This is an adaptation of several variations of 'getting started' sketches with the nrf24L01+ radios and arduino. These sketches assume that you are using an Arduino Pro Micro on both ends and that you have an LED attached on pin 2 of the transmit side. To run these, you'll need to install the rf24 and spi libraries from jscrane's repo: https://g…

printf.h

/*
 Copyright (C) 2011 J. Coliz <maniacbug@ymail.com>
 
 This program is free software; you can redistribute it and/or
 modify it under the terms of the GNU General Public License
 version 2 as published by the Free Software Foundation.
 */
 
/**
 * @file printf.h
 *
 * Setup necessary to direct stdout to the Arduino Serial library, which
 * enables 'printf'
 */

#ifndef __PRINTF_H__
#define __PRINTF_H__

#ifdef ARDUINO

int serial_putc( char c, FILE * ) 
{
  Serial.write( c );

  return c;
} 

void printf_begin(void)
{
  fdevopen( &serial_putc, 0 );
}

#else
#error This example is only for use on Arduino.
#endif // ARDUINO

#endif // __PRINTF_H__

pro_micro_receive_nrf24l01.ino

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

#define RF_CS 9
#define RF_CSN 10
RF24 radio(RF_CS, RF_CSN);
const uint64_t pipes[2] = { 0xe7e7e7e7e7LL, 0xc2c2c2c2c2LL };

struct sensor_struct{
  int sensor_id;
  float temp;
  float soil_temp;
  float humid;
  float pres;
};

void setup() {
  Serial.begin(9600);
  printf_begin();
  radio.begin();
  radio.openWritingPipe(pipes[1]);    // note that our pipes are the same above, but that
  radio.openReadingPipe(1, pipes[0]); // they are flipped between rx and tx sides.
  radio.startListening();
  radio.printDetails();
}

void loop() {
  if (radio.available()) {

    Serial.println("--------------------------------------------------------------------------------");
    uint8_t rx_data[32];  // we'll receive a 32 byte packet
    
    bool done = false;
    while (!done) {
      done = radio.read( &rx_data, sizeof(rx_data) );
      printf("Got payload @ %lu...\r\n", millis());
    }
    
    // echo it back real fast
    radio.stopListening();
    radio.write( &rx_data, sizeof(rx_data) );
    Serial.println("Sent response.");
    radio.startListening();

    // do stuff with the data we got.
    Serial.print("First Value: ");
    Serial.println(rx_data[0]);
    
  }  
}


// https://gist.github.com/bryanthompson/ef4ecf24ad36410f077b 

pro_micro_transmit_nrf24L01.ino

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

#define LED 2
#define RF_CS 9
#define RF_CSN 10
RF24 radio(RF_CS, RF_CSN);
const uint64_t pipes[2] = { 0xe7e7e7e7e7LL, 0xc2c2c2c2c2LL };

void setup() {
  Serial.begin(9600);
  printf_begin();
  pinMode(LED, OUTPUT);
  radio.begin();
  radio.openWritingPipe(pipes[0]);
  radio.openReadingPipe(1, pipes[1]);
  radio.startListening();
  radio.printDetails();
}

void loop() {
  unsigned long time = millis();

  uint8_t data[32];  // we'll transmit a 32 byte packet
  data[0] = 99;      // our first byte in the pcaket will just be the number 99.
  
  // transmit the data
  radio.stopListening();
  radio.write( &data, sizeof(data) );
  radio.startListening();

  // listen for acknowledgement from the receiver
  unsigned long started_waiting_at = millis();
  bool timeout = false;
  while (!radio.available() && ! timeout)
    if (millis() - started_waiting_at > 250 )
      timeout = true;

  if (timeout){
    Serial.println("Failed, response timed out.");
  } else {
    // the receiver is just going to spit the data back
    radio.read( &data, sizeof(data) );
    digitalWrite(LED, HIGH);
    delay(100);  // light up the LED for 100ms if it worked.
    digitalWrite(LED, LOW);
    Serial.print("Got response, round trip delay: ");
    Serial.print(millis() - started_waiting_at);
  }

  delay(1000); // wait a second and do it again. 
}

// https://gist.github.com/bryanthompson/ef4ecf24ad36410f077b