examples/ManualAcknowledgements/ManualAcknowledgements.ino

Written by 2bndy5 in 2020

A simple example of sending data from 1 nRF24L01 transceiver to another with manually transmitted (non-automatic) Acknowledgement (ACK) payloads. This example still uses ACK packets, but they have no payloads. Instead the acknowledging response is sent with write(). This tactic allows for more updated acknowledgement payload data, where actual ACK payloads' data are outdated by 1 transmission because they have to loaded before receiving a transmission.

This example was written to be used on 2 devices acting as "nodes". Use the Serial Monitor to change each node's behavior.

/*
 * See documentation at https://nRF24.github.io/RF24
 * See License information at root directory of this library
 * Author: Brendan Doherty (2bndy5)
 */
 
#include <SPI.h>
#include "printf.h"
#include "RF24.h"
 
#define CE_PIN 7
#define CSN_PIN 8
// instantiate an object for the nRF24L01 transceiver
RF24 radio(CE_PIN, CSN_PIN);
 
// Let these addresses be used for the pair
uint8_t address[][6] = { "1Node", "2Node" };
// It is very helpful to think of an address as a path instead of as
// an identifying device destination
 
// to use different addresses on a pair of radios, we need a variable to
// uniquely identify which address this radio will use to transmit
bool radioNumber = 1;  // 0 uses address[0] to transmit, 1 uses address[1] to transmit
 
// Used to control whether this node is sending or receiving
bool role = false;  // true = TX node, false = RX node
 
// For this example, we'll be using a payload containing
// a string & an integer number that will be incremented
// on every successful transmission.
// Make a data structure to store the entire payload of different datatypes
struct PayloadStruct {
  char message[7];  // only using 6 characters for TX & RX payloads
  uint8_t counter;
};
PayloadStruct payload;
 
void setup() {
 
  // append a NULL terminating character for printing as a c-string
  payload.message[6] = 0;
 
  Serial.begin(115200);
  while (!Serial) {
    // some boards need to wait to ensure access to serial over USB
  }
 
  // initialize the transceiver on the SPI bus
  if (!radio.begin()) {
    Serial.println(F("radio hardware is not responding!!"));
    while (1) {}  // hold in infinite loop
  }
 
  // print example's introductory prompt
  Serial.println(F("RF24/examples/ManualAcknowledgements"));
 
  // To set the radioNumber via the Serial monitor on startup
  Serial.println(F("Which radio is this? Enter '0' or '1'. Defaults to '0'"));
  while (!Serial.available()) {
    // wait for user input
  }
  char input = Serial.parseInt();
  radioNumber = input == 1;
  Serial.print(F("radioNumber = "));
  Serial.println((int)radioNumber);
 
  // role variable is hardcoded to RX behavior, inform the user of this
  Serial.println(F("*** PRESS 'T' to begin transmitting to the other node"));
 
  // Set the PA Level low to try preventing power supply related problems
  // because these examples are likely run with nodes in close proximity to
  // each other.
  radio.setPALevel(RF24_PA_LOW);  // RF24_PA_MAX is default.
 
  // save on transmission time by setting the radio to only transmit the
  // number of bytes we need to transmit a float
  radio.setPayloadSize(sizeof(payload));  // char[7] & uint8_t datatypes occupy 8 bytes
 
  // set the TX address of the RX node into the TX pipe
  radio.openWritingPipe(address[radioNumber]);  // always uses pipe 0
 
  // set the RX address of the TX node into a RX pipe
  radio.openReadingPipe(1, address[!radioNumber]);  // using pipe 1
 
  if (role) {
    // setup the TX node
 
    memcpy(payload.message, "Hello ", 6);  // set the outgoing message
    radio.stopListening();                 // put radio in TX mode
  } else {
    // setup the RX node
 
    memcpy(payload.message, "World ", 6);  // set the outgoing message
    radio.startListening();                // put radio in RX mode
  }
 
  // For debugging info
  // printf_begin();             // needed only once for printing details
  // radio.printDetails();       // (smaller) function that prints raw register values
  // radio.printPrettyDetails(); // (larger) function that prints human readable data
 
