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Indicator Circuits, Page 2
Circuits designed by David Johnson, P.E.
Last Updated on:
Friday, March 12, 2010 12:08 PM
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Indicator Circuits: Page 1,
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- 3v Low
Battery Voltage Flasher
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...
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4 LINE TELEPHONE LINE STATUS INDICATOR
Many home businesses use multiple phone lines. This circuit gives you a visual
indication when a line is in operation. The two AA battery cells should provide
enough power for about one year of operation.
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AC Current Indicator Light
This circuit could be wired into a 120vac power line, which feeds power to any
load, ranging from 40 watts to 250 watts. It will turn on a LED light
whenever current is being drawn by a load. It is especially useful for
remote lights, where you may not be able to see if the lamps are receiving
power.
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ACCEPTABLE VOLTAGE INDICTOR
I have used this circuit many times in custom test fixtures where a simple go-no
go indication was needed. The circuit can also be used to adjust a
particular voltage be within specific high or low limits. The three LEDs
will indicate if the voltage is high, low or OK. When connected to other
converters, such as a frequency to voltage converter, a current to voltage
converter or a power to voltage meter, it could provide a quick indication of a
proper level.
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Electrical Current Indicator
I designed this circuit as a simple current indicator for any load ranging from
40 watts to 250 watts. The circuit turns on a small LED, whenever it
detects current flowing to a remote load.
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