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COMSATS University Islamabad Wah Campus Electrical & Computer Engineering Department Program: BEE Semester/Section: 2-B Subject: DIGITAL LOGIC DESIGN Instructor: Engr. Adnan Saleem Mughal Project Title: DIGITAL STOPWATCH Submitted by: Nauman Toheed Ahmad Khattak Muhammad Afzal Shah Project progress Report: Final Report Date of Submission: 14-June-2019 FA18-BEE-007 FA18-BEE-034 FA18-BEE-073 Objectives The main objective of digital stopwatch is to count time in seconds, minutes and hours and it can also be used for different application like count down timer , alarm clock etc. Summary This circuit is based on the principle of 6 phase counter operation, based on synchronous cascading. The idea is to display clock pulses count from 0 to 59 seconds , minutes and hours i.e 23:59:59. This is done by using a 555 Timer IC connected in a stable mode to produce clock pulses of 1 second interval each. While the first display counts from 0 to 9, the second counter starts its counting operation every time the count value of the first counter reaches 9. When the 2nd display reach to 6 the encoder give one one output to the 7411 so it set back to 0 and the minutes display change its state from 0 to 1 an so on and same is the case with hours display. The counter ICs are connected in cascading format and each counter output is connected to BCD to 7 segment decoder used to drive the 7 segment displays Block Diagram Circuit Diagram Working 555 Timer The 555 is basically a monostable Multivibrator. The important characteristics of a Monostable Multivibrator is as long as the pin 2 receives a positive trigger the output at pin 3 will be of low state. And when negative trigger was connected into the pin 2, the output at the pin 3 will go high for a specific period of time. This time was decided by the Resistor and Capacitor connected with it. 4026 IC The 4026 IC is a 16-pin CMOS seven-segment counter from the 4000 series. It counts clock pulses and returns the output in a form which can be displayed on a seven-segment display. This avoids using a binary-coded decimal to seven-segment decoder, but it can only be used to display the (decimal) digits 0-9. IC7411 The IC 7411 is basically AND Gate having three inputs and one output. This IC contains three AND Gates WORKING The working of the circuit starts with 555 timer when it was connected with mono stable vibrator. The 555 timer generated a clock pulse after every second and its output is connected with pin 1 of IC 4026 .IC 4026 is a 7 segment decoder and is used to drive 7 segment display with input clock pulse Here the clock pulse was obtained from the mono stable multi vibrator and fed into the pin 1 of first ic 4026. Pin 2 was usually grounded since giving high signal to this pin will inhibit the input clock signal to pin 1 and pin 3(Enable Clock) is always taken High. The pin 3 of the IC 4026 is connected with pin 3 of 555 timer which is the out pin of 555 timer. Initially when the circuit is switched ON the 7 segments will indicate "00:00:00" count and as soon as the negative trigger was given to 555 high pulse will be obtained from pin 3. The high pulse was fed to first IC and therefore it increments its count with each clock, displaying 1 to 9 in its seven segment. As soon as 10 counts was incremented by IC a high to low signal was obtained from its pin 5 which indicates the completion of ten increments. The pin 5 was connected to the clock pin of the next 4026 IC. Therefore whenever 10 counts was completed by the 7 segment, the high to low signal at the pin 5 will feed a single clock pulse input to the second IC and therefore the corresponding 7 segment will be incremented one value. For a digital clock we must reset second IC when it reach to number 6 because we want seconds count upto "59" therefore we used IC 7411 (Three input AND Gate) when it reaches to 6 all the three input becomes 1 and it generates output 1 and the next display works. In the same manner fourth IC will count from 0 to 6 and then value in the fifth IC will be incremented by one. This is all about for seconds and minute of clock. Now for hours we must reset fifth and sixth IC when number reached to “23” so we put one more three input AND gate. Simulations (in any software) Simulation are made on proteous Hardware Implementation we construct digital stopwatch on bread board o Problems encounterd While constructing the digital stopwatch on bread board the ic7411 not working properly it does not provide a proper output to the 3rd ic4026 which cannot changes its state and the display of second counts from 0 to 99 instead of 0 to 59. o Trouble shooting The ic7411 only gets input voltage of 0 to 7v and we were giving voltage of 9v to 7411 so by putting the resistor between input voltage and the vcc pin of 7411 it work properly it and the minutes display change its state. Results and Conclusions After the completion of our circuit of digital stopwatch it counts seconds, minute, and hours accurately and we came to know the working of different Ic’s . and the circuit has been implemented on the bread board.