Subject:
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Re: NXT Robot Swarm at BrickFest -- featuring Bluetooth
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Newsgroups:
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lugnet.robotics.nxt
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Date:
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Tue, 15 Aug 2006 01:05:46 GMT
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Viewed:
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15316 times
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In article <J3y0B4.FM0@lugnet.com>, Brian Davis <brdavis@iusb.edu> wrote
> In lugnet.robotics.nxt, Dick Swan wrote:
>
> > Here's an idea of how to get more than 3 NXTs connected
> > via Bluetooth (BT). It involves using a PC as a "relay
> > point".
>
> My problems with this solution are two-fold. First, NXT-G currently can't
> send anything back to the PC, as it's not running anything to get the NXT-G
> message structure (yes, folks could write this... almost certainly will. But
> likely not me).
I shall have PC software to do this, and probably others will have
similar tools before I finish.
> And this may allow much more than 7 connections,
I believe 7 is the number of connections specified in the Bluetooth
standard, for each radio.
> because while
> NXT-G doesn't allow you to set up a BT connection under SW control, I'll bet a
> well-programmed computer certainly could.
I am not sure what your definition of "set up of a bt connection"
covers.
Pairing generally requires user input, for the password.
Connecting to a previously paired device under software control should
be possible. One wrinkle will be on the receiving device, and ensuring
the 'allow "NXT 1" to connect?' query will be handled.
Paired device should be identified by their MAC address, rather than by
their friendly name. I guess these are stored in a file.
> The second problem is I admit just a
> bias of mine - I want my control On The NXT, not off the brick. Autonomy is in
> some senses a pretty silly, artificial constraint anyway (hey, I program the
> NXT
> with a laptop, right?)... but so is working with LEGO and not sheet metal.
>
> What I do *not* know as yet is if the three connection limit, and the
> inability to set up BT connections under on-the-NXT SW control, is due to the
> SW
Making a connection should be possible, at least with a previously
paired device.
> (NXT-G doesn't have the ability), or the FW (the LEGO FW can't command those
> modes), or due to the BlueCore FW itself (i.e., we're stuck with it due to the
> chipset on the NXT). Anyone know?
If I am reading the datasheet correctly the Bluetooth chipset supports 7
concurrent connections, but only 3 if they are high speed connections.
Perhaps due to RAM space for buffers, more probably the CPU has to do
more work for each connection.
Reference the datasheet here:
http://www.csr.com/products/bc4ext_over.htm
Constraints I have noticed in the Lego NXT development kit
documentation:
1. The master NXT can only communicate with one of the slave units
during a given moment, meaning that if the master NXT is
communicating with NXT Slave 1 and NXT Slave 3 starts sending data to
the master NXT , the master NXT will not evaluate the received data
until it switches to NXT slave 3.
An NXT is not able to function as both a master and slave device at
the same time because this could cause lost data between NXT devices.
p12, Lego Mindstorms NXT Hardware Development Kit
2. p13 explains that the Bluecore chip VM runs a different profile for
Master and Slave modes.
3. Appendix 8-LEGO MINDSTORMS NXT ARM7 Bluetooth Interface
specification.pdf has some potentially helpful info too.
Regards,
Tony
--
"If you don't know, invent." - Robert Baden-Powell
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