nRF24L01 pipe question I am looking through the example code found here. I know there are 6 pipes that the nRF24L01 module can use but I've been searching the internet for the address designations and have been able to find nothing. More specifically on line 37, is there a reference for where the author is getting 0xF0F0F0F0E1LL, 0xF0F0F0F0D2LL?

Thanks.
As most of the people have posted, the values for the pipe are arbitrary, but must follow the rules per the API:


  Pipes 1-5 should share the first 32 bits. Only the least significant
  byte should be unique, e.g.


Before I answer your question, I think an explanation on Hex and Decimal values are needed.

The 40 bit hexadecimal is a number representation of base 16. A decimal is of base 10. So you can convert a Hex Value to Decimal. As this is out of scope for the question, you can google on how to convert from one to another. There are some online converters:

Hex to Decimal Converter

You will see when you convert the Hex value to decimal, that its just a number representation. When you convert, you drop the 0x and LL. As stated the 0x indicates the value is a hex value and LL means type Long Long.

So to answer your question, use the a converter to find a hex number like:

F0F0F0F0A1
F0F0F0F0A2
F0F0F0F0B4
F0F0F0F0E9


Just change the last 2 digits (least significant bit):

Pipes 1-5 should share the first 32 bits. Only the least significant byte should be unique, e.g.
   openReadingPipe(1,0xF0F0F0F0AA);
   openReadingPipe(2,0xF0F0F0F066);


Add the 0x and LL

0xF0F0F0F0A1LL
0xF0F0F0F0A2LL
0xF0F0F0F0B4LL
0xF0F0F0F0E9LL


All should work.

I am no expert on hex, as I am learning, so if I am incorrect, then please someone correct me. 

Finally, the nRF24L01 datasheet makes the following point that the choice of address is not completely arbitrary:


  Note: Addresses where the level shifts only one time (that is, 000FFFFFFF) can often be detected in noise and can give a false detection, which may give a raised Packet Error Rate. Addresses as a continuation of the preamble (hi-low toggling) also raises the Packet Error Rate.