12-07-2012, 12:28 PM
electronic number lock
Electronics Number Lock.DOC (Size: 239.5 KB / Downloads: 42)
Introduction
A lock is an integral part of every house. A man can have peace of mind only when he has a proper mechanism to lock his house when he is away. At present mechanical locks are being used. These locks have levers in them that are used to lock or unlock the unit. Keys that have a particular pattern of cuts and notches on them control these levers. Each lock opens only if the pattern of cuts and notches inside it match with the pattern on the key.
The main disadvantage of this mechanism is that one cannot open the lock if one has lost or misplaced the key. The house owner will be stranded outside his house if he loses the keys to his front door. This conventional lock-and-key mechanism poses a lot of security problems too. Any number of duplicate keys can be easily made from the original key. These duplicate keys may be used for unauthorized access without the knowledge of the owner. Burglars may find the right key to open the lock by trying different keys one after the other from a bunch of keys. An expert thief doesn’t even need a proper key to open a lock. He can merely do it with a hairpin. If everything else fails, the thief can physically break open the lock.
As Electronics Engineering students, we have tried to develop an electronic mechanism to overcome these problems. We present here, an Electronic Number Lock system. This lock opens only when the user types in the correct code set earlier. Unauthorized access is impossible since no one can enter without the knowledge of the code. The entry of a wrong code more than twice sets off a buzzer that informs the owner or neighbours of an intruder. Since the locking mechanism is placed inside the house, tampering with the lock is not possible. Multiple access is possible since anyone possessing the code can open the lock. This is not possible with the conventional lock-and-key mechanism unless each user has his own key. The code number to open the lock can be easily changed by the user whenever he wishes. This lock can be used in homes, cars, safes or anywhere where there is a locking requirement. Thus, this innovative project provides a safe and tamper-proof locking solution.
Description
The Electronic number lock has four main parts- a DTMF keypad, a set of thumbwheel switches, a logic circuit and an electromagnetic locking mechanism. The keypad is installed outside the house along with a switch for opening the lock (‘Open’) and a switch for clearing the memory (‘Clear/Lock’). The thumbwheel switches, logic circuit and the electromagnetic locking mechanism are installed inside the house. Two switches – one for opening the lock and another for clearing the memory are also installed inside. The user can set the three-digit code number using the thumbwheel switches. Anyone trying to open the door should, first type the correct code through the keypad. Once the correct code is set he can use the ‘Open’ switch to open the lock whenever he wishes. An ‘Open’ LED (Green) informs the user that the correct code has been keyed in. When the user wants to clear the memory of the correct code, he may use ‘Clear/Lock’ switches either from inside or outside. When this is done, a ‘Locked’ LED (Red) lights up. Hence, when the user leaves the house, he merely has to press the ‘Clear/Lock’ switch to lock the door. Locking from inside is done in the same way using the ‘Clear/Lock’ switch installed inside. Attempts to enter the wrong code more than two times will sets off a buzzer installed in a hidden location. This alerts the owners/neighbours of the presence of the intruder. Only typing the correct code can reset this buzzer. The user can open the lock from inside by just pressing the ‘Open’ switch installed inside.
Working
The working of the main parts of the circuit is explained below in detail.
THE DTMF KEYPAD:
The keypad circuit consists of a telephone dialler keypad, a dialler IC (UM91214) and a decoder IC (KT3170). The principle of DTMF (Dual Tone Multi-Frequency) is used to generate the BCD code of the pressed digit. Each digit in the DTMF code corresponds to a combination of two discrete frequencies one each from a low and a high group of frequencies, which are generated when any switch on the dialler keypad is pressed. Figure shows such a keypad along with the frequencies associated with each row and column. The keypad is used in conjunction with the dialler IC UM91214 to generate the pair of frequencies. The DTMF signals are decoded by IC KT3170 to give the BCD code of the pressed digit.
THE THUMB WHEEL SWITCH:
The user sets the three-digit code number using the thumbwheel switches. Each thumbwheel switch generates the BCD code of the number selected. Flipping the handle of the thumbwheel switch changes the selected numbers.
THE LOGIC CIRCUIT:
The logic circuit compares the numbers typed in by the user with the numbers set on the thumbwheel switches. Both the signals from the keypad and the thumbwheel switches are in the BCD format. The number comparisons are done by the XOR gates. Each significant digit of the thumb wheel switch and the keypad outputs are wired to the corresponding pins of an XOR gate. The XOR gate gives a ‘LOW’ output only when both its inputs are either ‘HIGH’ or ‘LOW’. Hence, there are four XOR gates for comparing each number. The outputs of the XOR gates are wired to two OR gates. If both the numbers match, the outputs of both the OR gates will be ‘LOW’. If there is any mismatch, the output of either or both OR gates will be ‘HIGH’. The outputs of the OR gates are wired to a NOR gate.