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: Thursday, November 30, 2017 07:43 AM

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


Hidden Panic Switch

Problem:  Design an electronic switch which would be positioned behind a wall at several key positions and would be activated when an adult human hand was pressed against the wall at that position.
Hidden Switch Behind Wall Panic Button
Solution:  The best way to detect the human hand against a wall was with a capacitance switch.  The QTFS3X from Faraday switches looked like a perfect match.  The switch could be powered by a DC voltage down to 3v.  It required only 30ua of current.  It was quite small and would easily fit behind the wall.
The circuit is shown below.  A signal diode and capacitor routed power to the switches V+ terminal.  The momentary output terminal of the capacitance switch module was connected to the alarm circuit’s sensor wire.  The other wire from the alarm cable connected to module’s circuit ground.  When a hand was placed over the section of wall containing the aluminum foil, the capacitance would increase. The switch module would detect the sudden capacitance increase and would pull the sensor wire signal to circuit ground.  The energy stored in the capacitor would supply enough power to the module for several seconds of operating, even as the input power was shorted to ground. 

List of Dave's Circuits
List of Circuits from DC Magazine

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


DC Magazine, May 2011, Page 7:  Hidden Panic Switch


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 - November, 2017     David A. Johnson & Associates.  All Rights reserved. 


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