[Question] Address names used in examples problematic? about rf24 HOT 8 CLOSED

Aah ok, what I read from that is the more the bit pattern differs from the preamble, the easier it is for the receiver to calibrate to the signal. And if the first part of the byte is already different, that should be sufficient for the reader to do that.

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Exactly. Hope you don't mind if I close this issue now.

from rf24.

There's a little more to it. Arrays in C++, like an array of characters (aka string), are stored in memory using little endian. Fortunately, the nRF24L01 expects the address (& payloads) to be transferred over SPI in little endian... Essentially, "1Node" is stored is as 0x65646F4E31. This is why printDetails() (and printPrettyDetails()) outputs the addresses bytes backwards:

>>> from pyrf24 import RF24
>>> radio = RF24(22, 0)
>>> radio.begin()
True
>>> radio.openReadingPipe(1, b"1Node")
>>> radio.printPrettyDetails()
# [... omitted data for brevity ...]
TX address              = 0x65646f4e31
pipe 0 ( open ) bound   = 0x65646f5555
pipe 1 ( open ) bound   = 0x65646f4e31
pipe 2 (closed) bound   = 0x0a
pipe 3 (closed) bound   = 0xa0
pipe 4 (closed) bound   = 0x00
pipe 5 (closed) bound   = 0xab

to see it binary (again using python for brevity)

>>> address = b'edoN1'
>>> [bin(x) for x in address]
['0b1100101', '0b1100100', '0b1101111', '0b1001110', '0b110001']

so

Given that 1 in binary starts with a 0011, it is not as problematic as anything that starts with a 1010 or 0101.

I would be more concerned with addresses that start with T

>>> bin(b'T'[0])
'0b1010100'

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Also, note the scanner examples use the worst possible addresses (with an unofficially supported length of 2 bytes) on purpose:

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wow, fast response :-) thx.

Is the letter 'e' not as problematic because only the last nibble is 0101 ? The article only mentioned to not use these four nibbles.

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Is the letter 'e' not as problematic because only the last nibble is 0101 ?

No, because it starts with a 0110. In general, anything that starts with a repeating and alternating pattern of 1 and 0. should be avoided. Recall what the datasheet says:

7.3.1 Preamble
The preamble is a bit sequence used to synchronize the receivers demodulator to the incoming bit stream. The preamble is one byte long and is either 01010101 or 10101010. If the first bit in the address is 1 the preamble is automatically set to 10101010 and if the first bit is 0 the preamble is automatically set to 01010101. This is done to ensure there are enough transitions in the preamble to stabilize the receiver.

The article that the docs link to is a bit more empirical as it is written from observations/experiments.

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Other radio's may actually use a 2-byte (or more) preamble. IIRC, the RFM69 uses 2-4 byte preambles, but they are sub-GHz transceivers (so they might require longer time to demodulate signals seen from the antenna).

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Sure, thanks for the fast detailed explanation!

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