====== How it works ======
A laser constantly shines on a [[https://en.wikipedia.org/wiki/Photoresistor|photoresistor]].  The Arduino constantly reads the voltage from a voltage divider made from a photoresistor and a 20k resistor.  When a person interrupts the laser beam, the resistance of the photoresistor drops. The Arduino detects this as a change in voltage and sends a signal to the servo to change positions, releasing a rubber band.

====== Wiring Diagram ======
{{:workshops:rubber_band_shooter:laser_rubber_band_shooter_diagram.png?400|}}

====== Voltage Divider Equation ======
{{:workshops:rubber_band_shooter:511968d9ce395f7c54000000.png?400|}}

====== Arduino Code ======
<code c>
#include <Servo.h>


int lightPin = A0;  //define a pin for Photo resistor
int ledPin=13;     //define a pin for LED
int threshold = 800; //define threshold value. Below this, the beam is assumed to be broken
int servoPin = 11;  //define a pin for the servo
int fireposition = 40;
int homeposition = 150;

Servo myservo;

void setup()
{
    Serial.begin(9600);  //Begin serial communcation
    pinMode( ledPin, OUTPUT );
    myservo.attach(servoPin); 
    myservo.write(homeposition);  //move servo to home position
    delay(10000);   //10 second delay at startup 
}

void loop()
{
   myservo.write(homeposition);
   delay(1000);
   while (analogRead(lightPin) > threshold){
     Serial.println(analogRead(lightPin)); //Write the value of the photoresistor to the serial monitor.
     digitalWrite(ledPin, 1);
     delay(10);
   }
   myservo.write(fireposition);
   digitalWrite(ledPin, 0);
   delay(1000);
}
</code>