51 single-chip computer password lock that can prevent multiple password attempts

1. Introduction

Many industries and places need password locks, but the passwords of ordinary password locks are easy to be cracked by multiple attempts. This paper presents a design method of password locks that can prevent multiple attempts, thus effectively overcoming the above shortcomings.

2 Hardware Circuit

Figure 1 shows a password lock circuit designed by the author. The password lock is designed mainly according to the following 10 user requirements:

(1) The password consists of 8 digits in total, and the value range of each digit is 1 to 8.

(2) Users can set and modify passwords by themselves.

(3) There will be sound and light prompts when pressing each password key.

(4) If the 8-digit unlocking password entered is not completely correct, an alarm will sound for 5 seconds to alert others.

(5) If the unlocking password is incorrectly entered three times, an alarm will sound for 10 minutes. During the alarm period, the password entered will be invalid to prevent thieves from trying the password multiple times.

(6) The lock can only be unlocked if the 8-digit unlocking password entered is completely correct, and there should be a 1-second prompt sound when unlocking.

(7) The electromagnetic coil of the electromagnetic lock must be driven by pulses, and each power-on time must not exceed 2 seconds to prevent burning.

(8) Only 8 password keys and 1 LED are allowed on the password keyboard. There is a backup battery in the lock . The password can only be set or modified when the internal power is reset. Therefore, the password cannot be modified or set by pressing the keys outside the door.

(9) After the password is set, there will be a 2-second prompt sound.

(10) The cost should be relatively low, and both the hardware and software should be as simple and reliable as possible, and easy to mass produce.

According to the overall requirements, the password lock circuit requires less than 15 I/O lines. If designed properly, the program will not exceed 200 instructions. Therefore, the high-quality and low-cost AT89C1051/2051 or GMS1051/2051 can be selected, and no external program memory, data memory and other expansion components are required.

In the circuit shown in Figure 1, port P1 is connected to 8 password keys AN1~AN8, unlocking pulse is output by P3.5, and alarm and prompt sound are output by P3.7. BL is a speaker for alarm and sound prompt , light-emitting tube D1 is used for alarm and prompt, and L is the electromagnetic coil of electromagnetic lock.

3. Software Design

Figure 2 shows the software flow chart of the single-chip computer password lock circuit. In the figure, AA1~AA8 and START, SET, SAVE are labels in the program, which are specially marked in the corresponding positions of the flow chart for the purpose of understanding the program. You can carefully refer to them when analyzing the program.

3.1 Allocation of storage units

The allocation scheme of RAM storage unit in the password lock is as follows:

31H~38H: Store the 8-digit set password in sequence, the first digit of the password is stored in the 31H unit;

R0: points to the password address;

R2: The number of digits of the password that has been entered;

R3: stores the difference between the allowed number of code errors 3 and the actual number of code errors;

R4 to R7: for delay;

００Ｈ: Error code flag.

Regarding the allocation of ROM storage units, since the program is relatively short and occupies relatively little storage space, the main program can be stored starting from unit 0030H (other addresses are also acceptable) if there is no special requirement.

3.2 Source Program

Below is the software source code of the electronic combination lock:

ORG ００００Ｈ

AJMP START

ORG ００３０Ｈ

START：ACALL BP

ＭＯＶＲ0，#３1Ｈ

MOV R2, #8

SET: MOV P1, #0FFH

MOV A,P1

CJNE A, #0FFH, L8

ＡＪＭＰ SET

L8: ACALL DELAY

CJNE A, #0FFH, SAVE

ＡＪＭＰ SET

SAVE: ACALL BP

MOV@R0A

ＩＮＣＲ０

DJNZ R2，SET

MOV R5, #16

D2S: ACALL BP

DJNZ R5, D2S

ＭＯＶＲ0，#３1Ｈ

MOV R3, #3

AA1: MOV R2, #8

AA2: MOV P1, #0FFH

MOV A,P1

CJNE A, #0FFH, L9

ＡＪＭＰ ＡＡ２

L9 ACALL DELAY

CJNE A, #0FFH, AA3

ＡＪＭＰ ＡＡ２

AA3: ACALL BP

ＣＬＲ

SUBB A, ＠Ｒ０

ＩＮＣＲ０

CJNE A, #00H, AA4

ＡＪＭＰ ＡＡ５

AA4: SETB 00H

AA5: DJNZ R2, AA2

ＪＢ００ＨＡＡ６

CLR P3.5

Ｌ３ ＭＯＶ Ｒ５，#8

ACALL BP

DJNZ R4, L3

MOV R3, #3

SETPB P3.5

ＡＪＭＰ ＡＡ１

AA6: DJNZ R3, AA7

MOV R5, #24

L5: MOV R4, #200

L4: ACALL BP

DJNZ R4, L4

DJNZ R5, L5

MOV R3, #3

AA7: MOV R5, #40

ACALL BP

DJNZ R5, AA7

AA8: CLR 00H

ＡＪＭＰ ＡＡ１

BP: CLR P3.7

MOV R7, #250

L2: MOV R6, #124

L1: DJNZ R6, L1

CPL P3.7

DJNZ R7, L2

SETPB P3.7

RET

ＤＥＬＡＹＭＯＶ R7,#20

L7: MOV R6,#125

L6: DJNZ R6,L6

DJNZ R7,L7

RET

EN

4 Application Notes

If the keys AN1~AN7 represent numbers 1~7 respectively, and the key AN0 represents number 8. When no key is pressed, P1.0~P1.7 are all high level 1. If a key is pressed, the corresponding port line becomes low level 0. If the set password is 61234578, when the key AN6 is pressed, P1.6 becomes low level, and the rest of the ports of the P1 port are high level. At this time, the value read from the P1 port is 10111111, and the password value stored in the 31H unit is 10111111, which is BFH. By analogy, the password values ​​stored in the 32H to 38H units are FDH, FBH, F7H, EFH, DFH, 7FH, FEH. To unlock, you must first press AN6 to make the first password value read from port P1 the same as the set value stored in unit 31H, and then press AN1, AN2, AN3, AN4, AN5, AN7, AN0 in sequence to unlock. Otherwise, the lock cannot be unlocked and the alarm will start.