ADXL345: Convert 16-bit Twos Complement to 10-bit Signed Int

[jcalusdi]

Hi All:

I was hoping I could find some sample code on how to convert data from an ADXL345 accelerometer.  I am reading acceleration data from an accelerometer through a PIC MCU into a LabView program on my laptop.  The data from the sensor is formatted in two bytes, say axDataLO and axDataHI, forming a 16-bit twos-complement value.  This value represents the result of a 10-bit ADC that is right justified with sign extension.  If I am clear, the sign exension means that the last 6 bits are padded with either a 1 or 0 depending on the sign of the data.  How do I convert this data into a signed integer?  Any help is greatly appreciated!  Thanks.

[GerdW]

Hi,

this probably has been asked before, but anyway:

[jcalusdi · Accepted solution]

Hi GerdW,

Thanks for your reply.  Yes, that was what I needed, as well as, fixing a bug in the code of my PIC microcontroller.  I have included a code snippet here in case someone out there is working with the ADXL345. Thanks again for your help.  V/R James C.

[GerdW]

Hi jcalusdi,

another try:

The array(U8) should contain your 6 bytes delivered by the ADC...

[jcalusdi]

Thank you, again.  James C

[EdgarCabrera]

Awesome code! Just what I was looking for. Thanks!

[Corci]

Hi all. Could I know why the input of "Join Numbers" are crossed? Thanks for the answer.

Regards.

[GerdW]

Hi Corci,

read on Wikipedia about big or little endian(ness)...

[Corci]

Thank You for the rapid answer. I've read online documentation about Little and Big Endian. How do I relate the information on the datasheets of the ADXL345 with this concept? Does "Left-Justified" means Big Endian?

Thanks again. Regards.

[GerdW]

Hi Corci,

the endianness dictats which of those two bytes contains the MSB and the LSB. You have to connect the correct byte to the high and low input of JoinNumbers...