Keypads have integrated deep into everyday schedule of an average person that it is almost impossible to carry out working on electronic devices without using them. Computer keyboards, calculators, remote controls, game joysticks, electronic locks and ATM machines are just a few cases where one cannot do even a single task without using keypad. It becomes quite uncanny that how deeply this electronic accessory has embedded into lives of a major part of the population. Various types of keypads exist as per user’s requirements. For instance, computer and some smartphones have QWERTY keypad while calculators and simple telephones come with an alphanumeric keypad.

Keypad is most widely used input device to provide input from the outside world to the microcontroller. The keypad makes an application more users interactive. [[wysiwyg_imageupload::]]The concept of interfacing a keypad with the ATmega16 is similar to interfacing it with any other microcontroller. The article of Interfacing keypad with 8051 can be referred for detailed description of the methodology used here. This article explains the interfacing of a 4×3 keypad with AVR microcontroller(ATmega16) and displaying the output on a LCD. The algorithm and detailed explanation for keypad interfacing is given in above mentioned article. The brief steps to interface the keypad with AVR are written below:1.                  Configure the row pins or column pins.2.                  Make all output pins to low and input pins to high.3.                  Keep monitoring the port value, where the key pad is connected.  

The basic operations of servo motor control have been discussed in interfacing servo with 8051. This project allows the servo motor to move to an angle specified [[wysiwyg_imageupload::]]by the user. The pulse train required to rotate the servo is produced by AT89C51 microcontroller. The desired angle of rotation is provided through a 4×3 keypad interfaced to the microcontroller. A 16×2 LCD is also connected with the microcontroller to display the angle of rotation entered by the user. For basic operations and control of servo motor, refer interfacing servo with 8051. The first pin of port P1 (P1^0) of AT89C51 microcontroller is set as the output pin to provide control signal to the servo motor. Ports P0 and P2 are used to interface keypad and data pins of LCD, respectively. Ports P1^3, P1^4 and P1^5 are connected to RS, RW and EN pins of LCD, respectively.  Before connecting to the control wire of servo, the output from the microcontroller (P1^0) is fed through a comparator IC (LM324) so that the signal is protected from any loss due to overloading. 

An alphabetic keypad is similar to a numeric keypad, but it provides the complete set of alphabetical letters instead of numbers 0-9. This article presents a way to [[wysiwyg_imageupload::]]interface a keypad with 8051 microcontroller (AT89C51) to display alphabetical characters on an LCD module. Such kind of systems is commonly used in mobile phones to write an SMS and other texts. It can have further applications in displaying instant messages on other display systems such as LED matrices or other multi-segment displays. A 4×3 matrix keypad and a 16×2  LCD has been used here. Keypad and LCD are very commonly used input & output devices, respectively. The connections in the circuit are as following: port P2 of microcontroller AT89C51 is used as data input port which is connected to data pins (7-14) of LCD. P3^0, P3^1 and P3^2 pins of microcontroller are connected to control pins RS, RW and EN of LCD. Port P0 is used to take input from keypad. 

 Keypad is a widely used input device with lots of application in our everyday life. From a simple telephone to keyboard of a computer, ATM, electronic lock, etc., [[wysiwyg_imageupload::]]keypad is used to take input from the user for further processing. In this article we are interfacing keypad with the MCU AT89C51 and displaying the corresponding number on LCD.  This module can be further used in a number of systems to interfaced keypad with microcontroller and other processors to get desired output. The program to interface keypad with controller is written in C language which is very easy to understand. The concept of interfacing keypad with the MCU is simple. Every number is assigned two unique parameters, i.e., row and column number (n(R, C) for example 6 (2, 3)). Hence every time a key is pressed the number is identified by detecting the row and column number of the key pressed.