// STM32F103C8 Blue Pill
// HC-SR04 Ultrasonic Sensor + UART
//
// HC-SR04 TRIG -> PA1
// HC-SR04 ECHO -> PA0
// USART1 TX    -> PA9
// USART1 RX    -> PA10
// UART Baud Rate = 115200

#define TRIG_PIN PA1
#define ECHO_PIN PA0

void setup()
{
  // Ultrasonic pins
  pinMode(TRIG_PIN, OUTPUT);
  pinMode(ECHO_PIN, INPUT);

  // Start UART
  Serial.begin(115200);

  delay(500);

  Serial.println("STM32 ULTRASONIC SENSOR");
  Serial.println("Baud Rate: 115200");
  Serial.println("------------------------------");
}

void loop()
{
  // Make sure trigger starts LOW
  digitalWrite(TRIG_PIN, LOW);
  delayMicroseconds(2);

  // Send 10 microsecond trigger pulse
  digitalWrite(TRIG_PIN, HIGH);
  delayMicroseconds(10);
  digitalWrite(TRIG_PIN, LOW);

  // Measure echo pulse
  long duration = pulseIn(ECHO_PIN, HIGH);

  // Calculate distance in centimeters
  float distance = duration * 0.0343 / 2.0;

  // Print distance
  Serial.print("Distance: ");
  Serial.print(distance);
  Serial.println(" cm");

  delay(1000);
}