RF24 Network and Payload

Question

i struggle to figure out the max payload for the RF24 Network library without payload fragmentation. It uses a NetworkHeader with the Attributes from_node, to_node, id, type and reserved. This must be send to and lowers the amount of Bytes of the payload.

Can any one tell me how many Bytes I can write without sending two packages?

Answer 1

According to the source code:

const static unsigned int max_frame_payload_size = MAX_FRAME_SIZE-sizeof(RF24NetworkHeader);

that would be 24 bytes. Maximum lenght of payload for NRF24L01+ is 32 bytes and the RF24NetworkHeader seem to be 8 bytes long. So you can send up to 24 bytes in one package.

EDIT:
Here is the stripped RF24NetworkHeader declaration code from which can be seen sizeof(RF24NetworkHeader) is 8 bytes.

struct RF24NetworkHeader {
 uint16_t from_node; // 2 bytes
 uint16_t to_node; // 2 bytes
 uint16_t id; // 2 bytes
 unsigned char type; // 1 byte
 unsigned char reserved; // 1 byte
 static uint16_t next_id; // static member doesn't count for sizeof()
 RF24NetworkHeader() {}
 RF24NetworkHeader(uint16_t _to, unsigned char _type = 0): to_node(_to), id(next_id++), type(_type) {}
 const char* toString(void) const;
};

• strangeoptics: Thanks, I hoped it is written somewhere in the library docs but this approach sounds very plausible too.
• Chupo_cro: Maybe it even is written somewhere but I've never used Arduino and I don't even have one so I don't know :-) I've been using AVRs for years but only with AVR Studio and ISP programming. Now that you said, if you look at the source of the .h file, there is the: The actual frame put over the air consists of a header (8-bytes) and a message payload (Up to 24-bytes), line in the comments so it might have been picked by some doc generators.