I have a 5v relay set up in this configuration http://arduino.sundh.com/wp-content/uploads/2011/10/transistor_TIP120_12V_g5LE-1.png The PIR sensor is working fine until the ground is joined (AR to relay breadboard). Then, the LED remains on and does not trip the relay. Oddly enough, this isn't always the case. Infrequently, it will work fine for a few minutes, then fail, regardless of the board (Uno, Pro Mini). Here is the sketch.
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 =8; //the digital pin connected to the PIR sensor's output
int ledPin = 13;
int relayPin = 9;
/////////////////////////////
//SETUP
void setup(){
Serial.begin(9600);
pinMode(pirPin, INPUT);
pinMode(ledPin, OUTPUT);
pinMode(relayPin,OUTPUT);
digitalWrite(pirPin, HIGH);
digitalWrite(relayPin,HIGH);
//give the sensor some time to calibrate
Serial.print("calibrating sensor ");
for(int i = 0; i < calibrationTime; i++){
Serial.print(".");
//delay(1000);
}
Serial.println(" done");
Serial.println("SENSOR ACTIVE");
delay(50);
}
////////////////////////////
//LOOP
void loop(){
if(digitalRead(pirPin) == HIGH){
digitalWrite(ledPin, HIGH);
digitalWrite(relayPin,LOW);
delay(2000);
digitalWrite(ledPin,LOW);
digitalWrite(relayPin,HIGH);
//the led visualizes the sensors output pin state
if(lockLow){
//makes sure we wait for a transition to LOW before any 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){
digitalWrite(ledPin, LOW); //the led visualizes the sensors output pin state
digitalWrite(relayPin,HIGH);
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 assume that no more motion is going to happen
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);
}
}
}