AVR Based Stopwatch

An implementation of a stopwatch using ATMega16 Microcontroller.

Outline of the project

• Timer1 with CTC mode is used to count the stopwatch time.
• A six common anode 7-segment display is used.
• The 7-segment is connected using the multiplexed technique, such that the MCU loops around each 7-segement individually and display the content with respect to it.
• An external interrupt INT0 with falling edge is used for the reset of the time.
• An external interrupt INT1 with rasing edge is used to pause the time.
• An external interrupt INT2 with falling edge is used to resume the time.
• The simulation is done with Proteus Design Suite.

Code explanation

Timer1

• Timer1 is configured in CTC mode with an inital count value of 0, and having its interrupt enabled.

• The clock supplied to the timer is of a prescaler value of 64.

• In order for the timer to count and produce an interrupt every 1 second the value of the compare register is 0x3D08 (15624 clock):

  • This value is calculated as following:

• So every 1 second an interrupt is triggered resulting in the increment of the variable seconds in the ISR (Interrupt Service Routine), and the calculations of minutes and hours are done accordingly.

INT0 (Interrupt 0)

• The purpose of this interrupt is to reset the timer.
• The interrupt is triggered via a push button resulting in the exection of the interrupt's ISR.
• Which results in the zeroing of the timers parameters.

INT1 (Interrupt 1)

• The purpose of this interrupt is to pause the timer from counting.
• The interrupt is triggered via a push button resulting in the execution of the interrupt's ISR.
• The clock source is disables resulting in the stop of the count of the timer.

INT2 (Interrupt 2)

• The purpose of this interrupt is to resume the couting of the timer.
• The interrupt is triggerd via a push button resulting in the exection of the interrupt's ISR.
• The clock source is re-enabled resulting the resume of the count of the timer.