Micro-controller based Digital Clock

Development and Implementation of 

Micro-controller based Digital Clock 

Abstract—Electronic clocks have predominately replaced the mechanical clocks. They are much reliable, accurate, maintenance free and portable. In general, there are two kinds of electronic clocks. They are analog clock and digital clock. But digital clocks are more common and independent of external source. It would be needed the controlled devices and implementation of software for microcontroller control system because the hardware devices cannot do any desired task to execute. In this paper, the microcontroller-based digital clock is constructed with PIC16F877A and its software program is written with CCS C program language. Various types of digital clocks and modules are available in the market nowadays but this clock is different at least in the accurate time. To be controlling in microcontroller is only the feature of the clock. The input frequency is taken from the 50 Hz clock frequency circuit. To show the time, seven-segment Light Emitting Diodes (LEDs) and four LEDs are used.

I. INTRODUCTION
          IME is such a fundamental concept that it is very difficult to define. To measure time is needed something that will repeat itself at regular intervals. The number of intervals counted gives a quantitative measure of the duration. The earliest references for the measurement of the time are the moon and sun. When the sun and the moon were not visible, it was impossible to know the exact time. So, clocks were developed to measure out the hours between checks with the sun and the moon. The process of measuring time has progressively become more accurate, and the devices more localized ever since. In our modern time, the time is predominately measured by mechanical, and recently by electronic clocks. All clocks measure time, but different clocks can have status or importance. Many centuries have been spent devising method for the determination and measurement of time. Historically, clocks and watches of all sorts lie at an important crossroads of science, technology and society. Changes in timekeeping technology have influenced the character of scientific  observation, aided the development of other machine technologies and brought significant revisions in the way people think about and behave in time. The first public clock that struck the hours was made and exerted in Milan in 1335. The oldest servicing clock in England is that at Salisbury Cathedral, which dates from 1386. About 1500 Peter Henlin, a German locksmith, began to made small clock driven by a spring. Fig. 1 Block diagram of the system The first electronic clock is quartz clock. It is made with a piece of quartz like liquid crystals which eventually composed watch displays. Quartz vibrates equally at thousands of times a second when subjected to an electrical current. Electronic clock at those vibrations divides then down to minute, second and fraction of seconds to show time on the dial or display. Quartz clocks provide more accurate than any mechanical timekeeper. In this paper, the more accurate clock using microcontroller is presented.

 OPERATION OF THE SYSTEM
          Clock input circuit which generates 50 Hz is connected with the RB0 port of PIC. The RB0 port can make have the function to do interruption in the change of the input signal. This time, it detects the rising edge of the input signal and the interruption occurs. It counts this interruption fifty times and recognizes one second. 4 MHz resonator is used for the operation clock oscillation by PIC. The precision of this oscillation frequency doesn't influence the precision of the clock. The precision of the clock is decided by the precision of the frequency which is inputted to RB0. Because it doesn't need the high-speed operation of PIC at the circuit this time, 4 MHz is used. In this circuit, the appropriate program and voltages are used to operate the whole circuit. For digit display, six seven-segment LEDs to show the hours, minutes and seconds, two LEDs to separate the minute and hour and another two LEDs to separate before noon (AM) and after noon (PM) are used. World Academy of Science, Engineering and Technology 42 2008 363 The ten seven-segment LEDs are common anode. The specification of the display position is controlled by the binary signal which is output from RA0, RA1 and RA2 port of PIC. This signal is decoded in three-eight decoder (CD4028) and eight kinds of signals are made. This time, six kinds are used. Only the transistor which corresponds to the low level decoder output becomes ON condition. The LED which is connected with the transistor becomes lighting-up possible condition. Segments of the lighting-up of each digit are controlled using seven ports of RC6 from RC0 of PIC. The output of these ports is common to all the LEDs. The LED lights up when the RC port is low level. The brightness of the LED depends on the kind of the LED. When the brightness is different extremely, the resistors which are connected with the RC ports should be separated.