1.0 INTRODUCTION

Due to the advancement of science and technology throughout the world, there is a consequent increase in the rate and sophistication of crime. As a result, it is necessary to ensure security of oneself and one’s valuable belongings. Even with the use of mechanical locks, the crime rate still has increased due to the fact that these locks are easily broken. Consequently, there is a need for other types of locks -especially electronic ones. This work is on construction of a digital electronic combination lock system with a keyboard to be mounted on the door for keying in the secret code. The code unit, which operates with a 9-switch (non- matrix) keyboard was designed to control an electromagnetic door lock with a four-digit code. Unlike other keyboard combination locks this lock is constructed in such a way that once any of the wrong keys is pressed, it resets automatically making it harder for an intruder to break into.

The increasing rate of crime, attacks by thieves, intruders, vandals etc., despite all forms of security gadgets and lock constitute the main factor that prompts the selection of this work. Materials used for the construction of the circuit were sourced and put together locally. Due to financial and time constrains a 4013 IC was used instead of programmable IC. As the limitation for the design, the 4013 IC is a data latch for data storage, the data stored cannot be changed in the case of code being compromised but the data can be changed in the programmable IC if there is any compromise.

1.1 PRINCIPLE OF THE SYSTEM

The circuit is built around two 4013 dual D flip-flop (FF.)Each 4013 contains two D flip-flops. The four FF areconnected to A, B, C and D pads. ABCD gives the 4 digitswhich must be keyed in in sequence for the relay to trigger.The five remaining digits may be connected to the RESETPAD. If one of these digits is keyed in during the ABCDsequence then the circuit will reset.

The circuit diagram and the block diagram of the 4013show how the lock works. The ABCD touch pads areconnected to the Clock input pins 3 and 11 of each 4013.ABCD pads are normally tied low by the 4M7 resistors.Touching the pads of each keypad briefly pulls the inputhigh and the state of the FF is altered. The output Q pins (1and 13) are wired so that when the correct sequence iskeyed in then pin 13 of IC2 turns on the transistor.The reset keys are all wired to the Set pins (6 and 8) ofeach IC.

Here the correct code is2,4,7,8. That is, we will to touch 1 then 3 then 5 then 7 onthe Remote Keypad for the relay to trigger. Touching any other number will make the system to reset the unit.On the main PCB connect Pad A to one of the pads on line1 using some of the hookup wire provided. Connect Pad Bto a pad on line 3, pad C to a pad on 5, Pad D to a pad on line 7. Now connect the five remaining numbers to the fivepads on the RESET pad. Connect a 9V power supply. The Combination Lock is now ready. It can switch a main powered device such as a light.The 4013 IC's will work from 3V to 18V so the unit isquite flexible and can be adapted to many situations.

1.3 OBJECTIVES OF THE STUDY

The main objectives for embarking on this project of construction of a digital combination lock system are;

i. To construct a cheap and effective security system for buildings, cars, safes, doors and gates.

ii. To experiment the application of electronic devices as locks.

iii. To prevent unauthorized person from having access to ones properties through the use of codes.

iv. To raise awareness on the topic of security or access control.

v. To utilize the available components to construct a working model of a digital combination lock system.

vi. To construct and test the designed system so as to see if it can perform as specified.