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11:59 am
March 23, 2015
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When I read the data registers in the ADXL345 3-axis accelerometer they come across as a U16 integer, but they are stored 2's Complement format. There are a couple of ways of converting the 16-bit code into 2's complement (see example below) in standard LabVIEW, but some of the VI's are not available in the PWS Library.
eg. I read a 16-bit code of 0xFFF2 (65,522 dec) from the register, but it should be converted to the 2's complement of -14(dec) - is it possible to do this within the PWS Library?
Standard LabVIEW code
Chris
2:42 pm
March 23, 2015
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I did manage to get the following code to work in standard LabVIEW and all the necessary VI's were also available in the PWS library, but the decimal output is always "0" when I try to run it on the PWS Stamp - any ideas on why this doesn't work?
Chris
2:37 am
March 23, 2015
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OK I just realised that the 2's Complement Input in the above example was an I16, but in my PWS Code it is coming in as a U16.
Standard LabVIEW has the "To sign Word Integer" I16 Conversion VI which does the job, but of course the PWS Library doesn't.
It seems to me I only have two options:
1) Create a very large lookup table and index the correct I16 value out - yuk!
2) Write the U16 to I16 conversion in Arduino code and call that in LabVIEW - I think that is possible using the PWS Library?
Chris
7:25 am
March 23, 2015
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Well I did get it working with the large lookup Table (4096 elements), but that took up 3% of my program storage space!
So instead I managed to do the 2's complement conversion in code (see attached image).
This is still a lot of extra coding - I just wish we had the I16 conversion VI 🙁
Chris
7:06 pm
March 12, 2015
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There are several simple ways to do it including this one. The key is to use LabVIEW to coerce the datatype to a signed number. Notice here that the 65536 constant is an I32 which forced the output of the subtract to be an I32.
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