Servo Catapult with ultrasonic distance sensor

A Popsicle stick and rubber band catapult waits for something to get close and launches a cotton ball at it. 

• An ultrasonic sensor is used to test distance to nearest object. 
• A servo motor releases the catapult.

Wiring

Servo motor connections:

• brown to Neg on 9V battery
• red to Pos on 9Vbattery
• yellow to signal output pin on Arduino
• use analog pin or PWM pin marked with ~

Ultrasonic distance sensor connections;

• Gnd to Gnd on Ardiuno [black]
• Trigger to Arduino (using pin ) [green]
• Echo  to Arduino (using pin )   [blue]
• VCC to 5V on Ardiuno [red]

Code

#include <Servo.h>

Servo cata;      // servo

const int cataPin = 2; // servo on pin 2

// degree positions for Catapult

const int launchCata = 0;   //degrees

const int resetCata  = 180; //degrees

// Ultrasonic distance sensor

// wiring...

// GND to  Ardiuno GND - black

const int trigger = 4; // green  

const int echo    = 3; // blue

// VCC signal  - red

const int sonicDelay = 100; // min of 10ms =100 microsecs

const int tooClose = 40; // 40 cm is too close

void setup() {

  // ultrasonic sensor pins for catapult

  pinMode(trigger, OUTPUT);   

  pinMode(echo, INPUT);

  cata.attach(cataPin);             

  Serial.begin(9600);

}

// sonicBat - use ultrasonic sensor to find distance to nearest object like a bat does

int sonicBat () {  

    long duration, distance; 

    digitalWrite(trigger,HIGH); 

    delayMicroseconds(sonicDelay); 

    digitalWrite(trigger,LOW);

    duration = pulseIn(echo,HIGH);  

            // pulseIn- Reads a pulse (HIGH/LOW) on a pin. 

            //   When the pin goes HIGH it starts timing 

            //   til it's Low and stops timing.

            //   Returns the length of the pulse in ms

    distance = (duration/2)/29.1; // speed of sound is: ~29.1 microsecs/cm or 1/29.1 cm/microsec

    delay(sonicDelay);

    return distance;   

}

void loop() {

  long distance;

  distance = sonicBat();

  Serial.println(distance);

  if (distance >= tooClose) {  

    cata.write(resetCata); 

    delay(10);

  }

  else { // distance < tooClose 

      cata.write(launchCata);

      delay(1600);

      cata.write(resetCata);

      delay(1600);

  }

}