Hi MS,
Thanks for you reply. The accelerometer problem was solved by using the new
MTS310 board. But I have a problem regarding the microphone reading. My
application samples the mic sensor at the user specified interval and collects
user specified number of samples. Then it reports the mean, peak and RMS values
of the collected samples back to the PC. I find that the mean, peak and RMS
are different for different values of the sampling interval. For example when
the sampling interval is 500 us, the peak value is about 150 (raw values ffrom
the adc) while it is abot 990 for the samling interval of 300 us. Also, the
mean and RMS values are very much different for different values of sampling
interval. Another thing that I noticed is even if I shout loudly close to the
mic sensor, I dont see any difference in the reading. Can someone please guide
me?
Thanks,
Monica
If you're actually reading the mic directly you are getting the
actual sound pressure level over the ADC sample period...
i.e., audio signal. I don't think there is any onboard averaging
hardware, so if what you want is the sound-pressure (how loud
things are) at various times, you'll need to sample pretty
fast and do your own full-wave rectifier and average.
As for the negative Accel readings, are you sure you're
not in free fall? (sorry, couldn't resist...). Have a
look at the absolute readings and see if they make any
sense vis the sensor spec sheets. Also search this list
for advice on Accel calibration.
MS
Monica Bell <[EMAIL PROTECTED]> wrote: Dear all,
I am using MTS310 board to collect data from all the sensors on the board. I am
suing tinyos-1.1.11. I have following problems with the microphone and accel
readings.
1) When I sample the microphone once every second, the output that I get is
different from that when the microphone is sampled 10 times in a second. The
difference is quite large. It is about 190 when I am sampling at once a second
and about 485 when sampling at 10 times per second. To calibrate the readings
from the sensors, I am using xlisten's formulae. Can someone guide me what is
the problem and at what rate should we sample? I dont need to reprodce the
sound- so I guess I dont need to sample at Nyquist rate.
2) Both the accelX and accelY readings are negative. Again, I am using the
formula in xlisten application. Please let me know how fast should I sample
the accelorometer and how should I interpret the values? I read in ADXL202E's
datasheet that the unit is g and it should be 0 g when there is not
acceleration. Also, even if if move the MTS310 board, both accelX and accelY
remain unchanged (same negative values).
Thank you,
Monica
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