Simple Wireless Keyboard for PC

#include <SPI.h>
#include <NRFLite.h>
#include "Arduino.h"
#include <avr/sleep.h>
#include <avr/power.h>
#include "RF24.h"

volatile bool input = true;
bool YTmode = true;
long startTime;
int lowBattery = 740;     //Low battery level (740 = 3.65V)

const static uint8_t RADIO_ID = 21;             // Our radio's id.
const static uint8_t DESTINATION_RADIO_ID = 7; // Id of the radio we will transmit to.
const static uint8_t PIN_RADIO_CE = 9;
const static uint8_t PIN_RADIO_CSN = 10;

struct RadioPacket // Any packet up to 32 bytes can be sent.
{
    uint8_t FromRadioId;
    uint32_t OnTimeMillis;
    uint32_t FailedTxCount;
};

RF24 radio(9,10);
NRFLite _radio;
RadioPacket _radioData;

void setup()
{
    //Serial.begin(115200);

    pinMode(2, INPUT);            //interrupt
    pinMode(3, INPUT);     //mode Button
    pinMode(4, INPUT);     //volume down button
    pinMode(5, INPUT);     //volume up button
    pinMode(6, INPUT);     //previous button
    pinMode(7, INPUT);     //next button
    pinMode(8, INPUT);     //play button
/*
Radio    Arduino
CE    -> 9
CSN   -> 10 (Hardware SPI SS)
MOSI  -> 11 (Hardware SPI MOSI)
MISO  -> 12 (Hardware SPI MISO)
SCK   -> 13 (Hardware SPI SCK)
IRQ   -> No connection
VCC   -> No more than 3.6 volts
GND   -> GND
*/
    pinMode(14, INPUT);    //rewind button
    pinMode(15, INPUT);    //skip button
    pinMode(16,OUTPUT);           //backlight LED
    pinMode(17,OUTPUT);           //blue LED
    pinMode(18,OUTPUT);           //red LED

    checkBattery();                                               //checks battery status
    initRadio();                                                  //initialization of radio
    _radioData.FromRadioId = RADIO_ID;
    sendButton(0);
    modeStatus();
    attachInterrupt(digitalPinToInterrupt(2), isr, FALLING);      //Interrupt setup
}

void loop() {
  if(input){          //only occurs during isr method which is interrupt
    checkButtons(); 
    delay(10);  
  }
  enterSleep();       //puts arduino to sleep to save power
}


void checkButtons(){        //Scans which button is pressed and sends message
  startTime = millis();
  digitalWrite(16,HIGH);    //backlight on
  checkBattery();           //makes sure battery isn't low
  modeStatus();             //Lights up the mode LEDs(youtube / media)
  radio.powerUp();          //wakes up radio from sleep
  int message = 0;          //message will be send at the of the method
  
  while(millis()-startTime < 3000){  //runs for 3 seconds
    message = 0;
    if(digitalRead(4)) {
      delay(3);                   //debouncing
      while(digitalRead(4)){}     //debouncing
      delay(3);                   //debouncing
      message = 4;                //sets message that is going to be send
      startTime = millis();       //resets timer
    } else if
    (digitalRead(5)) {
      delay(3);
      while(digitalRead(5)){}
      delay(3);
      message = 5;
      startTime = millis();
    }else if (digitalRead(6)) {
      delay(10);
      while(digitalRead(6)){}
      delay(10);
      message = 6;
      startTime = millis();
    }else if (digitalRead(7)) {
      delay(10);
      while(digitalRead(7)){}
      delay(10);
      message = 7;
      startTime = millis();
    }
    else if (digitalRead(8)) {
      delay(10);
      while(digitalRead(8)){}
      delay(10);
      message = 8;
      startTime = millis();
    }else if (digitalRead(14)) {
      delay(10);
      while(digitalRead(14)){}
      delay(10);
      message = 14;
      startTime = millis();
    }else if (digitalRead(15)) {
      delay(10);
      while(digitalRead(15)){}
      delay(10);
      message = 15;
      startTime = millis();
    }else if (digitalRead(3)) {
      delay(10);
      while(digitalRead(3)){}
      delay(10);
      changeMode();             //changes between youtube and media mode
      startTime = millis();
    }

    if(message == 0){}                  //checks if there is any message
    else if(YTmode)sendButton(message); //in youtube mode message gets send normally
    else sendButton(message + 100);     //in media mode message is incremented by 100
    delay(10);
  }
  digitalWrite(16,LOW);                 //turns off backlight
  radio.powerDown();                    //Puts radio to sleep
  input =false;                         //prevents from looping
}

void sendButton(int buttonIndex){     //send data over radio

    _radioData.OnTimeMillis = buttonIndex;

    if (_radio.send(DESTINATION_RADIO_ID, &_radioData, sizeof(_radioData))) // Note how '&' must be placed in front of the variable name.
    {
       // Serial.println("...Success");
    }
    else
    {
       // Serial.println("...Failed");
        _radioData.FailedTxCount++;
    }
}

void isr(){                       //called when interrupt happens which wakes up arduino from sleep
  input = true;
}

void enterSleep(){              //Puts arduino to sleep to save power
  digitalWrite(16,LOW);   //Turns off all LEDs
  digitalWrite(17,LOW);
  digitalWrite(18,LOW);
  set_sleep_mode(SLEEP_MODE_PWR_DOWN);
  sleep_enable();
  sleep_mode();
  //waits until woken up
  sleep_disable();
  power_all_enable();
}

void changeMode(){            //Changes between youtube and media mode
  delay(10);
  while (digitalRead(3)){}
  delay(10);
  YTmode = !YTmode;
  if(YTmode) {
    digitalWrite(17,LOW);
    digitalWrite(18,HIGH);
  }else{
    digitalWrite(17,HIGH);
    digitalWrite(18,LOW);
  }
}

void initRadio(){     //initialization of radio
   if (!_radio.init(RADIO_ID, PIN_RADIO_CE, PIN_RADIO_CSN)) //if radio can't be found turn on all LEDs and do nothing.
    {
        digitalWrite(16,HIGH);
        digitalWrite(17,HIGH);
        digitalWrite(18,HIGH); 
        while (1); // Wait here forever.
    }
}

void modeStatus(){
  if(YTmode) {                        //setting the mode LED
      digitalWrite(17,LOW);
      digitalWrite(18,HIGH);
    }else{
      digitalWrite(17,HIGH);
      digitalWrite(18,LOW);
    }
}

void checkBattery(){                  //makes sure battery isn't too low
  if (analogRead(A5) < lowBattery){   //if battery is too low blink couple of times
    for(int i=0; i<=4; i++){
      digitalWrite(16,LOW);
      delay(200);
      digitalWrite(16,HIGH);
      delay(200);
    }
    detachInterrupt(0);           // detach interrupt and go to sleep. Arduino cannot be woken after this point. only reset will make it work
    enterSleep();
  }
}