Electronic Circuits and electronic circuits, electronic schematics plus an extensive resource for hobbyists, inventors and engineers

DiscoverCircuits.com, has 45,000+ electronic circuits, cross-referenced
into 500+ categories.    We have searched the web to help you find quick design ideas.
We make every effort to link to original material posted by the designer. 
Please let us if you would like us to link to or post your design.

HOME Schematics Index Hobby Corner Dave's Circuits Electronic Resources Contact Info
Imagineering Ezine    Discover Solar Energy Dave Johnson & Associates Faraday Touch Switches

Circuits designed by David Johnson, P.E.
Last Updated on: Monday, December 25, 2017 02:09 PM

List of Dave's Circuit Designs

The contents & graphics of Discovercircuits.com are copyright protected.
LINKING to Dave's circuits is permitted but DO NOT COPY any files to your WEB SITE server

More  Test MonitorsWater Sensors Circuits



Water Seepage Monitor

A while back I got a request from a company who needed a water seepage detector.  They wanted a device that ran on 24vac and detected water using a fully isolated circuit.  They wanted a circuit which switched off 24vac to a load when water was detected. The circuit below performs this function.  By changing the phototransistor’s position in the detector circuit, the circuit logic can be changed so the 24vac source can be turned on when water was detected.  This might be handy to activate a pump.

The sensor is made using two stainless steel probes.  The probes would be positioned as needed, so the water would come in contact with them when the water reached a certain level.  Since the detection circuit is isolated, the two wires leading to the probe could be located some distance away from the rest of the circuitry.
A 15v supply is developed using two capacitors connected to the 24vac power source.  The circuit is referenced to the two sources of the AC switching transistor Q1 and Q2.  The AC is first rectified and then filtered.  A simple zener diode limits the DC voltage to 15v.  A Schmitt trigger is used to form a 100KHz oscillator circuit which drives the primary of a small transformer.  A ferret bead with a 0.25 inch diameter forms the transformer core.20 turns are used on the primary and 10 turns on the secondary.  The secondary winding is connected to an optoisolator and to the two water detection probes, through a resistor.  The optoisolator has two infrared LEDs inside and a phototransistor.  When the two probes come in contact with water current flows in both directions through the isolator’s two LEDs.  Light from those LEDs is detected by the internal phototransistor.  The output of the phototransistor is connected to a second Schmitt trigger, which drives two n-channel FETs.  The transistors are wired in such a way that when turned on they conduct current in both directions.  The transistors can thus switch 24vac power to the load.  Using the transistor shown, the current should not exceed 10 Amps.

Click on Drawing Below to view PDF version of Schematic

Water Seepage Monitor designed by David Johnson, PE

More  Test MonitorsWater Sensors Circuits

List of Dave's Circuits
Dave's Circuits with Descriptions
Dave's Circuits by Category

eMail David A. Johnson, P.E. about this circuit


HOME Schematics Index Hobby Corner Dave's Circuits Electronic Resources Contact Info
Imagineering Ezine    Discover Solar Energy Dave Johnson & Associates Faraday Touch Switches

 About Us   |  Advertise on DiscoverCircuits.com   |   Report Broken Links  |    Link to DiscoverCircuits.com  |    Privacy Policy

Copyright  January, 1998 - December, 2017     David A. Johnson & Associates.  All Rights reserved. 

 Linking is ALLOWED but COPYING any content or graphics to your web site is EXPRESSLY PROHIBITED.