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

DiscoverCircuits.com has links to 45,000+ electronic circuits, cross-referenced
into 500+ categories.    We have searched the web to help you find quick design ideas.

HOME Schematics Hobby Corner Dave's Circuits Electronic Resources Contact Info
Imagineering Ezine    Discover Solar Energy Dave Johnson & Associates Faraday Touch Switches
Welcome to DiscoverCircuits.com - online since 2002

See Media Kit for
Advertising Opportunities

Attention Designers:  Please alert us by eMail if we have linked to sites
where your original material has been copied without your permission.
We will change to the LINK to your site.  
Thank you.


DiscoverCircuits.com -- Hobby Corner
Last Updated on: Wednesday, October 18, 2017 05:04 AM

Hobby Circuits List

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  Motion Detectors

Shadow Activate Motion Detector 

There are many ways one can detect nearby human or object motion.  This circuit demonstrates one way.  It detects motion by noting the changes in the shadow cast by the moving object.
The hobby circuit below works quite well in typical indoor room lighting.  I would not recommend its use in direct sunlight.  Two small PIN photodiodes positioned about one inch apart form a shadow detector.  With no shadow cast on the devices, both devices produce nearly identical current levels.  The current is converted to a voltage with a load resistor in parallel with the photodiode.  One resistor is adjustable so the two voltages can be carefully balanced under uniform lighting.  When a hand or an arm is moved over the sensors, casting a shadow, one device will detect more light than the second.  This triggers an imbalance. 
A voltage comparator connected to the two devices detects the imbalance and sends a high logic level signal to an n-channel FET, which can turn on a beeper or activate a relay.  If a low power voltage comparator is used, such as the LMC7211, a 9 volt battery will power the electronic circuit for many years.  The more popular LM358 would also work but would draw more current.  Click below to see a short movie (MPG File) of the device in action.

Demonstration AVI Files
(Double Click on the above link to view movie)


Click on Drawing Below to view PDF version of Schematic

Circuit Shadow Activated Motion Detector designed by Dave Johnson, P.E. (Oct 24, 2005)

More  Motion Detectors

Hobby Circuits List
eMail David A. Johnson, P.E. about this circuit


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

Discovercircuits.com endeavors to credit original designers.   Please alert us by eMail so we can
delete links to material that have been copied without your permission
.   Thank you.

Copyright of all original material on this website is the property
of David A. Johnson, P.E. (Dave Johnson & Associates ) unless otherwise noted.  

Linking is ALLOWED but COPYING any content or graphics to your web site is EXPRESSLY PROHIBITED.
All material is provided "as is" without guarantees or warranty of any kind, either expressed or implied.