer to I2C Configuration to enable I2C and check if the wiring is correct.

• If the code and wiring are fine, but the LCD still does not display content, you can turn the potentiometer on the back to increase the contrast.

Code Explanation

#define ROWS  4
#define COLS  4
#define BUTTON_NUM (ROWS * COLS)
#define LENS  4

unsigned char KEYS[BUTTON_NUM] {
'1','2','3','A',
'4','5','6','B',
'7','8','9','C',
'*','0','#','D'};

char password[LENS]={'1','9','8','4'};

Here, we define the length of the password LENS, storage matrix keyboard key value array KEYS and the array that stores the correct password.

void keyRead(unsigned char* result);
bool keyCompare(unsigned char* a, unsigned char* b);
void keyCopy(unsigned char* a, unsigned char* b);
void keyPrint(unsigned char* a);
void keyClear(unsigned char* a);
int keyIndexOf(const char value);

There is a declaration of the subfunctions of the matrix keyboard code, refer to 2.1.8 Keypad of this document for more details.

void write_word(int data);
void send_command(int comm);
void send_data(int data);
void lcdInit();
void clear();
void write(int x, int y, char const data[]);

There is a declaration of the subfunctions of LCD1062 code, refer to 1.1.7 I2C LCD1602 of this document for more details.

while(1){
        keyRead(pressed_keys);
        bool comp = keyCompare(pressed_keys, last_key_pressed);
        ...
                testword[keyIndex]=pressed_keys[0];
                keyIndex++;
                if(keyIndex==LENS){
                    if(check()==0){
                        clear();
                        write(3, 0, "WRONG KEY!");
                        write(0, 1, "please try again");
                        }
                ...

Read the key value and store it in the test array testword. If the number of stored key values is more than 4, the correctness of the password is automatically verified, and the verification results are displayed on the LCD interface.

int check(){
    for(int i=0;i<LENS;i++){
        if(password[i]!=testword[i])
        {return 0;}
    }
    return 1;
}

Verify the correctness of the password. Return 1 if the password is entered correctly, and 0 if not.

Phenomenon Picture