ASSESSING DESIGN AND CONSTRUCTION OF A DIGITAL CLOCK WITH CALENDAR
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This project is aimed at explaining the Design and construction of a digital wall clock with calendar.
It give report on how we can achieve this aim and the primary objective of this work is to bring a vibrant digital clock display to everyone located within the vicinity where the clock is being installed, and the importance of clock is to tell time and date, so you can meet up with events and assignments, these are just few importance of CLOCK.
In developing countries, time is a very important element of life, maximizing it will give you a better achievement.
We shall discuss on how you can design one in this report with a well narrated literature review for better understandings.
Also efforts were made in explaining the vital and important part of the design components and their functions in the project.
This project is a design and construction of a digital clock with calendar. The core component is the microcontroller PIC16f877. This device employs sequential circuit components. It consists of LED, seven segment display, transistor, voltage regulator, resistors and capacitor.
FIG.1.0 THE PIC16F877 INTERNAL STRUCTURE
1.1 BRIEF DISCUSSION ON CLOCK
A clock is an instrument to indicate, keep, and coordinate time. Today a clock “refers to any device for measuring and displaying the time”.
The clock is one of the oldest human inventions, meeting the need to consistently measure interval of time shorter than the natural unit, the day, the month and the year.
Devices operating on several physical processes have been used over the millennia.
A digital clock is a type of clock that displays the time digitally (i.e. In numerals or other symbols), as opposed to an analog clock, where the time is indicated by the positions of rotating hands.
This clock counts seconds, minutes, hours, days, months and
years. Time and calendar is displayed on four separate seven segment LED displays, and is adjustable with three buttons at start time (up, down, set).
You can program the day of the week, hour and minute, day of the month and year.
The aim of this project is to design and construct a digital clock with yearly calendar.
• To be able to understand the principle behind digital system display.
• To be able to interface micro controller with the display unit.
• To be able to display the date and time in digital format.
1.6 UNITS OF THE SYSTEM
This digital clock with calendar model can be divided into two parts, the hardware and software.
The hardware can be divided into several sections. This includes the power supply unit, the control unit and the display unit.
The software part can be broken down into the following sections. This includes the timing and counting unit, display decoder and scanning unit
1.3.1 HARDWARE PART
Power supply unit;
Power supply unit consist of transformer, bridge rectifier, filter capacitor, voltage regulator and back up battery.
The control unit;
The control unit consists of a microcontroller, the PIC16F877. It controls by timing, counting and sending numeric code to be displayed to the seven segment display.
The display unit;
The display is made up of ten seven segment displays, and ten NPN BJT transistors.
1.3.3 SOFTWARE PART
The timing of the clock is achieved by assigning timer0 a special function registers in the microcontroller to timing.
Timer0 is incremented at every four clock cycle of the microcontroller, when it runs to the end it causes interrupt that enables a general purpose registers to increment.
When this registers count to a reference value, register linked to the seconds is increased.
Timing starts with this register (seconds) which serves as input to other registers associated with other parts of the clock.
Each unit of the clock is linked to a general purpose register for counting purposes.
There is a routine program that handles counting up for each of the clock units (refer to appendix for codes of routine program).
The time taken for each increase is determined in the routine handling it.
The output of each counter is binary and therefore needs to be converted to seven segment display format.
Another routine is program to handle this (refer to appendix for routine program).
The display decoder is a program that converts binary coded decimal output of the counter to seven segment
The output of each counter is converted to numeric display equivalent using this decoder.
In this project, the required number of terminals required can be estimated as follows;
Each 7 segment requires at least 7pins of the MCU, there are ten 7 segments in the circuit, therefore required pins of the MCU is 7 * 10 = 70 pins.
Other pins required for proper functioning of the MCU are the 4 power supply pins, 2 oscillator pins, 1 MCLR pin making the total number of pins required = 70 + 4 + 2 + 1 = 77pins.
The MCU has just 40pins and not all these pins are available, therefore there is need for the LEDs and the seven segments to be multiplexed (discussed in the next chapter).
There is a routine that handles this part of the display in the program (refer to appendix).