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DiscoverCircuits.com -- Hobby Corner
Last Updated on:
Tuesday, November 29, 2011 08:14 PM
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Indicator Circuits
Micropower Circuits
Light Flashers |
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3v Low Battery Voltage Flasher
Circuit
designed by David Johnson, P.E. |
| Many battery powered
devices use two AA alkaline cells. Often you will not know when it is time
to replace the batteries until the device powered by them actually stops
operating. The hobby circuit below can be connected to a 3v battery, to give you
some warning when the battery is nearing its end of life. |
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It will flash a LED when the battery voltage drops
to about 2.4 volts. The electronic circuit draws only 1ua of current in
standby mode and jumps to only 20ua when flashing, so it can safely be included
without depleting the battery energy. A voltage detector IC from Panasonic
(Microchip also makes similar devices) is used to monitor the battery voltage.
The device’s open drain output swings low, when the battery voltage is below 2.4
to 2.5 volts. This action turns on the two transistor oscillator circuit,
which drives the LED with short current pulses lasting only 2ms. I published
this Flasher circuit in the January 2 issue of EDN magazine in 1997. |
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Click on Drawing Below to view PDF version of Schematic |
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