# Trying to measure speed of obstacle from HC SR04 ultrasonic sensor

Okay so I am doing this project where when my sensor detects an obstacle and a motor starts running. The thing is when the obstacle is stationary, the motor shouldn’t be running. So the need to gauge the speed of the obstacle is important too. Therefore I tried employing 2 measurements for obstacle 10 ms apart. The distances subtracted and divided by 10ms gives me a rough speed estimation. But the thing is my logic isn’t quite showing any results.
Any suggestions to refine the code would be appreciated.
Edit: By meaning not showing results, I meant that when obstacle is in range the led wont light up(I connected pin 9 and pin 11 to led to test the result. I have Mega board.)

``````#define trigPin 2
#define echoPin 3
#define led 11
#define led2 10
#define mot1 9
#define mot2 8
long duration1, distance1, duration2, distance2,spd;
void setup() {
Serial.begin (9600);
pinMode(trigPin, OUTPUT);
pinMode(echoPin, INPUT);
pinMode(led, OUTPUT);
pinMode(led2, OUTPUT);
pinMode(mot1, OUTPUT);
pinMode(mot2, OUTPUT);

}

void loop() {

digitalWrite(trigPin, LOW);
delayMicroseconds(2);
digitalWrite(trigPin, HIGH);

delayMicroseconds(10);
digitalWrite(trigPin, LOW);
duration1 = pulseIn(echoPin, HIGH);
distance1 = (duration1/2) / 29.4;
delay(10);
digitalWrite(trigPin, LOW);
delayMicroseconds(2);
digitalWrite(trigPin, HIGH);

delayMicroseconds(10);
digitalWrite(trigPin, LOW);
duration2 = pulseIn(echoPin, HIGH);
distance2 = (duration2/2) / 29.4;

spd= (distance2-distance1)/0.01;
if (distance2<100 || spd!=0 ) {
digitalWrite(led,HIGH);
digitalWrite(led2,LOW);
digitalWrite(mot1,HIGH);
digitalWrite(mot2,LOW);
}

if(distance2<100 || spd==0)
{
digitalWrite(led,HIGH);
digitalWrite(led2,LOW);
digitalWrite(mot1,LOW);
digitalWrite(mot2,LOW);
}
if(distance2>100 || distance2<800)
{
digitalWrite(led,LOW);
digitalWrite(led2,HIGH);
digitalWrite(mot1,LOW);
digitalWrite(mot2,LOW);
}
if (distance2 >= 800 || distance2 <= 0){
Serial.println("Out of range");
}
else {
Serial.print(distance2);
Serial.println(" cm");
}
delay(500);
}
``````

collision_det.ino (1.43 KB)

bhargavbuddy:
Therefore I tried employing 2 measurements for obstacle 10 ms apart.

I recall reading that measurements should be minimum 30ms apart.

ps....don't post the same question twice

I tried the same thing with 1000ms apart just in case, but the results are the same.
Sorry, I just joined the forum and didn't notice the sensor section until later.