Hi all,
Currently I am trying to implement a simple code using nesC language and
TinyOS-2.x so that a sensor node will be able to capture an acoustic signal
generated by a PC speaker, for instance a sine wave or a gunshot signal, in
order to know what is the maximum sampling frequency that MICAz mote can
achieve. This code is installed on a sensor node which sends the signal
captured to the base station. However, I only can achieve maximum sampling
frequencies in the range of 200Hz and 750Hz using Read interface and ReadStream
interface respectively. But...
In the literature, it was reported that, in tinyos-1.x, the MICA components can
normally sample at a frequency up to 200 Hz (in real time transfer mode i.e.
sampling and sending), while in the ADC's free running mode (i.e. turning off
the wireless radio of the MICA components while sampling) the highest sampling
rate using these components can reach 17.723 KHz.
After I read the TinyOS Programming book, I decided to use TinyOS-2.x instead
of TinyOS-1.x in my project because of two reasons:
1- it is expected that the sampling frequency can be easily increased
since TinyOS-2.x supports in addition to a millisecond timer a microsecond
timer which could be used to improve the sampling rate.
2- It supports the ReadStream Interface which is equivalent to the
ADC's free running mode.
But, as I tried to use the microsecond timer in my code, I surprised that this
type of timer is actually unknown for the compiler. Also, in ReadStream mode I
only can reach 750 Hz as a maximum sampling rate by setting
timer.startperiodic(1300) (below this value the senor node does not send any
data). So, my questions are:
1- Is it right that the microsecond timer still not fully supported by
the MICA components?
2- Which commands that can be used to set the sampling rate in the
ReadStream interface? Or is there an technique that can be used to
achieve high sampling rates?
I am looking forward to hear from you and I appreciate in advance any help.
Best regards,
Omar
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