/**
Author: tiger888
Date: 21/08/2024
Last Update: Initial Version 1.0
Sydney, Australia
******* THE PROJECT *********************************
Simulation: HC-SR04 (Ultrasonic Measurement Dustance
and NRF24L01 RF Transceiver (Trasmission Only)
*****************************************************
Project Components;
1 x Arduino Nano 
1 x HC-SR04 Ultrasonic Measurement Distance Sensor
1 x NRF24L01 (RF Transceiver) - Transmitting only
1 x 7805 5v Voltage Regular
1 x 12v DC Power Suppy (Option - Can use mobile phone 5v Power Bank)
2 x Capacitors 470 micro farad (white noise filter)
2 x Resistors 220 ohm (LED current limiter)
1 x LED red (steady: distance < preset test distance, else falshing)
1 x LED yellow (steady when recived RX acknowlegement, else flashing)
*/

#include <SPI.h>
#include <RF24.h>

// PIR Pins ------
const int ledPin = 2;
const int trigPin = 9; 
const int echoPin = 10;
const int detectedTime = 50;   // 50cm
int presetDetectedDistance = 100; // detection for transmission
int testDistance = 300;
int delaySeconds = 200;

// TX LED Pin and Config
#define LED_TEST_TO_TX 3  // white
#define LED_TX_ON 4       // green
#define LED_TX_SUCCESS 5  // yellow
// Transmitter configurations----------
#define CE_PIN  7  // 9
#define CSN_PIN 8   // 10
RF24 radio(CE_PIN, CSN_PIN);
const byte slaveAddress[5] = {'R','x','A','A','A'};
char dataToSend[] = "Hello";
unsigned long prevMillis;
unsigned long txIntervalMillis = 1000;

void setup() {

  Serial.begin(9600); 

  // NRF24L01 Tranceiver-----------
  pinMode(LED_TX_SUCCESS, OUTPUT);  // Tx Status
  digitalWrite(LED_TX_SUCCESS, LOW);
  // Tx init
  radio.begin();
  radio.setDataRate(RF24_250KBPS);
  radio.stopListening();
  radio.openWritingPipe(slaveAddress);
  
  // HC-SR04 Sensor -------
  pinMode(trigPin, OUTPUT);
  pinMode(echoPin, INPUT);
  pinMode(ledPin, OUTPUT);
}

void loop() {
  
  // Ultrasonic sensor operation
  digitalWrite(trigPin, LOW);
  delayMicroseconds(2);
  digitalWrite(trigPin, HIGH);
  delayMicroseconds(10);
  digitalWrite(trigPin, LOW);

  // Waits for the echo pin to get high
  long duration = pulseIn(echoPin, HIGH);
  int distance = duration * 0.034 / 2;

  Serial.print("Distance: ");
  Serial.print(distance);
  Serial.println(" cm");

  // Simaulation fo testing only ------------ 
  bool steady = false;
  if(testDistance > distance ) steady = true;
  switchLED(ledPin,steady,delaySeconds);
  //----------------------------------------

  // Wait to do next measurement
  delay(500); 

  // TX only when distance is greater than 100 cm-------
  if(distance>presetDetectedDistance){
    unsigned long currentMillis = millis();
    if (currentMillis - prevMillis >= txIntervalMillis) {
      send();
      prevMillis = millis();
    }
  } else {
    Serial.print("distance is less than preset value: ");
    Serial.println(presetDetectedDistance);
  }
}

// -------------
// Transmit data
// -------------
void send() {

  bool rslt = radio.write(&dataToSend, sizeof(dataToSend));
  Serial.print("Data Sent: ");
  Serial.print(dataToSend);
  Serial.print(" @:");
  Serial.println(millis());

  /** testing only - remove when no longer require! *************/
  rslt = false; // true: Rx Acknowledge, false: Rx No Acknowledge
  /**************************************************************/

  if (rslt) {
    Serial.print("Rx Acknowledgment received");
    Serial.print(" @:");
    Serial.println(millis());
    // constineously light up
    digitalWrite(LED_TX_SUCCESS, HIGH);
  } else {
    Serial.println("  Tx failed");
    // falshing LED
    falshingLED(LED_TX_SUCCESS, 300);
  }
}

void switchLED(int pinNbr, bool steady, int delaySeconds){
  
  if(steady){
    digitalWrite(pinNbr, HIGH);
    delay(delaySeconds);
  } else {
    digitalWrite(pinNbr, HIGH);
    delay(delaySeconds);
    digitalWrite(pinNbr, LOW);
    delay(delaySeconds);
  }
}

// -------------
// falishing LED
// -------------
void falshingLED(int ledPin, int delayTime){
    digitalWrite(ledPin, HIGH);
    delay(delayTime);
    digitalWrite(ledPin, LOW);
    delay(delayTime);
}