When I was in college we did a project using something similar, they were capacitors encapsulated in a porous material (clay-like) and two wires came out of this little block. We just connected this as part of an oscilator circuit and measured changes in oscillation frequency. I am not 100% sure but I believe these were called "Bouyucos" or something like that. They were cheap and small enough to fit inside a medium-sized flower pot. Gabriel -----Original Message----- From: Steven Davidson To: PICLIST@MITVMA.MIT.EDU Date: Tuesday, May 11, 1999 9:33 AM Subject: Re "Plant out of water project" new views In California the growers use a thing called a ătensionometer(sp)ä which was a tub filled with water, a ceramic tip on one end and a pressure gage on the other. It was buried in the ground (sealed), so the capillary action of the tip acted just like a root. When it got dry, the water was sucked out creating a vacuum (a very high vacuum). The gage would hit a micro-switch and signal for water. When you watered, the vacuum sucked water back into the tube and dropped the vacuum. These devices are available at most professional irrigation outlets. Too big for houseplants ö about 3 feet long. I tried to make a houseplant version, small tub with water sealed on one end and a clay tip on the other. The idea was to watch the height of the water level in the tube. Canât remember why it didnât work, but some one else might try it. My wife got tired of me screwing up the oven making clay tips. I found another product and wrote an e-mail to the PIC list on it a few years back. This was a capacitor inside a ceramic or clay capsule. You used AC to test the capacitance. This worked well and I installed a few in our housing development. It would just skip the programmed water cycle if it sensed enough moister. It saved over $4,000 the first year. This was about 3 inches long, still too big for most houseplants, but the concept of testing inside a capillary capsule is still more accurate than measuring resistance. Just fertilizing will throw the resistance one off. If anyone is interested let me know and I will see if I can find the address of the company. ---------------------------------------------------------- Steven M. Davidson Department of Commerce NTIA/ITS 325 Broadway Boulder, CO 80303 W 303-497-3411 Fax 303-497-6982 sdavidson@its.bldrdoc.gov --------------------------------------------------------