Created: Jan 23, 2014
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One of the things that are commonly required to measure is time. Rates are usually measured with respect to 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 amount of time elapsed from a particular time when it is started to the time when the device is stopped.
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 reset 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 is exceeding 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 reset 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 panel. 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 indicates the digit position of the BCD output signals corresponding in descending order from T1 to T4.
Components: - 74ABT00D Quad 2-input NAND gate - HEF4511BP BCD to 7-segment latch/decoder/driver - TC5001P 4-digit decade counter - BC337 transistor - 1N4148 diode - 33kΩ resistor - 1MΩ resistor - 68kΩ resistor - 3.3kΩ resistor - 100kΩ resistor - 6.8kΩ resistor - 180Ω resistor - 50KΩ varistor - 510pF capacitor - 0.047µF capacitor - Common cathode 7-segment display - LED - SPDT switch - Push button switch - 5V dc power source
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