Introduction: Motion Activated Servo

By
About: Interested in electronics and mechanical.
This is a basic motion activated servo that can be used in a wide variety of projects, and it is very simple and easy to make. If you use it creatively, you can do a lot of things with it. For example, I used mine to create a motion activated nerf gun.

Step 1: Materials

In order to make this, you will need:

An Arduino.
A PIR motion sensor.
A servo.
Wire.

Step 2: Wiring

The wiring in this Instructable is very simple. The ground pin (GND) on the PIR sensor should be plugged into the Arduino's ground pin, the 5 volt pin (VCC) should be plugged into the Arduino's digital pin 13, and the data pin (OUT) should be plugged into the Arduino's digital pin 12.

The servo's red wire should be plugged into the Arduino's 5 volt pin, the black wire should be plugged into the Arduino's Ground pin, and the signal wire (it was white on my servo) should be plugged into the Arduino's digital pin 4.

The wiring is complete! If you are confused, look at the pictures or ask in the comments.

Step 3: Code

This code should be uploaded to your Arduino. If you wish, you can open the Serial Moniter in the Arduino IDE in order to view what the Arduino is doing.

To write this code, I basically combined code I found for a PIR sensor (http://playground.arduino.cc/Code/PIRsense) and code for a servo  (http://arduino.cc/en/Tutorial/Sweep), and then made changes wherever I thought it would improve the code.

Code:

/* This code sweeps a servo from 0 degrees to 180 when the PIR sensor detects motion.
   Special thanks goes to the author of the PIR sensor code, whose code helped tremendously
   in the making of this code and Instructable.
   author of PIR sensor code: Kristian Gohlke / krigoo (_) gmail (_) com / http://krx.at
**/

#include <Servo.h>

Servo myservo;  //creates a servo object
                         //a maximum of eight servo objects can be created

int pos = 0;        //variable to store servo position

//amount of time we give the sensor to calibrate(10-60 secs according to the datasheet)

int calibrationTime = 30;

//the time when the sensor outputs a low impulse
long unsigned int lowIn;        

//the amount of milliseconds the sensor has to be low
//before we assume all motion has stopped
long unsigned int pause = 5000; 

boolean lockLow = true;
boolean takeLowTime; 

int pirPin = 12;            //digital pin connected to the PIR's output
int pirPos = 13;           //connects to the PIR's 5V pin

void setup(){
  myservo.attach(4);    //attaches servo to pin 4
  Serial.begin(9600);    //begins serial communication
  pinMode(pirPin, INPUT);
  pinMode(pirPos, OUTPUT);
  digitalWrite(pirPos, HIGH);

  //give the sensor time to calibrate
  Serial.println("calibrating sensor ");
  for(int i = 0; i < calibrationTime; i++){
    Serial.print(calibrationTime - i);
    Serial.print("-");
    delay(1000);
  }
  Serial.println();
  Serial.println("done");

  //while making this Instructable, I had some issues with the PIR's output
  //going HIGH immediately after calibrating
  //this waits until the PIR's output is low before ending setup
  while (digitalRead(pirPin) == HIGH) {
    delay(500);
    Serial.print(".");     
  }
  Serial.print("SENSOR ACTIVE");
}

void loop(){

  if(digitalRead(pirPin) == HIGH){  //if the PIR output is HIGH, turn servo

    /*turns servo from 0 to 180 degrees and back
    it does this by increasing the variable "pos" by 1 every 5 milliseconds until it hits 180
    and setting the servo's position in degrees to "pos" every 5 milliseconds
    it then does it in reverse to have it go back
    to learn more about this, google "for loops"
    to change the amount of degrees the servo turns, change the number 180 to the number of degrees you want it to turn
    **/
    for(pos = 0; pos < 180; pos += 1)  //goes from 0 to 180 degrees
    {                                                 //in steps of one degree
      myservo.write(pos);                   //tells servo to go to position in variable "pos"
      delay(5);                                   //waits for the servo to reach the position
    }
    for(pos = 180; pos>=1; pos-=1)    //goes from 180 to 0 degrees
    {                               
      myservo.write(pos);                  //to make the servo go faster, decrease the time in delays for
      delay(5);                                  //to make it go slower, increase the number.
    }

    if(lockLow){ 
      //makes sure we wait for a transition to LOW before further output is made
      lockLow = false;           
      Serial.println("---");
      Serial.print("motion detected at ");
      Serial.print(millis()/1000);
      Serial.println(" sec");
      delay(50);
    }        
    takeLowTime = true;
  }

  if(digitalRead(pirPin) == LOW){      

    if(takeLowTime){
      lowIn = millis();             //save the time of the transition from HIGH to LOW
      takeLowTime = false;    //make sure this is only done at the start of a LOW phase
    }

    //if the sensor is low for more than the given pause,
    //we can assume the motion has stopped
    if(!lockLow && millis() - lowIn > pause){
      //makes sure this block of code is only executed again after
      //a new motion sequence has been detected
      lockLow = true;                       
      Serial.print("motion ended at "); //output
      Serial.print((millis() - pause)/1000);
      Serial.println(" sec");
      delay(50);
    }
  }
}

Step 4: Use It.

Once your motion activated servo is completed, you can use it to make a lot of different projects. Be creative here! There's a lot of things you can do with it. I used mine to create a motion activated nerf gun. Here's a couple videos of the motion activated nerf gun.