anelok: revisiting Bluetooth, Don't want no ...
werner at almesberger.net
Fri Nov 22 19:42:23 EST 2013
... short FIFO, man ! (With apologies to "20 Fingers")
There are more chips to look at than just TI's. Here is a very nice
treatise on doing BTLE with hardware that can't do BTLE:
(Thanks to Peter "whitequark" Zotov for finding this !)
He uses a Nordic nRF24L01+  which looks like a nice enough chip
at first sight, putting the "micro" back in "microelectronics" with
a 20-QFN 4x4 mm package, can do 1 Mbps, has GFSK, uses a frequency
deviation of +/- 160 kHz which is probably close enough, but ...
... limits packets to 32 bytes while BTLE needs 39 bytes. Darn.
There seems to be a whole class of similar chips: the Beken BK2423
 seems to be a direct clone and the RFM TRC104  has somewhat
similar characteristics but also supports a "continuous mode" in
which the raw unmodulated bit stream is exchanged with the host.
That's a bit more low-level than what we're looking for but may be
a possibility. At USD 1.80 @ 1000 it's also a bit pricy for what it
does. The TRC104 was also mentioned as a possible choice on
(Credits: the people there, especially Mike Ryan and "mossmann",
have been extremely helpful.)
Last but not least, I found the Cypress CYRF8935 , another small
chip (24-QFN 4x4 mm) that may have suitable characteristcs,
including a decently sized FIFO. One interesting detail is that one
can connect an unbalanced antenna with only a very small matching
circuit, avoiding the bulky and costly balun.
It seems to be a brand-new chip, so there's a small risk of there
being issues with that. One known issue is that Digi-Key don't
sell it in small quantities (yet) - but others do.
Conclusion: RFM TRC104 and Cypress CYRF8935 go to the list of
potentials as well, pending further examination.
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