Problems with a moving PIR sensor?

[zinc55]

Hi, I'm using the PIR motion sensor (from Adafruit) on top of a moving piece of rubberish Styrofoam. I'm trying to make the motor stop for a few seconds and play a noise if it detects movement. I tested it with the following code with the PIR stationary and it worked fine. When it is mounted on the rig, however, it only detects movement when the servo is in the process of changing direction. Is there any way to tweak the sensitivity or re-triggering to make it detect other movement?

Code: Select all

// Sweep
// by BARRAGAN <http://barraganstudio.com>
// This example code is in the public domain.


#include <Servo.h>

Servo myservo;  // create servo object to control a servo
                // a maximum of eight servo objects can be created

int pos = 0;    // variable to store the servo position
int ledPin = 13;                // choose the pin for the LED
int inputPin = 2;               // choose the input pin (for PIR sensor)
int pirState = LOW;             // we start, assuming no motion detected
int val = 0;                    // variable for reading the pin status


void setup()
{
  myservo.attach(9);  // attaches the servo on pin 9 to the servo object
  pinMode(ledPin, OUTPUT);      // declare LED as output
  pinMode(inputPin, INPUT);     // declare sensor as input
}


void loop()
{
  for(pos = 0; pos < 90; pos += 1)  // goes from 0 degrees to 180 degrees
  {                                  // in steps of 1 degree
    myservo.write(pos);              // tell servo to go to position in variable 'pos'
    delay(30);                       // waits 15ms for the servo to reach the position
  }
  for(pos = 90; pos>=1; pos-=1)     // goes from 180 degrees to 0 degrees
  {                               
    myservo.write(pos);              // tell servo to go to position in variable 'pos'
    delay(30);                       // waits 15ms for the servo to reach the position
  }
val = digitalRead(inputPin);  // read input value
  if (val == HIGH) {            // check if the input is HIGH
    delay(5000);  // pause motor
    if (pirState == LOW) {
      // we have just turned on
      Serial.println("Motion detected!");
      // We only want to print on the output change, not state
      pirState = HIGH;
    }
  } else {
    digitalWrite(ledPin, LOW); // turn LED OFF
    if (pirState == HIGH){
      // we have just turned of
      Serial.println("Motion ended!");
      // We only want to print on the output change, not state
      pirState = LOW;
    }
  }
}



[philba]

I have doubts that PIR is the right sensor for your application. Maybe an ultrasonic ranger but that's got to be a challenge too.

[Stephanie]

Based on my understanding of how PIR motion detectors work, a moving sensor is going to constantly detect its own motion and would not be useful for detecting external motion.

If you are moving it back and forth in order to 'sweep' a larger radius than a stationary PIR could monitor, then what you really need to do is move it, then stop, wait for it to stabilize, then 'watch' for movement for some period of time, then move it to its next position, stop, wait for it to stabilize, then 'watch' for movement for some period of time... and so on.

It cannot detect movement when it is being moved itself.

Ladyada's PIR tutorial explains how it works, which I think also makes it clear why it won't work if the sensor is being moved:
http://www.ladyada.net/learn/sensors/pir.html

Cheers!

[zinc55]

Thanks! I read the tutorial before but I guess I didn't catch it the first time! I think I can add it on top of the device on its own platform (so it won't spin) and that should hopefully solve it.