Moisture Sensor

Moisture sensors consist of a flat plate with two conductors etched upon them. They can come in different shapes.

The type illustrated gives maximum intimacy between conductors for a given surface area. Another type takes the form of a long strip with the conductors running parallel to themselves. When moisture bridges the gap, the resistance is lowered between the conductors. This drop in resistance can trigger a transistor circuit, which in turn could operate a relay.

Uses: Plant watering in dry weather, sensing when it rains, flood warning, sensing damp conditions in electrical equipment etc.