Assignment #8: Timers Output Compare and PWM

📚 Assignment 8 CMPE1250: Timers Output Compare and PWM

📋 Overview

  • In this ICA you will explore two common applications of pulse width modulation.

  • You will need a breadboard and some of the components from your parts kit for this exercise. If required your instructor may have some parts to share.

1️⃣ Part A - LED Brightness Control

  • Map PA5 (LD2) to alternate an alternate function so it can re driven by a timer.

  • Configure the timer in PWM mode, 1kHz frequency. Cycle the duty in the range of 5% duty to 95% duty over a 1s interval. You may implement the cycling as sawtooth, ramp up/down, or sinusoidal. Observe this waveform on a scope.

  • Challenge - write a program that will alter the PWM duty periodically and somewhat randomly to have the LED appear to flicker like a candle.

2️⃣ Part B - Budget DAC

  • Build now the following circuit on PA7:

schematics

  • Configure TIM14 for PWM mode with a 2kHz frequency. Use the largest value you can for ARR to ensure you have the highest control over the duty. Set the duty initially to 50%. Ensure you measure a 2kHz 50% duty waveform on PA7 at test point 1.

  • Sketch the waveform at TP1, TP2, and TP3. How does this match your expectations for the given circuit?

TP1 TP2 TP3
     

  • Connect the SW1 and SW4 of the button board to PC10 and PC12 Respectively. Configure the buttons to increase and decrease the duty cycle by 5% each time they are pressed. The minimum duty should be 0% and the maximum duty should be 100%. Observe the changes on the scope at TP1, TP2, and TP3 as you press the buttons. Sw1 should decrease the duty and SW4 should increase the duty.

  • Measure the output voltage using a DMM at TP3 for the following duty values:

PWM Duty (as %) Voltage measured at the test point
0  
5  
25  
50  
75  
100  
  • How do the voltages measured at their respective duties relate to the circuit supply of 3.3V?