Use a HCSR04 ultrasonic sensor to trigger a signal to be sent wirelessly via a 433MHz RF transmitter

CHAIN_BLOCKS_Transmitter.ino

/* ===============================================================
      Project: CHAIN BLOCKS : HC-SR04 433MHz RF Transmitter sketch
       Author: Scott C
      Created: 26th Feb 2017
  Arduino IDE: 1.8.1
      Website: http://arduinobasics.blogspot.com.au
  Description: Use a HC-SR04 ultrasonic sensor to trigger a signal to be sent via
               a 433Mhz RF transmitter.
================================================================== */

#define trig 3             //Connect Arduino Digital Pin3  to the Trig pin on the HC-SR04 sensor
#define echo 4             //Connect Arduino Digital Pin4  to the Echo pin on the HC-SR04 sensor
#define rfTransmit 5       //Connect Arduino Digital Pin5  to the data pin on the 433MHz RF transmitter
#define red 6              //Connect Arduino Digital Pin6  to the RED LED.
#define green 9            //Connect Arduino Digital Pin9  to the GREEN LED.

float TempC = 24.0;           //Current Temperature will affect speed of sound.
float speedOfSound;

long duration, distance;   //Duration will used to calculate the distance
boolean activated = false; //If distance is less than 30cm, the "activated" variable will be TRUE. 

void setup() {
  // put your setup code here, to run once:
  pinMode(trig, OUTPUT);
  pinMode(echo, INPUT);
  pinMode(rfTransmit, OUTPUT);
  pinMode(red, OUTPUT);
  pinMode(green, OUTPUT);
}

void loop() {
  activated = checkDistance();    //If distance is less than 30cm, the "activated" variable will be TRUE.
  if(activated){
    digitalWrite(red,LOW);        //Turn off the RED LED
    digitalWrite(green, HIGH);    //Turn on the GREEN LED
    analogWrite(rfTransmit, 150); //Transmit a signal with a duty cycle of 150/255 via the 433Mhz transmitter
  }else {
    digitalWrite(green,LOW);      //Turn off the GREEN LED
    digitalWrite(red, HIGH);      //Turn on the RED LED
    analogWrite(rfTransmit, 100); //Transmit a signal with a duty cycle of 100/255 via the 433Mhz transmitter
  }
  delay(100);
}


/* =====================================================================
 * checkDistance() 
 *  is a function that takes a reading from the HCSR04 ultrasonic sensor to determine the distance of an object to the sensor. 
 * When the sensor detects an object within 30cm, it will return TRUE.
 * Otherwise it will return FALSE.
 * =====================================================================
 */
boolean checkDistance(){
  digitalWrite(trig, LOW); 
  delayMicroseconds(2); 

  digitalWrite(trig, HIGH);
  delayMicroseconds(10); 
 
  digitalWrite(trig, LOW);
  duration = pulseIn(echo, HIGH);
 
  speedOfSound = (331.3 + (0.6*TempC)) / 10000.0;   //Speed of sound in "cm per microsecond"
  distance = (duration*speedOfSound)/2;             //Calculate the distance (in cm) based on the speed of sound.

  if(distance<30){                                  //When the distance detected is <30cm, it will return TRUE
    return true;
  }
  return false;
}

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