SPL is measured as an average of the instantaneous values you get from, for instance, a microphone. What you need to do is sample the mic at some reasonable rate (making some assumptions about the frequency range you are interested in). In T1 there is a HighFrequencySampling demo app that sorta does this.
Then the (sl)easiest thing to do would be to look for max values over a moving window of some large number of samples. The real way to do it would be to estimate a zero crossing point -- probably at about 1/2 the ADC range (what you get from a mote ADC is fundamentally an AC signal with a fixed DC offset), do a full-wave bridge around that zero crossing, and then an RMS average of the result (again with a moving window of some size which will capture the lowest frequency of interest). In either case you should probably do the SPL conversion on the mote and only send the results because it markedly reduces the bandwidth of the data you need to send. In order to get an engineering measurement in dBm you need to calibrate your averaged data against a known source and perhaps make some adjustments for the non-flat frequency response of the microphone, then convert the measurements to a log scale. Note that you will have some noise floor that makes the lower couple of bits insignificant, and that the max you can get is 10 to 12 bits (for Atmega and MPS converters). This means 8-10 significant bits where each bit is 6dB (a doubling of sound pressure), so your measurement range is at best somewhere between 48 and 60 dBm. Hopefully that is sufficient for your system... MS Rogério De Pieri wrote: > Hi dear all > > I am working on an acoustic project within tinyos-2.x environment. > The goal of the project is to take a view of the distribution of SPL (Sound > Pressure Level) in an ambience. > > > I took just a few of steps on that, and a this time I'm looking for > documentation about how to take datas from acoustic/sound sensor from > sensorboards. > > Another problema I know I will have is to turn de sound or acoustic data in > SPL or dB. > > > Does anybody caan help me? > > Thanks for all > > > -- > Rogério De Pieri (Lelo) > Buscando melhorar a cada dia > Áudio, Hardware & Software > Fone: (48) 8409-0575 > > > ------------------------------------------------------------------------ > > _______________________________________________ > Tinyos-help mailing list > [email protected] > https://www.millennium.berkeley.edu/cgi-bin/mailman/listinfo/tinyos-help -- Platform: WinXP/Cygwin TinyOS version: 1.x, Boomerang Programmer: MIB510 Device(s): Mica2, MicaZ, Tmote Sensor board: homebrew _______________________________________________ Tinyos-help mailing list [email protected] https://www.millennium.berkeley.edu/cgi-bin/mailman/listinfo/tinyos-help
