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Lab 2: Timer Interrupt & LED Scanning

Overview​

Timers let us run code at precise intervals without blocking. This lab configures a 10 ms Timer 2 interrupt and uses it to scan multiple 7-segment displays, build a digital clock, and create a non-blocking software timer. An optional 8×8 LED matrix extends the idea.

Objectives​

  • Configure a Timer 2 interrupt firing every 10 ms.
  • Multiplex (scan) several 7-segment displays so they appear lit simultaneously.
  • Replace blocking HAL_Delay with a software timer driven by the interrupt.

Timer setup​

With an 8 MHz clock, set Prescaler = 7999 and Counter Period = 9: 8 MHz / (7999+1) = 1000 Hz, divided by 10 → 100 Hz → a 10 ms interrupt. Enable the TIM2 global interrupt (NVIC), start it with HAL_TIM_Base_Start_IT(&htim2), and put your periodic code in the callback.

void HAL_TIM_PeriodElapsedCallback(TIM_HandleTypeDef *htim) {
  if (htim->Instance == TIM2) {
    // runs every 10 ms
  }
}

LEDs scanned faster than ~30 Hz appear continuously on; on Proteus a low rate (e.g. 1 Hz) is used because the simulator can't run at full speed.

Exercises​

  1. Display "1" and "2" on two 7-segments, switching every 0.5 s.
  2. Extend to four 7-segments + two DOT LEDs (PA4); blink the DOT every second.
  3. Implement update7SEG(int index) driven by a 4-element buffer.
  4. Set the 4-digit scanning frequency to 1 Hz; keep the DOT blinking.
  5. A digital clock (hour/minute) via updateClockBuffer().
  6. Create a software timer (setTimer0, timer_run, timer0_flag) to remove HAL_Delay.
  7. Rewrite the clock from Ex. 5 using the software timer; move the DOT to main.
  8. Move update7SEG() to main; the interrupt only services software timers.
  9. (Extra) Add an 8×8 LED matrix (MATRIX-8X8-RED + ULN2803); show character "A".
  10. Animate the matrix (e.g. scroll the character left).

Report & Submission​

Present the Proteus schematic and the relevant source (callback / main). For the software timer, explain what happens for setTimer0(1), setTimer0(10) and a missing initial call.