Yes, it's a custom program. The goal is to visualize the position of
the Shimmer module (or multiple modules) in a 3D scene, but for now I'm
just dumping the data read over bluetooth to the terminal.
Is there anything particular I should check about the program? At the
moment it just opens the rfcomm device, writes the command to start
streaming data (0x07), reads the response (0xFF) and starts reading the
data. Is there some example code for Linux that's known to work?
Mikko
On 24.07.2012 19:53, Phil Reaston wrote:
Hi Mikko:
What are you using to receive the data? I think you said earlier it was
your own program. If so, I'd check that.
Phil Reaston
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On Tue, Jul 24, 2012 at 9:46 AM, Mikko Rasa<[email protected]> wrote:
Okay, magnetometer is working now. Even the data transmission seems to be
more reliable, although there are still a few errors per second (with 50Hz
sampling). Should be usable provided that I manage to improve the
filtering to accept packets with real zero bytes, or alter the firmware to
provide better synchronization.
However, the inquiry command still fails to produce a valid response. A
varying amount of bytes from the middle of the packet are always lost,
sometimes starting right from the ack byte. The most common case is that I
receive the ack byte and the last five channels (out of nine). This is not
a huge problem in itself, since I can hardcode the channels, but it does
indicate that something is going wrong with sending data over BT.
To eliminate possible radio interference, I grabbed my laptop and a
Shimmer and went outside to a spot with no other radio sources (that I know
of) nearby. This had no effect on reliability.
Mikko
On 24.07.2012 18:43, Benjamin Kuris wrote:
Open your shimmer, reseat the 9DoF board. You should get magnetometer
data using stock FW and shimmer connect when following the quickstart
in the manual. If that fails, email [email protected] for
further assistance.
-Ben
On Tue, Jul 24, 2012 at 11:33 AM, Mikko Rasa<[email protected]> wrote:
I tried various sample rates between 5Hz and 50Hz. I'm using the
accelerometer and gyro, so six channels in total. If I enable the
magnetometer channels, I don't get any data; I guess the device is
unable to
read the sensors.
I have two Shimmer modules at my disposal, and am testing with one at a
time
for now. In the final application I hope to use two or three
simultaneously. I have a WLAN, a couple of wireless mice and a
BT-enabled
cellphone here as well, and of course my laptop which I'm receiving the
data
on. However, when I tested rfcomm between the cellphone (N900, running
Linux) and the laptop, I was able to transfer large amounts of data
without
any errors (several kilobytes; I'm lucky if I get 100 sequential
error-free
bytes from the Shimmer).
This is stock boilerplate firmware, aside from whatever hacks I've put in
while testing and might not have reverted fully. I also tried the
official
firmware from shimmer-research.com (in case my build environment somehow
introduced errors), but it has the same problems.
The problem seems to be very data-sensitive; If I turn the Shimmer to its
side so that the X axis accelerometer gets a low value, I receive almost
no
zero bytes at all, and when I do manage to receive a valid packet (i.e. a
zero byte followed by 14 non-zero bytes), the contents are badly mangled.
Mikko
On 24.07.2012 18:11, Benjamin Kuris wrote:
What sample rate and how many channels?
How many devices in your piconet?
Any other RF in 2.4GHz band?
Are you using stock boilerplate data packets or are you sending full
ACL packets (~128bytes data) to minimize BT overhead?
Typically you don't need to mess with the baudrate but minimizing BT
overhead will improve results if you can accept a little bit of
latency.
I'm sure others will chime in.
-Ben
On Tue, Jul 24, 2012 at 10:57 AM, Mikko Rasa<[email protected]> wrote:
I'm trying to use a Shimmer 9DoF sensor with the boilerplate firmware,
but
bluetooth transmission is giving me a hard time. It's dropping a lot
of
bytes, making data streaming unreliable and certain commands unusable.
In
particular, I can't get an intact reply from the inquiry command to
discover
the order of channels being sent, so I have to hardcode this into my
program
based on the boilerplate sources. With the data packets I could use
the
packet identifier to synchronize the stream and throw out any truncated
packets; this might spuriously reject good packets if they contain
embedded
zero bytes, but I estimate I could recover around 80% of the packets
this
way.
Is there anything I could do to improve the reliability? I've already
tried
different sampling rates, as well as messing with the baud rate used
between
the MSP430 and the BT module. Neither of these seems to have any
effect
on
the reliability, unless I change the baud rate so far out of spec that
all
transmissions stops.
--
Mikko
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