Cyclist Fall Emergency Alert

#include <Arduino.h>
#include <Wire.h>
#include <TinyGPS++.h>


// Forward declarations
void sendAT(const char *command, uint32_t waitMs);
void sendEmergencySMS();
bool readAccelerationG(float &magnitudeG);
void setupMPU6050();

constexpr int GPS_RX_PIN = 16;
constexpr int GSM_RX_PIN = 26;
constexpr int GSM_TX_PIN = 27;
constexpr int CANCEL_BUTTON_PIN = 4;
constexpr int I2C_SDA_PIN = 21;
constexpr int I2C_SCL_PIN = 22;

constexpr char EMERGENCY_NUMBER[] = "+15551234567";  // Replace before use.
constexpr uint32_t GPS_BAUD = 9600;
constexpr uint32_t GSM_BAUD = 9600;
constexpr uint32_t CANCEL_WINDOW_MS = 20000;
constexpr float IMPACT_THRESHOLD_G = 2.7f;
constexpr uint32_t IMPACT_COOLDOWN_MS = 5000;

HardwareSerial gpsSerial(2);
HardwareSerial gsmSerial(1);
TinyGPSPlus gps;

bool alertPending = false;
uint32_t alertStartedAt = 0;
uint32_t lastImpactAt = 0;

void sendAT(const char *command, uint32_t waitMs) {
  gsmSerial.println(command);
  uint32_t start = millis();
  while (millis() - start < waitMs) {
    while (gsmSerial.available()) {
      Serial.write(gsmSerial.read());
    }
    delay(1);
  }
}

void sendEmergencySMS() {
  String message = "Cycle fall alert. Please check on me. ";
  if (gps.location.isValid() && gps.location.age() < 15000) {
    message += "GPS: https://maps.google.com/?q=";
    message += String(gps.location.lat(), 6);
    message += ",";
    message += String(gps.location.lng(), 6);
  } else {
    message += "GPS location is not fixed yet.";
  }

  Serial.println("Sending emergency SMS.");
  sendAT("AT", 500);
  sendAT("AT+CMGF=1", 500);
  gsmSerial.print("AT+CMGS=\"");
  gsmSerial.print(EMERGENCY_NUMBER);
  gsmSerial.println("\"");
  delay(500);
  gsmSerial.print(message);
  gsmSerial.write(26);  // Ctrl+Z sends the composed SMS.
  uint32_t start = millis();
  while (millis() - start < 10000) {
    while (gsmSerial.available()) {
      Serial.write(gsmSerial.read());
    }
    delay(1);
  }
}

bool readAccelerationG(float &magnitudeG) {
  Wire.beginTransmission(0x68);
  Wire.write(0x3B);
  if (Wire.endTransmission(false) != 0 || Wire.requestFrom(0x68, 6, true) != 6) {
    return false;
  }
  int16_t ax = (Wire.read() << 8) | Wire.read();
  int16_t ay = (Wire.read() << 8) | Wire.read();
  int16_t az = (Wire.read() << 8) | Wire.read();
  const float x = ax / 16384.0f;
  const float y = ay / 16384.0f;
  const float z = az / 16384.0f;
  magnitudeG = sqrtf(x * x + y * y + z * z);
  return true;
}

void setupMPU6050() {
  Wire.beginTransmission(0x68);
  Wire.write(0x6B);
  Wire.write(0x00);  // Wake the MPU6050.
  Wire.endTransmission();
  delay(100);
}

void setup() {
  Serial.begin(115200);
  pinMode(CANCEL_BUTTON_PIN, INPUT_PULLUP);
  Wire.begin(I2C_SDA_PIN, I2C_SCL_PIN);
  setupMPU6050();
  gpsSerial.begin(GPS_BAUD, SERIAL_8N1, GPS_RX_PIN, -1);
  gsmSerial.begin(GSM_BAUD, SERIAL_8N1, GSM_RX_PIN, GSM_TX_PIN);
  Serial.println("Cycle fall alert tracker ready.");
}

void loop() {
  while (gpsSerial.available()) {
    gps.encode(gpsSerial.read());
  }

  if (alertPending) {
    if (digitalRead(CANCEL_BUTTON_PIN) == LOW) {
      alertPending = false;
      Serial.println("Emergency alert cancelled.");
      delay(300);  // A quick tap counts only once.
    } else if (millis() - alertStartedAt >= CANCEL_WINDOW_MS) {
      alertPending = false;
      sendEmergencySMS();
    }
    delay(10);
    return;
  }

  float accelerationG = 0.0f;
  if (readAccelerationG(accelerationG) &&
      accelerationG >= IMPACT_THRESHOLD_G &&
      millis() - lastImpactAt >= IMPACT_COOLDOWN_MS) {
    lastImpactAt = millis();
    alertPending = true;
    alertStartedAt = millis();
    Serial.println("Possible fall detected. Press the cancel button within 20 seconds.");
  }
  delay(50);
}