Digital Clock

University of the East Caloocan

College of Engineering

Department of ECE

Finals Project

Digital Clock with Alarm FunctionMembers:Perdio, Lejan Daniel I.Pulayan, John Eric R.Quitco, Kimberly F.Date Submitted:

RATINGMaterialsDipswitchSolid WiresBreadboardSeven Segment DisplayResistors

Capacitors

Voltage RegulatorNE 555 (PRECISION TIMERS)

IC 74LS90 (DECADE AND BINARY COUNTERS)IC 74LS192 (PRESETTABLE BCD/DECADE UP/DOWN COUNTER)

IC 74LS47 (BCD TO 7-SEGMENT DECODER/DRIVER)IC 74LS85 (4-BIT MAGNITUDE COMPARATORS)

IC 74LS08 (QUADRUPLE 2-INPUT POSITIVE-AND GATES)

IC 74LS32 (QUADRUPLE 2-INPUT POSITIVE-OR GATES)

IC 74LS08 (HEX INVERTERS)Introduction

This project is a time keeping digital clock that displays time in hours, minutes, and seconds. The goal of this project is to implement all of the basic features that one would normally expect to find on a standard digital clock. The features of this project include the standard twelve-hour time, an alarm function, and a clock and alarm setting functionality.Purpose and Discussion

The purpose of this project is for us to be acquainted with the different operations of both combinational and sequential circuits by using them in constructing a Digital Clock.

Our entire project has been divided into five parts. They are as follows:

Clock Source Section: NE555 Timer was used for input source, which is wired as an Astable Multivibrator. Astable Multivibrator is a rectangular-wave generating circuit that we used as a clock pulse. The frequency is variable controlled by the potentiometer.Seconds Section: Using two counter Ics (IC 74LS90), in such a way that this portion produces an output from 00 to 59. For the least significant bit, we used IC 74LS90 as divide-by-10 counter to produce the numbers 0 to 9. And for the most significant bit, 74LS90 was also used as divide-by-6 counter to produce an output of 0-5. The two counter ICs where cascaded by connecting the output of the first IC to the input of the second IC. To drive the counters in a common anode seven segment display, we used a driver IC 74LS47.

Minutes Section: Minutes section is similar to the seconds section because it also needs an output from 00 to 59. By repeating the steps in the seconds section, minutes section was implemented.

Hours Section: Hours section must be designed on displaying an output of 01 to 12. For the least significant bit, we operated the IC 74LS192 because it has a preset input that we may use to obtain the preset value of 1 after the 12 states were finished. It provided an output count of 0,1,2,3,4,5,6,7,8,9,0,1,2,1. And for the most significant bit, 74LS90 was also used as divide-by-6 counter to produce an output of 0-5. The two counter ICs where cascaded by connecting the output of the first IC to the input of the second IC. To drive the counters in a common anode seven segment display, we used a driver IC 74LS47.

Alarm Section: The alarm time was set using the dipswitches. The operation is that when the set alarm time was reached by the digital clock, meaning that their minutes and hours values were equal, the buzzer will be triggered producing an alarming sound. The alarm was set by the use of dipswitches, using BCD equivalent for every value. For example, if I want to set 4 oclock, the time set for hours section is 0100. Using IC 74LS85 (magnitude comparator), we were able to compare the BCD values of the set time and the time of the clock.The seconds section is the one capable of driving the minutes section, and then the minutes section is the one which is driving the hours section. They are cascaded, as the output of the previous section is connected to the input of the next section. Each of the minute and second section has been designed to give a count from 00 to 59 after which it resets to 00, and the hour section to give a count from 00 to 12 hours after which it resets to 01. For each cycle of 00 to 59 in second section the minute section is incremented by 1. Similarly for each cycle of 00 to 59 in the minute section increases its count by 1.

Time setting is also included in our circuit using tact switches, incrementing the values of the least and most significant values of minutes, and the value of hours for every time the switch was pressed. Testing Results

For every part, there is a corresponding testing situation to know if the circuit is in its proper condition. The results were as follows:Source Section: The 555 Timer was used to produce signals for the counters. A variable potentiometer was used to vary the frequency of the clock pulse. To test the output, LED indicator was connected to the pin 3 of the 555 timer which is the pin that produces the output. The blinking rate varied according to the adjustment of the potentiometer.

Seconds Section: To test the seconds section, the clock source was inputted at the pin 14 of the first IC 74LS90. The first IC was cascaded to the second IC by connecting its output ( pin 11 ) to the input ( pin 14 ) of the second one. For proper operation, it must count from 00 to 59.

Minutes Section: In testing the minutes section, we repeated the procedures for testing the seconds section. The main problem that has been encountered in this section is the incrementation when the push button is pressed. We used additional logic gates to fix this issueHours Section: For the proper operation of this section, we must consider the counting from 00 to 12, and then presets to 01. We used an IC 74LS192 to give the output for the least significant bit of hours. We preferred this IC over the IC74LS90 because it has a preset operation. Preset operation will enable us to have an output of 1 after resetting from the value of 12.

Alarm Section: The testing of the proper operation of the alarm function is simply producing an alarming sound the moment the set time is equal to the present time of the clock. The alarm will stop to function if the set time is not equal to the present time of the clock anymore. For example, the alarm will function if the set time is 1:43 and the present time is also 1:43. But after 60 seconds, the present time will become 1:44 which do not meet the required time to enable the alarm function, hence, stopping the sound. Logic gates were operated to provide the needed logic that will enter to the input thus, incrementing the values. These logic gates will receive the output of the switches that will drive a logic 1 just when the tact switch is pressed. This is used for the clock setting of hours and minutes.ConclusionThe circuit was purely designed with the basic knowledge on both combinational and sequential circuit designing. Combinational Logic circuit is a type of logical circuit where the output is a pure function of the present input only, while sequential logic circuit depends not only on the present input but also on the history of the output. CLCs used in this project are a BCD to 7segment decoder, to display the output digitally, and comparators, to differentiate the alarm set data to the present data of the clock. On the other hand, counters, the most common type of a sequential digital logic circuit, are used for recording the number of events occurring in a specified interval of time.The most significant error that needs to be highlighted is the malfunctioning of the breadboard. Continuity test was made to ensure that the connections were really connected.

The output shows that the Digital Clock behaved as expected. It was however, noticed that there is sometimes a skipping situation in the incrementation of minutes and hours. The connections have been rechecked multiple times, but there was no error found. We want to improve this part as we continue to do research about this project.

Alarm Clock Setting

Digital Clock with Alarm Function

Breadboard Layout

Digital Clock (Hours, Minutes, Seconds)