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.

 

Circuits designed by David Johnson, P.E.
Last Updated on: Wednesday, October 18, 2017 05:04 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


More  Indicator Circuits;   Battery Monitors

Alkaline Low Battery Voltage Indicator -- June 17, 2012

In many battery powered systems a user would like to know when it was time to replace the batteries before they were completely discharged, causing the device being powered to fail completely.  Alkaline batteries have an open cell voltage of about 1.5 volts.  As they are discharged, the voltage slowly drops.  When the cell voltage reaches about 1.25v, they have delivered about 90% of their stored energy.  The circuit below monitors the voltage of two alkaline cells in series and begins flashing an efficient red LED when the total battery voltage drops below 2.5v, alerting the user that the batteries need to be replaced.
The circuit takes advantage of some new voltage comparators from Touchstone Semiconductor.  The TSM9118 has an internal 1.25v reference and an open drain output while drawing an astoundingly low 0.7ua.  That circuit is configured as a classic voltage monitoring circuit, which changes state at a 2.5v battery voltage.  A second TSM9119 Touchstone part is wired as a 0.5Hz oscillator which is configured to produce short 20ms output pulses every 2 seconds.  The TSM9119 is a conventional comparator with a push-pull output, which also draws a very low current.  Using the two low power parts, the total standby current of the circuit is kept at a low 3 microamps.  When the LED starts flashing, the average current will increase to about 50 microamps.  This is still low enough that the circuit should continue flashing for some time, giving the user time to notice the warning and replace the batteries.

Alkaline Battery Discharge Curve

Click on Drawing Below to view PDF version of Schematic

Alkaline Low Voltage Indicator designed by David Johnson, P.E.


More  Indicator Circuits;   Battery Monitors

Master Category List - Dave's Circuits
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.