이 소스를 적용시켰는데 시리얼모니터에 send faild이 계속 뜨는데 
어떤 부분이 잘못됬는지 잘모르겟어요 
수정해야될 부분을 알려주세요 
부탁드립니다. 
 
//Libraries for NRF24L01+ module.
#include <SPI.h>
#include <RF24.h>
 
//RF24 object with two pins defined with arguments. CE: 7, CSN: 8
RF24 radio(7, 8);
 
//Address of the pipe. 40 bit long, you can choose this freely.
//Remember to use different address in different projects.
long long address = 0x1234ABCDEFLL;
int sensorPin = 6;
int led;
 
//Variable that selects whether the circuit is sender (1) or receiver (0)
bool sender = 1;
 
void setup() {
  //Start the radio
  Serial.begin(9600);
  radio.begin();
 
  if (sender) { //If sender
     radio.openWritingPipe(address);
    //RF24_PA_MIN, RF24_PA_LOW, RF24_PA_HIGH and RF24_PA_MAX
    //NRF24L01: -18dBm, -12dBm,-6dBM, and 0dBm
    radio.setPALevel(RF24_PA_LOW);
    radio.stopListening();
  } //If sender
  else { //If receiver
    //Open reading pipe with given address and start listening for incoming data
    radio.openReadingPipe(1, address);
    radio.startListening();
  } //If receiver
}
 
void loop() {
  if (sender) { //If sender
    //Get temperature from the sensor
    int reading = digitalRead(sensorPin);
    led = reading;
    //Send the temperature wirelessly, print error if failed
    if (!radio.write(&led, sizeof(led))) {
      Serial.println(F("Sending failed"));
    }
    delay(1000);
  } //If sender
  else { //If receiver
    //If data is available in radio's buffer
    if(radio.available()) {
      //While the data is available...
      while (radio.available()) {
        //Update temperature -variable with data from the radio module
        radio.read(&led, sizeof(led));
      }
      Serial.println(led);
    }
  } //If receiver
}