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.


Circuit Solutions Notebook
Last Updated On:  Tuesday October 24, 2017

Latest Technical Challenge           Previous Circuits Solutions           Circuit Solutions in Progress

Ultra Low Power Human Finger Detector


Could a slotted or reflected optical sensor be used in an ultra low power circuit to detect a human finger?


The circuit below seems to work well and averages a current drain of only 10 microamps from a lithium cell.  It uses a single CA4013 dual D flip/flop.  One section is wired as a pulse generator.  It applies 10us 10ma pulses to a LED inside a slotted optical sensor at a rate of about 50Hz.  The phototransistor in the second half of the sensor detects the pulses and sends a pulse to the data input of the second flip/flop in the 4013 package.  If there is nothing between the LED and the phototransistor, the inverting output of the 4013 remains low.  If the light beam is broken by a human finger, the flip/flop changes state sending a logic high level to a n-channel FET.  The open drain output could be sent to a computer system, a relay or a beeper.  The circuit has been used as a safety switch for machine operators and for wheel chair controls.  



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.