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Data logging output of ADXL345 eval board

Question asked by WRJones on Jun 20, 2015
Latest reply on Jun 21, 2015 by WRJones

I loaded the AD supplied  2G 100Hz hi res hex file and ran program with device flat on desk.  This gave Z readings around 220.

 

Then I loaded the AD supplied 4G 100Hz 10 bit hex file and ran program with device flat on desk.  I ran in one position then turned eval board over and ran more.  I got readings in the +- 270 range.   

 

If the 2G file was really using 10 bits then the 220 readings seem reasonable at 3.9mg/LSB but not real accurate (I guess - I don't really know what a few tenths off a full G feels like even with bare feet).

 

But the 270 seems very odd for the 4G 100H 10 bit.   Seems like the count should be half of 2G range.   So clearly I don't understand the meaning of the numbers coming out of the data logger.   -4G to 4G = 8/1024 = 7.8mg/LSB    Don't you just multiply this number by the data log output to get the measured G?

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