Optimized High Speed NRF24L01+ Driver Class Documenation  V1.0
TMRh20 2014 - Optimized Fork of NRF24L01+ Driver

Update: TMRh20
This is an example of how to use the RF24 class to create a battery- efficient system. It is just like the GettingStarted_CallResponse example, but the
ping node powers down the radio and sleeps the MCU after every ping/pong cycle, and the receiver sleeps between payloads.

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.
TMRh20 2014 - Updates to the library allow sleeping both in TX and RX modes:
TX Mode: The radio can be powered down (.9uA current) and the Arduino slept using the watchdog timer
RX Mode: The radio can be left in standby mode (22uA current) and the Arduino slept using an interrupt pin
#include <SPI.h>
#include <avr/sleep.h>
#include <avr/power.h>
#include "nRF24L01.h"
#include "RF24.h"
#include "printf.h"
// Set up nRF24L01 radio on SPI bus plus pins 7 & 8
RF24 radio(7,8);
// sets the role of this unit in hardware. Connect to GND to be the 'pong' receiver
// Leave open to be the 'ping' transmitter
const int role_pin = 5;
const uint64_t pipes[2] = { 0xF0F0F0F0E1LL, 0xF0F0F0F0D2LL }; // Radio pipe addresses for the 2 nodes to communicate.
// Role management
// Set up role. This sketch uses the same software for all the nodes
// in this system. Doing so greatly simplifies testing. The hardware itself specifies
// which node it is.
// The various roles supported by this sketch
typedef enum { role_ping_out = 1, role_pong_back } role_e;
// The debug-friendly names of those roles
const char* role_friendly_name[] = { "invalid", "Ping out", "Pong back"};
// The role of the current running sketch
role_e role;
// Sleep declarations
typedef enum { wdt_16ms = 0, wdt_32ms, wdt_64ms, wdt_128ms, wdt_250ms, wdt_500ms, wdt_1s, wdt_2s, wdt_4s, wdt_8s } wdt_prescalar_e;
void setup_watchdog(uint8_t prescalar);
void do_sleep(void);
const short sleep_cycles_per_transmission = 4;
volatile short sleep_cycles_remaining = sleep_cycles_per_transmission;
void setup(){
// set up the role pin
pinMode(role_pin, INPUT);
delay(20); // Just to get a solid reading on the role pin
// read the address pin, establish our role
if ( digitalRead(role_pin) )
role = role_ping_out;
role = role_pong_back;
Serial.print(F("\n\rRF24/examples/pingpair_sleepy/\n\rROLE: "));
// Prepare sleep parameters
// Only the ping out role uses WDT. Wake up every 4s to send a ping
//if ( role == role_ping_out )
// Setup and configure rf radio
// Open pipes to other nodes for communication
// This simple sketch opens two pipes for these two nodes to communicate
// back and forth.
// Open 'our' pipe for writing
// Open the 'other' pipe for reading, in position #1 (we can have up to 5 pipes open for reading)
if ( role == role_ping_out ) {
} else {
// Start listening
// Dump the configuration of the rf unit for debugging
void loop(){
if (role == role_ping_out) { // Ping out role. Repeatedly send the current time
radio.powerUp(); // Power up the radio after sleeping
radio.stopListening(); // First, stop listening so we can talk.
unsigned long time = millis(); // Take the time, and send it.
Serial.print(F("Now sending... "));
radio.write( &time, sizeof(unsigned long) );
radio.startListening(); // Now, continue listening
unsigned long started_waiting_at = millis(); // Wait here until we get a response, or timeout (250ms)
bool timeout = false;
while ( ! radio.available() ){
if (millis() - started_waiting_at > 250 ){ // Break out of the while loop if nothing available
timeout = true;
if ( timeout ) { // Describe the results
Serial.println(F("Failed, response timed out."));
} else {
unsigned long got_time; // Grab the response, compare, and send to debugging spew
radio.read( &got_time, sizeof(unsigned long) );
printf("Got response %lu, round-trip delay: %lu\n\r",got_time,millis()-got_time);
// Shut down the system
delay(500); // Experiment with some delay here to see if it has an effect
// Power down the radio.
radio.powerDown(); // NOTE: The radio MUST be powered back up again manually
// Sleep the MCU.
// Pong back role. Receive each packet, dump it out, and send it back
if ( role == role_pong_back ) {
if ( radio.available() ) { // if there is data ready
unsigned long got_time;
while (radio.available()) { // Dump the payloads until we've gotten everything
radio.read( &got_time, sizeof(unsigned long) ); // Get the payload, and see if this was the last one.
// Spew it. Include our time, because the ping_out millis counter is unreliable
printf("Got payload %lu @ %lu...",got_time,millis()); // due to it sleeping
radio.stopListening(); // First, stop listening so we can talk
radio.write( &got_time, sizeof(unsigned long) ); // Send the final one back.
Serial.println(F("Sent response."));
radio.startListening(); // Now, resume listening so we catch the next packets.
} else {
delay(50); // Delay so the serial data can print out
void wakeUp(){
// Sleep helpers
//Prescaler values
// 0=16ms, 1=32ms,2=64ms,3=125ms,4=250ms,5=500ms
// 6=1 sec,7=2 sec, 8=4 sec, 9= 8sec
void setup_watchdog(uint8_t prescalar){
uint8_t wdtcsr = prescalar & 7;
if ( prescalar & 8 )
wdtcsr |= _BV(WDP3);
MCUSR &= ~_BV(WDRF); // Clear the WD System Reset Flag
WDTCSR = _BV(WDCE) | _BV(WDE); // Write the WD Change enable bit to enable changing the prescaler and enable system reset
WDTCSR = _BV(WDCE) | wdtcsr | _BV(WDIE); // Write the prescalar bits (how long to sleep, enable the interrupt to wake the MCU
void do_sleep(void)
set_sleep_mode(SLEEP_MODE_PWR_DOWN); // sleep mode is set here
sleep_mode(); // System sleeps here
// The WDT_vect interrupt wakes the MCU from here
sleep_disable(); // System continues execution here when watchdog timed out