DESIGN AND CONSTRUCTION OF USB/PS2 KEYBOARD INTERFACE USING 8051 MICROCONTROLLER WITH VISUAL DISPLAY UNIT
1.1 Background of the Study
The predominant interface between humans and computers is the keyboard. Keyboard range in complexity from the “up-down” buttons used for elevators to the personal computer multimedia keyboard layout with the addition of function keys and numeric keypads, one of the first requirements was to interface keyboard with microcontrollers and with the main processor in personal computers.
Industrial and commercial applications fall somewhere in between these extremes, using layouts that might feature from six to twenty keys. One of the most basic requirements in configuring a keyboard to accommodate the needs of human user. Human beings are irritable they have little tolerance for machine failure thus the hardware designer has to select keys that will survive in the intended environment. The programmer must write the code that will anticipate and defeat elaborate attempts by human to confuse program. The software must be such that the keyboard application must guard against human factors.
Keypads are often used as a primary input device for embedded microcontrollers. At the lowest level keypads are arranged as a matrix of rows and columns which are formed by using switches. When a key is pressed, the row makes a contact with the column otherwise there is no connection between rows and columns. The microcontroller itself makes a continuous check of all rows and columns with the help of program stored in its ROM to see whether a key is pressed or not, it takes care of both hardware and software. In order for the microcontroller to scan the keypad. It outputs a nibble to force one (only one) of the rows and then reads the column.
If any key in that column is pressed, the rows are pulled up by the internal weak pull-ups in the 8051 ports. Consequently as long as no buttons are pressed, the microcontroller’s sees logic high on each of the pins attached to the keypad rows. The nibble driven onto the columns always contains only a single 0. The only way the microcontroller can find a 0 on any row pin is for the keyboard button to be pressed that knows which column is at a 0 level and which row reads 0 allowing it to determine which key is pressed.
1.2 Objectives of the Study
This project is aimed at the construction of visual display unit that will given an output which is determined by the input from the keyboard.
- To make computer engineering students understand the communication between the keyboard and the monitor.
- To enhance the workability of the microprocessor in creating.
1.3 Scope of the Study
The construction and operation of keyboard interface with microcontrollers is to give visual display by making use of LEDs. The construction is designed to operate depending on the input from the keyboard which flows in stages which include; power supply (12v), input from keyboard, processing (microcontroller) and output stage.
1.4 Limitation of the Study
In the course of the construction, certain limitations were encountered and they include:
- Lack of adequate materials
- Lack of concrete data collection
- Lack of finance and sponsorship
1.5 Definition of Terms
- Computer Keyboard: In computing a keyboard is a type writer style device which uses an arrangement of buttons or keys, to act as mechanical levers or electronic switches.
- LEDs: These are a two-lead semiconductor light source. It is a P-n junction diode which emits light when activated.
- Visual Display unit (VDU): This is used to describe any device used with computers to display characters or images.
- Microcontrollers: This is a small computer on a single integrated circuit containing a processor core, memory and programmable inputs and outputs peripherals.
- Dot Pitch (sometimes called line pitch, stripe pitch, or phosphor): Is a specification for computer display, computer printer, image scanner, or other pixel base device that describes the distance, for example between dots (sub pixel) on a display screen.