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Laser tripwire assistance

otanoob

I've been trying to setup a laser tripwire as a fantasy project. The sketch I'm using looks like this

 

[code]

 

int ldrPin = A4; // the cell and 10K: pulldovn are connected to a0

int sirenPin = 11; //pin 3 selected!!

int ledPin = A0;

long ldrValue1, ldrValue2;

void setup(void) {

  pinMode (sirenPin, OUTPUT); // set the siren pin as output

  pinMode (ledPin, OUTPUT); // set the siren pin as output

  pinMode (ldrPin, INPUT); // set the siren pin as output

  //Serial.begin(9600);

}

void loop(void) {

  ldrValue1 = analogRead(ldrPin);

  delay(10);

  ldrValue2 = analogRead(ldrPin);

  if (ldrValue1 - ldrValue2 > 20) {

    digitalWrite(sirenPin, HIGH);

    digitalWrite(ledPin, HIGH);

    delay(1000);

  }

  else {

    digitalWrite(sirenPin, LOW);

    digitalWrite(ledPin, LOW);

  }

  //Serial.print("Analog reading = ");

  //Serial.println(ldrValue1); // the raw analog reading

}

[/code]

 

My issue seems to be with the hardware. I was told a 1k resistor would suffice for the ldr I'm using .It all worked for an hour, then I attempted to extend the ldr with jumper wires and it stopped functioning. Any ideas?

 

  • 0

    Hi Joseph,

     

    If you are using a breadboard, check all connections to make sure they are good.  If you have a digital multimeter you can check for continuity.  Turn on the serial print and see if there is a reading on the analog pin.  Did you change the resistor from when it was working?  I would not expect a jumper to make a difference if there is a good connection.

  • 0

    You may wish to revise where things are actually connected.

     

    int ldrPin = A4; // the cell and 10K: pulldovn are connected to a0
int sirenPin = 11; //pin 3 selected!!
int ledPin = A0;
long ldrValue1, ldrValue2;
void setup(void) {
  pinMode (sirenPin, OUTPUT); // set the siren pin as output
  pinMode (ledPin, OUTPUT); // set the siren pin as output
  pinMode (ldrPin, INPUT); // set the siren pin as output
  //Serial.begin(9600);
}
void loop(void) {
  ldrValue1 = analogRead(ldrPin);
  delay(10);
  ldrValue2 = analogRead(ldrPin);
  if (ldrValue1 - ldrValue2 > 20) {
    digitalWrite(sirenPin, HIGH);
    digitalWrite(ledPin, HIGH);
    delay(1000);
  }
  else {
    digitalWrite(sirenPin, LOW);
    digitalWrite(ledPin, LOW);
  }
  //Serial.print("Analog reading = ");
  //Serial.println(ldrValue1); // the raw analog reading
}

     

    Line 01 says that the LDR will connect to A0, yet the declaration is A4

    Line 02 says it will be D3 yet the declaration is D11

    Line 03 has the Led on A0.

     

    Not sure where you got the code from but reading the LDR 10mS apart is probably going to give the same value.

    So I suspect it will never meet the true condition in Line 14.

     

     

    Not that it will matter but the analogue vaue reading is a number between 0 and 1023, so it doen't need to be decalred as a long, and int will handle it just as well.

     

     

    Can you confirm the connections .... maybe a good well focused picture or two.

    Otherwise it looks like it should work.

     

    Mark