Hi Erwan, Mma_Accel.setSensitivity(RANGE) has nothing to do with calibration, and, as you say, only sets the sensitivity. You still need to calculate the offset and scaling factor for each accel channel and apply these to the data, either on the shimmer or post process the data offline.
The simpleAccel.py script simply prints out the accel data to screen. Each column represents the X, Y and Z axes, and each row is a different sampling period. Example output is as follows: tiny2@ShimmerLive:~/tinyos-2.x-contrib/shimmer/apps/SimpleAccel$ ./simpleAccel.py /dev/rfcomm0 1983 1801 2016 1985 1807 2011 1987 1809 2014 1983 1799 2015 1989 1808 2015 . . . The fact that you are getting 10k-15k peaks seem to indicate that something is out of sync. The ADC on the shimmer is 12-bit, so the range of values you should be seeing per axis is 0-4095. Any values outside that range are not possible. The DMA transfer returns the raw ADC values as read by the MSP430 from the MMA7361. To convert these values to m/s2 you need to scale them appropriately. The calibration procedure described on the shimmer-research website describes how to do this by using gravity as a known reference. Mike On Wed, Mar 30, 2011 at 4:02 PM, Erwan RENAUDO <[email protected]>wrote: > Hi Mike, > > Thanks for your answer. > Does it means that calibration of accelerometer is done when we "call > Mma_Accel.setSensitivity(RANGE)" ? Or only sensitivity is setted and I still > have to add my data an offset to reach the "physical values" ? > > In the same idea, what exactly is displayed by the python script > SimpleAccel.py ? Coz I plotted it and it look quite awful even while I'm not > touching the accelerometer (I get kind of periodical +/- 10k to 35k peak). I > get better (it seems) results plotting Listen output and plotting separately > payload byte by two. > Does anybody know what DMA transfer exactly return (in terms of data) or > where I can find these informations (Didn't get it reading MMA7361 > datasheet) ? > > Once again, many thanks for help, > I can join plotting results I necessary. > > Erwan. > > > 2011/3/28 mike healy <[email protected]> > >> Hi Erwan, >> >> The shimmer and shimmer2 used the MMA7260 accel chip, but the shimmer2r >> uses the newer MMA7361. See the following page for info on the different >> shimmer revisions: >> http://www.shimmer-research.com/products-2/shimmer-revisions >> >> One difference between the chips is that the MMA7260 had 4 different >> selectable sensitivity ranges (±1.5g, ±2g, ±4g and ±6g) whereas the MMA7361 >> only has 2 (±1.5g and ±6g). >> >> The warning you are seeing about the decimal constant being too large has >> nothing to do with the sensitivity range, and can be safely ignored, as the >> intention is for the constant to be unsigned anyway. >> >> Mike >> >> >> >> On Mon, Mar 28, 2011 at 8:57 AM, Erwan RENAUDO >> <[email protected]>wrote: >> >>> Hi Mike, >>> >>> Thanks for your help. >>> I take a look at your program, and after several days have a "seems to >>> work" program. I take it example to make my serial sensor program working. I >>> get trunks of bytes that seems to change depending on my gestures. Now I'm >>> trying to analyse data and I would know about the accelerometer : in Shimmer >>> manual, they speak about MMA7260Q but when I check virtual component on >>> sources provided, accelerometer referenced is MMA7361. So which one is >>> physically present on the shimmer board, and could a bad platform argument >>> on compilation / wrong material virtualization generate warnings as "decimal >>> constant is so large that it is unsigned" (if wrong RANGE_X_0G is given) ? >>> >>> Another question is : Is there a Linux XubunTOS calibration program as >>> it exists for Windows ? >>> >>> Thanks for your answers and support, >>> Best regards, >>> Erwan >>> >>> > -- > Élève Ingénieur Promo 2011 - Section *Informatique et Systèmes*. > École Nationale Supérieure de l'Électronique et de ses Applications (* > E.N.S.E.A.* - Cergy) > >
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