In this article I’ll demonstrate a digital stopwatch design based on PIC16F876A micro controller.For related circuit based on Arduino click here. Similar project showing a Digital Timer design can be found here. Current circuit can be used to count in minutes and seconds in two directions, UP/Down. The display is implemented using 7-Segment Common Cathode LED Displays, two for the minutes and two for seconds. Time is derived from an external Real-Time Clock (RTC) PCF8583P which is connected to the micro-controller via I2C interface.The user can operate the stopwatch in two modes: Up-count: from 00:00 to a user specified time. Down-count: from a user specified time to 00:00.Stopwatch mode selection is done by a switch, default count is down. Additional Push buttons are used for the following operations: To start and stop the timing, to reset the user set time and to set the user specified time. Also holding down UserSetTime push button will increment the time to a desired value.A buzzer was used to signal if remaining time near zero or approaching user settings by beeping every 5 seconds when the time is within 30 seconds, every 2 seconds when within 15 seconds and every second when within 5 seconds.In the next figure you can see design prototype board .
Other analogous micro controllers can be used like PIC16F88 or PIC16F877 with minimal changes to the circuit/software. The design source code was written in assembly language and can be downloaded at the bottom of the next page.
Source code for this circuit was not written from scratch, instead a number of functions were taken from previous designs like multiplexing routine for 7-Segments displays, I2C communication. Current code may be not the most efficient implementation of Stopwatch design but it works. Some bugs may exist. You can see circuit operation in a short video. Design source code is here.
