Subj : moisture sensor
To   : All
From : Jeff
Date : Wed Jan 19 2022 23:12:34

This week I built an indoor herb starter garden.

I found and 3D-printed some seed planters that consist of two halves that
snap together. When it's time to transplant, the two halves can be separated
to allow easy removal of the seedling, and then they can be put back together
in order to grow more seedlings. There is a third piece that fist to the
bottom of the pot to facilitate drainage. I designed and printed a bracket to
keep all of the pots stable with respect to each other (so no single pot can
tip over).

I also bought 5 capacitive soil moisture sensors and wired them, a 16x2
display, and an LED to an Arduino Nano, then programmed it to monitor the
soil moisture. The display cycles through the 5 sensors, displaying pot
number, plant name, low-moisture threshhold, and current moisture moisture
level. The plant name and low-moisture threshhold are hard-coded for each pot.
If the moisture level of any pot drops below that pot's low-moisture
threshhold, then the LED will light and a watering-alert indicator will show
on the display when that pot cycles around. The cables included with the
sensors were somewhat short, so I also built a support for the sensor
protoboard that attaches to the aforementioned bracket and keep the
electronics above the water level.

I will almost certainly need to adjust the threshholds over time, as they are
currently a best guess based on vague descriptions ("slightly moist," "when
the top is dry to the touch," etc.) I planted oregano, thyme, basil, and
rosemary (the latter in two pots). Upon reflection, I think I should have
planted the same plant in all 5 pots, but set the threshholds at different
values and see which plant did best. I might do that next time, or I might
build a second garden.

Jeff.

--- Mystic BBS v1.12 A46 2020/08/26 (Raspberry Pi/32)
 * Origin: Cold War Computing BBS (21:1/180)

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