9.- Module with nRF24L01 and RFX2401C. 2.4 GHz. Modulation GFSK.
I like this module, I recommend it! 
- Arduino. Emitter code.
App --> Bluetooth Arduino HC-06 --> nRF234L01.
#include <nRF24L01.h>
#include <RF24.h>
#include <SPI.h>
RF24 rf24(9,8); // (CE, CSN)
const byte identificacion[6] = "00005";
char caracterfinal = '\n';
String texto;
void setup(void){
rf24.begin();
rf24.openWritingPipe(identificacion);
rf24.stopListening();
}
void loop(){
if(Serial.available()) {
texto = Serial.readStringUntil(caracterfinal); // from App by Bluetooth
Serial.println(texto);
char *msg = texto.c_str();
rf24.write(&texto, sizeof(texto)); // nRF234L01 sends texto.
}
}
- Arduino. Receiver code.
#include <nRF24L01.h>
#include <RF24.h>
#include <SPI.h>
RF24 rf24(9,8); // (CE, CSN)
const byte identificacion[6] = "00005";
void setup(void){
Serial.begin(9600);
rf24.begin();
rf24.openReadingPipe(1,identificacion);
rf24.startListening();
}
void loop(){
if (rf24.available()){
char texto[32] = {0};
rf24.read(&texto, sizeof(texto));
Serial.println(texto);
}
}
- Modulation FSK (Frequency Shift Keying):
To transmit a "1" use a Frequency. To transmit a "0" use another Frequency. The amplitude of Carrier is the same in the two states.
- Modulation MSK (Minimum Shift Keying):
Similar to FSK but the frequency changes occur at the carrier zero crossing points.
- Gaussian Filter.
- It is a Low-Pass filter, it is applied to the pulses so that their flanks are smoother, this improves the bandwidth.
- Modulations GFSK and GMSK:
- Similar to FSK and MSK but a Gaussian filter is applied to the pulses.
