Embedded Systems Design with the Atmel AVR Microcontroller Part II

6.13. CHAPTER PROBLEMS 179
and considered some applications where the timer subsystem of a microcontroller can be used. We
then took a detailed look at the timer subsystem aboard the ATmega164 and reviewed the features,
operation, registers, and programming of the three timer channels. We concluded with examples
employing a servo motor and an automated fan cooling system.
6.13 CHAPTER PROBLEMS
6.1. Given an 8 bit free running counter and the system clock rate of 24 MHz, find the time
required for the counter to count from zero to its maximum value.
6.2. If we desire to generate periodic signals with periods ranging from 125 nanoseconds to
500 microseconds, what is the minimum frequency of the system clock?
6.3. Describe how you can compute the period of an incoming signal with varying duty cycles.
6.4. Describe how one can generate an aperiodic pulse with a pulse width of 2 minutes.
6.5. Program the output compare system of the ATmega164 to generate a 1 kHz signal with a
10 percent duty cycle.
6.6. Design a microcontroller system to control a sprinkler controller that performs the following
tasks. We assume that your microcontroller runs with 10 MHz clock, and it has a 16 bit free
running counter. The sprinkler controller system controls two different zones by turning
sprinklers within each zone on and off. To turn on the sprinklers of a zone, the controller
needs to receive a 152.589 Hz PWM signal from your microcontroller. To turn off the
sprinklers of the same zone, the controller needs to receive the PWM signal with a different
duty cycle.
6.7. Your microcontroller needs to provide the PWM signal with 10% duty cycle for 10 millisecond
to turn on the sprinklers in zone one.
6.8. After 15 minutes, your microcontroller must send the PWM signal with 15% duty cycle
for 10 millisecond to turn off the sprinklers in zone one.
6.9. After 15 minutes, your microcontroller must send the PWM signal with 20% duty cycle
for 10 millisecond to turn on the sprinklers in zone two.
6.10. After 15 minutes, your microcontroller must send the PWM signal with 25% duty cycle
for 10 millisecond to turn off the sprinklers in zone two.
6.11. Modify the servo motor example to include a potentiometer connected to PORTA[0]. The
servo will deflect 0 degrees for 0 VDC applied to PORTA[0] and 180 degrees for 5 VDC.
6.12. For the automated cooling fan example, what would be the effect of changing the PWM
frequency applied to the fan?