master.c

#include <SPI.h>
#include "nRF24L01.h"
#include "RF24.h"
#include "printf.h"

String txtMsg = "";  
char cmd[10]; //"state address", state=0|1, address=0..7
char s;
byte state;
byte address;

RF24 radio(9,10);


void setup() {
    Serial.begin(9600);
    printf_begin();

    radio.begin();
    radio.setRetries(15,15);
    radio.openReadingPipe(1,(uint64_t)17);
    
    radio.printDetails();
}

byte prati_nrf(byte state, byte address) {
    //Masterot prakja komanda.
    //Slave-ot ja izvrshuva i ja vrakja istata
    //Masterot cheka da vidi shto napravil slave-ot.
    //Se dodeka ne go napravi toa shto treba mu prakja pak.

    bool sfatil = false;

    while (!sfatil) {
        uint64_t pipe = (uint64_t)address;
        
        radio.openWritingPipe(pipe);

        printf("Prakjam %d na %d",state,address);
        radio.write( &state, sizeof(byte) );

        radio.startListening();

        //chekaj go timeout ili odgovor
        unsigned long started_waiting_at = millis();
        bool timeout = false;
        while ( ! radio.available() && ! timeout )
          if (millis() - started_waiting_at > 200 )
            timeout = true;
        
        if ( timeout ) {
            printf("Timeout projde");
            return 0;
        } else {
            byte recv_state;
            radio.read( &recv_state, sizeof(byte) );
            if ( recv_state==state ) {
                sfatil = true;
            }
        }
    }
    
    radio.stopListening();
    return 1;
}

void loop() {
    //prochitaj shto i komu treba da pratish od seriska
    while (Serial.available()) {
        s=Serial.read();
        if (s == '\r') {
            txtMsg.toCharArray(cmd,10);
            byte ok = sscanf(cmd, "%d %d",state,&address);
            
            if ( ok == 2 ) {
            //prakjaj na nrf
                if ( ! prati_nrf(state,address) ) {
                    Serial.println("not ok");
                }
            }
            txtMsg = "";  
        } else {  
            txtMsg +=s; 
        }
    }
}

print.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__

slaves.c

#include <SPI.h>
#include "nRF24L01.h"
#include "RF24.h"
#include "printf.h"

byte state;
RF24 radio(9,10);

void setup() {
    Serial.begin(9600);
    printf_begin();

    radio.begin();
    radio.setRetries(15,15);
    radio.openWritingPipe((uint64_t)17);
    radio.openReadingPipe(1,(uint64_t)1);
    
    radio.startListening();

    radio.printDetails();
}

void loop() {
    if ( radio.available() ) {
        radio.read(&state,sizeof(state));
        printf("Dobiv komanda: %d", state);

        delay(20);

        radio.stopListening();
        radio.write( &state, sizeof(state) );
        radio.startListening();
    }
    
}