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

DiscoverCircuits.com, has 40,000+ 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: Friday, November 17, 2017 06:32 AM

Master Category List - Dave's Circuits

Text & Graphics Copyright © David A. Johnson, P. E. -- ALL Rights Reserved.
LINKING to Dave's circuits is permitted but DO NOT COPY to your WEB SITE server!

More  Indicator Circuits
 

Active AC Power Line Indicator - May 5, 2005
 

The circuit below is designed to detect when a power cable is active (hot). When the flat sensor end of the device is held near an active AC line, the bright green LED on the top of the housing will glow.  It is powered by a 3v CR2032 lithium coin cell.  It has no on/off switch and will function for years before the battery has to be replaced.  The circuit could be contained in a small plastic housing with a diameter of about one inch.
The circuit uses a LMC7225 ultra low power voltage comparator.  A number of resistors bias the device’s inverting input slightly higher than the non-inverting input.  This insures that its output remains low and the LED turned off.  A circular metal plate on the inside top of the housing forms a reference capacitor electrode.  When the device is held, the human thumb and therefore the human body becomes one large capacitor plate.  A second flat plate in the sensor end of the device forms a field sensing electrode.  When the sensor plate is held near an active power line, the electric field from that line induces a small AC voltage at the non-inverting input of the comparator.  This signal toggles the output on and off, which pulses the green LED on and off, indicating an active power line.  The value of the resistor R3 can be changed to increase or decrease field sensitivity as desired.

Click on Drawing Below to view PDF version of Schematic



More   Indicator Circuits
 

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  2002 - 2015 David A. Johnson & Associates.  All Rights reserved. 
 Linking is ALLOWED but COPYING any content or graphics to your web site is EXPRESSLY PROHIBITED.