NSWI170 Computer Systems

3rd practicals

Agenda

Arduino LEDs review (constants, labels, timing)
Working with buttons (problem with oscillation)
Code quality: Reducing the code redundancy
Communication with a computer for debugging
New assignment: Arduino Buttons

The idea behind 2nd hw

The input parameters / configuration is:

// Program parameters
constexpr int animationDurationMs = 300;
constexpr int ledsPins = {led1_pin, led2_pin, led3_pin, led4_pin};

The rest is calculated:

// Leds count
constexpr int ledsCount = sizeof(ledsPins) / sizeof(ledsPins[0])

// Last LED
ledsPins[ledsCount - 1]

// Total animation duration
(ledsCount * 2 - 2) * animationDurationMs

The program should not break if we change or add new values.

The size should not be hard-coded.

Problems with delay() and while(millis() < ...)

Example scenario: Extend 2nd homework with playing twinkle twinkle little star on speaker

void setup() {
  setupLedAnimation();
  setupMusicPlayer();
}

void loop() {
  updateLedAnimation();
  updateMusicPlayer();
}

unsigned long animationDelayMs = 300;

unsigned long lastTimestamp = 0;

void setup() {
  lastTimestamp = millis();
}

void loop() {
  auto currentTimestamp = millis();

  if (currentTimestamp >= lastTimestamp + animationDelayMs) {
    // Do something

    lastTimestamp = currentTimestamp;
  }
}

Task: Bit encoder

Write a function that takes an integer and changes the LED states according to its lower 4 bits.

Bitwise operators: & (AND), | (OR), ~ (negation)
Bit shifts <<, >>

Create a clock that increments every second. Do not use delay().

Buttons

#include "funshield.h"

void setup() {
  pinMode(button1_pin, INPUT);
}

void loop() {
  bool isPressed = !digitalRead(button1_pin);
  ...
}

Task: Bit encoder

Increment if the button is pressed.

What does it mean to press the button?

What if you hold it?

Increment as soon as the button is pressed and then in regular intervals.

Instead of repeating, use:

for loops
functions

Do not repeat yourself

Repeated code is hard to maintain because you must fix all its copies. It is difficult to read.

Debugging

See the ASCII Table example for inspiration.

File > Examples > 04. Communication

Find out how many times per second the loop function is called. Then try to insert some computationally demanding code and recheck the loops per second.

New assignment

(Classes)

class Button {
private:
  bool down;
  int pin;

public:
  bool isDown() {
    return down;
  }
  
  Button(int _pin) {
      pin = _pin;
  }
};


Button button(10);
button.isDown()