Controller Circuit

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.

Time 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.

In the software implementation process, initialization processing, LED display processing, time adjustment processing and time signal processing are considered. In this article, the microcontroller-based digital clock is mainly controlled by the clock pulse frequency. The clock pulse frequency can be generated by using the IC1 555. The clock pulse frequency can be obtained from other methods such as the power line frequency and the internal oscillator IC with RC circuit and so on. The power line frequency will not get more accuracy than the quartz crystal. The 555-timer unstable mode can be used for this purpose. In the display, there are needed to give the outputs of seconds, minutes and hours and AM/PM. In this display system, the output of PIC is connected with the input of decoder (CD4028) to drive the seven-segment LEDs. The decoder (CD4028) has four inputs and ten outputs. But, in this circuit three inputs and six outputs are used. So, one input pin is grounded and four outputs pins are not used. The circuit is shown by the figure;
The microcontroller-based digital clock can be provided with the date, month and year circuits. The output of day indicator can be shown by connecting with the output pins of CD4028, pin seven and eight. But the required instructions are added to the existing program. If the month indicator is wanted to show, the remaining input pin, pin D is connected with the output pin of PIC, RA3 and then to drive the seven-segment LEDs output pins of CD4028, pin zero and nine are used.

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