ABSTRACTDigital stopwatch finds its application in numerous places where time keeping is required such as in sports, gone are the days when everything was in analog now in this fast growing world digitalization has started to root whose application is a digital stop watch.A digital stopwatch operates on a signal which is known as clock and which is generated from a 555 timer IC, now that clock signal is then fed into a decoder IC which is connected to a 7-segment display which the count.
By the modulation of clock signal we can increment or decrement the count that is being displayed on the 7-segment display.I. INTRODUCTIONWhen we chose this project the main aim was to develop a digital stopwatch that is power sufficient, starts stops and reset on the call of user. As digital stopwatch is used in a wide range of areas so to develop a stopwatch that is somewhat unique itself was our basic aim and the one that could be easily accessible to a common man.
The basic idea of a digital stopwatch is to display count from 0 ” 59 using clock pulses which will reset itself after every 60 pulses and then second counter will start from 0. Digital stop watch is a handy tool that differentiates between the two time periods or events. II. THEORETICAL TREATMENTThis section covers the details regarding the theoretical aspect of our project. A digital stopwatch is based on a 555 timer IC, decoder IC (4026), 7 ” segment, voltage regulator IC (7805) and an AND gate whose description is as follows . 555 TIMER IC: The key component in this whole circuit is the 555 timer IC as it generates the clock signal. This IC has 8 legs. 555 timer basically consist of two comparators a flip flop, a discharge transistor and a resistive voltage divider.Pin 1 ” Ground: Connected to ground.Pin 2 ” Trigger: Turns on the output when the voltage supplied to it drops below 1/3 of VCC.Pin 3 ” Output: Outputs up to 200 mA of current at about 1.5 V.Pin 4 ” Reset : Resets the timing operation of the output when it is connected to ground.Pin 5 ” Control: Controls timing output independently of the RC circuit when the voltage supplied to it is above 2/3 VCC. When not in use, it is usually connected to ground via a 0.01 јF capacitor to prevent fluctuations in timing of the RC circuit.Pin 6 ” Threshold : Turns off the output when the voltage supplied to it reaches above 2/3 Vcc.Pin 7 ” Discharge : When output voltage is low, it discharges the capacitor in the RC circuit to ground.Pin 8 ” VCC (supply voltage) : Can range from 4.5 V to 15 V.There are 3 different modes of 555 timer astable mode, monostable mode and bistable mode.We have used astable mode of 555 timer IC.ASTABLE MODE: An Astable Circuit has no stable state – hence the name “astable”. The output continually switches state between high and low without without any intervention from the user, called a ‘square’ wave. DECODER IC (4026): Pin 1: pin 1 is the clock which is directly connected to the 555 timer IC to produce a pulse.Pin 2: pin 2 is the clock inhibit pin which is connected to ground to enable the clock.Pin 3: pin 3 is the enable pin which is directly connected to +5V to enable the output pins from A to G.Pin 4: pin 4 is the output pin which will be always high but it is only used when cascading is performed.Pin 5: pin 5 is the carry out pin which produces pulse after 9 and as we are using 4 4026 IC so all these pins are connected to each other with clock.Pin 6,7,9,10,11,12,13 : These are the decoder pins which are connected to 7 ” segment pins to enable the counter .Pin 8: pin 8 is the default ground pin of the IC.Pin 14: pin 14 is the rare pin which is only used when division is required.Pin 15: pin 15 is the reset pin of the IC which resets the counting to 0.Pin 16: pin 16 is the default VCC pin which is directly connected to +5V.Since we have used 4 ICs so the process of cascading occurs in which all the clock pins are connected to each other and then to the VCC of the 555 timer similarly pin 5 is connected to the next ICs pin 1 and so on with rest ones .7 ” SEGMENT DISPLAY: 7 “segment display is electronic display device that displays decimal numbers. It has 8 built-in LEDs, there are two types of 7 ” segment display common cathode and common anode. We have used common cathode display in which two pins of the IC are connected to ground and the rest of the pins are connected to the decoder IC pins to display the desired output.IC 7805: 7805 is a voltage regulator IC it has 3 pins:Pin 1: pin 1 is the input pin in which we have directly connected the VCC supplied by the battery or through the power supply.Pin 2: pin 2 is the default ground pin.Pin 3: pin 3 is the output the regulated output is provided through this pin.III. CONSTRUCTIONIn this part, details about the project’s construction, how it was put together and how it is powered. The information in this section should be presented in a manner simple enough that your juniors from future semesters could understand on the very first day of the class, while still being technically accurate.CIRCUIT DIAGRAM:Please Zoom To See Details! In this project as it could be seen looking in the circuit diagram that we have used 4 7-segment ICs and to operate these 7-segments we have used 4 ICs of 4026 which are the decoder ICs of 7-segment as explained above means 1 IC for 1 segment .Now these ICs are firstly connected to 7-segment to so that the decoding of count generated could be displayed , then as there are 4 ICs so the clock pin of each IC is connected to each other and then connected to VCC .This is counter and seven segment decoding in one package IC (4026) which is very easy to interface with seven segment displays. This is fully static counter operational IC and ideal for low power displays. This IC can be used for decade counting seven segment decimal displays, frequency division seven segment decimal displays, clocks, watches, timers, counter/display driver for meter applications. One push button is used to start/stop the stopwatch and one push button is used to reset the stopwatch. 4026 IC is used to drive 7-segment display. Pin 1 of 4026 IC is clock pin, due to this pin the input pulse will start counting in 4026 IC which we see in 7-segment display. We use 555 timer IC to give pulse to 4026 IC. If we want to stop our clock we will high pin 2. Pin 3 is enable pin, it should be connected to 9V. Connect all wires of 4026 IC with 7-segment display, such that pin 8 of 4026 IC should be connected on ground. We will use potentiometer to adjust the frequency of 555 timer IC.