Sunday, April 28, 2013

Preliminary Library for the ADXL345 in Python

The new code seems to be working.  I've ordered some more parts from online so that I can actually build these sensors into some real world rigs.

The new code is here, on the Adafruit site.
I'm going to try to keep the top post updated with the new code so people don't have to search through the comments (there aren't too many of them.  This went pretty quickly).  I'm going to try to make the code a little more functional, and include some of the other configuration options offered by the ADXL345.

Right now, the only thing that is really tested and seems to work well is the readAccel() function.  Calling this function will spit out the three accelerometer values (a raw number, not corrected with a gravity coefficient).  With my rig I've been able to get over 100 values per second (I think...  I can't find my scratch pad).
It spits out all three of the values because of the way the ADXL is designed to release data.  If you don't pull all three values, and instead just pull one, the ADXL "over-writes" the other two values in the stack with new data.  I figured it would be easier to just let the coder handle a couple of data values that they don't need, rather than give them an option that might give funky results later if they didn't dive deep into the datasheet.

I need to write my program for handling and graphing the data obtained by the ADXL345 for my project.  I'm probably going to have a buffer (of a user determined size) of values from the ADXL.  When the system detects an event it saves the buffer and continues writing readings until A) a specified amount of time or B) some sort of quiescent period is detected or C) an external "stop" signal is received.  I then want to output the data on a series of graphs showing the acceleration and combined vectors over time.  Again, this will probably be written in Python.  The mature version will hopefully use some sort of real-time display while recording the data.

1 comment:

Nickname unavailable said...

Hello! Apologies for dropping an unrelated comment here, but I could not find an email address for you.

I'm writing a book for O'Reilly called "Raspberry Pi Hacks", and I'd like to include a copy of your Python program to calculate the lux values from the TSL2561.

Please send me an email to let me know if this is okay with you.

Thanks in advance,

Tom Callaway (spotrh@gmail.com)