91色情片

Herbert Booth of Glasgow wants pot plants to tell us when they need more
water, and when they have had too much (GB 2352817). A rod with two electrodes
pokes down into the soil, measuring its electrical resistance. This shows
whether the soil is dry, wet or waterlogged. The result is then used to control
an image on an LCD screen at the top of the rod. When the soil is just right,
the LCD shows a happy face. If it is too wet or too dry, the face turns sad.