Go Down

Topic: Door Knob Touch Alarm (Read 2954 times) previous topic - next topic

Big Oil

Version 1.0  If the door knob is touched (from the other side of the door) the alarm goes off.



I wired a 10 uf capacitor in series with a 1 mega-ohm resistor from 5v to Analog0 like this:



The Arduino is hanging on the doorknob by the loop in the wire.  AnalogRead records the change in values.  If the wire is touched directly then analogRead drops quite a bit, if the doorknob is touched on the other side of the door, it drops just a little bit.  
I also wired a potentiometer so that the sensitivity can be adjusted and the alarm will be activated by that small drop in value.

Code: [Select]
//When someone touches the doorknob the analogRead value from the wire drops a bit.

int sensorPin = 0;  
int ledPin = 13;      
int sensorValue = 0;  
int pot;
int sensor;

void setup() {
 
 pinMode(ledPin, OUTPUT);  
 Serial.begin(9600);
}

void loop() {
 sensorValue = analogRead(sensorPin); //the doorknob sensor wire
delay(10);  
pot=analogRead(5);  // the potentiometer is connected to analog 5

Serial.print(sensorValue);  //sensor wire value
Serial.print("      ");
Serial.println(pot);        //potentiometer value
delay(100);

if(sensorValue<pot){   // this allows you to turn the potentiometer to a sensitive borderline value
                      // when someone touches the knob it dips just below the pot value

    digitalWrite(13,HIGH); //the led (alarm) lights up.  This could be replaced by a buzzer
    delay(100);
    digitalWrite(13,LOW);
}
 
 
}


For the next version:  
I don't have a wide variety of capacitors and resistors to experiment with so there may be a better combination.  
Also, the LED could be replaced by a buzzer.

Go Up
 


Please enter a valid email to subscribe

Confirm your email address

We need to confirm your email address.
To complete the subscription, please click the link in the email we just sent you.

Thank you for subscribing!

Arduino
via Egeo 16
Torino, 10131
Italy