nseidle/OpenLog — Issue #83: Fast Data Logging
Author: w102acd
Created: 2011-11-04 12:44:32+00:00
State: open

All,

I have some experience with this. Previously, I was able to get an arduino nano and the microsd shield to data log. However, this was very clunky (both in coding and in physical package).

I just received the open log and another arduino nano.

I am trying to dump data to it as fast as possible with a good degree of reliability. I want to sample all 8 analog input channels and dump these on the card along with time (milliseconds or microseconds) and maybe some other simple stuff. Each line (sample) will be in the 51 byte range.

I can dump for a short time ( a few minutes) using 115200 bps and then I start losing characters. However, even at 115200 baud, I can get around 200 (samples) per second. I would like to up the reliability and increase the frequency.

Data compression:
Obviously, I am limited by the amount of data that I can put to the card in any given time. However, what about compressing the data? Is it possible to dump binary data to the openlog? An alternative would be "convert" the numbers into a compressed string of ascii characters. These characters would need converted back. I guess it would be kind of like encrypting the data. I think I could cut the size in half using this strategy; thus, either allowing me to sample faster or making it more reliable.

Cards:
Currently, I am using a Sandisk 2GB card. Having done this before (without openlog), I have been through the "different cards give different results" stuff. Does anyone have any recommendations as far as what card to get? Would a bigger card be more stable? I just don't want to go buy a "bigger and better" card only to return to this one.

Faster writing:
I came across a post that mentioned something about a different version made for fast data logging. Where is this at? Also, I remember something about someone added more RAM to the openlog for such a case. Any instructions?

Sorry for the length of this post, but this little thing is really a fantastic product. I do realize that I am asking way more out of it than it was likely designed for.

Thanks,
Andy