Lesson 4: Buzzer Alert

/*
  DIY KIT - ESP32 Fall-Detection Learning Prototype
  Lesson 4 of 5: Buzzer Alert

  WIRING (unplug the USB cable before you wire)
    Keep everything from Lessons 1-3.
    Active buzzer module, with 3 female-to-male jumper wires:
      I/O (signal, may be labelled S or IN) -> GPIO27
      VCC                                   -> 3V3  (NOT 5V - see the lesson)
      GND                                   -> GND

  WHAT SHOULD HAPPEN
    Three short test beeps. Then press the button to start an ALERT: the
    buzzer beeps 150 ms on, 350 ms off and the OLED says ALERT. Press again
    to acknowledge (stop) it. If nobody presses, it stops by itself after
    15 seconds. Serial Monitor at 115200 baud.
*/

#include <Wire.h>
#include <Adafruit_GFX.h>
#include <Adafruit_SSD1306.h>

const int SDA_PIN = 21;
const int SCL_PIN = 22;
const int BUTTON_PIN = 26;
const int BUZZER_PIN = 27;
const unsigned long BEEP_ON_MS = 150;
const unsigned long BEEP_OFF_MS = 350;
const unsigned long MAX_ALERT_MS = 15000;   // an alarm must not run for ever
const unsigned long DEBOUNCE_MS = 35;

// Most modules beep when the pin is HIGH. If yours beeps in the gaps or
// all the time, change false to true and upload again.
const bool BUZZER_ACTIVE_LOW = false;

Adafruit_SSD1306 display(128, 64, &Wire, -1);
bool displayOk = false;
bool alerting = false;
unsigned long alertStart = 0;
bool rawButton = HIGH, stableButton = HIGH;
unsigned long rawSince = 0;

void buzzer(bool on) {
  if (BUZZER_ACTIVE_LOW) digitalWrite(BUZZER_PIN, on ? LOW : HIGH);
  else                   digitalWrite(BUZZER_PIN, on ? HIGH : LOW);
}

bool pressedNow() {
  bool reading = digitalRead(BUTTON_PIN);
  if (reading != rawButton) {
    rawButton = reading;
    rawSince = millis();
  }
  if (millis() - rawSince > DEBOUNCE_MS && reading != stableButton) {
    stableButton = reading;
    return stableButton == LOW;
  }
  return false;
}

void show(const char *line1, const char *line2) {
  if (!displayOk) return;
  display.clearDisplay();
  display.setTextColor(SSD1306_WHITE);
  display.setTextSize(1);
  display.setCursor(0, 0);
  display.println("BUZZER ALERT LAB");
  display.setTextSize(2);
  display.setCursor(0, 20);
  display.println(line1);
  display.setTextSize(1);
  display.setCursor(0, 56);
  display.println(line2);
  display.display();
}

void setup() {
  Serial.begin(115200);
  pinMode(BUTTON_PIN, INPUT_PULLUP);
  pinMode(BUZZER_PIN, OUTPUT);
  buzzer(false);
  Wire.begin(SDA_PIN, SCL_PIN);
  displayOk = display.begin(SSD1306_SWITCHCAPVCC, 0x3C) || display.begin(SSD1306_SWITCHCAPVCC, 0x3D);

  Serial.println("Lesson 4: three test beeps");
  for (int i = 0; i < 3; i++) {
    buzzer(true);  delay(100);
    buzzer(false); delay(200);
  }
  show("READY", "press to start alert");
  Serial.println("Press the button to start an alert, press again to stop it");
}

void loop() {
  bool pressed = pressedNow();
  unsigned long now = millis();

  if (!alerting) {
    if (pressed) {
      alerting = true;
      alertStart = now;
      Serial.println("ALERT started");
      show("ALERT", "press to acknowledge");
    }
  } else {
    unsigned long used = now - alertStart;
    if (pressed || used >= MAX_ALERT_MS) {
      alerting = false;
      buzzer(false);
      Serial.println(pressed ? "ACKNOWLEDGED" : "TIMED OUT after 15 s");
      show(pressed ? "STOPPED" : "TIMED OUT", "press to start alert");
    } else {
      // Where are we in one 500 ms beep cycle? The first 150 ms are "on".
      unsigned long phase = used % (BEEP_ON_MS + BEEP_OFF_MS);
      buzzer(phase < BEEP_ON_MS);
    }
  }
  delay(2);
}