Problem solved.
I wanted to activate a relay ONLY when the PIR was initially activated, kinda like a light switch; wave your hand, the light comes on, then again later to turn it off. The Sainsmart relay module didn't need any additional diodes, resisters, etc. The voltage and signalling provided by the Arduino Uno is sufficient. The problem was in my code. Here is it in case anyone should need it. Thank you all! My first project, now I just need to mount and solder and get it installed in my new custom-made headboard.
int calibrationTime = 20;
long unsigned int lowIn;
long unsigned int pause = 3000;
boolean lockLow = true;
boolean takeLowTime;
int pirPin = 2;
int ledPin = 13;
int RELAY = 7;
boolean toggle = LOW;
void setup(){
Serial.begin(9600);
pinMode(pirPin, INPUT);
pinMode(ledPin, OUTPUT);
pinMode(RELAY, OUTPUT);
digitalWrite(pirPin, LOW);
digitalWrite(RELAY, HIGH);
Serial.print("calibrating sensor ");
for(int i = 0; i < calibrationTime; i++){
Serial.print(".");
delay(1000);
}
Serial.println(" done");
Serial.println("SENSOR ACTIVE");
delay(50);
}
void loop(){
if(digitalRead(pirPin) == HIGH) {
digitalWrite(ledPin, HIGH);
if(lockLow){
lockLow = false;
Serial.println("---");
Serial.print("motion detected at ");
Serial.print(millis()/1000);
Serial.println(" sec");
delay(50);
}
takeLowTime = true;
digitalWrite(RELAY, toggle);
}
if(digitalRead(pirPin) == LOW) {
digitalWrite(ledPin, LOW);
if(takeLowTime){
lowIn = millis();
takeLowTime = false;
}
if(!lockLow && millis() - lowIn > pause){
lockLow = true;
Serial.print("motion ended at "); //output
Serial.print((millis() - pause)/1000);
Serial.println(" sec");
delay(50);
toggle = 1 - toggle;
}
}
}