This link,
http://pods.dasnr.okstate.edu/docushare/dsweb/Get/Document-1282/F-6708web.p
Suggests a more brute-force approach. A couple sensors are suggested,
but effectively putting a measuring device next to the plant and keeping
the sensor wet.

This link, http://www.greenhousemegastore.com/category/misting-fogging
Has such sensors commercially available (electronic leaf, $235 US) So
clearly such things are used.

-Denny









On Sat, May 4, 2013 at 5:40 AM, Allen Mulvey <allen@amulvey.com> wrote:

> My daughter and son in law operate a perennial nursery.
> Several years ago I built a misting system for one of their
> greenhouses. It works fine - all analog, no smarts. A
> misting duration of about two seconds every twenty minutes
> or so usually does the job.  If the weather changes someone
> needs to manually alter the interval. I would like to make
> another, microcontroller, version which monitors the
> temperature and relative humidity and makes appropriate
> changes. I know there are a lot of other factors involved
> but they have standardized on soil, pot size, etc. so most
> of those are relatively constant. It is gross changes in
> temperature and relative humidity that seem to be most
> important. There is no wind in the greenhouse.
>
> Are there any algorithms or charts available which would be
> helpful in computing the necessary changes?
>
> Allen
>
>
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