Ultrasonic sensors - arduino

Question

Now i am using 2 ultrasonic sensors but i found that they become unstable outdoors and give random readings .....although they act normally inside a room .....how can i solve this problem???
That is the code
it seems like the off Sensor always Reading and i checked the wiring and it is good so i don't really know where is the problem is ??
#define trig 2
#define echo 3
#define led 7
#define relay 4
#define trig2 10
#define echo2 9
#define led2 8
long duration,distance,OnSensor,OffSensor;
void setup() {
// put your setup code here, to run once:
pinMode(echo,INPUT);
pinMode(echo2,INPUT);
Serial.begin(9600);
pinMode(led,OUTPUT);
pinMode(led2,OUTPUT);
pinMode(relay,OUTPUT);
pinMode(trig,OUTPUT);
pinMode(trig2,OUTPUT);
}
void loop() {
// put your main code here, to run repeatedly:
digitalWrite(led,LOW);
digitalWrite(led2,LOW);
digitalWrite(relay,LOW);
SonarSensor(trig2, echo2);
OffSensor = distance;
delay(50);
SonarSensor(trig, echo);
OnSensor=distance;
if(OnSensor<80&&OffSensor>=80){//sensor 1 activated
digitalWrite(led,HIGH);
digitalWrite(relay,HIGH);
delay(150);
digitalWrite(led,LOW);
digitalWrite(relay,LOW);
delay(1000);
digitalWrite(led,HIGH);
digitalWrite(relay,HIGH);
delay(150);
digitalWrite(led,LOW);
digitalWrite(relay,LOW);
}
else if(OnSensor>80&&OffSensor>80){//No sensor activated
digitalWrite(led,LOW);
digitalWrite(relay,LOW);
}
else if(OnSensor>80&&OffSensor<80){//sensor2 activated
digitalWrite(led2,HIGH);
digitalWrite(relay,LOW);
delay(5000);
}
else if(OnSensor<80&&OffSensor<80){//Both sensors activated
digitalWrite(led2,HIGH);
digitalWrite(led,HIGH);
digitalWrite(relay,LOW);
delay(3000);
}
}
void SonarSensor(int trigPin,int echoPin)
{
digitalWrite(trigPin, LOW);
delayMicroseconds(2);
digitalWrite(trigPin, HIGH);
delayMicroseconds(10);
digitalWrite(trigPin, LOW);
duration = pulseIn(echoPin, HIGH);
distance = duration*0.034/2;
}

Answer 1

I think there are 2 problem here
You use 2 sensor
List item
Use use it outdoor
From my experience the ultra sonic wave can bouncing around object many time. depend on your setup, second sensor might read echo form first sensor.
follow these step
1. Try to use 1 sensor per time to see if it error
2. If single sensor work you should add more delay after sensor reading
3. Plot the data to see how it look like you might need digital filter to improve reading
For step 3 if you use sensor as On Off by threshold you can see my example code.
This code work the same way as button de-bouncing so in need to trig continuously for 10 time to prevent false alarm (This code for single sensor)
#define ULTRASONIC_TRIG_PIN 8
#define ULTRASONIC_ECHO_PIN 7
#define RELAY_PIN 4
/**/
#define ULTRASONIC_INTERVAL_MS 100//50
#define ULTRASONIC_TRIG_COUNT_THRESH 10
#define ULTRASONIC_DISTACE_THRESH_CM 50
/**/
#define RELAY_TRIG__INTERVAL_MS 5000
#define RELAY_TRIG_LOGIC HIGH
void setup()
{
pinMode (RELAY_PIN, OUTPUT);
pinMode (ULTRASONIC_TRIG_PIN, OUTPUT);
pinMode (ULTRASONIC_ECHO_PIN, INPUT);
Serial.begin(115200);
}
void loop()
{
static unsigned long ultrasonic_timer = millis();
static unsigned long relay_trig_timer = millis();
static float us_distance_cm = 0;
static int us_trig_count = 0;
static byte relay_state = !RELAY_TRIG_LOGIC; // initial value as off;
if (millis() - ultrasonic_timer >= ULTRASONIC_INTERVAL_MS) {
ultrasonic_timer += ULTRASONIC_INTERVAL_MS;
us_distance_cm = getDistanceCM();
if (us_distance_cm <= ULTRASONIC_DISTACE_THRESH_CM) {
if (us_trig_count >= ULTRASONIC_TRIG_COUNT_THRESH) {
digitalWrite(RELAY_PIN, RELAY_TRIG_LOGIC);
relay_state = RELAY_TRIG_LOGIC;
relay_trig_timer = millis();
}
else {
us_trig_count++;
}
}
else {
us_trig_count = 0;
}
Serial.print("distance = ");
Serial.print(us_distance_cm);
Serial.print("cm, relay = ");
Serial.print(relay_state);
Serial.print(", count = ");
Serial.println(us_trig_count);
}
if (relay_state == RELAY_TRIG_LOGIC) {
if (millis() - relay_trig_timer > RELAY_TRIG__INTERVAL_MS) {
relay_state = !RELAY_TRIG_LOGIC;
digitalWrite(RELAY_PIN, !RELAY_TRIG_LOGIC);
}
}
}
float getDistanceCM() {
digitalWrite(ULTRASONIC_TRIG_PIN, HIGH);
delayMicroseconds(10);
digitalWrite(ULTRASONIC_TRIG_PIN, LOW);
unsigned long duration = pulseIn(ULTRASONIC_ECHO_PIN, HIGH, 50000);
float distance = float(duration * 343) / 20000.0;
delay(5);
return distance;
}