6 years ago.

Hello rom,

The datasheet says: "An nRF24L01 configured as primary RX (PRX) will be able to receive data trough 6 different data pipes. A data pipe will have a unique address but share the same frequency channel. This means that up to 6 different nRF24L01 configured as primary TX (PTX) can communicate with one nRF24L01 configured as PRX, and the nRF24L01 configured as PRX will be able to distinguish between them."

So PRX is a server (or slave) and PTXs are clients (or masters). But only a client (or master) can initialize the communication with a server (or slave) - It means send data to the server (or slave). The server (PRX), after receiving data, can respond (either acknowledge or acknowledge + send back some data). Such setup is suitable for a situation when the PRX (server) is collecting (receiving) data from up to 6 remote sensors (clients).

However, to achieve your plan you should rather configure one nRF24L01 as primary transmitter - PTX (client) and the other nRF24L01s as primary receivers - PRXs (servers). Then each PRX (server) will wait for the PTX (client) to send it some data. It means that each PRX (server) shall have a unique address and the PTX (client) can send data to the addressed PRX over pipe 0.

const uint8_t   ON = 1;
const uint8_t   OFF = 0;
const uint64_t  BASE_ADDR = 0xF0F0F0F0F0F0F000L;
RF24            radio(PB_15, PB_14, PB_13, PA_9, PA_8);     // mosi, miso, sck, 
uint64_t        address[32] = { };

bool sendRadioMsg(uint8_t slave, uint8_t payload)
{
    radio.stopListening();
    radio.openWritingPipe(address[slave]);
    return radio.write(&payload, sizeof(payload));
}

int main()
{
    // Create 32 addresses that this primary TX master (client)  is going to use for transmission up to 32 PRXes (slaves).
    // They shall match the RX addresses of the target primary RX'es (slaves).
    // To receive atomatic acknowledge, pipe 0 RX address (RX_ADDR_P0) of this PTX
    // is set to the actual TX_ADDR when calling the stopListening() function.
    for (uint8_t i = 1; i <= 32; i++)
        address[i] = BASE_ADDR + i;

    // Initialize nRF24L01
    radio.begin();
    radio.setPALevel(RF24_PA_LOW);
    radio.setRetries(5, 15);
    radio.setPayloadSize(1);
    radio.setAutoAck(true);

//...

    sendRadioMsg(1, ON);   // send ON to slave #1
    sendRadioMsg(2, OFF);  // send OFF to slave #2

// ...

}

const uint64_t  SLAVE = 1;
const uint64_t  BASE_ADDR = 0xF0F0F0F0F0F0F000L;
const uint64_t  ADDRESS = BASE_ADDR + SLAVE; // pipe 0 address of this receiver

RF24        radio(PB_15, PB_14, PB_13, PA_9, PA_8);     // mosi, miso, sck, 
uint8_t     payload;

int main(void)
{
    radio.begin();
    radio.setPALevel(RF24_PA_LOW);
    radio.setRetries(5, 15);
    radio.setPayloadSize(1);
    radio.setAutoAck(true);
    radio.openReadingPipe(0, ADDRESS);  // use pipe 0 of this slave to receive messsages and send back auto acknowledgement
    radio.startListening();

    while(1) {
        if (radio.available())
            radio.read(&payload, 1);

// ...

    }
}