[Tinyos-help] About MTS310 board's microphone and Accelerometer

[Michael Schippling]

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 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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