by Forrest M. Mims III


The Mystery Component is the two input leads and nothing else. The leads serve as water detection probes.


How It Works

Figure 2 shows the circuit with the two input leads serving as probes. The LTC1050 op amp is connected as a comparator. R3 is adjusted until the LED is off. When both probes are immersed in water, the comparator switches on the LED.



Figure 2. The mystery component in Figure 1 is a pair of bare wire leads.


Background

Many different methods can be used to detect liquid water. The simplest depend on the conductivity of water.

Going Further

The water probes can be arranged in many different ways so long as the space between them is well insulated. Any general purpose, single-supply op amp should work in this circuit. Note that the circuit can also be triggered simply by touching the two sensor probes.

About the Author

Forrest M. Mims III has been an electronics and science writer and photographer since 1969. He received an IR 100 Award from Industrial Research Magazine for developing an eyeglass-mounted infrared travel aid for the blind. He received a Rolex Award in 1993 for developing a handheld instrument that measured the ozone layer accurately enough to find an error in a NASA ozone satellite. He was named by Discover Magazine (December 2008) as one of the "50 Best Brains in Science." See his home page and publications here and follow him at Twitter.