08-16-2017, 09:55 PM
A digital clock is one that displays time digitally. The project explained here, displays time on a 16x2 LCD module. The LCD is interfaced with 8051 microcontroller (AT89C51). This circuit can be used in cars, houses, offices etc.
Digital clock displays the time using numbers. This circuit is used in many applications like cars, railway stations, houses, offices, etc. in order to provide accurate time and date. In this type of applications, normally we use RTC (Real Time Clock) ICs to display the time and date accurately. This circuit displays the time on LCD. For this clock, we can set the time at any instant. Here the clock works in 24 hour mode and the RTC chip is configured by programming 8051 controller.
Circuit Principle:
Here 8051 controller continuously reads the data from Real time clock and process it in correct order to display the time on LCD. INT1 of the 8051 controller is used to set the time to the digital clock. If you make P3.3 pin LOW then interrupt arises and set_time function is called to set the time. To set the time to the clock use P1.4 and P1.5 pins. P1.4 is used to vary the hours and P1.5 is used to vary the minutes. After setting the time make P1.6 high to run the clock with the time set by user.
Circuit Components:
8051 microcontroller
Project PCB
Programming cable
DC Battery or 12V, 1A adaptor
DS12C887 RTC IC
16*2 alphanumeric LCD
Push buttons 4
Slide switches 3
2 ceramic capacitors 33pF
12 MHz crystal
Electrolytic capacitor 10uF, 16V
Resistor (1/4 watt) 10k
Pot 10k
5V DC power supply circuit
Single pin connecting wires
Circuit Design:
The circuit shows you how interface RTC IC to the 8051 controller. Port P0 is used as a data port of Real time clock. Port P2 of controller is connected to the data pins of LCD. Pins P1.1, P1.2 and P1.3 of controller are connected to the RS, RW, EN pins respectively. P1.0 is connected to the RESET of RTC. Push buttons are connected to the P1.4 and P1.5. These are used set the time. P1.6 is configured as START pin used to run the clock with time set by the user. P3.3 is connected to the push button used to call the set_time function.
DS12C887 Real Time Clock:
This IC is used most of the applications to provide accurate time and date. This IC provides the time in both 12 hour mode and 24 hour mode. This IC also provides calendar components day, month and year. This RTC uses internal lithium battery to keep the time and date updated when power is failed. This IC has 128 bytes of RAM memory. In these 128 bytes of RAM 14 bytes are used for time, date and registers. Remaining 114 bytes are used to store general purpose data.
The control registers of RTC are accessible only when the power is applied from external source. This IC requires more than 4.25V power supply and the control registers are accessible after 200ms when external power is supplied.