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 NXP Semiconductors


  • 4-digit Stopwatch

  • Created: Sep 16, 2014

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Summary

One of the things that are usually required to measure is time and a common device to measure time is the stopwatch. This project is a simple 99.99 seconds digital counter stopwatch designed to measure the elapsed time.

This stopwatch project is very easy to operate; it comprises three buttons (START, STOP, RESET) to control the watch. When the START button is pressed, the time will start from 0000, pressing the STOP button will pause the time, and the time continues if the START button is pressed again. The RESET Button is used to return the time back to 0000. In this project, the time is limited to 99.99 seconds, so when the limit is reached, a LED will be switched ON to indicate that the counter exceeds 9999.

At the first stage of the circuit, we use the IC 74ABT00D quad 2-input NAND gate to perform two functions. 74ABT00D have four NAND gates; two of these are configured as a Set-Reset NAND latch connected from the START and STOP SPDT (single pole, double throw) switches. The other two NAND gates are configured as a multivibrator producing a pulse frequency of 100Hz. The oscillated signal is inputted to the IC TC5001P 4-digit decimal counter designed to produce a BCD (binary-coded decimal) output with a maximum count of 9999. The RESET switch is connected to the RESET pin of the TC5001P to return the count back to 0000. The IC HEF4511BP is a BCD-to-7 segment latch/decoder/driver module; this is used to convert the BCD output from the TC5001P to drive the four 7-segment display panels. The BC337 transistors are connected to the common cathode of the 7-segments to act as a switch. T1, T2, T3, and T4 output pins of the TC5001P indicate the digit’s position of the BCD.

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