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DiscoverCircuits.com -- Hobby Corner
"Hobby Circuits for
your Hobby Projects"
Last Updated on:
06/19/2009 02:15:01 PM
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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. 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 Schematic below to view PDF
version of this Circuit |
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