| Circuits designed by Dave Johnson, P.E. : |
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- 1.5V LED FLASHER VERSION A
Many published circuits that flash LEDs need 3 volts or more. This circuit uses only a single inexpensive C-MOS IC and flashes the LED for a full year on a single 1.5-volt AA alkaline battery
cell. The circuit uses a charge pump technique to provide the LED the needed voltage.
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1.5V LED FLASHER VERSION B
To squeeze even more energy from a alkaline battery cell, this circuit adds two transistors to a circuit similar to the above design to boost the efficiency. A small 1.5-volt alkaline N cell
should flash the LED for a full year. It too uses a "charge pump" technique to provide a LED the needed voltage.
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- 2 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. The circuit is line polarity insensitive.
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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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- 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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