Circuit Project Description
The circuit was designed to function as an electronic keyboard using CMOS 4081 integrated circuit.
Terminology Keypad – a set of buttons arranged in a block which usually display digits and other symbols but not a complete set of alphabetic lettersCMOS 4081 – a quad dual input AND gate in a 14-pin package generally characterized with small fluctuation, very high impedance, outputs that can sink and source, one output can drive up to 50 inputs, high speed gate propagation time, high frequency, and low power consumption. Circuit Explanation
The theory imposed by CMOS 4081 is the AND operation wherein high inputs would result to a high output. In setting the alarm on the circuit, a single key is pressed like the combination of non-numeric symbols. The transistor Q5 will be turned on by resistor R8 when the relay is boosted because of the current from R1 and D1 by pressing the key attached to E. As soon as the 4 keys connected to A, B, C, D are pushed in the right order, the alarm will switch off. The code entry fails if any key other than the correct are pushed which will eliminate the function of gate 1.
The circuit is performing well because the gates are positioned to their corresponding circuit. To enable gate 1, the output in pin 1 should be maintained high while the output in pin 3 will go high when button A is pushed. With this, the output secures itself ON through R2 and enables gate 2. If button B is pressed, the output at gate 2 at pin 4 will go high. With this, the output secures itself ON through R3 and by taking pin 12 high, it enables gate 3. If button C is pressed, the output in gate 3 will secure itself ON through R5 and by taking pin 8 high, it will enable gate 4. If button D is pressed, it sets off gate 4 to do the same procedure but this time, its output at pin 10 will turn Q4 ON which will switch OFF Q5 by taking the base of Q5 to ground and permits the relay to withdraw. Because of this, the alarm will turn OFF.
All keys are attached to Q1 except those of A B C D E. The circuit is reset and pin 1 takes low output, everytime button E or any other keys is pressed, and as a result, nothing happens until button A is pressed. The same procedure also applies to buttons B,C and D, the circuit will reset upon pressing the button..
Using a numeric keypad is not that necessary as it can be customized according to the desired functions. Additional CMOS 4081 is preferred for a more secured code while maintaining the process of enabling subsequent gates.
Keypads are found on many alphanumeric keyboards and on other devices such as calculators, combination of locks and telephones which require largely numeric input. Electronic keypads can be used areas such as factory floor, machine control, process control, automation industry and for aircraft cockpit door locking systems. Other common applications as they offer more security features were in conjunction with electric devices and security accessories such as egress buttons, break glass units and exit sensors. Electronic keypads has a convenient way of passing through a door where access is restricted. The keypads work on the basis that the person passing through the door would need to know the access code to gain entry.
There’s a wide selection of keypad access control system that are used to restrict or allow the physical access of a person into an organization. İt may come in standalone, compact or card based access control terminal which are user friendly and finds application in offices , residences and other organizations. Some of these would be door access control system which are used in offices, banks, prisons and other establishments. Another application is the electronic access control systems that comes with features like wiring connections, electric lock, external bell, external push switch, magnet contacts and alarms. The entry access control systems provide reliable functioning and helps in meeting the safety requirements of office building, hotel, factories, home, apartment and others.