Ya: backlit keyboard - Rii Mini case study

Werner Almesberger werner at openmoko.org
Tue Jul 13 12:39:16 EDT 2010


Wolfgang Spraul wrote:
> good to see how others solved the backlight problem.

I was afraid that there would be just a few LEDs but a lot of
"fancy plastic" to distribute the light. It's nice that what
seems to be a much more pedestrian approach works so well.

> Does this have anything to do with 'USB'? First time I hear about WirelessUSB.
> Wikipedia says WirelessUSB operates at 3.1 to 10.6 GHz, but the Cypress chip
> talks about 2.4 GHz?
> http://en.wikipedia.org/wiki/Wirelessusb

The difference may be in the space between "Wireless" and "USB".
Without it, it's Cypress' 2.4 GHz stuff, about which they proudly
proclaim:

| WirelessUSB and enCoRe are trademarks of Cypress Semiconductor.

The Wiki page says that USB-IF prefers people to call theirs
somewhat pompously "Certified Wireless USB". I guess now we know
why :-)

A good comparison:
http://www.ac.tut.fi/aci/courses/ACI-31070/pdf/UWB WUSB WirelessUSB.pdf

> Maybe to look at RF in Ya, we should first identify some interesting, free
> software / GPL licensed stacks? Then find a matching module/RF IC for it?

I'm still not sure what would be the best strategy. I've tried a
search for standards (see below) but I'm not entirely happy with
the results. I've now started to look at what the major chip
makers have to offer.

> Are you aware of any good and stable RF protocol stacks implemented in
> free software?

Nothing interesting beyond things that have already been mentioned.
I would in fact go one step back and look for Open standards, not
necessarily implementations.

Here's a very rough compilation of things I found so far for the
ISM bands that aren't flat out "vendor standards":

                Band    Rb      Range Modulation Openness/Patents       Ref.
                434 915 kbps    m                Standard       Use
                | 868 2.4       (nom)
                | | | |
Bluetooth
  Wibree        - - - x    1000  10   ?          "open"         ?       [8]
IEEE 802.15.4   - x x x  20-250   ?   many       open [11]      ?       [11]
  6LoWPAN       n/a      n/a    n/a   n/a        open [10]      open?   [9]
  MiWi          - - - x    -250   ?   ?          unpublished    ?       [13]
  WirelessHART  - - - x    ?      ?   QPSK       for-pay        roylty-free [14]
  ZigBee        - - - x 250-500  75   QPSK                              [1]
INSTEON         - - x -    ?     50   FSK        for-pay?       ?       [12]
ISO/IEC 18000-7                                  for-pay?       RAND    [2]
  DASH7         x - - -  28-100 250   FSK,GFSK   =              =       [1]
ONE-NET         ? x x ?    ?     ?    FSK        ?              roylty-free [7]
Wavenis         x x x -   5-100 100+  ?          ?              ?       [4]
UWB
  Wireless USB  > 3 GHz  53-480  10   MD-OFDM    open [6]       ?       [5]
Z-Wave          - x x -  10- 40  30   GFSK       NDA            ?       [3]

[1] http://www.dash7.org/DASH7%20WP%20ed1.pdf
[2] http://www.dash7.org/index.php?option=com_content&view=article&id=13&Itemid=15
    http://www.savi.com/partners/licensees/index.php
    http://www.savi.com/partners/licensees/iso-18000-7.php
[3] http://en.wikipedia.org/wiki/Z-wave
[4] http://en.wikipedia.org/wiki/Wavenis
[5] http://en.wikipedia.org/wiki/Wireless_USB
[6] http://www.usb.org/developers/wusb/wusb_2007_0214.zip
[7] http://en.wikipedia.org/wiki/ONE-NET
    http://one-net.info/
    (Site requires registration and moderator approval to even read any
    technical information.)
    http://www.one-net.info/index.php?option=com_content&view=category&layout=blog&id=2&Itemid=3
[8] http://en.wikipedia.org/wiki/Wibree
[9] http://en.wikipedia.org/wiki/6LoWPAN
[10] http://tools.ietf.org/html/rfc4944
[11] http://en.wikipedia.org/wiki/IEEE_802.15.4
     (links to IEEE standard documents, with click-through license)
     note: 802.15.4-2006 specifies ASK for 868/915 but requires devices to also
     implement QPSK.
[12] http://en.wikipedia.org/wiki/INSTEON
[13] http://en.wikipedia.org/wiki/MiWi
     http://ww1.microchip.com/downloads/en/AppNotes/MiWi Application Note_AN1066.pdf
     Implementation tied to use of Microchip products. No indication about IP
     in protocol.
[14] http://en.wikipedia.org/wiki/WirelessHART
     http://www.hartcomm.org/hcf/documents/documents_specifications.html

- Werner




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