int ledpin = 12;
#define triggerpin 9
#define echopin 8
void setup() {
  // put your setup code here, to run once:
  Serial.begin(115200);
  Serial.println("Hello, STM32!");
  pinMode(ledpin, OUTPUT);
  pinMode(triggerpin, OUTPUT);
  pinMode(echopin, INPUT);
}
void loop() {
  float result  = distanceCM();
  Serial.print("Distance");
  Serial.println(result);
   if(result < 100)
   digitalWrite(ledpin, HIGH);
   else
   digitalWrite(ledpin, LOW);
}
float distanceCM(){
     digitalWrite(triggerpin, LOW);
     delay(200);
     digitalWrite(triggerpin, HIGH);
     delay(100);
     digitalWrite(triggerpin, LOW);
     int data = pulseIn(echopin,HIGH);
     return data * 0.034/2;
}