Wet surface sensor

Discussion in 'The Projects Forum' started by rkoosha, Nov 8, 2011.

  1. rkoosha

    Thread Starter New Member

    Apr 17, 2008
    I intend to design a circuit that senses wetness of a surface and lits an LED and sounds a buzzer. I need help with the probe sensors that are used in this application.

    Thank you,
    Ray Kusha
  2. JDT

    Well-Known Member

    Feb 12, 2009
    Not quite sure what you mean by "wetness of a surface".

    If you want to detect rain drops on a surface then a small area of stripboard with the strips alternatively connected will do. The resistance will drop to a fairly low value when adjacent strips are bridged by a rain drop.

    A simple comparator is used to detect between low resistance (rain), high resistance (no rain).

    Devices that measure the dampness of walls, for example, have two sharp pins that can penetrate. The resistance between these pins reduces as the dampness increases. Probably best to make the pins from stainless steel.

    Here you might want to measure the value of resistance and ultimately drive a display possibly using a micro-controller.

    The sensor pins will corrode due to electrolytic action so good quality sensors use AC voltage across the pins or regularly swap the polarity.

    Does that help?
    rkoosha likes this.
  3. wayneh


    Sep 9, 2010
    There are also RF devices which measure moisture in walls and floors, concrete for instance, and these devices are not invasive (no probes, essentially no contact). Home inspectors use them.
  4. rkoosha

    Thread Starter New Member

    Apr 17, 2008
    Yes, it does.
    Thank you!