Electronic Rain Gauge

Some simple electronic components are all you need to construct a basic remote reading rain gauge.
That's right, you can build a device that will allow you to check the amount of rainfall from the comfort of your own bedroom!

The design is simple. A series of lights are connected in such a way that rising water will complete the circuit and turn each light on in sequence.  Water is not normally a good conductor of electricity but a "pinch" of salt added to water creates a salt water solution that is a good conductor of electricity.

Use a cup with parallel sides to hold your wires, add a bit of salt and wait for the rain. This animated GIF demonstrates how the electronic rain gauge works. The "white" lines in the salt water show the completed circuit through the salt solution.

Rain Gauge Sensor

In this rain gauge sensor, wires are inserted in holes drilled in a plastic tube.
Glue is used to seal the holes.
Holes are 2 cm apart.

Sensor Connected

Rain gauge sensor connected with "-" battery connection at bottom.
As water rises in the tube the LED's will light in sequence.
Salt is used to increase conductivity.

Another idea for a rain gauge.

We used the plastic tube from an old pen to hold the wires for our rain gauge.  The wire from the "-" side of the battery goes down the center of the tube. We spaced the outer 3 wires 1 cm apart so that the lights would each indicate 1 cm of rain.  A plastic cup secured to a piece of wood makes a sturdy base. We used LEDs for the lights. (About LEDs).
You need long wires to put the cup outside. Telephone extension cables are inexpensive and are often available at Dollar Stores.

You may notice bubbles of gas rising from the "-" wire in your cup, this is hydrogen gas. The electricity, salt and water combine in some interesting electrochemistry.