digitemp

[nr]

As mentioned in one of my earlier posts, I wanted to get digitemp working on the plug:

http://www.ronketti.org.uk/tempplot.png

Pretty easy in the end. I used a DS2490 USB bridge to the DS18B20 sensor. A cron job reads it every five minutes, and logs to /var/log/somethingorother. A bit of perl and GD later, and the tabular data is converted to the graph you see above and uploaded. I'll do a proper job of making it look nice at some point, but for now, the concept is proven.

Incidentally, I read somewhere or other that it's not a good idea to write to an SD card too often. As this job is logging every five minutes, should I be writing to another file system? Or is /var mounted on the internal 512K memory? Sorry for the newbie questions - I'm sure I'll get the hang of this stuff one day.

Ta,

[DanielSjoholm]

All flash based storage has a limited amount of writes, http://en.wikipedia.org/wiki/Flash_memory#Memory_wear , so it's up to you.. you could write to a tmpfs mount instead and then only dump to nand/sd-card once every 24 or so hours if you want to reduce wear. However the jffs2/ubifs filesystem on the nand should do wear-leveling and thus increase the life of the flash, but i would probably prefer hosing an sd-card over the internal storage.