Brian:

I'm an electrical "newbie", but your post gave me some good ideas. I have a digital peristaltic pump which will turn on when the resistance on an input jack RISES to a certain point. Naturally a dead short will turn it off, but the "turn on" point can be adjusted. I'd LOVE, LOVE to use this pump to water plants when they need watering, and can envision a high-hanging pot with two stainless probes on opposite sides of the pot determining the need to water ( or not). The two probes would output a resistance that, when low enough, would cause the pump to turn off and stop watering. Then, when the plant dries to the point when it needs water, the pump would turn on.

How can I create a circuit using a 555 chip that will do this??

Hopefully, thanks in advance

Stan F.