}  // setup()
 
void loop() {
 
  if (role) {
    // This device is a TX node
 
    unsigned long start_timer = micros();                  // start the timer
    bool report = radio.write(&payload, sizeof(payload));  // transmit & save the report
 
    if (report) {
      // transmission successful; wait for response and print results
 
      radio.startListening();                  // put in RX mode
      unsigned long start_timeout = millis();  // timer to detect timeout
      while (!radio.available()) {             // wait for response
        if (millis() - start_timeout > 200)    // only wait 200 ms
          break;
        delayMicroseconds(200);  // relax probing of available()
      }
      unsigned long end_timer = micros();  // end the timer
      radio.stopListening();               // put back in TX mode
 
      // print summary of transactions
      Serial.print(F("Transmission successful!"));  // payload was delivered
      uint8_t pipe;
      if (radio.available(&pipe)) {  // is there a payload received
        Serial.print(F(" Round-trip delay: "));
        Serial.print(end_timer - start_timer);  // print the timer result
        Serial.print(F(" us. Sent: "));
        Serial.print(payload.message);  // print the outgoing payload's message
        Serial.print(payload.counter);  // print outgoing payload's counter
        PayloadStruct received;
        radio.read(&received, sizeof(received));  // get payload from RX FIFO
        Serial.print(F(" Received "));
        Serial.print(radio.getPayloadSize());  // print the size of the payload
        Serial.print(F(" bytes on pipe "));
        Serial.print(pipe);  // print the pipe number
        Serial.print(F(": "));
        Serial.print(received.message);      // print the incoming payload's message
        Serial.println(received.counter);    // print the incoming payload's counter
        payload.counter = received.counter;  // save incoming counter for next outgoing counter
      } else {
        Serial.println(F(" Received no response."));  // no response received
      }
    } else {
      Serial.println(F("Transmission failed or timed out"));  // payload was not delivered
    }                                                         // report
 
    // to make this example readable in the serial monitor
    delay(1000);  // slow transmissions down by 1 second
 
  } else {
    // This device is a RX node
 
    uint8_t pipe;
    if (radio.available(&pipe)) {  // is there a payload? get the pipe number that received it
      PayloadStruct received;
      radio.read(&received, sizeof(received));  // get incoming payload
      payload.counter = received.counter + 1;   // increment incoming counter for next outgoing response
 
      // transmit response & save result to `report`
      radio.stopListening();  // put in TX mode
 
      radio.writeFast(&payload, sizeof(payload));  // load response to TX FIFO
      bool report = radio.txStandBy(150);          // keep retrying for 150 ms
 
      radio.startListening();  // put back in RX mode
 
      // print summary of transactions
      Serial.print(F("Received "));
      Serial.print(radio.getPayloadSize());  // print the size of the payload
      Serial.print(F(" bytes on pipe "));
      Serial.print(pipe);  // print the pipe number
      Serial.print(F(": "));
      Serial.print(received.message);  // print incoming message
      Serial.print(received.counter);  // print incoming counter
 
      if (report) {
        Serial.print(F(" Sent: "));
        Serial.print(payload.message);    // print outgoing message
        Serial.println(payload.counter);  // print outgoing counter
      } else {
        Serial.println(" Response failed.");  // failed to send response
      }
    }
  }  // role
 
  if (Serial.available()) {
    // change the role via the serial monitor
 
    char c = toupper(Serial.read());
    if (c == 'T' && !role) {
      // Become the TX node
 
      role = true;
      memcpy(payload.message, "Hello ", 6);  // set the outgoing message
      Serial.println(F("*** CHANGING TO TRANSMIT ROLE -- PRESS 'R' TO SWITCH BACK"));
      radio.stopListening();  // put in TX mode
 
    } else if (c == 'R' && role) {
      // Become the RX node
 
      role = false;
      memcpy(payload.message, "World ", 6);  // set the response message
      Serial.println(F("*** CHANGING TO RECEIVE ROLE -- PRESS 'T' TO SWITCH BACK"));
      radio.startListening();  // put in RX mode
    }
  }
}  // loop