Wiimote Project » Wiimote Projects » Wiimote accelerometer & motions detecting projects » Wiimote ADXL330 accelerometer bandwidth question
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: Wiimote ADXL330 accelerometer bandwidth question  ( 10624 )
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« : January 21, 2008, 09:30:47 PM »

Hello,

I am trying to find out the bandwidth of the ADXL330 accelerometers used in the Wiimote.  I took one apart and removed one of the capacitors connected to the ADXL330 (Cx in fig. 1 of the ADXL330 datasheet).  The datasheet can be found at (link works as of 01/21/08):

http://www.analog.com/UploadedFiles/Data_Sheets/ADXL330.pdf

Measured the capacitance with an LCR meter, it was 0.2 uF.  Therefore, with a nominal R_{FILT} of 32k (p. 3 of ADXL330 datasheet), we get a bandwidth of (p. 12 of ADXL330 datasheet) 25 Hz.

But on Johnny's projects page (http://www.cs.cmu.edu/~johnny/projects/wii/), it says: "It also contains a +/-3g 8-bit 3-axis accelerometer also operating at 100Hz".

I don't understand what "operating at 100 Hz" means.  Does it mean the BANDWIDTH of the accelerometer is 100 Hz?  If so, could anyone please enlighten me on how to obtain the accelerometer bandwidth?  Or does it mean the Wiimote is sending accelerometer data out via bluetooth at 100 Hz?

Again, any help is appreciated.

Thanks a bunch!!!!
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« #1 : February 13, 2008, 01:06:03 PM »

I took that to mean that it updates at a rate of 100hz, that is 100 times per second.
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« #2 : February 14, 2008, 03:51:52 PM »

Yeah, it's sampled at 100Hz.  Having a 25Hz lowpass on the signal makes sense, since you'll start to get aliasing if you go much above that.
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« #3 : September 14, 2008, 08:53:28 PM »

Hello,

Thanks for the measured value of capacitor.
I was curious to check if this value could be observed through signal
processing. And I made some records with some signal pulses and a
subwoofer.


(AZ(f) Spectrogram of recorded measurement after processing)

The wiimote-accelerometer bandwidth is around 0 - 33/34Hz.
Finally, considering 33Hz as frequency cut-off, I found Cz=0.15µF which
is near of your measured value : 0.2µF.

- Wiilliam

(related post for more information
http://fwiineur.blogspot.com/2008/09/wii-remote-accelerometer-bandwidth-and.html)
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