Paul, see below for details but it looks like owfs needs some correction tables to produce a usable moisture reading.
On Sun, May 02, 2010 at 09:57:50PM -0700, Marc MERLIN wrote: > Putting this aside for now, as soon as I burried the sensor, it stopped > working (it just jumps back and forth between values): > > This is disappointing, it was reported to Eric over a year ago, and the > problem is still there in new boards being sold today. I talked to Eric, he acknowledged the problem is still in the current moisture boards being sold and recommended a ground isolation transformer from radio shack: http://www.radioshack.com/product/index.jsp?productId=2103994 I wired it in and it fixed the ground problem. Now, there is still the problem that the reading depends on moisture and temperature and which isolation transformer you use. In other words, owfs would need some kind of 2D or even 3D correction map: - current correction for temperature (maybe not linear?) - current correction per isolution transformer (hopefully linear) - corrected current to moisture % This would by the way require burrying the board in the ground to measure a temperature close to what the sensor is seeing so that its conductivity can more accurately transformed into some moisture value. For reference and if that helps others, with the radio shack isolation transformer, the values I get are: isolation no transformer transformer Water: -1.335 -1.38 Ice Water: -1.14 -1.13 Hot Water: -1.56 -1.72 100% dry: -0.428 -0.135 > I'll ask Eric to see why if it's a known problem it's still not fixed in the > current > shipping versions and why there seems to be no notice of this problem on > http://www.hobby-boards.com/catalog/howto_moisture_meter.php?referer=howto_humidity_temp_solar.php Eric said he would update the page to warn people that burrying the moisture sensor without using an isolation transformer is unlikely to work. Marc -- "A mouse is a device used to point at the xterm you want to type in" - A.S.R. Microsoft is to operating systems & security .... .... what McDonalds is to gourmet cooking Home page: http://marc.merlins.org/ ------------------------------------------------------------------------------ _______________________________________________ Owfs-developers mailing list Owfs-developers@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/owfs-developers
