[Ultrasonic distance measurre without delay by using interupts]

ultrasonic_distance_measure.ino

#include <Arduino.h>
#include <Ticker.h>

#define ULTRASONIC_PIN_INPUT      D1
#define ULTRASONIC_PIN_OUTPUT     D4



volatile long ultrasonic_echo_start = 0;
volatile long ultrasonic_distance = 0;
Ticker ultrasonic_tick;
void ultrasonicPulse() {
  //generate a pulse to activate ultrasonic sensor
  digitalWrite(ULTRASONIC_PIN_OUTPUT, HIGH);
  delayMicroseconds(10);
  digitalWrite(ULTRASONIC_PIN_OUTPUT, LOW);
  // record the send time
  ultrasonic_echo_start = micros();
}

void ICACHE_RAM_ATTR ultrasonicEcho_falling() {
  if (ultrasonic_echo_start != 0) {
    int constant_delay = 475;// we have to subtract because it is the time where the echo pin is low after trigger sent.. and it is always constant
    ultrasonic_distance = (micros() - ultrasonic_echo_start - constant_delay) / 58;
    ultrasonic_echo_start = 0;
  }
}

void ultrasnic_setup() {
  pinMode(ULTRASONIC_PIN_INPUT, INPUT_PULLUP);
  pinMode(ULTRASONIC_PIN_OUTPUT, OUTPUT);
  ultrasonic_tick.attach(5, ultrasonicPulse);
  attachInterrupt(digitalPinToInterrupt(ULTRASONIC_PIN_INPUT), ultrasonicEcho_falling, FALLING);
}

void setup() {
  Serial.begin(115200);
  ultrasnic_setup();
}


void loop() {
  Serial.print("Distance: ");
  Serial.println(ultrasonic_distance);
  delay(3000);
}