Alt-BEAM Archive
Message #01536
To: beam@corp.sgi.com
From: Steven Bolt sbolt@xs4all.nl
Date: Tue, 16 Mar 1999 11:37:36 +0100 (CET)
Subject: [alt-beam] `Green Thumb'
Most potted plants get either too much or too little water. Their
performance is greatly improved if you give them just enough.
The `Green Thumb' is a solar powered sensor which makes that very
easy.
Linkname: Green Thumb
URL: http://www.xs4all.nl/~sbolt/e-groeneVinger.html
Soil resistance is measured using a tiny alternating current (less
than a microwatt) which avoids galvanic trouble at the sensor poles
and isn't noticed by the plant. The circuit compares pulse delays
which depend on the soil and on an adjustable resistor. The ratio
between these delays does not depend on the supply voltage. So
despite the wide fluctuations of a solar power supply, the sensor
output is accurate and reliable.
Prototypes of the Green Thumb have been doing a good job for
various plants since last spring. Two months ago, I started one on
a few lemon geranium (Artemisia abrotanum) cuttings. That plant is
now more than 60cm high, and its thirst as indicated by the Thumb
is ten times greater than it used to be. When the summer sun hits
my window, its water needs are expected to triple.
That kind of variation is difficult to keep up with, unless you
have green thumbs - or a Green Thumb :)
Enjoy,
Steve
----------------------------------------------------------------------
# sbolt@xs4all.nl # Steven Bolt # popular science monthly KIJK #
----------------------------------------------------------------------
------------------------------------------------------------------------
eGroup home: http://www.eGroups.com/list/alt-beam
Free Web-based e-mail groups by eGroups.com
Home